EEVblog #1164 - Xbox Baptism Of Fire

[AndyC_772]

If the PCB itself is UL 94V-0, what actually starts burning? The connector itself? Isn't that a non-flammable plastic?

[Rasz]

But I still don't see how the crack on the connector will be remedied by the external device.

no no, external device is to prevent lawsuit, not fix the fault. Thats what recalls in US are for.

[Rerouter]

Its common enough in the automotive stuff, Solder joint begins to fail due to vibration / flexing stress, the joint gets hotter, the joint degrades further, the board begins to carbonize around the joints, and this starts spiraling towards a hard short near the input connector.

Combine this with all the dust, and sweat/oil that builds up over the years and you have a nice bit of kindling.

[Whales]

If the PCB itself is UL 94V-0, what actually starts burning? The connector itself? Isn't that a non-flammable plastic?

It's touching the case.

Also: if you can get the charring to go far enough it might become conductive.  Then all hell breaks loose.

[helius]

94V-0 means self-extinguishing, not non-flammable. If a source of heat is present, the material can smolder.
Dust may also be present and an ignition hazard.

[james_s]

AFCI's are a huge pain in the ass and will trip if you have any inductive loads such as motors or ballasts on the same branch circuit. They are also highly susceptible to RF interference as seen here.

Guy I work with just finished building a new house.  First power outage he fired up his generator, only to find out none of the AFCI's would hold under gen power.  Brilliant!

AFCIs are terrible, a friend of a friend builds houses, he told me the #1 issue they deal with post-sale is people complaining about the AFCIs and wanting standard breakers installed. The NEC requires AFCIs almost everywhere now, they're expensive, run hot, and are notorious for nuisance trips. IMHO they're a band-aid for something that really ought to be outlawed, the spring loaded push-in terminals on the back of cheap receptacles. I have personally dealt with three of those that burned up, one of which was in my own house. The terminals develop a bad connection, heat up and get worse. At least with mine I was fortunate that the wire melted off and opened the circuit before it caused any further damage.

[Clear as mud]

"Arc Fault Circuit Interrupter" (AFCI)

These seem standard in US outlets since 2014?

With each code revision, the National Electrical Code has been requiring them in more and more places, in residential buildings.  But they're not quite standard in practice, yet.  It depends on the jurisdiction.  Many have not yet adopted the 2014 or 2017 codes, so they're still enforcing only the 2011 or 2008 version.

Many electricians don't like them because of nuisance trips, but my own view is that they've been around for over a decade, so the manufacturers have had time to work out the problems with them.  I installed some AFCI breakers in my own house, and the only time I had one trip was when there actually was an arc on the circuit.

However, they remain 10 times the cost of a standard breaker, and I think they're not worth that cost, in terms of value of property protected.  The amount of extra loss incurred due to not having AFCI breakers is less than the cost of the AFCI breakers to protect everything.

[james_s]

It only applies to new construction or remodel jobs too, you don't have to upgrade existing systems. Some AFCIs may be better than others but those that I've dealt with caused a lot of nuisance trips, especially with anything containing a universal motor. The breakers themselves got alarmingly warm too, which tells me there's a significant amount of parasitic consumption. It may not be a lot per breaker but when you figure a typical panel might have 20 or more breakers that adds up.

I'm wishing that I had replaced my panel with a more modern unit back before the requirements got so draconian. At this point it would cost me so much to make a modest improvement in safety and usability that it's not worth it and I'll just stick with my original 1979 panel. It would be better if it were allowed to upgrade an old system without bringing it all the way up to present day compliance, it would still be an improvement over what is there.

[akimmet]

AFCI breakers are still the bane of residential electricians in the USA. All known makes still have issues with nuisance tripping and high current electric motors. The second there is enough load to bog down the motor, the AFCI will trip. Toasters are another common cause of nuisance trips.

I can understand the safety aspect, but I agree with James_s. Banning the use of back-stabs and wall-nuts would do much more for preventing electrical fires than AFCI breakers ever would. This is somewhat like when GFCI outlets were first required in potentially wet locations. It took over two decades before GFCI outlets became good enough to not be annoying.

Probably the second most annoying thing is tamper-resistant outlets. Even the good ones can be difficult to operate with some plugs. I have seen people jam a screwdriver in the slots to break the break the tamper-resistant interlock, so things plug in easier.

[sibeen]

Banning the use of back-stabs and wall-nuts would do much more for preventing electrical fires than AFCI breakers ever would.

Could someone please post a photo of these items so that I can understand what you lot are on about.

[LapTop006]

Per Wikipedia:

An arc-fault circuit interrupter (AFCI) also known as an arc-fault detection device (AFDD) is a circuit breaker that breaks the circuit when it detects an electric arc in the circuit it protects to prevent electrical fires. An AFCI selectively distinguishes between a harmless arc (incidental to normal operation of switches, plugs, and brushed motors), and a potentially dangerous arc (that can occur, for example, in a lamp cord which has a broken conductor).
...
The electronics inside an AFCI breaker detect electrical current alternating at characteristic frequencies, usually around 100 kHz, known to be associated with wire arcing, which are sustained for more than a few milliseconds. A combination AFCI breaker provides protection against parallel arcing (line to neutral), series arcing (a loose, broken, or otherwise high resistance segment in a single line), ground arcing (from line, or neutral, to ground), overload protection and short circuit protection.
...
AFCIs are also known to be sensitive (false tripping) to the presence of radio frequency energy, especially within the so-called high frequency spectrum (3-30 MHz) which include legitimate Citizens Band and Amateur Radio operations. Sensitivities and mitigation have been known since 2013.

That last bit has a link referencing this ARRL post.

[james_s]

Banning the use of back-stabs and wall-nuts would do much more for preventing electrical fires than AFCI breakers ever would.

Could someone please post a photo of these items so that I can understand what you lot are on about.

There's not much to see with the back stab terminals. There are just some holes in the back of receptacles and switches, you strip the wire and poke it in the hole and a spring loaded contact engages holding the wire in and making the electrical connection. The problem is that the contact area is tiny and the contact is nothing more than a bent strip of sheetmetal. Over time it oxidizes and heats up, losing its springiness which of course makes the connection worse and it gets hotter and the cycle repeats until it burns up. They are awful and should be banned, I refuse to use them but contractors love them because they save so much electrician time.

Those TR receptacles mentioned by someone here are another thing I loathe. They cost more than commercial grade but they're built like the cheap residential grade. It's often hard to get plugs into them and hard to get test probes into them too. They're required everywhere now and it's stupid, I'm never going to have kids and if I did I'd put childproof covers on the accessible receptacles. When I've had to get something inspected I install the cheapest TR receptacles I can find, then swap them out with nice commercial grade stuff after the inspector has signed off.

[Paul Moir]

Could someone please post a photo of these items so that I can understand what you lot are on about.

I have a minute to take a picture for clarity.  First is backstab, second is using the terminal lug.  The former is not considered acceptable around here but rather by convention then code I think.  Note the little catch that makes forming the wire quick and easy, and the checkering on the terminal plate to prevent having the wire dragged around when tightening the screw.  It takes 5 seconds to make rather than 2 for the backstab.    Keen eyed will spot this Canadian variant.

[akimmet]

Here is a website showing what are commonly called "wall nuts" in North America.
Like "back stab" outlets, they hold the wire in with pressure from a spring clip.

https://www.wago.com/us/wire-splicing-connectors/push-wire-connector-for-junction-boxes/p/773-104

[james_s]

Those Wago connectors come on a lot of light fixtures these days. I throw them away and use wire nuts instead, far more secure connection and not much harder to install. The push-in stuff works fine for a while, but it doesn't age well.

[sibeen]

Here is a website showing what are commonly called "wall nuts" in North America.
Like "back stab" outlets, they hold the wire in with pressure from a spring clip.

https://www.wago.com/us/wire-splicing-connectors/push-wire-connector-for-junction-boxes/p/773-104

I design switchboards up to a few thousand amps as part of my day job and those Wago 'push wire' type terminals are ubiquitous, and there's nothing wrong with that as they are being used for sensing and not as moderately high current carrying style connectors.

Using those 'back stab' type outlets just seems rather crazy and really head scratching considering the hoops that the National Electricity Code in the USA and Canada make the rest of the industry go through. I live in one of the IEC lands and we look at the household switchboards that are made in the US and they really look like something out of the 80s compared to an equivalent IEC rated switchboard. At least three times the size and as clunky looking as all getout.  I'm amazed that the NEC is so stringent at the start of the electrical distribution within a house/factory etc, and will then let a really cheap piece of crap be installed as the final distribution point. 

[Brumby]

I've seen those backstab connections causing issues in desk lamps.  I can't imagine the potential for problems with anything pulling even moderate current.     *shudder*

[james_s]

I design switchboards up to a few thousand amps as part of my day job and those Wago 'push wire' type terminals are ubiquitous, and there's nothing wrong with that as they are being used for sensing and not as moderately high current carrying style connectors.

Using those 'back stab' type outlets just seems rather crazy and really head scratching considering the hoops that the National Electricity Code in the USA and Canada make the rest of the industry go through. I live in one of the IEC lands and we look at the household switchboards that are made in the US and they really look like something out of the 80s compared to an equivalent IEC rated switchboard. At least three times the size and as clunky looking as all getout.  I'm amazed that the NEC is so stringent at the start of the electrical distribution within a house/factory etc, and will then let a really cheap piece of crap be installed as the final distribution point.

I had the opportunity to help a friend replace his panel when I was visiting the UK, it was interesting to see up close how different it all is. I found the European style panels to be cramped and rather flimsy looking although they seem to do the job given houses there have a tiny number of circuits in comparison. You can get compact panels in the US too but they're lousy, get 20-30 circuits typical of an average sized house in there and the panel is packed full the day it is installed, with no room for future expansion. My own panel is one size up from the compact ones and it's too small, I'd really like to install a fullsized panel, they're about 3' tall and luxuriously spacious, lots of room to route wires and space for expansion. The good industrial style ones have solid copper bus bars.

I do find it ridiculous that such cheap terminals are allowed, I never use anything less than spec grade (commercial/industrial) hardware and I often use hospital grade receptacles where they are heavily used. The higher cost of the hardware is peanuts compared to the total cost of the job and high quality receptacles don't get all sloppy and loose after a few years.

[sibeen]

Of course some allowance needs to be made for the difference in voltages used in the two systems and therefore the different levels of current. A nice, clean, healthy 240 or 230 volts versus that cheap and nasty 120 or 110 volt stuff. And don't get me started on the frequency!

[james_s]

What's wrong with the frequency? 60Hz means smaller, lighter motors and transformers, less flicker in iron ballast discharge lamps (less of an issue than it used to be) and no real downside. Also we have 240V here too, nearly all large appliances like ovens, cookstoves, electric clothes dryers and stuff like large air compressors are 240V. For whatever reason, US domestic service tends to be higher capacity than elsewhere in the world. A typical service to a modest single family home is 200A 240V. There tends to be less on a given circuit, for example my friend's house in the UK has nearly the entire second floor on one single ringmain, pop that and the whole upstairs goes dark. My house has multiple separate circuits for lighting on each floor, and multiple circuits for receptacles. If you manage to trip the breaker you usually still have lights.

Whatever the case, that (EE) friend and I have had some pretty extensive discussions on the matter and we have both come to the conclusion that neither system is a clear winner, both have advantages and disadvantages, mostly they're just different.

[Whales]

What's wrong with the frequency?

Personally: 60Hz transformer hum sounds less comforting (impatient?).  It never bugged me until I noticed it in other people's recordings.

Yes that's a valid reason to make a whole country change grid freq. When I'm supreme leader: this and more.  Dropout fuses on every home switchboard, 2.4GHz electric blankets, majority of freq spectrum opened up for public use, ban on audio frequencies that I can't hear (the people might be talking about me behind my back!), etc 

[sibeen]

James_S, I was joking, hence the smiley. 

[McRib]

I used to mod and repair these and I believe they changed the design of the power supply to use stranded wire from the receptacle to the ps board. There was quite a few solder repairs i did on that style Xbox but none after the change.

[james_s]

Personally: 60Hz transformer hum sounds less comforting (impatient?).  It never bugged me until I noticed it in other people's recordings.

I noticed the 50Hz hum for about the first 24 hours, motors, transformers, everything sounded a bit weird, then I got used to it and when I got back home the 60Hz stuff sounded a bit weird for a few hours. Where it was really noticeable was old style discharge lights where the 50Hz flicker was much more pronounced. Now that so many things use switchmode power supplies the frequency is less and less relevant.

I recently learned that Japan has two separate power grids, one 50Hz and one 60Hz, that has to be inconvenient, especially in the past. Seems odd to me that they never standardized, wouldn't most 50Hz infrastructure work at 60Hz? Just spin the generators faster?

[IanMacdonald]

I'm guessing that incredibly complex board is an arcing detector. The use them in houses in some parts of the USA. Likely the dry joint on the socket connections was the problem.