Single phase, 2 phase, 3 phase etc

[westie101]

It suggests that a lack of discussion at higher levels particularly in the case on CNE which is very prone to loss of neutral/earth.

If you think of cable design, the original 4core was: -
4 cores (copper and later aluminium) with paper insulation
an outer belt baper insulation surrounding the cores
a lead sheath
a layer of hessian soaked in bitumen
2 laters of steel tape (though SWA is used)
another layer in hessian

When PME came legal the design changed, initially 3 designs were specified by the industry with them being spread amongs the 'Leccy Boards for trial
They all had 3 aluminium cores with paper insulation, then the differences began, with a choice of copper or aluminium stranded N/E or a solid aluminium sheath.
All covered by a PVC sheath.
It was discovered over time that if the PVC was damaged aluminium sheaths could then corrode from ground water and the N/E would be lost, hence the start of the famous "Neutral Fault"
The companies using the solid aluminium sheath were by far the worst affected (guess what one I work in).
I would say we have in to double figures of these a year and it is a huge concern.

From the older designs apart from theft we don't have any!

Yet the non PME is seen as the greater hazard
Go Figure

I suspect that it comes from EU concerns, as out of the UK concern about correct polarity is not the issue we have, so treating the neutral as live makes sense from that point of view

(it was the same with core colours for 3 phase, we were, I have been told, pretty much the only country that wanted seperate colours for the individual phases. The rest of the EU was happy to have 3 brown and 1 blue as they were used to sort phase rotation on an individual basis!)

 

[JohnW2]

If you think of cable design, the original 4core was: - ... When PME came legal the design changed, initially 3 designs were specified by the industry with them being spread amongs the 'Leccy Boards for trial
They all had 3 aluminium cores with paper insulation ... All covered by a PVC sheath. ... It was discovered over time that if the PVC was damaged aluminium sheaths could then corrode from ground water and the N/E would be lost, hence the start of the famous "Neutral Fault"

Yes, but you are talking about the "famous Neutral Fault" arising in a 3-phase cable, presumably usually one of your 'mains'. What about the service cables? The final bit of the (overhead) supply to my house consists of PVC/PVC singles attached for a substantial distance (20-30m) to the wall of a neighbouring property, travelling through/behind various bits of plant-life (which needs regular pruning). It is far from beyond credibility that, for example, some less-than-careful pruning could one day sever (just) the neutral, in which case (in the presence of loads) the neutral within my installation would become 'live' - and that would be equally probable whether it were a CNE or simple neutral. Have you not, in your 43 years, never seen that sort of thing happen?

Kind Regards, John

 

[bernardgreen]

We had a "lost neutral" on the PME supply to the 13 houses, bouncy neutrals for a while .
We had a phase to phase short in a UG cable under the High Street for which the short term fix was to put the shorted conductors onto the same phase at the substation. This created large unbalance and high neutral currents and thus neutrals in houses and small businesses bouncing all over the place.
A hill top site ( radio comms ) lost its neutral ( LV overhead three phase + N up the hill ), some equipment shut down on over or under volt protection but some sent smoke signals. The supply was changed to HV 3 phase no neutral up the hill and a tranny next to the hill top.
A few others that did not affect / involve me come to mind.
Theft of the neutral to ground strap at a sub-station meant neutral was via bonds in houses MET to water pipes. The pipes being all metal along the street meant the bonds were carrying the full load and being under size caught fire in three adjacent kitchens. Subsequent damage to a gas pipe resulted in an explosion.

 

[westie101]

It is far from beyond credibility that, for example, some less-than-careful pruning could one day sever (just) the neutral, in which case (in the presence of loads) the neutral within my installation would become 'live'

Yes that does happen I will grant you (forgot about these) but again they are not common.

But answer this, should a core that may become live if a fault occurs be treated as live 100% of the time. Or would it be better to warn users that in some conditions it may become live?

 

[JohnW2]

It is far from beyond credibility that, for example, some less-than-careful pruning could one day sever (just) the neutral, in which case (in the presence of loads) the neutral within my installation would become 'live'

Yes that does happen I will grant you (forgot about these) but again they are not common.

Fair enough.

But answer this, should a core that may become live if a fault occurs be treated as live 100% of the time. Or would it be better to warn users that in some conditions it may become live?

I think you know my personal view, which I think is the same as yours. As I said, "in some conditions" (2 appropriate faults) a CPC etc. could become live, but it would, IMO, be quite crazy to call it a 'live conductor' for that reason! (thankfully, 'they' haven't gone quite that far!).

Kind Regards, John

 

[Iggifer]

I haven't read the entire thread, granted. But even though it SHOULDN'T be a live conductor, there's no definitely no harm in assuming it IS live. But I definitely wouldn't go so far as to call it a 'live' conductor

 

[JohnW2]

I haven't read the entire thread, granted. But even though it SHOULDN'T be a live conductor, there's no definitely no harm in assuming it IS live.

Not just 'no harm', but one needs to assume that it 'could' be live, no matter how improbable.

But I definitely wouldn't go so far as to call it a 'live' conductor

Indeed - and that's what this side-discussion is all about. To my mind, calling it a 'live conductor' achieves nothing other than confusing an awful lot of people!

Kind Regards, John

 

[ban-all-sheds]

"Live" doesn't imply any minimum PD to earth, does it?

And what's "neutral" called in an IT installation?

 

[JohnW2]

"Live" doesn't imply any minimum PD to earth, does it?

Not that I'm aware of - I don't think we really have much of a clue as to what it means. BS7671 requires it to be 'energised in normal use' (whatever that means), westie's one requires it to be 'charged' (whatever that means), and someone here suggested that it 'carries current during normal use'. Nothing quantitative and nothing which really helps me to understand!

Kind Regards, John

 

[AdrianUK]

My service head is 2 phase + neutral (from a 3 phase distributor). Only one phase is connected.

This is a throw-back from the days of the original DC supply to the town - it would have been +ve DC, 0V & -ve DC, the two fuses being in the +ve DC & -ve DC supplies

 

[PBC_1966]

I know I'm reviving this thread after 3 months, but with reference to whether one regards the neutral as a live conductor or not, it hasn't been mentioned that the IEE Wiring Regs./BS7671 definition changed at some point. I'm not sure of the exact date, but certainly if you go back as far as the 14th edition it specified that an earthed neutral was not, by definition, a live conductor.

None of this alters the fact that the great majority of the world's population probably know what they mean by a "live" conductor/wire/part - and that understanding of theirs would very rarely include a neutral conductor!

And just because the IEE/IET (whichever it was at the time) decided to change the definition in its own set of standards, you can't expect everybody to follow suit when they've spent their whole lives speaking of a neutral as not being a live conductor.

Most houses in Germany (for example) have three phase wiring. This is why it hobs here have awkward alternative connections mostly for the UK. German hobs tend to just be plugged in with a three phase plug.

Much of Europe seems to have preferred 3-phase domestic supplies in the past, even for relatively small power levels. I've seen old homes in France fed with a 15A 3-phase supply, which must certainly make for an interesting job of load balancing with anything but the smallest of appliances.

Here in the United States, we're at the other end of the scale, and 3-phase power for a regular home is rare. Single-phase (3-wire, 120/240V) is standard for residential services, and sometimes for the largest of homes at up to 400A (although 100 to 200A is more usual for the average house). In many residential neighborhoods, 3-phase power is not even available, due to the way that the HV distribution is arranged. Some apartment buildings and similar dwellings can be found with 3-phase supplies to the building, but each apartment is then normally fed with only two phases of the three.

At the one extreme you have portable appliances built for sale on the world market. Here while you have two input terminals labeled "L" and "N" or two wires coloured brown and blue the reality is you have no idea whether the "neutral" connection is actually a neutral. Maybe the appliance will be used in a country like germany where plugs are unpolarised or a country like france where while the plugs are polarised they are apparently less than steller about wiring them up the right way round. Maybe the appliance is being used on a 240/127 3 phase supply or a 240/120 split phase supply and connected between two phases so there is no neutral. You just don't know so your only option is to treat both wires as "live" and design accordingly. In this world fuses in both the "L" and "N" connections are considered good practice.

And there's a similar sort of variation here with any single-phase 240V device. Depending upon the particular supply configuration with which it's being used, both conductors may be at 120V with respect to ground, one may be at ground potential and the other at 240V, both may be at 240V to ground, or one may be at 120V and the other at 208V.

At the other extreme you have practices like those used by UK DNOs. Their strategy is to make damn sure the neutral stays tied to earth and hence there is no need to regard it as "live" and in some cases it is even possible to use it as a protective earth. Protective devices in the neutral are strictly forbidden, switches/isolators in the neutral are at the very least strongly discouraged.

And that's pretty similar over here. The incoming neutral also has an earth electrode connected to it at each service entrance, and the main switch or circuit breaker for an installation does not normally disconnect the neutral.

Anyone fancy looking at older versions of the wiring regs to see what terminology they used?

As I said above, I can tell you with certainty that the 14th edition (1966) and previous editions did not regard the neutral as a live conductor. Maybe it changed with the 15th edition, since that one was when a lot of internationalization took place? (Introduction of the TT/TN terms etc.).

(it was the same with core colours for 3 phase, we were, I have been told, pretty much the only country that wanted seperate colours for the individual phases. The rest of the EU was happy to have 3 brown and 1 blue as they were used to sort phase rotation on an individual basis!)

Or some already used two brown plus a black, or two black plus a brown, which seems daft to me. If you're going to identify the phases by color (which is sensible), why not identify all of them?

My service head is 2 phase + neutral (from a 3 phase distributor). Only one phase is connected.

This is a throw-back from the days of the original DC supply to the town - it would have been +ve DC, 0V & -ve DC, the two fuses being in the +ve DC & -ve DC supplies

In some places when d.c. supplies were converted to a.c. it was common to run the new 4-core 3-phase feeder along a main street, then splice the existing 3-wire feeders from side streets into the new cable such that each side street was fed from two of the three phases. It still provided the necessary balancing between phases on the overall system, but avoided the need to recable every street.

 

[ericmark]

For a supply given in accordance with the Electricity Safety, Quality and Continuity Regulations 2002, it shall be deemed that the connection with Earth of the neutral of the supply is permanent. Outside England, Scotland and Wales, confirmation shall be sought from the distributor that the supply conforms to requirements corresponding to those of the Electricity Safety, Quality and Continuity Regulations 2002, in this respect.

Combined protective and neutral (PEN) conductors shall not be isolated or switched except as permitted by Regulation 543.3.4.
Except as required by Regulation 537.1.4, in a TN-S or TN-C-S system the neutral conductor need not be isolated or switched where it can be regarded as being reliably connected to Earth by a suitably low impedance. For supplies which are provided in accordance with the Electricity Safety, Quality and Continuity Regulations 2002, the supply neutral conductor (PEN or N) is considered to be connected to Earth by a suitably low impedance. (Amended July 2008)

What this is saying is with a TT system, or non UK system the neutral may raise to 50 volts above true earth, so it must be considered as live. Also of course neutral carries current so when it passes through iron or steel it needs to be with the phase wires. The change was wording only, before is considered neutral as same as earth unless x is true, now it considers neutral not same as earth unless unless x is not true. So in real terms no change.

It is only the English which has changed. The only USA system we don't use is where one winding of a delta output is centre tapped and earthed. We have both split phase and three phase, our voltage is double or half the USA. In building sites we use half the USA voltage and in domestic double the USA voltage however unlike the USA we don't use the 460 volt of a split phase without the neutral. In France split phase is used a lot with hobs often having half the hob on one leg and half the hob on other leg and in UK we have to link the two halves together. But neutral is always used we don't have 460 volt heaters. The reverse with our 55-0-55 or 63-0-63 (110 volt) supplies here we never use the neutral it is always used line to line. In theroy the cables should be brown, black, green/yellow although for some reason we often in practice use blue. The plugs and sockets in theroy should be marked L1, L2, and E but are often marked L, N, and E. Not a clue why in practice we have blue and N with cables and plugs and sockets with 55-0-55 volt supplies after all the cable and plugs are yellow where with 230 volt they are blue so not as if same cable used for both voltages.

 

[ban-all-sheds]

the cable and plugs are yellow where with 230 volt they are blue

AFAIK the cable colour is just a convention, not a standard or requirement.

AFACIT blue and yellow "arctic" cable has exactly the same spec. (Whatever you choose the spec to be, given that "arctic" is meaningless )

 

[PBC_1966]

What this is saying is with a TT system, or non UK system the neutral may raise to 50 volts above true earth, so it must be considered as live.

Not sure what you mean by a "non U.K." system, but it makes no sense to say that there's a chance of the neutral rising above 50V with respect to true earth in a TT installation but not in TN, given that we could have two homes next to each other, one TT and the other TN-C-S and fed from the same LV network, and even the same pole. A break at a certain point in the neutral could cause the neutral incoming to the house to rise above 50V regardless of whether the house is wired for TT or TN-C-S (or indeed TN-S).

The only USA system we don't use is where one winding of a delta output is centre tapped and earthed.

I don't think I've ever heard of corner-grounded delta being used in the U.K. either, but I stand to be corrected. Admittedly it's not too common here either, but can be found in a few situations. The 4-wire delta (one winding center tapped) is also regarded as something of a "legacy" system now, maintained but in many areas no longer offered for new services.

The reverse with our 55-0-55 or 63-0-63 (110 volt) supplies here we never use the neutral it is always used line to line. In theroy the cables should be brown, black, green/yellow although for some reason we often in practice use blue.

In theory, with 55-0-55 it should be brown, brown, and green/yellow throughout as it's single phase. With the 63/110V 3-phase it should be brown/black/grey for the phases where run together and then brown/brown where split to single-phase branches.

The plugs and sockets in theroy should be marked L1, L2, and E but are often marked L, N, and E. Not a clue why in practice we have blue and N with cables and plugs and sockets with 55-0-55 volt supplies after all the cable and plugs are yellow where with 230 volt they are blue so not as if same cable used for both voltages.

AFAIK the cable colour is just a convention, not a standard or requirement.

Cable color is irrelevant and not mandated anywhere. I often used yellow Arctic with blue 240V connectors for caravan hookup leads, since I felt that the yellow is more noticeable and less likely to be damaged.

As for markings on the BS4343 connectors, surely it's a case of not being able to mark them for every possible use? While the yellow connectors might be most often used in the U.K. on 110V CTE (or 63/110) supplies, there's nothing to say that they cannot be used for a "straight" 110V (or similar) system with one conductor earthed. Ditto for Arctic flex, and it wouldn't make a whole lot of sense to use twin browns to satisfy 110V site supply requirements when it would then make identification of the conductors more difficult for regular 240V or similar uses.

 

[ericmark]

BS7671:2008 is not law either so even the colours given in that don't have to be complied (although appendix 7 calls them harmonized cable core colours so may be they are law?) with, but with our (UK) 110 volt system clearly the blue is a live wire, in fact it is also a line wire, so clearly it is good practice to consider blue as live. Table 7A phase 2 of AC = black so for 110 volt brown, black, green/yellow for DC it would be brown and grey. It was the grey which was added when harmonized, before that we had brown, black, black and green/yellow in Europe except UK which was red, yellow and blue for phases with black for neutral with green then green/yellow for earth. Again good reason to consider blue as live.

If one looks at a light switch in UK normally the electrician will over sleeve the blue with brown however never seen that done with 110 volt. I did see a burn out of a machines wiring loom where a 110 volt transformer was replaced with a transformer which was centre tapped. A fault line 2 to earth caused the burnout where there were no fuses on the line 2 as originally it would have been neutral so originally did not require a fuse. I have also seen Honda generators where the output was 57.5 - 0 - 172.5 where the earth was connected to centre tap on one winding for the 110 volt option so the neutral was over 50 volts from earth. When I found this I removed the 230 volt option and made generator 110 volt only, however I did not like the idea of the earth only being connected to one winding the earth loop impedance would have been rather high.

We tend to call them phase colours, but clearly also used with split phase, I suppose where a generator is wired zig - zag configuration then could be called 2 phase? But in the main we don't have 2 phase supplies. With a split phase the two supplies are in phase with each other so it is still single phase. I am not saying it does not exist but 2 phase supplies must be quite rare. In Europe since we don't use the two supplies of a split phase without the neutral it would not really matter if the supply was 2 phase or split phase. However in the USA where they use 240 volt equipment across the two phases it clearly would matter.

I remember in Algiers in Algeria we had a three phase 110 volt supply. Some one had connected a 220 volt air conditioner across two phases, and it was failing on a regular basis. Reason was only getting 190 volt as the two supplies were not in phase. So the motor overload was regularly tripping and wearing out prematurely. Other 220 volt equipment would have also been slow, but the AC was a real problem. We got an auto transformer quite a hefty one to take start load to cure problem.

I suppose with USA being 120 volt then 2 phases would be 207 volt so maybe a 220 volt AC would work, but using a 240 volt AC would have the same problem as in Algeria. All the camps in Algeria were running off generators so 220 volt with Dutch electrician and 240 volt with English electrician this was 1980 before we harmonized. So only the offices in Algiers had this problem.