Anyone Else Outraged About 3 Phase?

[drussell]

NEMA 1-15R receptacle, legal for new builds until 1968, met code until 1972.

HAHA, that's sure a weird looking version of a NEMA 1-15...  Usually the two prongs are centered vertically instead of being based on a back housing that could support the ground prong.    Makes sense, though, since production must be extremely limited on those by now.

Those are still available here for replacement purposes where a circuit is supplied by a legacy 2-wire, un-grounded cable and it is impractical to fish a ground wire to the box.  They are still valid and allowed, just not for new installations.  Most of the time though, for retrofit people go with a GFCI with the ground left open, which last time I checked that specifically, was still allowed as long as you put the little stickers on any downstream plugs that you put a 3-prong plug on which doesn't actually have the ground connected.  It is certainly sub-optimal, and you lose any shielding effect for devices with a grounded chassis, but it is allowed. 

I could go over to Home Depot right now and buy one.

(They're like $10 each instead of the $0.50 for a regular receptacle, but they're still there on the shelf.  )

EDIT:

As for earthing. Glass houses and all that.

I was talking about the whole system being above ground due to some fault.

We still use plenty of two-prong extension cords and devices over here.  Your disco-lights or music system from the example might not even have a ground, though if it's professional level gear it will, and then, yeah, you're back to grounds which aren't actually grounds or minor differences between panels causing ground loops, etc.  Welcome to being a pro sound and lighting engineer, we fight that crap all the time on gigs.  But that has nothing to do with three phase vs single phase.  The same issue exists either way. 

Most small things around here don't require the actual ground, but your neutral sure should still be at ground potential.

[themadhippy]

BS546 plugs - note the huge earth pin, current from 1934 up to 1947 when the standard was changed

The 15a variant is still  widely used thought the uk as the connector of choice for theater dimmer circuits.

[Cerebus]

BS546 plugs - note the huge earth pin, current from 1934 up to 1947 when the standard was changed

The 15a variant is still  widely used thought the uk as the connector of choice for theater dimmer circuits.

I have fought to plug in more 15A plugs that were just in reach while teetering on a 15 foot ladder and clutching a length of 2" steel piping than I care to remember. The 2A variant is still current domestic usage for things like plugged standard lamps on switched lighting circuits. There's one not three feet from me.

[james_s]

Someone else has noted that it's normal to take the three phases and neutral down the whole street and tap different phases at different points for different building's supplies. It's quite possible that your next door neighbour is on a different phase - something to bear in mind if you're having a party in the garden and someone decides to throw an extension cord over the fence to power the disco lights from the neighbour's mains, while you power the music from your house's mains.

You're missing the fact that the OP is in North America, where a different system prevails. Rather than picking off individual phase+neutral pairs for each property, there's a centre tapped transformer, typically every 1-3 houses (primary connected across two of the three phases), usually on a pole. This supplies two phases at 180º from each other and a neutral. Each phase is nominally 120V with respect to the neutral and 240V with respect to each other. It's normal to bring two phases and a neutral in from the transformer, and bond the neutral to earth at the distribution board. Hefty appliances get a 240V supply, others 120V.

So, three phase is a wholesale change of supply in North America, not just bringing in the missing phases. You'll need a 3 phase transformer in place of the existing two phase.

In my (typical suburban America) neighborhood the main arterial road between towns has 7200V 3 phase run along it. One of those phases is tapped off and run underground to feed my neighborhood, it then feeds pad mounted transformers that are mostly buried in vegetation a few feet behind the sidewalk, each of those powers anywhere from 2 to 6 houses. This is a very typical arrangement, residential streets sprouting off from arterials will get a single phase off of the nearest 3 phase distribution feed, they stagger them to keep the load balanced. It's not unheard of for there to be all three phases running down a street with houses, but I've never seen a house in North America that had 3 phase power. Apparently in some agricultural areas it is done occasionally.

Larger buildings are almost always 3 phase, even residential apartments will have a 3 phase feed but only two phases will be brought into each unit, wired to standard split phase domestic panels. This results in 208V instead of the usual 240V for higher powered loads, so things like clothes dryers, kitchen stoves and water heaters and wall heaters are slower than they would be in a typical house. Most of the time standard 240V appliances are used.

[james_s]

Somebody missed the "wink". He was taking the piss out of me (in a friendly fashion).

Nah, I saw it, but certain things that are fundamentally wrong drive me nuts, but I'm probably partially insane already anyway... 

so what was fundamentally wrong? two-phase power has two phases, three-phase power has three phases, split-phase is a single phase because 180deg doesn't count as a seperate phase

Whatever is grammatically most correct doesn't really matter, colloquially at least it is referred to as "single phase power" and technical people know that it is a single split phase.

[james_s]

NEMA 1-15R receptacle, legal for new builds until 1968, met code until 1972.

HAHA, that's sure a weird looking version of a NEMA 1-15...  Usually the two prongs are centered vertically instead of being based on a back housing that could support the ground prong.    Makes sense, though, since production must be extremely limited on those by now.

Those weird ones are what's available now for replacements. When we were preparing my late grandmother's house to be sold I had to replace a few receptacles in the original ungrounded portion of the house and those were all I could get. They're made that way because it's cheap, they use all the same molded parts as the standard 3 prong receptacles but don't install the ground contacts and the face doesn't have the opening. I think they look stupid but I guess I can understand not making a niche item like ungrounded NEMA-15 receptacles the same way they used to.

[Gyro]

Someone else has noted that it's normal to take the three phases and neutral down the whole street and tap different phases at different points for different building's supplies. It's quite possible that your next door neighbour is on a different phase - something to bear in mind if you're having a party in the garden and someone decides to throw an extension cord over the fence to power the disco lights from the neighbour's mains, while you power the music from your house's mains.

I once worked in a Lab where we discovered that adjacent workbenches were on different phases! 

415V 3 phase ceiling drop to the end of each row of three benches and... 

[Yansi]

Usually 3 phase is delivered to a substation that splits the single phases to different streets. It does not make economic sense to put all 3 phases down every street just in case one person wants it as it adds to the cabling required. No point in the OP going frantic. You want an industrial power supply? move to an industrial location.

That is not unfortunately the full truth.

Calculate how much power you can transfer with a single phase using amount X of copper. Then calculate same, using the same amount X of copper split for three phases.

As what you said, is a mathematically proven nonsense. Also, having separate loads on each phase create load imbalances and a lot more issues and stupid inconveniences.

[drussell]

Whatever is grammatically most correct doesn't really matter, colloquially at least it is referred to as "single phase power" and technical people know that it is a single split phase.

Single phase...  Sure...  Split phase...  Sure!

It is just most certainly not TWO PHASE!   

[Yansi]

Someone else has noted that it's normal to take the three phases and neutral down the whole street and tap different phases at different points for different building's supplies. It's quite possible that your next door neighbour is on a different phase - something to bear in mind if you're having a party in the garden and someone decides to throw an extension cord over the fence to power the disco lights from the neighbour's mains, while you power the music from your house's mains.

I once worked in a Lab where we discovered that adjacent workbenches were on different phases! 

415V 3 phase ceiling drop to the end of each row of three benches and... 

So what? There is exactly 0 issues with that.

Even for the garden party, there is absolutely 0 issues supplying AV tech from different phases. What may be a real issue tho, is you may have two different potential in between yo grounds/neutrals, if you bring the power from two very different places. Big AV setups are alway powered from threephase anyway.

[drussell]

Those weird ones are what's available now for replacements. When we were preparing my late grandmother's house to be sold I had to replace a few receptacles in the original ungrounded portion of the house and those were all I could get. They're made that way because it's cheap, they use all the same molded parts as the standard 3 prong receptacles but don't install the ground contacts and the face doesn't have the opening. I think they look stupid but I guess I can understand not making a niche item like ungrounded NEMA-15 receptacles the same way they used to.

Indeed.

That's much stated much more clearly than my attempt above. 

[drussell]

Someone else has noted that it's normal to take the three phases and neutral down the whole street and tap different phases at different points for different building's supplies. It's quite possible that your next door neighbour is on a different phase - something to bear in mind if you're having a party in the garden and someone decides to throw an extension cord over the fence to power the disco lights from the neighbour's mains, while you power the music from your house's mains.

I once worked in a Lab where we discovered that adjacent workbenches were on different phases! 

415V 3 phase ceiling drop to the end of each row of three benches and... 

So what? There is exactly 0 issues with that.

Even for the garden party, there is absolutely 0 issues supplying AV tech from different phases. What may be a real issue tho, is you may have two different potential in between yo grounds/neutrals, if you bring the power from two very different places. Big AV setups are alway powered from threephase anyway.

Exactly!

I don't understand that the problem would be, or the reason for the facepalms??! 

That is all perfectly normal, other than any potential ground loops.
It has nothing to do with the number of phases on the supply.

[drussell]

Usually 3 phase is delivered to a substation that splits the single phases to different streets. It does not make economic sense to put all 3 phases down every street just in case one person wants it as it adds to the cabling required. No point in the OP going frantic. You want an industrial power supply? move to an industrial location.

That is not unfortunately the full truth.

Calculate how much power you can transfer with a single phase using amount X of copper. Then calculate same, using the same amount X of copper split for three phases.

As what you said, is a mathematically proven nonsense. Also, having separate loads on each phase create load imbalances and a lot more issues and stupid inconveniences.

I don't understand what you're getting at there....  Could you elaborate a little, please?

[Gyro]

Someone else has noted that it's normal to take the three phases and neutral down the whole street and tap different phases at different points for different building's supplies. It's quite possible that your next door neighbour is on a different phase - something to bear in mind if you're having a party in the garden and someone decides to throw an extension cord over the fence to power the disco lights from the neighbour's mains, while you power the music from your house's mains.

I once worked in a Lab where we discovered that adjacent workbenches were on different phases! 

415V 3 phase ceiling drop to the end of each row of three benches and... 

So what? There is exactly 0 issues with that.

Even for the garden party, there is absolutely 0 issues supplying AV tech from different phases. What may be a real issue tho, is you may have two different potential in between yo grounds/neutrals, if you bring the power from two very different places. Big AV setups are alway powered from threephase anyway.

Exactly!

I don't understand that the problem would be, or the reason for the facepalms??! 

That is all perfectly normal, other than any potential ground loops.
It has nothing to do with the number of phases on the supply.

Because it was back in the '80s, pre RCD days. We would often have extension blocks strung between benches, lots of test gear, High power RF amplifier development and 415V between the live pins on adjacent mains 13A sockets.

[Cerebus]

Whatever is grammatically most correct doesn't really matter, colloquially at least it is referred to as "single phase power" and technical people know that it is a single split phase.

Single phase...  Sure...  Split phase...  Sure!

It is just most certainly not TWO PHASE!   

Given two sinusoidal signals of amplitude \$V : A = V sin (\omega t + \phi_1) \text{ and } B = V sin (\omega t + \phi_2) \text { where } \phi_1 \neq \phi_2 \$ we would say that we were presented with two phases. The phase angles are different.

Why is this a special case when \$ \phi_1 \neq \phi_2  \text{ and } \phi_1 = 0, \phi_2 = \pi\$?

 

[themadhippy]

Because it was back in the '80s

for once the uk wiring regs got sensible,it used to be no  outlets on a different phase less than 6 foot apart,then it was allowed as long as you fitted  warning labels,now  it dont matter

[madires]

Well, you can call it whatever the fuck you want on your side of the pond, I suppose, but here that is ALWAYS considered EXPLICITLY WRONG.  You would probably be thrown off the jobsite here for saying things like that because it would be obvious you don't know what you're talking about and that's how people get killed.  It is NOT two phases!  It is one single phase from the supply, just center tapped.  Here, you never, ever, ever call that two phases, that would refer to TWO of the actual MAIN supply phases. 

What is the reasoning behind "split-phase != 2-phase system"? Both legs of the US split-phase give you 120V to neutral and 240V between the legs. A 3-phase system works exactly the same, just with a different phase angle and therefore a different voltage between phases. And it's the same story for a multi-phase system with more than three phases. The phases are 360°/n apart (n = number of phases).

You wouldn't ever have three center tapped transformers feeding a site.

I have never claimed that! That was a theoretical contemplation and I clearly stated:
"Of course, each house has only access to its local center-tapped single phase".

Please try to think about the basic idea! Each phase of a 3-phase HV grid powers a split-phase pole transformer (input: phase to neutral/earth, output: split-phase with the center-tap connected to neutral/earth). So all the output's center-taps are connected (your reference point). That means the top legs are 120° degrees apart, same for the bottom legs. And since top and bottom legs are 180° apart you get six phases, theoretically.

If you get a three phase supply, it is three different, non-center-tapped transformers supplying 120-120-120, hence the reason you get 208V for commercial/industrial stuff.

I don't disagree.

Edit:
I think I found the reason for the misunderstanding of 2-phase systems. There is a 2-phase system with the two phases 90° apart, which is created by a Scott-T transformer fed by a 3-phase system.

[drussell]

Because it was back in the '80s

for once the uk wiring regs got sensible,it used to be no  outlets on a different phase less than 6 foot apart,then it was allowed as long as you fitted  warning labels,now  it dont matter

Haha, that's pretty funny, although I suppose you COULD try to stick your finger in both sockets at once for a really cool hairdo at your voltages. 

Here, for decades our kitchen counter plugs have normally been required to have both phases available on a single plug, so if you casually stick your fork tine or skewer or whatever in the top HOT and another in the bottom HOT of a duplex plug, you get a marginally nifty 240V hairdo, but probably not quite the same as the one you have when you wake up from the smouldering slam against the wall that you folks would get from what would be your 380+ volt ZAP!

[Gyro]

Yep. Faults and bodges could happen (more so back then). It should be safe, as long as you're aware of it... We weren't.

[Monkeh]

Here, for decades our kitchen counter plugs have normally been required to have both phases available on a single plug, so if you casually stick your fork tine or skewer or whatever in the top HOT and another in the bottom HOT of a duplex plug, you get a marginally nifty 240V hairdo, but probably not quite the same as the one you have when you wake up from the smouldering slam against the wall that you folks would get from what would be your 380+ volt ZAP!

Thankfully, you can't put a fork or a skewer in ours..

[drussell]

Here, for decades our kitchen counter plugs have normally been required to have both phases available on a single plug, so if you casually stick your fork tine or skewer or whatever in the top HOT and another in the bottom HOT of a duplex plug, you get a marginally nifty 240V hairdo, but probably not quite the same as the one you have when you wake up from the smouldering slam against the wall that you folks would get from what would be your 380+ volt ZAP!

Thankfully, you can't put a fork or a skewer in ours..

Are you sure about that?  Sounds like a challenge! 

We have tamper-resistant sockets as a requirement here now too (I hate them with a passion) but if you think someone can't push in the ground protector door to defeat it just like the ground prong does, I guess you've not been around enough curious younglings or drunk teenagers or whatnot...   

[james_s]

Because it was back in the '80s, pre RCD days. We would often have extension blocks strung between benches, lots of test gear, High power RF amplifier development and 415V between the live pins on adjacent mains 13A sockets.

How else would you do it though? If you've got a 3 phase drop to a row of benches you're going to either have the entire load on one phase, or you'll have adjacent benches on different phases somewhere in the row.

[elekorsi]

I was shocked when somebody wrote that it is normal to have 200A single phase supply to the house  These are ridicoulous currents for domestic supply... I just cant understand why they are not using 3 phase supply in america

As others wrote, in europe every building has a 3 phase power supply, here most common main fuses are 3x20A or 3x25A. Now compare that to single phase on 110V   
And everything is so simple, as you have the same voltages everywhere. 230V/400V in your own house/worklab, same in industry. In industry most of equipment is on the same voltage level, of course some big motors are running on medium voltage.
The beautiful thing is that i can test most of industrial equipment anywhere i am...

[TimFox]

Thankfully, you can't put a fork or a skewer in ours..

No, but you can open the shutter with a screwdriver into the ground socket and insert stripped wires into the other two sockets.  Removing the screwdriver will hold the two wires in place.

[Gyro]

Because it was back in the '80s, pre RCD days. We would often have extension blocks strung between benches, lots of test gear, High power RF amplifier development and 415V between the live pins on adjacent mains 13A sockets.

How else would you do it though? If you've got a 3 phase drop to a row of benches you're going to either have the entire load on one phase, or you'll have adjacent benches on different phases somewhere in the row.

Put them on a single phase and use the other phases for lighting, heating, aircon etc. Either that or use different phases either side of the central corridor (there was no need to drop 3 phases for 3 benches).

Actually that building had very poor phase balance anyway. It was a converted tyre warehouse with a suspended ceiling added (no expense spared for engineers working on mil stuff). The main supplier fuses in the cable head blew with monotonous regularity and the housing had distorted and was leaking pitch from the heat. The company wouldn't stump up for a higher current feed (I'm not sure that outlying bit of the industrial estate would support it).