Anyone Else Outraged About 3 Phase?

[langwadt]

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.

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.

single phase, split phase is not two phase

[Cerebus]

single phase, split phase is not two phase

I think you meant to say:

Single phase, split phase is not two phases.

When being pedantic, always check your spelling, punctuation and grammar.  But yes, technically you are correct.

[drussell]

Wow, is there ever a lot of misconceptions and misunderstandings surrounding this....
I'll take some pictures today once it gets light out to show how it's typically done around here.

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.

Wait...  What?!!

Why would it matter if you use extension cords from mains supplied from different phases?  You're not connecting anything across the phases or shorting them together.   

If your neighbor is on a different phase, it is no different than having two outlets in your own home supplied by different phases in all those homes over there that do have three phase.

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.

Uhh, no.  First of all, the pole transformer is connected from one phase to the grounded neutral, NOT across phases.  Most residential streets only have one phase strung along them.  The feed lines between those streets that come from distribution will have all three, and individual streets are connected to different phases to balance out the load as seen from upstream.

While perhaps in some very rural setting you would have your own transformer for one house, here in the city it is typically more like 4-10+ houses per transformer when it is overhead and probably 20+ houses if it's underground buried lines.  Small towns with larger properties (like my place at the lake where it is half an acre, the pole pig is shared between me and the house across the street) might share a transformer between just two or three properties, but that would be ridiculous in the city.

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.

Correct.

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.

Almost correct.  It's not two phases, it is a single centre-tapped phase, with the centre-tap grounded, often called "split-phase".

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.

That depends.  If you're near something commercial, there will be three phase right there and it is just a matter of bringing in the other phases, although most commercial stuff or multi-unit residential units have their own dedicated transformers, sometimes on the commercial site itself, with the transformer owned by the customer, otherwise three pole mounted or a ground-pad-located transformer-in-box owned by the utility so you'd still be on the hook for some sort of transformer-installation-charge (even if you don't have to actually pay for the transformer itself) if you're using the power company's transformer(s).

The customer here is responsible for the service.  For overhead installations here, the customer is responsible for supplying and installing the main panel and disconnect (usually an integrated panel which includes the main breaker for disconnect here for residential installations,) the feed to the meter base, the meter base itself and the feed wires up to the masthead, leaving at least 3-4 feet (I forget the exact spec) minimum of wire hanging out for them to be able to make connection and form proper drip loops.  You can pretty much pick whatever amperage main breaker you want as long as you have the appropriate size feed conductors from masthead-meter-panel disconnect. 

Long, LONG ago, like 1950s, you were allowed as low as 60A if you wanted.  70A then became the minimum (and strictly speaking is still allowed for VERY small dwellings like a single-bedroom apartment) but any normal single-family dwelling or one side of a duplex like mine that is over 700 sq. ft. is required to have a minimum 100A service.  Most typical homes here are now usually built with a 200A main breaker and appropriate input wiring from the start.

[langwadt]

single phase, split phase is not two phase

I think you meant to say:

Single phase, split phase is not two phases.

When being pedantic, always check your spelling, punctuation and grammar.  But yes, technically you are correct.

I'm no English expert but wouldn't it be ok to refer to a power system with two phases as "two phase" ?

[drussell]

I think you meant to say:

Single phase, split phase is not two phases.

When being pedantic, always check your spelling, punctuation and grammar.  But yes, technically you are correct.

I'm no English expert but wouldn't it be ok to refer to a power system with two phases as "two phase" ?

No, absolutely not!

Two phases would be 120° degrees apart!!

That would give you some intermediate voltage.

This is a center-tapped single phase, providing 180° separated 120-0-120

[Cerebus]

single phase, split phase is not two phase

I think you meant to say:

Single phase, split phase is not two phases.

When being pedantic, always check your spelling, punctuation and grammar.  But yes, technically you are correct.

I'm no English expert but wouldn't it be ok to refer to a power system with two phases as "two phase" ?

If one is being pedantic, one would use single quotes or a hyphen to explicitly indicate that you're using a compound noun. In all seriousness, it's a "What does the local style guide say?" example, the disagreement in number looks wrong to some eyes to others it doesn't. So formally, it's either singular "a two-phase" or "two phases", but in truth nobody really cares (I have just angered every sub-editor on every English publication with that last phrase).

[Cerebus]

I think you meant to say:

Single phase, split phase is not two phases.

When being pedantic, always check your spelling, punctuation and grammar.  But yes, technically you are correct.

I'm no English expert but wouldn't it be ok to refer to a power system with two phases as "two phase" ?

No, absolutely not!

Two phases would be 120° degrees apart!!

That would give you some intermediate voltage.

This is a center-tapped single phase, providing 180° separated 120-0-120

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

[Cerebus]

... - 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.

Wait...  What?!!

Why would it matter if you use extension cords from mains supplied from different phases?  You're not connecting anything across the phases or shorting them together.   

Somebody missed the hint - disco lights on one phase, music system on the other - one generally connects the music system to the disco lights to make them flash in time. Sure, it's all fine if there are no faults or 'creative' wiring (I have seen, in real life, someone use more than one plug socket wired together to get a higher current feed out of a nominal 13A socket). I said "bear in mind" not, "this is a recipe for immediate disaster", don't blow what I said out of all proportion.

Uhh, no.  First of all, the pole transformer is connected from one phase to the grounded neutral, NOT across phases.  Most residential streets only have one phase strung along them.  The feed lines between those streets that come from distribution will have all three, and individual streets are connected to different phases to balance out the load as seen from upstream.

I stand corrected. I've always assumed, when I've seen things like this:



that all three phases were being used to keep balance. Three wires, three phases, seems natural to take the xformer primary's feeds from phase to phase.

[drussell]

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... 

[mzzj]

Practically every family house in Czechia (where I come from) or in Germany (where I live) has a 3-phase connection. It supplies electric stoves, owens, pumps, woodworking machines etc. My father has even 3-phase DIY electric mowing machine.

Same here. Every house has 3-phase available and even some apartments nowadays have all 3 phases available in one apartment.
In my parents home even my bedroom had 3x16A 3-phase outlet 

IIRC most of the mainland Europe is wired in this way.

[langwadt]

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

[Cerebus]

IIRC most of the mainland Europe is wired in this way.

From my experience that's true for all the north western European countries (roughly everybody on the Baltic and North Seas). It's not for the UK, where a single phase is normal in individual dwellings. I can't speak for the counties with a Mediterranean coast, for some reason I've never been near a distribution panel to look in those places.

What happens in middle Europe is anybody's guess (You could take that as a general philosophical statement.  ) I expect someone will be along to enlighten us shortly.

[madires]

Two phases would be 120° degrees apart!!

That would give you some intermediate voltage.

This is a center-tapped single phase, providing 180° separated 120-0-120

The center-tapped single phase creates a 2-phase system. But if you have two phases out of a 3-phase system, then those two are 120° apart. And if the power distribution is based on a 3-phase system while each phase powers a transformer with a center-tapped output, then you've basically created a 6-phase system. Of course, each house has only access to its local center-tapped single phase. BTW, some industries use special multi-phase systems with much more than three phases to power huge motors. Typically they operate dedicated multi-phase generators for that purpose as they get only a 3-phase system from the power grid.

[mag_therm]

Not outraged at all, however I am 85% convinced that the traditional 3 phase grid is no longer appropriate, and probably wasteful a lot in terms of energy loss and all the complexity to control it these days.

Existing 3 phase generation should be converted to DC at point of generation.
The transmission grids would become 3 wire split DC, loosely regulated, with relaxed voltage control tolerances,
 and regional DC storage that can support outages for short periods.
Voltage step -down and regulation would be by inverters.

In our residence there are about 50 appliances and most convert to DC at the input as we know. Of the appliances that have motors, most either are or could be BLDC etc.

Similar applies in industrial consumption. VFDs with DC links are either common, or should be, replacing remaining  MV 3 phase machines.

I read the magazine 'Pac-World". The increasing complexity of Protection and Control,
is mainly to support the deficiencies, trying control instability of the aging 3 phase technologies (sinewave synchronization etc)
I think obtaining the required reliablity with a loosely regulated DC transmission system would be a lot simpler.
 
It is happening. India has (I think) world's largest, longest HVDC link just commissioned, and is talking about further 50 GW DC linkage across country.
China is doing similar.

[drussell]

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

Show me anywhere that you find a two phase supply to a site externally from the power company. 

Here, there is really only one situation where you see a two-phase, 120° supply, which makes it 208 volts to your range, clothes drier, etc. (and appliances here ARE rated for 240/208 with different wattage ratings) and that is a multi-unit apartment or condo building with more than, say, about 6 units, where they have a three phase supply to the actual building, but then each unit only has a standard two-pole-style residential panel instead of a commercial-style three-phase panel, where each individual unit is connected to two of the phases, balanced by the connections to each of the various units.

You can't get an actual two-phase from the power company.  You only end up with that when you run a device intended for split-phase 240 off two legs of the incoming three-phase.

[langwadt]

Two phases would be 120° degrees apart!!

That would give you some intermediate voltage.

This is a center-tapped single phase, providing 180° separated 120-0-120

The center-tapped single phase creates a 2-phase system. But if you have two phases out of a 3-phase system, then those two are 120° apart. And if the power distribution is based on a 3-phase system while each phase powers a transformer with a center-tapped output, then you've basically created a 6-phase system. Of course, each house has only access to its local center-tapped single phase. BTW, some industries use special multi-phase systems with much more than three phases to power huge motors. Typically they operate dedicated multi-phase generators for that purpose as they get only a 3-phase system from the power grid.

center-tapped is not two phases, 180deg doesn't count. you don't need special generators to generate more phases as soon as you have atleast two, all other phase angles can be created with linear combinations

[drussell]

Somebody missed the hint - disco lights on one phase, music system on the other - one generally connects the music system to the disco lights to make them flash in time. Sure, it's all fine if there are no faults or 'creative' wiring (I have seen, in real life, someone use more than one plug socket wired together to get a higher current feed out of a nominal 13A socket). I said "bear in mind" not, "this is a recipe for immediate disaster", don't blow what I said out of all proportion.

The only time that would be a problem would be a severe ground fault due to total lack of ground on one system and some sort of fault.  Maybe this is a common occurrence over there, hence the reason that you require an RCD/GFCI on the whole premises?  That wouldn't be any different, though, whether or not your neighbor is on the same phase as you or not.  If one of your neutrals is lifted above ground, it doesn't really matter whether it is single or three phases, the problem is the neutral not being at ground potential, and THAT is DANGEROUS!

Here we actually ground everything.  Every power pole is grounded to its own ground rod.  Every service entrance is grounded to a copper water main or ground rod or ground plate, etc and bonded to the neutral at the service entrance.

Uhh, no.  First of all, the pole transformer is connected from one phase to the grounded neutral, NOT across phases.  Most residential streets only have one phase strung along them.  The feed lines between those streets that come from distribution will have all three, and individual streets are connected to different phases to balance out the load as seen from upstream.

I stand corrected. I've always assumed, when I've seen things like this:



that all three phases were being used to keep balance. Three wires, three phases, seems natural to take the xformer primary's feeds from phase to phase.

No, that photo above is the three transformers supplying a full three-phase supply to commercial or large residential customers.  A standard residential street would only have one transformer, so there would only be three outgoing wires instead of four like in that photo.  (120 120 and neutral)

[madires]

center-tapped is not two phases, 180deg doesn't count. you don't need special generators to generate more phases as soon as you have atleast two, all other phase angles can be created with linear combinations

And how would you design a multi-phase motor for that? All windings have to be same and they have to be powered by the same voltage.

[Berni]

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

Show me anywhere that you find a two phase supply to a site externally from the power company. 

Here, there is really only one situation where you see a two-phase, 120° supply, which makes it 208 volts to your range, clothes drier, etc. (and appliances here ARE rated for 240/208 with different wattage ratings) and that is a multi-unit apartment or condo building with more than, say, about 6 units, where they have a three phase supply to the actual building, but then each unit only has a standard two-pole-style residential panel instead of a commercial-style three-phase panel, where each individual unit is connected to two of the phases, balanced by the connections to each of the various units.

You can't get an actual two-phase from the power company.  You only end up with that when you run a device intended for split-phase 240 off two legs of the incoming three-phase.

Its possible if you live in some weird places like Norway.

Unlike most of EU where mains is 230V star 3 phase they have 230V delta 3 phase. This means they get 230V between phases and its actually only like 135V on each phase, but not that it matters because they don't bring the neutral to the house. All of the normal single phase loads are wired across two phases and the cirucit breakers are all double pole to disconnect both. This causes major problems when you want to run a real 3 phase load like a motor that was made anywhere else.

So its kind of like a wierd in between of the EU 3 phase system and the US split phase system. Its a pretty stupid system where the only benifit is saving 1 wire for neutral.

[langwadt]

center-tapped is not two phases, 180deg doesn't count. you don't need special generators to generate more phases as soon as you have atleast two, all other phase angles can be created with linear combinations

And how would you design a multi-phase motor for that? All windings have to be same and they have to be powered by the same voltage.

transformers

[drussell]

The center-tapped single phase creates a 2-phase system.

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. 

But if you have two phases out of a 3-phase system, then those two are 120° apart. And if the power distribution is based on a 3-phase system while each phase powers a transformer with a center-tapped output, then you've basically created a 6-phase system. Of course, each house has only access to its local center-tapped single phase. BTW, some industries use special multi-phase systems with much more than three phases to power huge motors. Typically they operate dedicated multi-phase generators for that purpose as they get only a 3-phase system from the power grid.

No, no no... 

You wouldn't ever have three center tapped transformers feeding a site.  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...  Our typical 3-phase motors and stuff run on 208V from the 120-120-120 that can also be used to power individual loads instead of the 380-415V you folks use, unless you go up to one of the industrial supplies where things like 480 or 600V are used for very large motors, etc. but that would be a separate service, or more likely, a site where they own their own transformers, at least one supplying 120-120-120(/208) for normal loads and then another at 277/480, etc.

Many office buildings are wired with 277V lighting to reduce transformer requirements when they have a transformer on each floor, etc.  That is relatively common, but things like electrical boxes and switches are different dimensions (the box is taller) so they cannot be intermingled with the vast majority of stuff that is rated 250V MAX.

[drussell]

Not outraged at all, however I am 85% convinced that the traditional 3 phase grid is no longer appropriate, and probably wasteful a lot in terms of energy loss and all the complexity to control it these days.

Existing 3 phase generation should be converted to DC at point of generation.
The transmission grids would become 3 wire split DC, loosely regulated, with relaxed voltage control tolerances,
 and regional DC storage that can support outages for short periods.
Voltage step -down and regulation would be by inverters.

Let me guess...  you own a lot of stock in power semiconductor manufacturers?   

Large transformers are relatively efficient, cheap and reliable. 

Change that to giant inverters everywhere?  Really?   

Run all 3-phase induction motors off VFDs from now on?!  There's a reason they work so well on three phase, the rotating currents make a continuous stream.

Long distance, high voltage transmission is a completely different animal!  DC has some advantages there but the task of conversion and the conversion losses are non trivial.

[mag_therm]

Let me guess...  you own a lot of stock in power semiconductor manufacturers?   

Large transformers are relatively efficient, cheap and reliable. 

Change that to giant inverters everywhere?  Really?   

Run all 3-phase induction motors off VFDs from now on?!  There's a reason they work so well on three phase, the rotating currents make a continuous stream.

Long distance, high voltage transmission is a completely different animal!  DC has some advantages there but the task of conversion and the conversion losses are non trivial.

Hi drussell, Your comments more or less  reinforce my opinion.

I was involved not as stock holder, but just as engineer, with large industrial semiconductor inverters,
 some installation rated up to about 20 MW.
Other inverters rated 5MW at 100 kHz using IGBT.
As these were powered by similarly rated 6 phase 50/60 Hz transformers, I am aware of the cost comparisons between the iron devices and the semiconductor devices.
And furthermore aware the significant reductions in transformer cost as frequency rises.
A 30 kHz 10 MVA transformer would fit in the trunk of your car.

The ratings I mention above are not yet at grid distribution level,
but in my opinion that industrial technology is now ready to be scaled into the 200's MW level that are required for the newer power generation technologies.

[CatalinaWOW]

I'm with James on this.  I used to be outraged because there was a lot of surplus 3 phase equipment that I lusted after at very attractive prices, but not usable because 3 phase installation was outrageous (not unjustified, just way more than the cost of some fairly major gear) and the cost of rotary converters and other options was nearly as bad and consumed a lot of space.  Now that VFDs are capable and relatively inexpensive I don't care anymore.

[Cerebus]

Somebody missed the hint - disco lights on one phase, music system on the other - one generally connects the music system to the disco lights to make them flash in time. Sure, it's all fine if there are no faults or 'creative' wiring (I have seen, in real life, someone use more than one plug socket wired together to get a higher current feed out of a nominal 13A socket). I said "bear in mind" not, "this is a recipe for immediate disaster", don't blow what I said out of all proportion.

The only time that would be a problem would be a severe ground fault due to total lack of ground on one system and some sort of fault.  Maybe this is a common occurrence over there, hence the reason that you require an RCD/GFCI on the whole premises?  That wouldn't be any different, though, whether or not your neighbor is on the same phase as you or not.  If one of your neutrals is lifted above ground, it doesn't really matter whether it is single or three phases, the problem is the neutral not being at ground potential, and THAT is DANGEROUS!

Here we actually ground everything.  Every power pole is grounded to its own ground rod.  Every service entrance is grounded to a copper water main or ground rod or ground plate, etc and bonded to the neutral at the service entrance.

What did I say about not blowing things up out of all proportion?

As for earthing. Glass houses and all that.

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


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


BS1363 (The foot stabber)