If the UK leaves the EU, will the nominal voltage be changed back to 240v?

[stillp]

Industrial John, not commercial.

Fair enough. Whatever, it's the same figure one would get by allowing for the BS7671 guidance of maximum 5% (of nominal) within-installation VD on top of a -10% (of nominal) supply tolerance.

Kind Regards, John

Not quite, but near enough.

 

[ban-all-sheds]

Perhaps not at the moment. But if the DNO's are, in effect, given permission to operate to the lower limit by the new standard, don't you think it's likely they may well make use of that in the future?

They might.

Imagine increasing demand at the end of a long rural stretch of 240/415/480V (oops, make that 230/400/460V) distribution. If they can get away with allowing the voltage at the last house on the run dropping to 207V instead of having to maintain it at 216V minimum, don't you think they may well do so?

They might.

They may well even adjust the transformer taps to deliver over 250V at no load in order to satisfy the 207V minimum at full load at the distant end.

They might.

That means that the delvered voltage to that last house could well vary between over 250V during times of negligible load to 207V at peak demand.

You mean they would be experiencing a supply of 230V±10%.

 

[ban-all-sheds]

If there was no need for the actual parameters of the U.K. supply to change, then why was there any need to change the parameters on paper?

As you have been told many times, to create a single harmonised supply specification.

 

[stillp]

They may well even adjust the transformer taps to deliver over 250V at no load in order to satisfy the 207V minimum at full load at the distant end.

They might.

Not much more though, <253 V.

 

[ban-all-sheds]

By declaring that appliances manufactured from whatever date must be suitable to operate on 230V +/-10% perhaps? Or that they must be suitable for operation over the range of 207 - 253 volts? That doesn't mean that the supply in every country needs to have the exact same specification.

Yes it does.

That's the whole point.

 

[JohnW2]

What would you say if someone came here proposing to run a 10.75 kW (at 240V) shower (~42.9A at 230V) on a 40A MCB?

According to the requirements it is not allowed. ... That's how we are supposed to do it.

Maybe, but do you think it is 'right' in electrical terms?

If not, there should be a Cmax.

IMO, indeed so - and that Cmax should really be such that U0 x Cmax = maximum permitted supply voltage (not with the slight shortfall as with current Cmin!)! Does anything else make electrical/safety sense?

I do realise the point you are making.

how does it differ from your advising someone that a 10 kW (at 240V) shower would be OK on a 40A MCB, although you didn't know/realise that the OP's normal supply voltage was around 250V (shower current ~43.4A at 250V). Can an (arbitrarily calculated) 42.9A be less acceptable than a (possible) 43.4A?

... That's how we are supposed to do it. If not, there should be a Cmax.

Indeed - see above.

Are you saying 9.2kW @ 230V should not be on a 40A MCB?

If you don't regard it as 'safe' (and/or compliant with regs) to have a load drawing >40A through a 40A MCB, and if you accept that the supply voltage could theoretically be as high as 253V (hence about 43.5A), then presumably your electrical/common sense answer would be no? As I said, if you want a calculation that is going to be 'safe' for any permitted supply voltage, you have to calculate on the basis of the maximum permitted voltage. Why should 'a couple of amps' over the MCBs rating be OK if the supply voltage is 250V but not if it is 230V?

I can but presume that the rules we are told to follow account for the possible increase, whereas a rating above the allowed would obviously be excessive should the same occur.

We are told [in 433.1.1(i)], I would say not unreasonably, that In of the MCB must not be less than Ib, and I have always assumed that Ib represents the actual current which does (or may) flow, not a figure derived from calculation on the basis of an arbitrary number which has no relevance to any particular installation. Maybe that interpretation is wrong? As above, it seems odd to believe that a couple of amps above the In of the MCB is OK with some supply voltages but not with others.

Kind Regards, John

 

[JohnW2]

Fair enough. Whatever, it's the same figure one would get by allowing for the BS7671 guidance of maximum 5% (of nominal) within-installation VD on top of a -10% (of nominal) supply tolerance.

Not quite, but near enough.

Given Un=230, in what sense is [230 - (10% of 230) - (5% of 230)] 'not quite the same' as [230 - (15% of 230)]?

Kind Regards, John

 

[mattylad]

Skipping several pages.

If we leave the Eu will you employ someone to walk in front of your car with a red flag?

(Equally daft question lol)

 

[EFLImpudence]

If you don't regard it as 'safe' (and/or compliant with regs) to have a load drawing >40A through a 40A MCB, and if you accept that the supply voltage could theoretically be as high as 253V (hence about 43.5A), then presumably your electrical/common sense answer would be no? As I said, if you want a calculation that is going to be 'safe' for any permitted supply voltage, you have to calculate on the basis of the maximum permitted voltage. Why should 'a couple of amps' over the MCBs rating be OK if the supply voltage is 250V but not if it is 230V?

Well obviously because if you start with too high a value at 230V then at maximum voltage of 253V it is going to be even worse.

We are told [in 433.1.1(i)], I would say not unreasonably, that In of the MCB must not be less than Ib, and I have always assumed that Ib represents the actual current which does (or may) flow, not a figure derived from calculation on the basis of an arbitrary number which has no relevance to any particular installation. Maybe that interpretation is wrong?

I would say it is wrong, judging by the definition of nominal voltage.

230V plus 10% = current increase of 10%. For 9.2kW @ 230V = 40A plus 10% = 44A.
An MCB shall not trip at 113% of In. For In of 40A plus 13% = 45.2A.

 

[JohnD]

Skipping several pages.

If we leave the Eu will you employ someone to walk in front of your car with a red flag?

(Equally daft question lol)

If UK (possibly excluding Scotland) leaves the EU but wishes to be able to import and export goods and services, and to travel in and out without much hindrance, then we will have to continue to follow EU rules in many respects.

The difference will be that instead of being a leading member of the club and helping to make the rules, we will be outsiders having to conform but with no power.

 

[PBC_1966]

You mean they would be experiencing a supply of 230V±10%.

Yes. Which, as I said in the other thread which seems to have evolved into a parallel discussion of the same issue, means that the U.K. would have relaxed its standards, i.e. supply regulation would not be as good as it is at the moment/was in the past.

As you have been told many times, to create a single harmonised supply specification.

Which is also what I said earlier: There is no reason for the change other than to be able to say that the U.K. now shares some Europe-wide standard. You don't seem to be disagreeing with that but seem to think it a desirable end in itself, and not the "solution" to a non-existent "problem."

 

[PBC_1966]

By declaring that appliances manufactured from whatever date must be suitable to operate on 230V +/-10% perhaps? Or that they must be suitable for operation over the range of 207 - 253 volts? That doesn't mean that the supply in every country needs to have the exact same specification.

Yes it does.

That's the whole point.

A particular place has a supply specification with a voltage range A.

A piece of equipment is designed to operate over a voltage range B.

Range A is a subset of range B.

What prevents the piece of equipment with required voltage range B from working quite satisfactorily and safely when connected to a supply with a guaranteed voltage range A?

 

[PBC_1966]

If UK (possibly excluding Scotland) leaves the EU but wishes to be able to import and export goods and services, and to travel in and out without much hindrance, then we will have to continue to follow EU rules in many respects.

Let's clarify that: It would be to import and export goods and services to and from other EU countries.

But getting out of the EU would leave the U.K. in a much better position to trade with the rest of the world, since it would no longer be bound by the EU rules which dictate how the U.K. must trade with non-EU countries as well.

 

[stillp]

Fair enough. Whatever, it's the same figure one would get by allowing for the BS7671 guidance of maximum 5% (of nominal) within-installation VD on top of a -10% (of nominal) supply tolerance.

Not quite, but near enough.

Given Un=230, in what sense is [230 - (10% of 230) - (5% of 230)] 'not quite the same' as [230 - (15% of 230)]?

Kind Regards, John

Because the 5% is within the installation, and is therefore 5% of 207.

 

[PBC_1966]

According to the regs., isn't the percentage voltage drop supposed to be calculated using the nominal declared voltage? It always used to be.