EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: IDEngineer on March 27, 2019, 03:16:20 pm
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I just finished out the lower level of our two-level, daylight-rancher style house. The latest revision to the US National Electrical Code (NEC) basically requires those new arc fault detecting circuit breakers on every circuit. Those started out being required in just limited places, then crept into more and more parts of the house, until this time around the inspector said they were required everywhere.
They may be great for a lot of reasons, but they SUCK for people who actually work with real tools! And they cost 5X the price of a normal circuit breaker. That is not an exaggeration - a normal breaker is under $10 while these new ones are ~$50 each.
My latest complaint about them surfaced yesterday, when I needed to cut some PVC pipe. A masonry blade cuts PVC really well, so I have one for our Bosch compound pull-through miter saw. I got it all set up, plugged it in, and when I pulled the trigger the blade started to spin up and then slowed and stopped. Checked the new 20A breaker (the circuit uses 12 gauge romex) and sure enough, it was tripped. I reset it and the same thing happened. Lather, rinse, repeat several times. Finally, I used an extension cord to an older outlet on a normal 15A breaker (14 gauge romex circuit) and it worked perfectly for many, many cuts.
The fact that it worked fine on a normal, but lower amperage, 15A breaker proves it wasn't a sustained startup current problem. So what was happening? Think about it for a moment. What happens inside a brushed motor on a power tool, particularly during initial startup? Arcing. It's literally part of the design. 100% predictable. To their credit, these new arc fault breakers are sensing those arcs - very impressive - but they're also incompatible with brushed motor tools. I presume (but haven't tested) that a smaller brushed motor might not trip the breaker, but seriously... 10 inch miter saws (or chop saws, or band saws, or table saws, etc.) are NOT uncommon. Its motor has a plate rating of 15 amps, and from its size it is well under a full horsepower.
This feels like the incandescent light bulb issue. I wonder if folks will start hoarding normal breakers and swapping them out after the inspector leaves. At the moment I cannot use normal, everyday power tools on any of the new circuits in the house. That's simply ridiculous.
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Have you tried different makes of AFCI? They are not all created equal, and the false positive rate on some is awful.
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I've had arc fault breakers trip from my laser printer (draws big current spikes heating the fuser rollers) Oddly enough they never tripped from using my universal motor based tools although I mostly have dinkier hazard fraught tools for the most part.
I think a lot of the algorithm has to do with the total magnitude of the current draw. I can purposely make my light switch arc for several seconds without tripping a breaker but the circuit with the heavier load that has the laser printer on it trips easily. Your big saw may be causing it to trip as it already draws lots of current to begin with plus the arcing signature. Not much you can do about it though.
My brushmotor based vacuums never caused issues either.
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It is somewhat similar to smoke detector regulations.
Used to be that they were required only on the kitchen and perhaps only another place.
Nowadays, they are required everywhere.
My wife loves scented candles. She has to light them up outside the house, otherwise the smoke alarms may trip.
EDIT: I also hoard incandescent light bulbs. I use them as loads or inrush limiters. My pride and joy is a 200 watt incandescent. Made by GE. So old that the markings have vanished. I am going to inherit it to my grandsons some day... ;D
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hazard fraught tools
Nice, I'm absolutely going to use that in the future.
TonyG
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I loathe AFCIs, they're a bandaid for the hideously unreliable backstab terminals and poorly maintained equipment. They nuisance trip constantly but the powers that be don't care. The only real fix is install them for the inspection but save all the packages and return them after the inspector has signed off.
I'll put on my tinfoil hat and wonder if breaker manufactures lobbied to have the much more expensive AFCIs required.
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From what I understand they are required everywhere here in Canada too, yet I don't think I've ever actually seen them in use. I don't bother TBH. We've been fine all this time without them, and if anything, things are safer now than they were before so the odds of dangerous fire causing arcs are even smaller.
They are also a pain to wire because you can't just have the neutrals all go to the neutral bus bar, so it's harder to make the panel look clean.
Whoever made these required also did not take into account that brushed motors are still used in lot of things.
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Have you tried different makes of GFCI? They are not all created equal, and the false positive rate on some is awful.
These breakers sense ARC fault (AF), not ground fault (GF). A ground fault is a serious hazard, but in this case arcing is literally part of the design of a brushed motor. And this isn't some cheap Harbor Freight tool, either... it's a top-end Bosch, almost $1000 new.
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Have you tried different makes of GFCI? They are not all created equal, and the false positive rate on some is awful.
These breakers sense ARC fault (AF), not ground fault (GF). A ground fault is a serious hazard, but in this case arcing is literally part of the design of a brushed motor. And this isn't some cheap Harbor Freight tool, either... it's a top-end Bosch, almost $1000 new.
Er, sorry. I meant AFCI. The algorithms vary from make to make, and the performance does vary a lot.
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They are also a pain to wire because you can't just have the neutrals all go to the neutral bus bar, so it's harder to make the panel look clean.
Agreed, though I wired my own subpanel and did manage to make it look reasonable.
I like the concept of the arc fault breakers, but I wish code was more reasonable about where they are required. James_s says (above) they became a requirement due to those horrific quickie push-in connections on the backs of ultra-cheap outlets and switches... basically an expensive breaker is making up for cheap fixtures. I NEVER use those push-in connections, I take the time to curl and then screw down each wire because you get FAR more surface contact which is especially important on daisy chained circuits. I'd like it if inspectors would allow normal breakers if you take the time to properly screw down the romex. Then you can take your choice: Go lazy on the wiring and use the expensive and inconvenient breaker, or do things properly and use a normal breaker.
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Your big saw may be causing it to trip as it already draws lots of current to begin with plus the arcing signature.
Agreed, in addition to arcing in the first place, a big motor is going to be drawing a LOT of current at startup until the back EMF builds to start limiting it.
You'd think the NEC writers would understand that. It's not exactly brain surgery. "Ugg, big motor with brushes draw big arcs during startup. Me should allow for that."
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I had major renovations made to my home in the summer of 2017. Interestingly, AFCI breakers were not required, but GFCI breakers were required for all circuits serving outdoor outlets. Another requirement was that all inside outlets had to be "childproof". The holes in the outlets are blocked by plastic "blockers" (not sure what to call them) and you have to insert a plug "just right" to get it to go in. But, if you push hard enough, they just break and "disappear" inside the outlet. It doesn't require brute strength either, my wife has broken a couple.
About smoke detectors:
Used to be that they were required only on the kitchen and perhaps only another place.
Nowadays, they are required everywhere.
The code here now requires "linked" smoke detectors and that no detector is to be installed in the kitchen or adjacent rooms. The reasoning behind this is that kitchen detectors frequently "false positive" and invite the homeowner to interfere with them (which is not illegal but could void your insurance if there is a fire). Code does not require, but highly recommends a wall mounted extinguisher in the kitchen. We installed one in order to get a variance for a stairway that was an inch too narrow. We would have had to majorly screw with a load bearing wall to widen it.
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They are also a pain to wire because you can't just have the neutrals all go to the neutral bus bar, so it's harder to make the panel look clean.
Agreed, though I wired my own subpanel and did manage to make it look reasonable.
I like the concept of the arc fault breakers, but I wish code was more reasonable about where they are required. James_s says (above) they became a requirement due to those horrific quickie push-in connections on the backs of ultra-cheap outlets and switches... basically an expensive breaker is making up for cheap fixtures. I NEVER use those push-in connections, I take the time to curl and then screw down each wire because you get FAR more surface contact which is especially important on daisy chained circuits. I'd like it if inspectors would allow normal breakers if you take the time to properly screw down the romex. Then you can take your choice: Go lazy on the wiring and use the expensive and inconvenient breaker, or do things properly and use a normal breaker.
Yeah the back stabs are trash. Don't know why they are allowed. They seem to have way less spring pressure on the wire than the spring-cage Phoenix terminal blocks meant for way smaller wire.
I prefer the ones with the internal serrated nut, where you stick the wire in the back, but tighten down with the same screw that you would use for a traditional hook. Less of a pain than doing the hook neatly, just as secure.
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Yeah the back stabs are trash. Don't know why they are allowed. They seem to have way less spring pressure on the wire than the spring-cage Phoenix terminal blocks meant for way smaller wire.
One that I disassembled a while back was basically just a metal knife edge at an angle. You pushed in the wire and the knife edge bit into the copper, making "contact" and preventing the wire from being pulled out without inserting a tiny screwdriver to push back the knife edge. Think how small the contact surface is in that case... a literal EDGE touching one side of the wire! And if you're daisy chaining like many electrical contractors do, they just stick another wire into the hole on the other side. Now two knife edges are expected to carry 15A of current. Every series outlet on that circuit adds two more tiny little connections like that. No thanks!
That's why I curl and screw down every wire. It's a pain and takes longer, but you only do it once and then you easily have an order of magnitude more surface area at every such junction in the circuit.
Given all the hoops NEC requires of you, I'm amazed they allow such contacts to be used. Anywhere. For any reason. If they require a separately breakered circuit to power interconnected smoke alarms throughout a house, how can they justify THIS?!? |O :wtf: :rant:
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Those TR receptacles suck too, they're a pain to get plugs into, they cost as much as spec grade but they're built like the cheap residential trash. Those are another thing I've had to install to get through inspections then pull out and replace with proper commercial grade receptacles.
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Should be a rental service for these. Rent a panel full for inspection, then replace them all with the old style at occupancy.
Agree arc fault are garbage. Guy at work just built a home, required everywhere. Also installed a whole home generator. First time the power went out and the genset fired up, all his arc faults kept tripping making the generator useless.
Would replace them with normal myself. Especially serving a garage or shop.
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The whole problem is that the National Electric Code is funded by insurance companies and insurance companies are NOT in the business of paying claims. Anything that may save them from a claim is fair game and if you remove the lame “safety” device they have a reason not to pay a claim. Same goes for smoke and CO detectors. |O The nanny state has been trumped by the corporate nannies profit margins. :box:
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In my own case I'd like to replace my circa 1979 panel with something more modern and up to date, but to do that I'd have to install AFCIs and update a bunch of other stuff to bring it all up to code. Instead I'll just keep getting by with the old panel. It's really a shame you can't replace existing equipment with something newer and safer than what's there without bringing the whole system up to present day code.
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The whole problem is that the National Electric Code is funded by insurance companies and insurance companies are NOT in the business of paying claims. Anything that may save them from a claim is fair game and if you remove the lame “safety” device they have a reason not to pay a claim. Same goes for smoke and CO detectors. |O The nanny state has been trumped by the corporate nannies profit margins. :box:
Yes, this is true: replace them for standard breakers after the inspection and void any insurance.
I think the circuit breaker manufacturers are also involved with the body which makes the law.
Fortunately we don't' have many AFCIs and they certainly aren't a requirement yet.
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Yes, this is true: replace them for standard breakers after the inspection and void any insurance.
How many have covered a home owner cutting a tree down that crashes in a house?
Many areas it legal for a home owner to do their own electrical. So 'ignorant' home owner Bob replaces what he sees as a faulty breaker with a 'working' one...
Don't think its a black and white case on voiding your insurance by replacing them.
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Buy a beefy isolation transformer WITH neutral earth/ground connected/linked at the Secondary (may be wired that way already) so a portable GFCI/RCD at the transformer output trips on real faults
and any false panic arc zaps get lost in the transformer
and use those brush equipped tools in the shop/shed without drama or nuking your insurance policy
There is no way I'm going to blow money on brushless gear when the brush stuff is still working Day One great :clap:
LOL, are Arc Fault Circuit Breakers promoted by a subsidiary of Audiophools Inc perhaps... ???
:D
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Fortunately we don't' have many AFCIs and they certainly aren't a requirement yet.
They're in the 18th edition as a recommendation, won't be long until they are a requirement. However they are prohibitive in cost at the moment - around £200 for a combined AFDD and RCBO, presumably because there is no demand for them.
Even the SPDs are silly prices for what's inside them:
https://youtu.be/xyEJtIo7YZ0
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For our new house built in 2017, the only circuits not requiring AFCI or GFCI were the furnace, dryer, outdoor A/C unit, oven (cooktop is gas), and lighting in the unfinished basement. Kitchen circuits including disposal and dishwasher were required to be protected by AFCI/GFCI breakers. All circuits in living areas required AFCI breakers. Circuits feeding the receptacles in the bathrooms, garage, house exterior, and unfinished basement are protected by a GFCI receptacle in that circuit. Our smallish two bedroom house has 14 smart breakers and around 10 GFCI receptacles to keep an eye on.
It's not unusual for the wife and I to travel somewhere for a week or so a couple of times a year. What I don't like about all this protection is that "important" stuff like the refrigerator, alarm system, security camera system, and lighting automation are all on protected circuits. Any sort of nuisance tripping is a concern especially for these circuits.
We haven't experienced any nuisance tripping except for one recent case. We had a blizzard with very strong winds that created havoc in the local electrical distribution system. There was one substantial case of lights flickering and a momentary outage that led to four of our "smart" breakers tripping. All the houses in our neighborhood are new; I haven't talked to any neighbor that didn't have at least one false trip during that storm. We now know that an unclean power feed can cause things to trip; luckily we weren't away at the time.
Breaker panels are mounted exterior to the houses here. I'm surprised there isn't a problem with these expensive breakers being stolen for resale on eBay etc. Our 14 smart breakers would be expensive to replace.
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food going off in a refrigerator and getting you with food poisoning is probably more dangerous then the fire hazard posed by a refrigerator lol
or a dehumidifier or sump pump being turned off and destroying your house with moisture
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Using a stick arc welder must be fun.
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Mine were constantly tripped by Ethernet over Powerline modules.
Last Fall, I installed a couple of Gigabit Ethernet over Powerline modules.
A couple weeks later, when the weather got colder and the kids turned on electric heaters in their rooms, the circuit started tripping. This was good, because I found that my teenager decided to plug hers into a long, thin extension cord. But even after checking what was plugged into her lines, the breaker kept tripping.
I couldn't find anything else plugged into the circuit, so I bought a clamp ammeter. The circuit was tripping with 4 amps across the 20amp breaker. I thought back in time, unplugged the Ethernet over Powerline modules, and no more problems with the AFCI breakers.
2011 Siemen's breakers, if anyone is interested.
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Looks like the fun has already begun on consumers with these Arc Fault Ball Breakers ::)
Using a stick arc welder must be fun.
An inverter stick welder perhaps :-//
unlikely a properly wired, non crusty transformer welder will produce any false trip arc at the mains, because all the zapping happens at the isolated low voltage Secondary
That said, IIRC the few inverter welders I've come across, their positive and negative outputs are not related to the mains,
perhaps the donut chokes and HF transformers snuff out any arcs feeding out from the power cable
Not sure on all that, so... I'll have to buy a couple of Arc Fault Circuit Breakers one day (if cheap aka Ebay NOS) and blow an afternoon putting them through all sorts of trip actuating hell,
and see if they are useful for some applications,
or just another PITA rated half baked 'safety add-on' to waste more urban battlers time and money
playing reset games |O :rant: and poverty extensions on electrician call out fees :(
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An electrician I know says the AFCIs are the #1 source of callbacks for new homes, at least they were as of a few years ago. All sorts of appliances cause nuisance trips and the powers that be don't care. It's like the IT guys who lock everything down so tight that it's hard to get any work done. They don't care if people get work done so long as a breach or infection doesn't occur on their watch.
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:rant:
Other than cheaply made plug in devices, I’m having a hard time trying to imagine scenarios where a residential arc flash breaker would save me assuming that my household wiring is installed properly with good connections. I wonder if these new necessary safety devices are mostly to cover shoddy installation and shoddy approved devices like the spring connection back stab junk.
I really think these arc fault devices are a Band-Aid for a much deeper problem. It may be better to enforce standards on cheap plug in household devices to stop most of the problems; or is it just backlash due to the inability to enforce any standards in today’s global economy? :-//
So now we are supposed to install dodgy arc flash devices because of things like copper clad aluminum wire and dodgy capacitor droppers in things we can plug into the wall socket…. But wait, there’s more, we can purchase wall receptacles with built in dodgy USB chargers that if they catch fire could burn down the house and they carry safety ratings that are only tested by the manufacturer. :wtf:
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I've personally dealt with at least three receptacles that burned up, one in my own house and another that was very close to starting a house fire. The thing is, all of these involved cheap receptacles with spring loaded backstab terminals which unfortunately are perfectly legal and "properly installed" according to code. I've also seen a few cheap receptacles that melted when the contacts came loose.
I just wish they had mandated spec grade receptacles instead of mandating an expensive and poorly performing bandaid.
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I just wish they had mandated spec grade receptacles instead of mandating an expensive and poorly performing bandaid.
EXACTLY how I feel. And I said so, above. Or at least they could do an either-or solution, your choice of "cheap outlets and expensive breaker" or "proper outlets and normal breaker". But then electrical inspectors would actually have to LOOK at the work and not just do drive-by "inspections".
Maybe whomever's in charge of the NEC is covering their @$$ now for ever allowing those backstab fixtures in the first place. They can't hardly require the installed base to be retrofitted, so they do this to us instead.
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Electricians love the backstab terminals because they can have an apprentice run around and install a whole house full of them in a few hours, lets them win the low bid while maximizing their profit. Not to mention they get plenty of business later repairing faults and replacing worn out receptacles that won't hold plugs in. I'm pretty sure the unions are involved in what goes into the code too.
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How is this for a soldered then stabbed junction that my uncle did about 40 years ago. My uncle worked for the local electrical utility in the control room of a hydro electric plant. I guess he didn't trust wire nuts.
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That looks like an ugly amateur hack job if you ask me. All those wires on that ground screw are just begging to come loose and get somewhere you don't want them. That big gap of bare wire where the soldered joint is makes me cringe too. Definitely not to code, pigtails with good quality wire nuts would be legal, much cleaner looking and less likely to fail.
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How is this for a soldered then stabbed junction that my uncle did about 40 years ago.
My uncle worked for the local electrical utility in the control room of a hydro electric plant.
I guess he didn't trust wire nuts.
Uncle did an ok job, I'd run my 120 volt gear off it no problem, :-+
and a far better bet than the 'crossed fingers' tacky outlets of today :scared:
Personally, I would have taped up the greens with matching color electrical tape and a cable tie to keep it all snugged up so no strays to think about
and a copper or stainless washer with matching spring washer, and do a screw down on those earth ground wires.
Solder is a no no when screwing stuff down > it compresses/shrinks and tarnishes and generally invites DRAMA
...unless you screw past the solder and well into the copper strand/s
I would also tape up the whites and blacks with cable ties,
and let the next guy/gal troubleshoot the install in 60 years time, maybe... 8)
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How is this for a soldered then stabbed junction that my uncle did about 40 years ago. My uncle worked for the local electrical utility in the control room of a hydro electric plant. I guess he didn't trust wire nuts.
Soldered + screw terminals = failure at some point
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I NEVER put more than one wire under a screw. Instead, I wrap the single wire around the screw and then tighten it down, giving that one wire full contact "around the bend" on both sides of the wire - the underside of the screw head on one side, and the metal face of the terminal on the other side.
Those screws are not meant to be junctions between multiple wires. I've seen a few homeowners do that, and sadly at least one "professional" electrician, but that doesn't make it correct. Or wise. It risks the mechanical integrity of the resulting connection. Multiple wires under a single screw leads to loose connections, which not only increases the junction resistance (leading to hotspots and reduced current capacity) but also increases the odds that a wire will work free from the terminal and wander around to touch something it shouldn't.
This is why I always use the largest boxes I can... so I have gobs of volume such that 12 gauge wire and the proper number of wirenuts still all fit comfortably.
That is one scary photograph.
EDIT: Looking closer, it appears the insulation on the ground wires has a square cross section. That's not normal romex-style insulation, and it doesn't match the insulation on the other wires either. Hmmmm.
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EDIT: Looking closer, it appears the insulation on the ground wires has a square cross section. That's not normal romex-style insulation, and it doesn't match the insulation on the other wires either. Hmmmm.
To me it looks like the ground insulation is moulded around the other conductors giving it a concave sides and convex top and bottom.
In the UK our equivalent of Romex is "twin and earth" and we don't insulate the earth wire though it is supposed to have an identifying sheath applied at the terminations:
(https://media.rs-online.com/t_large/R4681912-01.jpg)
I have always found the type of terminals where you wrap a wire around a screw to be pretty rubbish, they're a pain to connect and not very reliable when connected because any wire movement tends to loosen the screw and/or pull the wire out from under it.
Most of our connections are tunnel terminals which are generally like this inside:
(http://www.punamenterprise.com/img/a1%20(8).jpg)
Though we do have various other types including push-fit ones like this:
(https://cdn.shopify.com/s/files/1/1370/0745/products/Wago-PushWire-Nut-See-Through_d18a99b4-159c-4ff1-ae07-af810a84bf21_grande.jpg?v=1499538506)
These "feel wrong" and I much prefer the lever version, but they seem to be very reliable in practice.
Back on-topic I agree that AFCI are the wrong solution to the problem of poor quality wiring. All I hear about them are nuisance tripping problems, failure to trip on actual arcs, high costs, difficulty of testing.
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Another issue with the AFCIs is they run hot, at least the older ones do, which suggests a significant amount of power waste. It's probably not much per breaker but when you figure a house could have 15-30 of them and they're all powered up all the time, 24 hours a day that adds up.
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To me it looks like the ground insulation is moulded around the other conductors giving it a concave sides and convex top and bottom.
That's a reasonable explanation.
I have always found the type of terminals where you wrap a wire around a screw to be pretty rubbish, they're a pain to connect and not very reliable when connected because any wire movement tends to loosen the screw and/or pull the wire out from under it. Most of our connections are tunnel terminals....
I agree tunnels would be superior, but I haven't seen them offered on outlets and switches here in the US. Maybe they are if you go up several grades from residential to industrial.
As for screw terminals, they actually work pretty well on those fixtures because they bend up the corners of the underlying terminal. That "captures" the wire once the screw is tightened, and provides strain relief so that movement of the wire doesn't transfer as rotation under the screw. Without those bends I would completely agree that the wire could loosen the screw.
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Another issue with the AFCIs is they run hot, at least the older ones do, which suggests a significant amount of power waste. It's probably not much per breaker but when you figure a house could have 15-30 of them and they're all powered up all the time, 24 hours a day that adds up.
There's the answer! Get the environmentalists to come out against AFCI's! They stole our incandescent bulbs, at least they can offset that by getting rid of AFCI's too.
Speaking of which, I'm waiting for the enviro's to come out against soft power switches. They already hate wall wart power supplies (they call them "vampires" because they suck a bit of current all the time, even with no load) and with VERY few exceptions soft power switches mean there's some powered circuitry back there somewhere, monitoring the momentary switch. I miss the days when if the power switch was open, the circuit was open - period. It's hard to get less expensive and more reliable than a SPST switch purchased in volume.
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Another issue with the AFCIs is they run hot, at least the older ones do, which suggests a significant amount of power waste. It's probably not much per breaker but when you figure a house could have 15-30 of them and they're all powered up all the time, 24 hours a day that adds up.
That's weird. The designs I've looked at only take a few milliwatts under idle conditions. They take a bit more under high load, but they still don't get very warm, and they only dissipate a tiny fraction of the load.
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I just finished out the lower level of our two-level, daylight-rancher style house. The latest revision to the US National Electrical Code (NEC) basically requires those new arc fault detecting circuit breakers on every circuit. Those started out being required in just limited places, then crept into more and more parts of the house, until this time around the inspector said they were required everywhere.
They may be great for a lot of reasons, but they SUCK for people who actually work with real tools! And they cost 5X the price of a normal circuit breaker. That is not an exaggeration - a normal breaker is under $10 while these new ones are ~$50 each.
It seems to me the problem is that the breaker isn't rated for large inrush currents. Breakers also come in fast, regular and slow blow types like the good old fuses. Normally the fast acting types are installed and they are prone to trip with heavy loads. Check that.
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We are talking about power tools, but I am much more concerned about these pedestrian kitchen appliances that will literally spark outrage from SWMBO or other family members when the whole circuit comes down.
Some additional comments about this here (https://community.nfpa.org/community/open-xchange/electrical/blog/2015/06/15/afci-protection), including the request for slow acting AFCIs (apparently they are not a thing here in the US).
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We are talking about power tools, but I am much more concerned about these pedestrian kitchen appliances that will literally spark outrage from SWMBO or other family members when the whole circuit comes down.
Some additional comments about this here (https://community.nfpa.org/community/open-xchange/electrical/blog/2015/06/15/afci-protection), including the request for slow acting AFCIs (apparently they are not a thing here in the US).
AFCIs are pretty much a US only thing. The rules in most countries focus on mimimizing the occurance of arc faults.
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We are talking about power tools, but I am much more concerned about these pedestrian kitchen appliances that will literally spark outrage from SWMBO or other family members when the whole circuit comes down.
Some additional comments about this here (https://community.nfpa.org/community/open-xchange/electrical/blog/2015/06/15/afci-protection), including the request for slow acting AFCIs (apparently they are not a thing here in the US).
AFCIs are pretty much a US only thing. The rules in most countries focus on mimimizing the occurance of arc faults.
Ah, but they want to bring them in here now. The manufacturers have realised they can make money from them..
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We are talking about power tools, but I am much more concerned about these pedestrian kitchen appliances that will literally spark outrage from SWMBO or other family members when the whole circuit comes down.
Some additional comments about this here (https://community.nfpa.org/community/open-xchange/electrical/blog/2015/06/15/afci-protection), including the request for slow acting AFCIs (apparently they are not a thing here in the US).
AFCIs are pretty much a US only thing. The rules in most countries focus on mimimizing the occurance of arc faults.
They are sold in the UK, and are being marketed rather dubiously, but AFAIK the recently update wiring regs don't even reccommend their use, let alone mandate them. John Ward on Youtube covered them recently
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It seems to me the problem is that the breaker isn't rated for large inrush currents. Breakers also come in fast, regular and slow blow types like the good old fuses. Normally the fast acting types are installed and they are prone to trip with heavy loads. Check that.
As discussed earlier in this thread, the problem (at least the one I'm seeing) stems from brushed motors that arc as part of their normal operation, and especially at startup. I have put large heating elements on the same circuit that draw nearly the full 20A without incident. But put a brushed motor on it and *click*.
These silly things are designed to detect arcs, and when you use a brushed motor, WHOA - there's an arc! |O :wtf: :rant:
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A brushed (series) motor has a much higher rush-in current compared to resistive heaters. At zero RPM the back EMF of the motor is zero.
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At zero RPM the back EMF of the motor is zero.
Yes, as I noted earlier in this thread (search on "back EMF"). Of course you're correct, it might be an inrush current problem. However, for fun I just tried the same miter saw, in the same location, on the same outlet - and it cut a dozen+ pipes without incident. That's 24+ start/stop sequences on the same motor that couldn't get a single successful start a couple of days ago without the freakin' AFCI tripping every single time.
How nice that a "safety" device has such consistent performance, eh? I'll take my standard breakers, please.
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Dirty commutator?
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At zero RPM the back EMF of the motor is zero.
Yes, as I noted earlier in this thread (search on "back EMF"). Of course you're correct, it might be an inrush current problem. However, for fun I just tried the same miter saw, in the same location, on the same outlet - and it cut a dozen+ pipes without incident. That's 24+ start/stop sequences on the same motor that couldn't get a single successful start a couple of days ago without the freakin' AFCI tripping every single time.
How nice that a "safety" device has such consistent performance, eh? I'll take my standard breakers, please.
But did you check what inrush current ratings the AFCI has? You have to find out whether it is tripping because of the inrush current or the sparks before drawing any conclusions. If it is tripping right away then I'd be inclined to put the blame on the inrush current.
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Any copper screw downs I perform, MUST support an elephant dragging at it,
...with the entire wall and cable clips giving way first !
Those press in fittings are a wank that relies on arc/spark theory to work, which in turn eventually tarnish and create poor/er contact, and or hot spots come energy loss.
BONUS > with a higher probability those Arc Fault Ball Breakers will nuisance trip, in the middle of a saw cut, drill press, plasma run, air compressor fill cycle,
and everyones favorite > computer power off just before posting an unsaved LONG informative comment and pictures at the EEVblog forum etc :(
IMHO: Those 120 volt sockets are dodgy at best compared to 240 volt Australian sockets (and UK ones too, which may be similar)
I'm surprised those higher current 120 jobs are still allowed, decades later...
--------------------------
...John Ward on Youtube covered them recently
I'll have to catch that AFCI video asap,
Mr. John Ward doesn't pull punches regarding electricals and tells it like it is,
or at the least, how he sees it :-+ :clap:
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It seems to me the problem is that the breaker isn't rated for large inrush currents. Breakers also come in fast, regular and slow blow types like the good old fuses. Normally the fast acting types are installed and they are prone to trip with heavy loads. Check that.
Citation, please?
Can you point me to a standard residential mains panel manufacturer's (for the North American market) data where this is the case? We do, indeed, have fuses that are rated for standard circuit use or time-delay types for starting motor loads, but I am not aware of any of the standard, commonly available manufacturers which offer different inrush current ratings for circuit breakers in these "regular" types of applications.
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It seems to me the problem is that the breaker isn't rated for large inrush currents. Breakers also come in fast, regular and slow blow types like the good old fuses. Normally the fast acting types are installed and they are prone to trip with heavy loads. Check that.
Citation, please?
Can you point me to a standard residential mains panel manufacturer's (for the North American market) data where this is the case? We do, indeed, have fuses that are rated for standard circuit use or time-delay types for starting motor loads, but I am not aware of any of the standard, commonly available manufacturers which offer different inrush current ratings for circuit breakers in these "regular" types of applications.
HOM120 (https://www.schneider-electric.us/en/product/HOM120/miniature-circuit-breaker-120v-20a/?range=7228-square-d%E2%84%A2-homeline%E2%84%A2-miniature-circuit-breakers&node=7054175548-homeline-plug-on-circuit-breakers) vs HOM120HM (https://www.schneider-electric.us/en/product/HOM120HM/miniature-circuit-breaker-120v-20a/), for example. Which was a pain to find and I leave finding the trip curves to you.
E: OK, so I tried anyway. Homeline breakers use QO trip curves, and.. they haven't published any for the QO-HM breakers.
How, exactly, is one meant to design an installation without this data? 'Murica...
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But did you check what inrush current ratings the AFCI has? You have to find out whether it is tripping because of the inrush current or the sparks before drawing any conclusions. If it is tripping right away then I'd be inclined to put the blame on the inrush current.
Yes, I checked for that as soon as I read your comment. There is nothing marked anywhere on the breakers themselves that gives an inrush current rating. So I took the GE part number off one of them, looked it up on GE's website, and the "specs" there also make no mention of the sorts of information that you, I, and other intelligent people would clearly appreciate.
That's why I ran the test again. Lacking actual specifications, all I can do is gather empirical data. The next step would be for me to hook up my current probe on the scope and capture the current waveform so we could know for certain what peak current it's drawing, but at this point the breaker's behavior is so unpredictable that I'm not sure we'd learn anything useful. It's not like GE is providing numbers against which we can compare. |O :rant:
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But did you check what inrush current ratings the AFCI has? You have to find out whether it is tripping because of the inrush current or the sparks before drawing any conclusions. If it is tripping right away then I'd be inclined to put the blame on the inrush current.
Yes, I checked for that as soon as I read your comment. There is nothing marked anywhere on the breakers themselves that gives an inrush current rating. So I took the GE part number off one of them, looked it up on GE's website, and the "specs" there also make no mention of the sorts of information that you, I, and other intelligent people would clearly appreciate.
That's why I ran the test again. Lacking actual specifications, all I can do is gather empirical data. The next step would be for me to hook up my current probe on the scope and capture the current waveform so we could know for certain what peak current it's drawing, but at this point the breaker's behavior is so unpredictable that I'm not sure we'd learn anything useful. It's not like GE is providing numbers against which we can compare. |O :rant:
https://apps.geindustrial.com/publibrary/checkout/DES-012?TNR=Time%20Current%20Curves%7CDES-012%7CPDF&filename=DES-012_TAB.pdf
Of course, you could have one of the other 371 types of breaker seen in the US, but that at least is the current model of GE AFCI..
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That's why I ran the test again. Lacking actual specifications, all I can do is gather empirical data. The next step would be for me to hook up my current probe on the scope and capture the current waveform so we could know for certain what peak current it's drawing, but at this point the breaker's behavior is so unpredictable that I'm not sure we'd learn anything useful. It's not like GE is providing numbers against which we can compare. |O :rant:
It still might be educational and informative to do some measurements.
Since it seems to reliably run fine during testing on your standard 15A circuit, I don't expect it to be drawing the >60A for 1s or >40A for 10s kind of surges at startup that a breaker like this should be holding during motor startup for a 20A breaker model.
I suspect that your original assessment is more likely, that the AFCI circuitry is being overly twitchy in this particular case rather than the overcurrent protection. This is a very common type of fault with AFCIs and extremely annoying. :)
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I suspect that your original assessment is more likely, that the AFCI circuitry is being overly twitchy in this particular case rather than the overcurrent protection. This is a very common type of fault with AFCIs and extremely annoying. :)
And considering it's apparently working reliably now, I wouldn't be surprised if it were a dirty commutator causing prolonged arcing..
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It seems to me the problem is that the breaker isn't rated for large inrush currents. Breakers also come in fast, regular and slow blow types like the good old fuses. Normally the fast acting types are installed and they are prone to trip with heavy loads. Check that.
Citation, please?
Can you point me to a standard residential mains panel manufacturer's (for the North American market) data where this is the case? We do, indeed, have fuses that are rated for standard circuit use or time-delay types for starting motor loads, but I am not aware of any of the standard, commonly available manufacturers which offer different inrush current ratings for circuit breakers in these "regular" types of applications.
Over here you can buy B, C or D types each of which have a different allowance for rush in currents.
https://en.wikipedia.org/wiki/Circuit_breaker (https://en.wikipedia.org/wiki/Circuit_breaker)
Type B is mostly used in homes.
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Over here you can buy B, C or D types each of which have a different allowance for rush in currents.
https://en.wikipedia.org/wiki/Circuit_breaker (https://en.wikipedia.org/wiki/Circuit_breaker)
Type B is mostly used in homes.
Indeed, and we use standard DIN-style breakers inside equipment, industrial panels and controls, etc. but they are not allowed to be used as mains disconnects like is typically used in a good portion of the rest of the world. We do use some pretty fancy (and very expensive), often multi-way adjustable breakers in some commercial applications for certain things, some special types of loads, but that has nothing to do with the 99+% of the residential or standard commercial wiring for typical branch circuits.
For example, a hodge-podge panel-box-cupboard like Dave's house in .au has isn't even close to being allowed by our standards for mains use. You must use a purpose-built mains-rated enclosure and matching breakers, not just build your own out of DIN-rail components.
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Over here you can buy B, C or D types each of which have a different allowance for rush in currents.
https://en.wikipedia.org/wiki/Circuit_breaker (https://en.wikipedia.org/wiki/Circuit_breaker)
Type B is mostly used in homes.
Indeed, and we use standard DIN-style breakers inside equipment, industrial panels and controls, etc. but they are not allowed to be used as mains disconnects like is typically used in a good portion of the rest of the world. We do use some pretty fancy (and very expensive), often multi-way adjustable breakers in some commercial applications for certain things, some special types of loads, but that has nothing to do with the 99+% of the residential or standard commercial wiring for typical branch circuits.
For example, a hodge-podge panel-box-cupboard like Dave's house in .au has isn't even close to being allowed by our standards for mains use. You must use a purpose-built mains-rated enclosure and matching breakers, not just build your own out of DIN-rail components.
Just because it's on DIN rail doesn't mean it isn't purpose-built and suitable.
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Just because it's on DIN rail doesn't mean it isn't purpose-built and suitable.
True enough, but I don't know of a situation where it would be allowed here for mains circuit disconnects.
Perhaps you know of examples where it has been judged as suitable by the local authorities?
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Just because it's on DIN rail doesn't mean it isn't purpose-built and suitable.
True enough, but I don't know of a situation where it would be allowed here for mains circuit disconnects.
Perhaps you know of examples where it has been judged as suitable by the local authorities?
In the USA and funny hat? Not a clue.
DIN-rail mount is almost universal elsewhere in the world. That is not to say it's mix-n-match, at least in the UK they have to be 'type approved', that is to say, the manufacturers secured a bullshit clause that two devices designed to the exact same standard and tested to the exact same standards are not interchangable (of course, they'd only be interchangable if the physical dimensions lined up properly, which some do, some don't)
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Just because it's on DIN rail doesn't mean it isn't purpose-built and suitable.
True enough, but I don't know of a situation where it would be allowed here for mains circuit disconnects.
Perhaps you know of examples where it has been judged as suitable by the local authorities?
I have seen numerous uses of fuses Din rail and otherwise used in monitoring large switchgear but not many breakers. I have seen breakers in PLC cabinets where a means of easy disconnect is needed before working on the system.
In the enclosed picture on the upper left is a row of 6 fuses at 480V 3ph. The small wires landed on the screw terminal blocks are low voltage Modbus connections
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I have seen numerous uses of fuses Din rail and otherwise used in monitoring large switchgear but not many breakers. I have seen breakers in PLC cabinets where a means of easy disconnect is needed before working on the system.
In the enclosed picture on the upper left is a row of 6 fuses at 480V 3ph. The small wires landed on the screw terminal blocks are low voltage Modbus connections
Indeed, they are used all over the place inside gear but not for the actual mains distribution and disconnects for the circuits that actually run to that equipment.
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Just a random selection, not the prettiest, but look ma, DIN rail.
E: Oh, and here's a nice neat and tidy one:
(https://www.diynot.com/diy/attachments/upload_2019-1-22_22-5-36-png.157304/)
Seems to be missing an intumescent around the tail entry, otherwise..
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Just a random selection, not the prettiest, but look ma, DIN rail.
Uhhh... yeah.... so where in North America is that?
...blue and brown wire and all.... :palm:
I specifically said that I'm talking about North America, which is where the OP is located and inquiring about equipment in:
standard residential mains panel manufacturer's (for the North American market)
...
Indeed, and we use standard DIN-style breakers inside equipment, industrial panels and controls, etc. but they are not allowed to be used as mains disconnects like is typically used in a good portion of the rest of the world.
...
True enough, but I don't know of a situation where it would be allowed here for mains circuit disconnects.
Perhaps you know of examples where it has been judged as suitable by our local authorities?
etc... emphasis added
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Yes, I get it, thank you.
I was simply posting some examples of how it is done, in purpose built enclosures, elsewhere, as opposed to cobbling things together. Need I quote and emphasise you there?
You did see my links to just one of the many variations in breakers available in the US for domestic use, right?
GEs site is as uniquely annoying as Schneiders, but this appears to be standard and reduced sensitivity for the same type panel:
https://apps.geindustrial.com/publibrary/checkout/GES-6202A?TNR=Time%20Current%20Curves%7CGES-6202A%7CPDF&filename=GES-6202A.pdf
https://apps.geindustrial.com/publibrary/checkout/GES-9884?TNR=Time%20Current%20Curves%7CGES-9884%7CPDF&filename=GES-9884.pdf
E: Actually, I'd say that's reduced and hilariously reduced - 10IN is already equivalent to a C curve I believe.. No motivation to look into those product lines more closely.
And yes, I'm editing like a madman as I fact check things I don't use regularly..
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Nice tidy Din Rail :clap:
but...
Don't you chaps in the UK link the Earth and Neutral bus bars together? :-//
or is that just in the bigger towns ?
or the utility co. does it already at some point before the premises?
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Nice tidy Din Rail :clap:
but...
Don't you chaps in the UK link the Earth and Neutral bus bars together? :-//
or is that just in the bigger towns ?
Earth and neutral bonding is handled in the appropriate location for the supply by the distribution network.
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AFAIK linking is mandatory here, regardless of how/what's supplied.
Also if it's linked at the board as well, less thinking if something goes bad in the street supply
because I'm not quite sure how and where they bond it
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Just a random selection, not the prettiest, but look ma, DIN rail.
E: Oh, and here's a nice neat and tidy one:
(https://www.diynot.com/diy/attachments/upload_2019-1-22_22-5-36-png.157304/)
Seems to be missing an intumescent around the tail entry, otherwise..
Nice an tidy, agreed.
Standard US home these days would be 150-200A @ 240V and most circuits 120v. Half the voltage and 2x the current. Never seen equipment rated as service entrance with din rail mount. I'm sure some exists, buts it the exception. Just the min space requirements for this type of equipment, doubt anything in your picture would meet. A 100A panel with that many breakers would be at least 2x the size here.
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I have seen numerous uses of fuses Din rail and otherwise used in monitoring large switchgear but not many breakers. I have seen breakers in PLC cabinets where a means of easy disconnect is needed before working on the system.
In the enclosed picture on the upper left is a row of 6 fuses at 480V 3ph. The small wires landed on the screw terminal blocks are low voltage Modbus connections
Indeed, they are used all over the place inside gear but not for the actual mains distribution and disconnects for the circuits that actually run to that equipment.
Over here everything in installations less than 30 years old is mostly DIN mounted. All the breakers in my home (including the one in the feed-in line) are DIN rail mounted. I don't see what the problem is as long as the breaker is suitable for the purpose. DIN is just a way to mount electrical components in an easy way.
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In Spain any panels installed in the last 25 years (or more) are DIN rail but code requires all breakers to break both poles so the panel is much bigger than if it had single pole breakers.
It bothers me that they install the exact size panel needed initially and then there is no space left over for later additions.
Also, code here allows stranded cables which I do not particularly like. I believe code requires adequate terminals to be installed but in fact nobody uses them and multi-strand cables are easily damaged when clamped in screw terminals. Lots of shoddy work to be seen here, probably much of it not up to code. I am attaching photos of my panel.
I thought it was universal convention that the power supply cables enter at the top of the breaker and load is connected to the bottom but I am surprised to see the opposite is true in other parts of the world. Here a kind of "comb" fits along all the connectors in a row so the inputs are all supplied.
Earth and neutral are connected at the distribution transformer and not at my panel as discussed here (https://www.eevblog.com/forum/beginners/single-pole-or-1p-n-circuit-breakers/msg2302359/#msg2302359).
Regarding arc fault breakers I have not seen them here yet. They seem to try to remedy the use of unsuitable connectors in switches. I would rather use better connectors and not use arc fault breakers.
Also, wire nuts are not allowed here. I believe that is a uniquely American thing.
E.T.A: In the photo below the top left is the general breaker, next to it is the general GFCI and then ten individual circuit breakers. All double pole.
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I do like the DIN rail design rather than proprietary mounting used in North American panels. I don't like how cramped the European panels are though, ours are physically much larger so there's a lot more space to route wires and work around. It's a problem even in the US that a lot of panels are filled on the day they are installed making it a much bigger task to add anything later. It would be nice if they required 25% empty capacity when installed.
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I do like the DIN rail design rather than proprietary mounting used in North American panels. I don't like how cramped the European panels are though, ours are physically much larger so there's a lot more space to route wires and work around.
I agree with you but there are reasons. I really like how in America you have hollow walls which make it easy to pass wires and plenty of space for big breaker panels in the basement. It makes work so much easier.
In Spain walls are brick and there is no way to pass new wires, which is a pain. Also, the panel is usually located in a wall behind the front door and you want to hide it as much as possible. It is sunk in the wall which means it has to be built-in during construction. Any changes mean major construction remodeling and a PITA.
Also wall boxes for switches and outlets are too small and a PITA to wire, especially with rigid wire and that is why they allow stranded cable.
For working the American system is much more convenient but buildings here are what they are.
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I do like the DIN rail design rather than proprietary mounting used in North American panels. I don't like how cramped the European panels are though,
Those pictures are not how all distribution panels in Europe are constructed. In the NL (for example) a typical panel is way less cramped.
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John Ward discusses Types of Earthing Systems
https://www.youtube.com/watch?v=AWxeb2MI37c (https://www.youtube.com/watch?v=AWxeb2MI37c)
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I do like the DIN rail design rather than proprietary mounting used in North American panels. I don't like how cramped the European panels are though, ours are physically much larger so there's a lot more space to route wires and work around. It's a problem even in the US that a lot of panels are filled on the day they are installed making it a much bigger task to add anything later. It would be nice if they required 25% empty capacity when installed.
Unfortunately due to a large amount of older buildings and manufacturers designing themselves into a corner, we mostly get stuck with somewhat cramped units, at least in the UK.
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Oh, I forgot one more thing that I really dislike about Spanish code and that is that, probably for historical reasons which make no sense today, circuits are divided into two categories, "lighting" and "power". Lighting may have a lower amp limit, I am not sure, but they do not have to have protective earth whereas power circuits do. I find that stupid and inconvenient. For example, I have my desktop computer right next to an outlet I cannot use because it has no earth and I need to run an extension cord to another outlet half way around the room. Really stupid. I mean, they saved a few euros.
I have thought about wiring the earth cable but the conduits are so tiny and tight that it is almost impossible to get the third cable through. Short term stupid thinking. :--
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That is a bit strange, here any light fixture that has metal parts is supposed to be earth grounded to prevent any external parts from ever becoming live. Oddly though this does not apply to portable lamps which almost never have grounded cords. I suspect there are odd quirks like this in the code of almost anywhere in the world. I do like that there are still significant differences from one place to another though, it keeps things interesting. In the era of globalization so many of the goods we get are virtually identical no matter where in the world you buy them.
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This is how it looks in Switzerland. The blue things next to the breakers allow to disconnect the neutral, this is used for insulation measurements. You actually get about 500 USD from the building insurance when you install a surge protector. I've never seen a AFCI here. The last picture is the old panel that was in the house before.
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Oh, I forgot one more thing that I really dislike about Spanish code and that is that, probably for historical reasons which make no sense today, circuits are divided into two categories, "lighting" and "power". Lighting may have a lower amp limit, I am not sure, but they do not have to have protective earth whereas power circuits do. I find that stupid and inconvenient. For example, I have my desktop computer right next to an outlet I cannot use because it has no earth and I need to run an extension cord to another outlet half way around the room. Really stupid. I mean, they saved a few euros.
I have thought about wiring the earth cable but the conduits are so tiny and tight that it is almost impossible to get the third cable through. Short term stupid thinking. :--
A similar regulation exists in Brasil, but since 1994 protective ground is mandatory for all circuits.
I guess the difference is that in Brasil's code, the illumination circuits cannot have outlets - everything you can manually plug into is considered a "power" circuit.
I personally love this separation, especially considering the way my 1981 house in the US is wired - a circuit contains an absolutely illogical combination of outlets and lights, some even upstairs/downstairs!
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A similar regulation exists in Brasil, but since 1994 protective ground is mandatory for all circuits.
I guess the difference is that in Brasil's code, the illumination circuits cannot have outlets - everything you can manually plug into is considered a "power" circuit.
In Switzerland it is allowed to mix illumination with power and most light switches do also have a power outlet. The code requires that protective ground for outlets is not looped trough lamps. This rule is there to prevent people from disconnecting protective ground from outlets when thy change the lamp.
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too small and a PITA to wire, especially with rigid wire and that is why they allow stranded cable.
That's got to be a good part of why our panels are so much larger. Trying to run standard 2/0 AWG conductors for a 200A service in from the back of the panel and bending 90 degrees into the breaker simply wouldn't happen in that space. Even in a US panel coming in the back and wrangling around can be a challenge.
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I remember when I wired up my hot tub, 50A circuit with 6AWG wire making that tidy was like trying to tie a knot in a crowbar.
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A mains board is 'tidy enough' if you can easily encourage any wire to fit in the jaws of an average size clamp meter, and then pushed back into it's place :phew:
Otherwise tight eye candy 'tidy' is a PITA to troubleshoot, service, upgrade or swap out clapped breakers. :horse:
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It's possible to make them tidy AND leave sufficient slack to do real work later. I generally run incoming wires along one full side of the breaker box, then loop back and connect to the breaker.
Some of the "professional" electricians I've seen, though, apparently get bonus points for making breaker boxes the biggest rat's nest possible. There have been a few times where I've been pulling out old romex and I have no idea how they could have ever routed it in there in the first place, it's so wound and interleaved with other romex runs - and each wire in the romex takes a DIFFERENT path through DIFFERENT wires. I swear they get almost 100% visual occlusion of the rear of the box. |O
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Would an arc fault breaker have stopped this? It was a Liebert UPS that suddenly became smoke and scrap. :scared:
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At least with North American panels, tidy is the difference between a professional job and an amateur hack. Make it nice and clean and the inspector is a lot more likely to sign off and not go looking for minor technicalities. Also if done right it's easy to work on later.
Same goes for receptacles. You're supposed to have 6" of wire from the entry point in the box, with the outer sheath stripped off to within 1" of the entry. You can spot an amateur job instantly by excess sheath left on the wires which are usually then cut off way too short.
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I checked out John Ward's great Youtube trilogy on Arc Fault Detection Devices
(quote JW: 'Arc Fault Deception Devices' ;D)
and there is no way I would have a 3 way 'all in one' combo wasting 3 Din rail spaces,
eventually nuisance tripping, or not at all, once the unit ages a bit and or exposed to hot/cold/dust/moisture snafus
If they become compulsory here, I'll opt for a larger main board or addon if necessary with separate module AFDDs or AFCDs,
so I can test and get them swapped out if they are duds/placebos,
and leave the working MCB and RCDs or RCBO combos alone to do their job. :-+
..and save serious dollars not having to pay out on clapped 3 space 'three in ones' :phew:
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Would an arc fault breaker have stopped this? It was a Liebert UPS that suddenly became smoke and scrap. :scared:
I don't know if an AFCI would stop that from happening, but a smoke detector would probably let you know that it's happening. :-DD
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I don't know if an AFCI would stop that from happening, but a smoke detector would probably let you know that it's happening. :-DD
The UPS blew up in the middle of the night and nobody witnessed the actual event, but the fire department arrived big time. The fire alarms and detectors worked. It was in a high rise building in downtown San Jose, Calif. The feed breaker to the unit did trip like it was supposed to do. It was 480V 3 phase in and 208V 3 phase out I believe it was 25KVA. It was a typical crappy Liebert brand that was replaced with a Mitsubishi.
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The company I used to work for had a big UPS that blew up at least twice, once it filled the whole floor with stinky smoke while we were there, another time it went off over the weekend and the fire department and facilities manager showed up. I think they finally replaced it completely after that second instance.