UK/USA/EU terminology NEC BS7671 etc

I'm trying to understand some of the posts here from the USA. Is a GFCI a breaker that monitors the current on the neutral and if it
drops due to current on the earth possibly going through a human caused the breaker to trip - in UK terms a Residual current device RCD?
Is a branch circuit a circuit for sockets which daisy chains a cable from the mains to all the sockets in turn but does not return to the mains after the last socket - in UK terms a radial circuit?
In the USA are cables sizes quoted in millimetres squared ever? Are the accessories and switch gear roughly called the same things?
Is the National Electrical Code available online at all, free? The IEE wiring regulations - British Standard 7671 in Britain isn't. Is the NEC used in countries other than USA?
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The best I can tell it is a similar device. The GFCI simply compares the current on the hot against what comes back on the neutral and trips if there is a 5ma difference.

Yes. The "branch" part means it is the last leg after the final overcurrent device in the system. Anything before the last O/C device is a "feeder" and the wiring between the first O/C device (service disconnect/main breaker) and the utility transformer is a "service" conductor. "Service entrance" conductors, a type of sercice conductor are the customer owned wires between the service point, usually the service head at the top of the mast and the service disconnect.

They started using some metric designations in the 2002 code cycle but that hasn't trickled down to wire size yet. It will take decades before people start using metric wire sizes here if the MCM/Kcmil deal is any indication. The only thing we understand is metric sized liquor bottles. ;-(

short answer ... no. There are some places that will have very small excerpts but NFPA will shut down any large quotes over copyrights.
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A Brit in Calif writes ....
* A GFCI is a RCD. * Ring circuits aren't used in domestic applications, circuits are radial * Dunno about the NEC question.
* And (sob!) a 20A circuit can only carry just over 2kW ... while waiting for my 1.5kW kettle to boil in the morning (to make tea with imported M&S tea bags) I fondly remember the speed with which my 3kW 240V electric kettle boiled in Berkshire!
D

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| I'm trying to understand some of the posts here from the USA. | Is a GFCI a breaker that monitors the current on the neutral and if it | drops due to current on the earth possibly going through a human caused | the breaker to trip - in UK terms a Residual current device RCD?
Sounds like GFCI (or GFI) is the same as RCD. In Japan it is called a leakage breaker.
| Is a branch circuit a circuit for sockets which daisy chains a cable | from the mains to all the sockets in turn but does not return to the | mains after the last socket - in UK terms a radial circuit?
Radial circuits are the norm in the USA. I've never seen a loop circuit. I understand the UK has these wire with a higher amperage and fuses in each socket for the lower amperage to be supplied. In the USA, breakers for lights and normal receptacles are 15 or 20 amps for the 120 volts. They supply several receptacles (some limits exist in some codes, and are further restricted for kitchens to ensure adequate power).
| In the USA are cables sizes quoted in millimetres squared ever? Are the | accessories and switch gear roughly called the same things?
Up to a point, the AWG (American Wire Gauge) is used. Beyond that kcmils is common (kilo circular mils). But I don't know if the mils is the same as square millimeters. I suspect it is not.
| Is the National Electrical Code available online at all, free? The IEE | wiring regulations - British Standard 7671 in Britain isn't. | Is the NEC used in countries other than USA?
I was able to download the 2005 draft code. The current code requires payment. This practice is not one I endorse, but fighting it meets a lot of resistance because the cost recovery for code development processes have always been from sales of copies. The Internet could very well force a change, but not without a big fight. Regardless, the process does have to be paid for in some equitable way.
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Phil,
Where did you find 2005 draft?
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| | | |> I was able to download the 2005 draft code. The current code requires | | Phil, | | Where did you find 2005 draft?
It was on the www.nfpa.org web site. But I don't remember where I found it. Try a site search.
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snipped-for-privacy@ipal.net wrote in message

Almost, the ring main circuit is fused at 30A, the fuses for each appliance are in the plug, not the socket. 3A and 13A are the most common fuses in plugs, but other ratings are available up to a maximum of 13A. If the fuse was in the socket, then you would have to change in when, for example, you unplugged a kettle, and plugged in a table lamp to the same socket. Anything plugged into a standard uk 13A socket, e.g. a shaver adapter, has to contain a fuse, as if it did not the only protection would be the 30A fuse or breaker in the consumer unit, which is far above the capacity of the appliance flex. These 13A BS 1363 rectangular pin plugs are the only ones normally used now in domestic and office type environments, and are normally wired in a ring main. They always have three pins. There was an older standard, BS 546, which specified round pin plugs, rated at 2, 5, 15 and 30A. These were not internally fused, are seldom seen now, except for the 15A, and less often the 5A ones, which are still used for stage lighting purposes. I don't know why we wire our 13Asockets in ring mains; somebody once told me that it was to reduce the use of copper after the second world war, when it was in short supply, but I don't know if this is true.
For industrial use at higher current ratings, the most common are the connectors which were known as BS 4343, but which are now BS EN 60309. These are the colour coded plugs which have 3,4 or 5 pins recessed within a circular plastic surround. Versions here are rated at 16, 32, 63 and 125A, in the USA, they are rated at 20, 30, 60 and 100 or 120A, I can't remember which, and I don't know the standard number for them. They don't seem to be as widely used over there as they are here.
British electrical distribution is very different to that in the USA. Over here the most common voltage is 11kV, but other Voltages, 6k6V, 22kV and 33kV for example are also used. We use relatively large three phase transformers in substations, not the small things stuck up poles that you have over there. The output from the substation is a three phase four wire star connected system. The neutral is connected to the star point, which is earthed (grounded).
The nominal Voltage is 400 from phase to phase, and 230 from phase to neutral. Until recently it was 415/240, but nothing has really changed, it was a European harmonisation thing. All four wires are run along each street, in towns and cities normally underground, and all wires are taken into buildings requiring a three phase supply. Houses are normally supplied with only a single phase and neutral, the phases normally being used in rotation in each building along the street, so there is probably 400V between your mains sockets, and those of the house next door. A typical substation would typically feed several hundred houses, while large buildings such as factories would normally have their own.
Several things to note; all three phases are symetrical about the earth point, we never have one with a higher Voltage on it. Our 230V is that Voltage from earth, it is not a centre tapped system with 115V on either side. We never have delta systems with one corner grounded. The Voltage is standardised throughout the country, you will not get anything other than 400/230V from the public supply, unless you are operating something *very* large, like a railway, or a steelworks.
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message

seen a loop circuit.

amperage and fuses in

for each

the most

to a maximum

have to change

in a table

uk 13A

if it did not

the consumer

flex. These 13A

used now in

wired in a

older standard,

and 30A.

except for the

stage
13Asockets in ring

of copper

but I don't

common are the

BS EN 60309.

recessed
rated at 16,

and 100 or

standard number for

they are

in the USA.

Voltages, 6k6V,

relatively large

things stuck up

substation is a

is connected

from phase to

really
wires are

underground, and

supply.
neutral, the

along the

sockets, and

typically
factories
about the

it. Our 230V

system with 115V

corner grounded.

will not get

unless you are

steelworks.
Stephens description is pretty much how it is in Australia also. But our nominal is/was 240/415 volts and as we are far from Europe are not as tied to their Harmonisation but I guess it will come and we will accept 230/400 volts.(not very significant any way) We have a lot of pole mounted transformers so I don't think they supply as many homes as the substation arrangement but the result is much the same.
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| Stephens description is pretty much how it is in Australia | also. | But our nominal is/was 240/415 volts and as we are far from | Europe are not as tied to their Harmonisation but I guess it | will come and we will accept 230/400 volts.(not very | significant any way) | We have a lot of pole mounted transformers so I don't think | they supply as many homes as the substation arrangement but | the result is much the same.
You'd have lower fault currents, and reduced need for high interruption ratings on residential circuit breakers, and reduced risk of a short failing to be cleared.
Changing the voltage on power distribution is not easy, unless it is done throughout the entire grid at the same time (gradually). But then, your standard probably gives your power industry more leeway to brown out in a crisis. Given Europe's voltages range from 220 to 240, and the tolerance over the nominal including those voltages, appliances and equipment will be generally made to work over that whole range. What you then get is the ability to drop as far down as 220/380 in energy crisis situations. In my mind it makes sense to just leave it the way it is at 240/415.
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| snipped-for-privacy@ipal.net wrote in message
| |> Radial circuits are the norm in the USA. I've never seen a loop circuit. |> I understand the UK has these wire with a higher amperage and fuses in |> each socket for the lower amperage to be supplied. | | Almost, the ring main circuit is fused at 30A, the fuses for each | appliance are in the plug, not the socket. 3A and 13A are the most | common fuses in plugs, but other ratings are available up to a maximum | of 13A. If the fuse was in the socket, then you would have to change | in when, for example, you unplugged a kettle, and plugged in a table | lamp to the same socket. Anything plugged into a standard uk 13A | socket, e.g. a shaver adapter, has to contain a fuse, as if it did not | the only protection would be the 30A fuse or breaker in the consumer | unit, which is far above the capacity of the appliance flex. These 13A | BS 1363 rectangular pin plugs are the only ones normally used now in | domestic and office type environments, and are normally wired in a | ring main. They always have three pins. There was an older standard, | BS 546, which specified round pin plugs, rated at 2, 5, 15 and 30A. | These were not internally fused, are seldom seen now, except for the | 15A, and less often the 5A ones, which are still used for stage | lighting purposes. I don't know why we wire our 13Asockets in ring | mains; somebody once told me that it was to reduce the use of copper | after the second world war, when it was in short supply, but I don't | know if this is true.
I guess my USA thinking influenced by understanding of some previous info. In the USA, our receptacles are 15 or 20 amp, and appliances are supposed to insure they are protected internally of lower levels of overloads, if applicable. The wire itself can be rated for what the applicance will use. If an appliance would overuse current then it is the appliance that should blow its own fuse. The difference between having the fuse in the plug and in the appliance would relate to any overload on the wire itself. But the wire doesn't overload, though it could short out, which would trip the breaker for the circuit. What I assumed was that the socket was protected by a fuse at the level suitable for cord short circuits since the loop circuit in the wall was rated rather high. But with a fuse in the plug, the cord wire is well protected, anyway.
In your case, a short or overload should blow the plug fuse well before the house fuse/breaker. Do plugs come with circuit breakers instead of fuses?
Now the question is, does the circuit in the wall run back to the same breaker at the end, or does it just come to and end and stop? One would be a loop and one would be radial.
What current levels are used for electric stoves, ovens, hobs, etc? We have them here up to 60 amps and they run on 240 volts (120 amps on 120 volts would be rather undesireable).
| For industrial use at higher current ratings, the most common are the | connectors which were known as BS 4343, but which are now BS EN 60309. | These are the colour coded plugs which have 3,4 or 5 pins recessed | within a circular plastic surround. Versions here are rated at 16, | 32, 63 and 125A, in the USA, they are rated at 20, 30, 60 and 100 or | 120A, I can't remember which, and I don't know the standard number for | them. They don't seem to be as widely used over there as they are | here.
You might be referring to the IEC pin-and-sleeve connectors. Those go all the way up to 690 amp versions (yes, six hundred and ninety).
| British electrical distribution is very different to that in the USA. | Over here the most common voltage is 11kV, but other Voltages, 6k6V, | 22kV and 33kV for example are also used. We use relatively large | three phase transformers in substations, not the small things stuck up | poles that you have over there. The output from the substation is a | three phase four wire star connected system. The neutral is connected | to the star point, which is earthed (grounded).
Questions:
How many homes would be on a single substation? What would be the total current rating for that substation secondary? What would be the fault current if there was a solid short circuit?
I prefer the small transformers for fewer homes, as it keeps the fault current levels low. But in dense urban areas, where transformer space is at a premium, there is often what is called "network service" which is a substation with a larger 3 phase transformer bank (sometimes more than one in parallel). The voltage is 208/120 in the star configuration. Customers are supplied with either three phase, or if they only need single phase, they are supplied with 2 of the three phase lines.
| The nominal Voltage is 400 from phase to phase, and 230 from phase to | neutral. Until recently it was 415/240, but nothing has really | changed, it was a European harmonisation thing. All four wires are | run along each street, in towns and cities normally underground, and | all wires are taken into buildings requiring a three phase supply. | Houses are normally supplied with only a single phase and neutral, the | phases normally being used in rotation in each building along the | street, so there is probably 400V between your mains sockets, and | those of the house next door. A typical substation would typically | feed several hundred houses, while large buildings such as factories | would normally have their own.
Can you get just 2 phases if you have a need for 400 volt single phase but not three phase? Is there equipment like circuit breakers and panels designed for 2 poles like that, or would you just have to use 3 phase stuff with one dead line?
| Several things to note; all three phases are symetrical about the | earth point, we never have one with a higher Voltage on it. Our 230V | is that Voltage from earth, it is not a centre tapped system with 115V | on either side. We never have delta systems with one corner grounded. | The Voltage is standardised throughout the country, you will not get | anything other than 400/230V from the public supply, unless you are | operating something *very* large, like a railway, or a steelworks.
Standardizing the voltage like that is a big plus. In the USA it is a mess. Much of that mess is because the use of Edison style split single phase result in most appliances using 120 volts but some using 240 volts. Commercial buildings have to use three phase because of the extra load, but they get 208/120, which screws up 240 volt stuff. That's why some 240 volt delta, with Edison style split on one winding, is still used. The extra B phase is then 208 volts to ground. And then these voltages are too low for medium industrial use, so we have to have 480/277 as well (Canada has 600/347). This resulted in lights designed for 277 (or 347) volts. And all of this is really because Edison wouldn't accept AC (if he had, then 3 phase would have made sense and the voltages would not have the 2:1 ratio). Also, Edison was a bit paranoid about electrocution, perhaps due to his mistaken belief that the neutral wire, when grounded, would provide protection, and didn't realize its failure was because that wasn't really a very good design.
I suspect 480 came about here due to the 60 Hz frequency. Crank up a generator designed for 400 volt 50 Hz, so it runs at 60 Hz, and you get 480 volts. That, and transformers that can't go much above 400 volts before starting to saturate at 50 Hz can do 480 with 60 Hz.
Personally, I think the ultimate solution would have been to never use the neutral wire as a current carrying wire. Then you could simply have a standardized line-to-line voltage that can be derived from either single phase or three phased. For example, if 260 volts were chosen for that standard, then 2 single phase windings at 130 volts, or 3 three phase windings at 150 volts, would produce that voltage. Then heavy industrial users can step to a higher (450/260 with my example voltage) level if they need it. By making sure nothing was ever made to use the line-to-ground voltage, it would keep things simple, while still having a voltage suitable for heavy home usage without incurring too much current.
Plain 120 volts is inadequate. But we do have 240 volts here; it's just that the ground tap is in the center instead of one end (which does reduce the shock risk for humans standing in water). That in itself wasn't a problem, but loads making use of it was where the voltage mess originated, in my opinion.
Alternatively, I wouldn't be crying a single tear had the USA gone with a system like the UK has, though with 480/277 at 60 Hz. But even 400/231 at 50 Hz would be fine (imagine if the entire world had gone with that).
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     snipped-for-privacy@ipal.net writes:

I know they are often called "ring mains", but the correct term is a "ring circuit". A "ring mains" is what you get in the street where the supply to homes is connected in a ring, which is very common in the UK at least.

Strictly, the fuse is to protect the appliance _lead_, not the appliance. If an appliance requires fusing to remain safe, then it is required to include its own fuse protection. With EU harmonisation, all appliance leads are required to be able to clear a fault without damage when protected at 16A as is done in many other EU countries, so all new appliances would be OK with 13A fuses anyway in theory. Older appliances with longer leads of small conductor size could have problems with this though, and appliances with leads of small conductor size are now restricted to something like 2 metre length max, so enough current flows to clear the fault current protective device quickly in the event of a short circuit.

No. The regs describe exactly what type of fuse a plug must have. There are plugs with RCDs(GFCIs) built in, but they aren't common, and still have to contain the regulation fuse anyway.

In the case of a ring circuit, both ends connect to the same 30A breaker in the panel. When 30A ring circuits were first introduced in 1947, it was also allowed to connect each end to a different 15A fuse, as it was thought people would convert their existing 15A radial circuits feeding a 15A round pin sockets into 30A ring circuits by forming the ring starting from two existing 15A outlets, saving the need to replace some of the wiring. In practice such conversions were probably rather rare, and the two 15A fuses scheme has not been allowed since the early days.

Traditionally, 30A or 45A circuits are installed for electric hobs or combined hobs/ovens (is that what you call a stove?) Electric hobs are very much out of fashion in UK, and electric ovens, unless very large, can mostly run from a standard 13A socket nowadays because they are better thermally insulated and very quickly heated with fanned hot air. As a result, the high current dedicated cooking circuits are often no longer installed at all.

One thing I noticed browsing US electrical department stores was the lack of high powered portable appliances. Someone already mentioned the lack of a 3kW kettle. I was looking to see how much my Microwave cost in the US, but could only find the cheaper version of my Sharp model without the browning element. Then it dawned on me that they couldn't sell a 2.7kW (IIRC) appliance in the US as you couldn't plug it in to a standard outlet on a kitchen worktop.

Several hundred -- usually quite a few residential roads.

1MVA is the rating of one I know.

The max permitted at the suppliers terminals in your home is 18kA single phase and 25kA 3-phase. Normally it's nowhere near this, and most people have a main cutout of a type which can only handle up to 10kA, and that's still plenty of spare margin. It is required that the PSCC (Prospective Short Circuit Current) at any premisies be taken into account when designing the installation. A case where you can run into problems is in an apartment block with integral substation; the apartment nearest the transformer might need to have some excess supply cable snaked around to increase the supply impedance slightly. I've seen a photo of an incident where this was not taken into account, and all the protective devices failed to clear the fault current, resulting in the wire exploding out of the wall.

One thing I notice in the US verses the UK is poor regulation -- turn on a higher current appliance and the lights dim. That's sufficiently rare in the UK that people usually think there's a fault if they see it happening. However, it's not clear to me where this voltage loss happens in US systems. A 2kW load is a noticable proportion of a 20kW pole mount transformer's capacity, but a quite insignificant proportion of a 1MW pad mount transformer, so transformer regulation could be an issue. Additionally, higher current for same load could create a very much more significant voltage drop in conductors, but I haven't checked to see how you size your conductors compared to ours, and if this is a significant factor. Another issue is that we in the UK tend to have dedicated lighting circuits, so they won't be competeing on the final branch circuit with any high current loads. That's 3 possible factors, but I have no idea their comparitive contributions to the overall observable affect in the US.

In the UK you can get just 2 phases. There is no switchgear for two phases -- people either use two sets of single phase switchgear, or use 3-phase with one not connected (the latter being essential if you have any appliances needing more than one phase, but I can't think of any such which don't need all 3 phases).
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| Strictly, the fuse is to protect the appliance _lead_, not the | appliance. If an appliance requires fusing to remain safe, then | it is required to include its own fuse protection. With EU | harmonisation, all appliance leads are required to be able to | clear a fault without damage when protected at 16A as is done in | many other EU countries, so all new appliances would be OK with 13A | fuses anyway in theory. Older appliances with longer leads of small | conductor size could have problems with this though, and | appliances with leads of small conductor size are now restricted | to something like 2 metre length max, so enough current flows to | clear the fault current protective device quickly in the event | of a short circuit.
So what kind of fault would happen on the lead (wire, cord, etc), that would not be protected by the fuse in the appliance itself, and would not trip the breaker or blow the fuse of the house circuit itself?
Fuses in plugs are uncommon in the USA. But I do recall seeing them in Christmas tree light strings many years ago. These were parallel strings where each individual light was at full voltage. Apparently it was considered that these wires were more subject to damage and ease of spreading a fire from a dried out tree was high.
|> What current levels are used for electric stoves, ovens, hobs, etc? | | Traditionally, 30A or 45A circuits are installed for electric hobs | or combined hobs/ovens (is that what you call a stove?) Electric | hobs are very much out of fashion in UK, and electric ovens, unless | very large, can mostly run from a standard 13A socket nowadays because | they are better thermally insulated and very quickly heated with fanned | hot air. As a result, the high current dedicated cooking circuits are | often no longer installed at all.
So what is in fashion instead of electric hobs? The combined hob/oven?
|> We have them here up to 60 amps and they run on 240 volts (120 amps |> on 120 volts would be rather undesireable). | | One thing I noticed browsing US electrical department stores was the | lack of high powered portable appliances. Someone already mentioned | the lack of a 3kW kettle. I was looking to see how much my Microwave | cost in the US, but could only find the cheaper version of my Sharp | model without the browning element. Then it dawned on me that they | couldn't sell a 2.7kW (IIRC) appliance in the US as you couldn't plug | it in to a standard outlet on a kitchen worktop.
The NEC now requires a minimum of 2 circuits of 20 amps with 20 amp receptacles in the kitchen countertop. But with only 120 volts, you are looking at 2400 watts maximum. This is one of the reasons I plan to have 240 volt receptacles in the kitchen of the house I will be building in a few years. There aren't that many appliances that work on 240 volts now (I have seen some larger microwave ovens that do), but maybe I can find some I could import from the UK as long as they are not fussy about how the grounding is done (center tapped here) and the 60 Hz. I would have to change the plug.
|> How many homes would be on a single substation? | | Several hundred -- usually quite a few residential roads.
So if each home has a capacity of 100 amps, and the diversity factor is say 10, you're still looking at thousands of amps normal capacity in the substation, which would translate to tens of thousands of amps of fault capacity. You'd be depending more on the wire resistance than in the transformer impedance to limit the fault current.
|> What would be the total current rating for that substation secondary? | | 1MVA is the rating of one I know.
Split over three phases that would be over 1380 amps of capacity. Given a typicaly large capacity transformer impedance of 5% to 7% you could be looking at fault currents of 20000 to 27000 amps, not considering the distribution wire resistance (which will lower it). That sounds a lot like the "network service" areas in the US.
| The max permitted at the suppliers terminals in your home is 18kA | single phase and 25kA 3-phase. Normally it's nowhere near this, | and most people have a main cutout of a type which can only handle | up to 10kA, and that's still plenty of spare margin. It is required | that the PSCC (Prospective Short Circuit Current) at any premisies | be taken into account when designing the installation. A case where | you can run into problems is in an apartment block with integral | substation; the apartment nearest the transformer might need to have | some excess supply cable snaked around to increase the supply | impedance slightly. I've seen a photo of an incident where this was | not taken into account, and all the protective devices failed to | clear the fault current, resulting in the wire exploding out of the | wall.
They they must be running some long or thin wires to get fault currents down to those levels.
| One thing I notice in the US verses the UK is poor regulation -- turn | on a higher current appliance and the lights dim. That's sufficiently | rare in the UK that people usually think there's a fault if they see it | happening. However, it's not clear to me where this voltage loss happens | in US systems. A 2kW load is a noticable proportion of a 20kW pole mount | transformer's capacity, but a quite insignificant proportion of a 1MW | pad mount transformer, so transformer regulation could be an issue. | Additionally, higher current for same load could create a very much more | significant voltage drop in conductors, but I haven't checked to see how | you size your conductors compared to ours, and if this is a significant | factor. Another issue is that we in the UK tend to have dedicated | lighting circuits, so they won't be competeing on the final branch | circuit with any high current loads. That's 3 possible factors, but I | have no idea their comparitive contributions to the overall observable | affect in the US.
The dimming is typically due to the lower available current, either due to longer or thinner wires, or lower capacity transformers. It's not regulation that is the issue, since voltage regulation is done mainly in the generation (exciter control) and transmission (tap changers).
Conductor sizes could, in theory, be similar. Both the UK and the US have 240 volt systems. It's just that the US puts the ground tap in the center of the transformer secondary and also runs a wire from it as the neutral (hence a 3 wire system). So for a given kW usage, we're looking at about the same amps total. But with more devices running from 120 volts, they tend to be current hogs on startup.
Recent (the last 20 to 40 years) home construction here does put lights on separate circuits from receptacles and dedicated appliances. Still, I see quite a whopper dimming of lights when I start the garbage disposal grinding motor. That's something I plan to try to get a 240 volt version in the future. I'm also considering isolating things that do that on their own transformer.
| In the UK you can get just 2 phases. There is no switchgear for two | phases -- people either use two sets of single phase switchgear, or | use 3-phase with one not connected (the latter being essential if | you have any appliances needing more than one phase, but I can't | think of any such which don't need all 3 phases).
You can derive 3 phases from 2 phases with a couple transformers if you need 3 phases.
The three phase transformer star would be like this:
* \ *--* / *
You get just 2 of the phases like this:
* \ * / *
You get a pair of 240-to-240 isolating transformers, one connected one each phase, so you have separate power sources like these angles:
* * \ / * *
Now connected together like this, you get the third angle between the ends:
* / \ * *
Ground one end with the grounded (neutral) of the original 2 phases:
* * \ / \ * * / *
It looks funny, but now you have three phase power. It's a 2 phase to 3 phase autotransformer.
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     snipped-for-privacy@ipal.net writes:

The fuse in the appliance itself can't protect the lead. However, I think I'm not understanding what you're asking.

Natural Gas hobs, or combined hob/oven where the oven is electric and the hob is gas. So the electric load is often now only the oven, and unless it's large, it can run from a standard 13A socket outlet.

They don't care about how the grounding is done. Products sold in the EU have to be suitable for use anywhere in the EU, and there's a mixture of supply types, some with live/neutral polarity unknown at socket outlets, and some where neither terminal is near ground potential.

On average, the supply cable from the substation is probably longer than in the US. I think my nearest substation is perhaps 400 yards (2 streets) away. Of course, some people will be right next to it.

I'm not well up on the substation transformers, but I believe they have some feature which increases the supply impedance during gross fault currents. I've no idea how it works.

By regulation here, I was refering to transformer output voltage variation with load.

I think that's misleading. For a given kW load plugged into a 120V outlet, I think you will need 4 times the crossectional conductor size to reduce your cable voltage drop percentage and power loss to the same as ours.

In US hotels, I often find the bathroom socket and light on the same circuit. The hairdrier often has a low power mode achieved with a diode rectifier. This causes the bathroom light to flicker rather badly at 60Hz...
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| snipped-for-privacy@ipal.net writes:
wrote: |> |>| Strictly, the fuse is to protect the appliance _lead_, not the |>| appliance. If an appliance requires fusing to remain safe, then |>| it is required to include its own fuse protection. With EU |>| harmonisation, all appliance leads are required to be able to |>| clear a fault without damage when protected at 16A as is done in |>| many other EU countries, so all new appliances would be OK with 13A |>| fuses anyway in theory. Older appliances with longer leads of small |>| conductor size could have problems with this though, and |>| appliances with leads of small conductor size are now restricted |>| to something like 2 metre length max, so enough current flows to |>| clear the fault current protective device quickly in the event |>| of a short circuit. |> |> So what kind of fault would happen on the lead (wire, cord, etc), that |> would not be protected by the fuse in the appliance itself, and would |> not trip the breaker or blow the fuse of the house circuit itself? | | The fuse in the appliance itself can't protect the lead. | However, I think I'm not understanding what you're asking.
There are two different kinds of reasons for a fuse to blow. One is that the load is pulling a little more thgan it should, which would gradually heat up the wire, possibly melting insulation. The lead itself will not cause this kind of problem. So a fuse in an appliance would protect the lead from an overload. The other problem is damage to the lead causing a short circuit. The breaker for the circuit in the wall will trip on this kind of problem.
|> So what is in fashion instead of electric hobs? The combined hob/oven? | | Natural Gas hobs, or combined hob/oven where the oven is electric | and the hob is gas. So the electric load is often now only the oven, | and unless it's large, it can run from a standard 13A socket outlet.
Among people who prefer all electric, would they still have the same thing but in electric version? Or is gas so preferred that you can't even find people that prefer electric?
|> The NEC now requires a minimum of 2 circuits of 20 amps with 20 amp |> receptacles in the kitchen countertop. But with only 120 volts, you |> are looking at 2400 watts maximum. This is one of the reasons I plan |> to have 240 volt receptacles in the kitchen of the house I will be |> building in a few years. There aren't that many appliances that work |> on 240 volts now (I have seen some larger microwave ovens that do), |> but maybe I can find some I could import from the UK as long as they |> are not fussy about how the grounding is done (center tapped here) |> and the 60 Hz. I would have to change the plug. | | They don't care about how the grounding is done. Products sold in the | EU have to be suitable for use anywhere in the EU, and there's a mixture | of supply types, some with live/neutral polarity unknown at socket | outlets, and some where neither terminal is near ground potential.
So does this mean the chassis is not connected to any wire, and a fault between a live wire and the chassis can go undetected (since it would not fault to ground) until a human becomes the path?
|> Split over three phases that would be over 1380 amps of capacity. |> Given a typicaly large capacity transformer impedance of 5% to 7% |> you could be looking at fault currents of 20000 to 27000 amps, not |> considering the distribution wire resistance (which will lower it). |> That sounds a lot like the "network service" areas in the US. | | I'm not well up on the substation transformers, but I believe they | have some feature which increases the supply impedance during gross | fault currents. I've no idea how it works.
Maybe saturable reactors?
|> The dimming is typically due to the lower available current, either due |> to longer or thinner wires, or lower capacity transformers. It's not |> regulation that is the issue, since voltage regulation is done mainly |> in the generation (exciter control) and transmission (tap changers). | | By regulation here, I was refering to transformer output voltage | variation with load.
The transformers on the poles here generally don't have taps to change. Those in the area substation (such as 69kV in, 12kV out) usually do, but the ones I've seen require de-energizing before changing, so it cannot be done on a day of heavy load to raise the voltage there. But there are more sophisticated tap changers on transmission transformers that can be changed by motor control while energized for fine adjustments during the load changes of the day.
But for a motor start, you'd have to have your own in-house voltage regulator to correct the lights dimming. There are such things you can get.
|> Conductor sizes could, in theory, be similar. Both the UK and the US have |> 240 volt systems. It's just that the US puts the ground tap in the center |> of the transformer secondary and also runs a wire from it as the neutral |> (hence a 3 wire system). So for a given kW usage, we're looking at about |> the same amps total. But with more devices running from 120 volts, they |> tend to be current hogs on startup. | | I think that's misleading. For a given kW load plugged into a 120V | outlet, I think you will need 4 times the crossectional conductor | size to reduce your cable voltage drop percentage and power loss to | the same as ours.
That's only if it is a single load. On average, when the loads get high, they tend to be balanced out because the connection distribution is good. It's when just one big load is on that there is an imbalance, but that is generally still just a fraction of the capacity. So at high load, where wire size matters, it's effectively a 240 volt load here.
|> Recent (the last 20 to 40 years) home construction here does put lights |> on separate circuits from receptacles and dedicated appliances. Still, |> I see quite a whopper dimming of lights when I start the garbage disposal |> grinding motor. That's something I plan to try to get a 240 volt version |> in the future. I'm also considering isolating things that do that on |> their own transformer. | | In US hotels, I often find the bathroom socket and light on the same | circuit. The hairdrier often has a low power mode achieved with a | diode rectifier. This causes the bathroom light to flicker rather badly | at 60Hz...
Hotels typically have cheap wiring. I've seen as many as 8 rooms on one single circult (everything, outlets and lights).
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     snipped-for-privacy@ipal.net writes:

OK, we call these two overload currents and fault currents respectively. If an appliance which uses a socket outlet has any likely failure mode which would otherwise be unsafe if it was not protected by a fuse, then it has to include a appropriate fuse within itself. I'm not sure but it may be that this only applies if the protection required is less than 16A, which is I believe the highest current protection used anywhere in Europe on standard domestic outlets. The fuse in the plug is to protect the lead from overload or fault currents. The next upstream protection would otherwise be 30A/32A for the ring circuit protection in the UK.

You can buy expensive ceramic and halogen hobs for people who want a hob which looks like one of those, but most people find gas much better to cook on and cheaper. Cheap electric hobs are used in low-end rented rooms.

No, the chassis of all microwaves is grounded. I just meant that the microwave won't be assuming that neutral will be at similar potential to ground, nor which is live and neutral. I would expect it would work without problems on a 240V centre-grounded supply.
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| snipped-for-privacy@ipal.net writes:
wrote:
wrote: |>|> |>|>| Strictly, the fuse is to protect the appliance _lead_, not the |>|>| appliance. If an appliance requires fusing to remain safe, then |>|>| it is required to include its own fuse protection. With EU |>|>| harmonisation, all appliance leads are required to be able to |>|>| clear a fault without damage when protected at 16A as is done in |>|>| many other EU countries, so all new appliances would be OK with 13A |>|>| fuses anyway in theory. Older appliances with longer leads of small |>|>| conductor size could have problems with this though, and |>|>| appliances with leads of small conductor size are now restricted |>|>| to something like 2 metre length max, so enough current flows to |>|>| clear the fault current protective device quickly in the event |>|>| of a short circuit. |>|> |>|> So what kind of fault would happen on the lead (wire, cord, etc), that |>|> would not be protected by the fuse in the appliance itself, and would |>|> not trip the breaker or blow the fuse of the house circuit itself? |>| |>| The fuse in the appliance itself can't protect the lead. |>| However, I think I'm not understanding what you're asking. |> |> There are two different kinds of reasons for a fuse to blow. One is that |> the load is pulling a little more thgan it should, which would gradually |> heat up the wire, possibly melting insulation. The lead itself will not |> cause this kind of problem. So a fuse in an appliance would protect the |> lead from an overload. The other problem is damage to the lead causing |> a short circuit. The breaker for the circuit in the wall will trip on |> this kind of problem. | | OK, we call these two overload currents and fault currents respectively. | If an appliance which uses a socket outlet has any likely failure mode | which would otherwise be unsafe if it was not protected by a fuse, then | it has to include a appropriate fuse within itself. I'm not sure but it | may be that this only applies if the protection required is less than 16A, | which is I believe the highest current protection used anywhere in Europe | on standard domestic outlets. The fuse in the plug is to protect the lead | from overload or fault currents. The next upstream protection would | otherwise be 30A/32A for the ring circuit protection in the UK.
The upstream 30A fuse/breaker would protect for a short circuit fault.
|>|> The NEC now requires a minimum of 2 circuits of 20 amps with 20 amp |>|> receptacles in the kitchen countertop. But with only 120 volts, you |>|> are looking at 2400 watts maximum. This is one of the reasons I plan |>|> to have 240 volt receptacles in the kitchen of the house I will be |>|> building in a few years. There aren't that many appliances that work |>|> on 240 volts now (I have seen some larger microwave ovens that do), |>|> but maybe I can find some I could import from the UK as long as they |>|> are not fussy about how the grounding is done (center tapped here) |>|> and the 60 Hz. I would have to change the plug. |>| |>| They don't care about how the grounding is done. Products sold in the |>| EU have to be suitable for use anywhere in the EU, and there's a mixture |>| of supply types, some with live/neutral polarity unknown at socket |>| outlets, and some where neither terminal is near ground potential. |> |> So does this mean the chassis is not connected to any wire, and a fault |> between a live wire and the chassis can go undetected (since it would not |> fault to ground) until a human becomes the path? | | No, the chassis of all microwaves is grounded. I just meant that the | microwave won't be assuming that neutral will be at similar potential | to ground, nor which is live and neutral. I would expect it would work | without problems on a 240V centre-grounded supply.
Now days (at least in the US) all appliances with the chassis connected to a wire should never assume a particular wire is neutral (even though in the US we now have a polarized receptacle/plug). A metal chassis should be connected to the ground wire. If that is the same in EU, then the only remaining issues are exact voltage and frequency, and those tend not to be problems in modern appliances.
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... This resulted in lights designed for 277 (or 347)

Some history here... Universal 3-phase for residential service was briefly considered in the USA, but rejected. The REA (Rural Electrification Agency) looked at various systems that could bring power to towns and isolated farmhouses in the 1930's and decided that it liked the economy of single (spilt) phase 110/220 service with a center tapped neutral and two hot legs. One of the major considerations was the ability to power farm machinery and it was determined that a major portion of motorized farm loads could be done with motors less than or equal to 10 horsepower, which were readily available in single phase models. For motorized loads over 10 HP, the (single phase) repulsion start - induction run motor was available.
What became the REA standard for farms and rural areas then became the standard for the US overall.
It is true that back in the 1880s, Edison preferred DC, but after Westinghouse demonstrated his AC system (developed by Tesla) in Chicago at the Worlds Fair in 1893, the overwhelming technical superiority and economics of long distance AC transmission quickly became the only practical system from the standpoint of future installations. DC distribution from that point onward, was limited to railroads and streetcars, (and a few large cities provided DC for elevator service in their central business districts).
Edison's long lasting contributions (in addition to inventions) were, the selection of a distribution voltage of 110 volts and the 3 wire circuit with a neutral, designed to effect a savings in copper and a reduction in voltage drop. The 3 wire system first appeared on Edison's DC central stations (120 VDC dynamos in series) but an equivalent circuit was developed for AC with center-tapped transformers.
It appears that none of the early systems, AC or DC were grounded. The importance of grounding for safety was not recognized. Grounding was a complex subject and early efforts appear to indicate that the motivation was primarily for lightning (equipment) protection vs. human safety.
Beachcomber
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| Some history here... Universal 3-phase for residential service was | briefly considered in the USA, but rejected. The REA (Rural | Electrification Agency) looked at various systems that could bring | power to towns and isolated farmhouses in the 1930's and decided that | it liked the economy of single (spilt) phase 110/220 service with a | center tapped neutral and two hot legs. One of the major | considerations was the ability to power farm machinery and it was | determined that a major portion of motorized farm loads could be done | with motors less than or equal to 10 horsepower, which were readily | available in single phase models. For motorized loads over 10 HP, the | (single phase) repulsion start - induction run motor was available. | | What became the REA standard for farms and rural areas then became the | standard for the US overall.
Apparently around the late 1950's and early 1960's some more three phase residential power showed up. I'm not sure why, but my guess is that it coincided with an emerging popularity of central air conditioning, first in larger homes, which needed larger units, and hence larger motors. As cheaper units brought it to smaller homes, single phase handled it and the demand for three phase dropped off.
| It is true that back in the 1880s, Edison preferred DC, but after | Westinghouse demonstrated his AC system (developed by Tesla) in | Chicago at the Worlds Fair in 1893, the overwhelming technical | superiority and economics of long distance AC transmission quickly | became the only practical system from the standpoint of future | installations. DC distribution from that point onward, was limited to | railroads and streetcars, (and a few large cities provided DC for | elevator service in their central business districts). | | Edison's long lasting contributions (in addition to inventions) were, | the selection of a distribution voltage of 110 volts and the 3 wire | circuit with a neutral, designed to effect a savings in copper and a | reduction in voltage drop. The 3 wire system first appeared on | Edison's DC central stations (120 VDC dynamos in series) but an | equivalent circuit was developed for AC with center-tapped | transformers.
I'm sure with lights being the "fad" load of the day, new AC service had to be compatible. So 110 volt AC worked on lights designed for 110 volt DC.
Still, I think even more savings could have been had by just dropping the neutral and going with straight 220 volt. It's those Edison lights that made that not practical. That and their exposed metal base which would have been a shock hazard on a 220 volt system with the ground tap in the center at the transformer instead of one end. But if a safe light for 220 volt 2 pole had been adopted, the wire cost would have been 2/3 as much. OTOH, you'd need 2 pole switches, and still some kind of ground.
I think the neutral-less circuit would be the best, but historically, I can't see an easy way to get to it.
| It appears that none of the early systems, AC or DC were grounded. | The importance of grounding for safety was not recognized. Grounding | was a complex subject and early efforts appear to indicate that the | motivation was primarily for lightning (equipment) protection vs. | human safety.
I read that Edison was in fact pushing for grounding the neutral, and even did so in his system. But we know today we need a separate wire for grounding. Edison was loath to use another wire. But if he had used the 220 volt 2-pin bulbs, he could make the neutral be purely a safety ground wire only (had he realized such a need).
My whole push for such a system is to get a single voltage, and one that is adequate for heavy residential loads like air conditioning and stoves. If that had been 220 volts (if I were picking it, I'd go a bit higher), then single phase could do it with two 110 volt poles, and three phase could do it with three 127 volt poles. As long as nothing was designed to use a neutral wire, then it would be the one voltage all around.
Alternatively, I'd like to see universal 3 phase or 2 legs of 3 phase. That way the voltage level would be consistent.
Today, I would not want 3 phase power unless it were practical for me to derive 240 volts from it, since many things like electric stoves are not designed for 208 volt systems (most models are not, but some are). What I mean is full performance. Most of those that are designed for just 240 volts do say they work at 208 volts, but with a reduced level of wattage, which I translate into taking longer to bring water to a boil.
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Phil:
What you say makes sense but there are a lot of competing interests here that might have problems with what you might not have mentioned.
First of all, Edison made thousands of lightbulbs at all different sorts of voltages. If you ever get a chance to visit the Edison Museum in Ft. Myers Florida, you can see these on display. Some of the coolest are the incandescent "searchlight" bulbs that operate on thousands of volts. The Edison system involved a search for the ideal filament optimized by resistance for what Edison should be the standard residential/commercial distribution voltage of 110 V. however. European incandescent lights, of the same physical size and wattage rating often run much hotter (because of the 220-240 volts). The resistance problem is not trivial at the higher voltage because, lets say R is more or less the same, the power dissapated is I squared R and that can be a lot of power at the higher voltage. Touch a 60 watt bulb in the US, and you will pull your fingers back and say that is hot. Touch a 50 watt Phillips bulb on a Euro 240 volt circuit and you could get 2nd degree burns. ( I know from personal experience, I've done this in visits to Europe).
Back to the neutral problem... You mentioned that it would be great to have a system without a neutral. From the point of view of installing ovens, air conditioners, or dryers, this might be desirable, but from the point of view of the electric utility servicing your property, maybe not so.
If there is a fault in the power line serving your residence, whereby lets say a primary operating at 34.6 kV comes in contact with the secondary feeders to your home (either 230 or 120/240). If you have a grounded neutral system, chances are good that the fuse on the primary will blow and you will live. However, even if the fuse on the primary does not blow, because of the grounding, the highest voltage that just fried your radio, TV, and CD player is likely to be very much more that 240 volts, but also very much less than 34.6 kV. Grounding and specifically a grounded-neutral is a very important safety feature for the utilities.
Likewise, for lighting protection, transients and surges, utilities have found grounded systems (and all the associated equipment such as arrestors, and reclosers) to be the best defense against equipment damage. Grounded systems also protect customers from bearing the full brunt of a lighting strike to exterior equipment (poles, overhead lines, substations).
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| First of all, Edison made thousands of lightbulbs at all different | sorts of voltages. If you ever get a chance to visit the Edison | Museum in Ft. Myers Florida, you can see these on display. Some of | the coolest are the incandescent "searchlight" bulbs that operate on | thousands of volts. The Edison system involved a search for the ideal | filament optimized by resistance for what Edison should be the | standard residential/commercial distribution voltage of 110 V. | however. European incandescent lights, of the same physical size and | wattage rating often run much hotter (because of the 220-240 volts). | The resistance problem is not trivial at the higher voltage because, | lets say R is more or less the same, the power dissapated is I squared | R and that can be a lot of power at the higher voltage. Touch a 60 | watt bulb in the US, and you will pull your fingers back and say that | is hot. Touch a 50 watt Phillips bulb on a Euro 240 volt circuit and | you could get 2nd degree burns. ( I know from personal experience, | I've done this in visits to Europe).
A 100 watt bulb designed for 120 volts and a 100 watt bulb designed for 240 volts are going to have quite different resistance, around 144 ohms and 576 ohms, respectively, at operating temperature. Actual designs do vary for many reasons, such as targeting a slightly higher voltage to make longer lasting bulbs. I hope your European experience did not involve trying to run an American lightbulb on their voltage. But it could be they intentionally run the bulbs at a hotter temperature for some reason. Are you sure it wasn't a halogen bulb in a traditional bulb shape?
Where higher voltage could be an issue with a lightbulb is when the filament breaks, leaving a gap sufficient for the voltage to arc across continuously. That's not a problem with typical bulbs at 240 volts, but could be interesting at voltages above 10 kV. Once it breaks, the full voltage is at the gap.
| Back to the neutral problem... You mentioned that it would be great to | have a system without a neutral. From the point of view of installing | ovens, air conditioners, or dryers, this might be desirable, but from | the point of view of the electric utility servicing your property, | maybe not so. | | If there is a fault in the power line serving your residence, whereby | lets say a primary operating at 34.6 kV comes in contact with the | secondary feeders to your home (either 230 or 120/240). If you have a | grounded neutral system, chances are good that the fuse on the primary | will blow and you will live. However, even if the fuse on the | primary does not blow, because of the grounding, the highest voltage | that just fried your radio, TV, and CD player is likely to be very | much more that 240 volts, but also very much less than 34.6 kV. | Grounding and specifically a grounded-neutral is a very important | safety feature for the utilities. | | Likewise, for lighting protection, transients and surges, utilities | have found grounded systems (and all the associated equipment such as | arrestors, and reclosers) to be the best defense against equipment | damage. Grounded systems also protect customers from bearing the full | brunt of a lighting strike to exterior equipment (poles, overhead | lines, substations).
My neutral-less power system is still a grounded one. The transformer secondary would be grounded at a center tap. What I propose does not differ at the transformer. In fact, that center tapped wire may even be carried into the house much like a neutral is today. But it would just be the ground-ING wire, not the ground-ED neutral wire. It would be attached to the ground electrode at the transformer and at the service entrance. But it would be treated the same as the ground-ING wire in the circuit wiring. GFCI leakage measurement would only look at the two hot wires. An extra safety precaution could also shunt trip the appropriate breakers if excess ground current is detected.
Imagine wiring up a circuit intended for a window air conditioner that has a NEMA 6-15 plug. There's no neutral on that, but there is a ground that isn't used for power.
For three phase, my system would have 15.47% more voltage on each of 3 transformer windings phased at 120 degrees, forming the common star/wye configuration. That center point would be grounded, but not carried to loads as a current carrying conductor.
What my system would do is standardize on a single voltage, which would be higher than the ground potential due to the center tap grounding. That would mean that anything designed for a single phase of that voltage could get what it expects by connecting to any 2 phases of 3 phase power.
If the voltage chosen were 240 volts, then the ground potential on each hot wire would be 120 volts for single phase and 139 volts on three phase. Of course that would lead to a saying that "three phase power is more dangerous". But then, I've heard that already.
BTW, 240Y/139 is available in some places, probably as a safer alternative to 240 delta. Motors designed for 240 delta and not using a neutral would work fine on 240Y/139. So would the 240 volt window air conditioner when connected to 2 of those hot wires (as long as it didn't cheat and use the ground wire to obtain 120 volts for some component within).
The power distribution would be wired the same. The only difference for the utility is they would have to have transformers with 15.47% more volts on the secondary for three phase users. But they usually use different transformers now, anyway. Using a bank of 240/120 single phase transformers to get 208Y/120 is a waste of half the capacity. For 480Y/277, they need a 277 volt secondary (347 in Canada). 415Y/240 could be done with 240/120 transformers, but it is pretty much non-existant in this country.
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