Is moving a light switch in the kitchen allowed/notifiable?

[EFLImpudence]

There's also the question (to which I've never been sure of the answer) of whether the 'design current' of a circuit relates to what the current would be at nominal supply voltage, or whether it should take account of the maximum permitted supply voltage. I assume you think the former?

Yes, I believe that's what nominal voltage is even if the actual voltage is never that low. The figure chosen, although unrealistic, to be in-line with Europe and, as discussed before, all values and calculations must allow for this.

I'm still not clear about this (as I said, never have been) - and your statement "...and calculations must allow for this" (in combination with your 'yes' answer) makes me even less sure.

When the nominal voltage was arbitrarily reduced to 230 without changing the actual voltage, the values and calculation criteria must have taken this into consideration.

If one has a shower rated at 7.5kW at 240V, when one calculates the 'design curent' for its circuit, does one do so {albeit invoving some guesstimating, unless one measures} assuming a nominal supply voltage of 230V

There's no need as it will be stated on the box, 7.5kW @ 240V, i.e. 7500/240 = 31.25A. That's what the shower is.
That's not using 240V as the nominal voltage. The MIs are telling you the current.

The fact that it works out at 30A @ 230V is immaterial as doing this would not be following the MIs. plus they will state that 32A CPD should be used.

(which seems a bit odd, since that is in the 'non-safe' direction), or does one caluculate/estimate design current "allowing for" the fact that the supply current could, in fact, be as high as 253V (which seems the 'conservative'/'safer' approach)?

That's not necessary either as that, too, must be allowed for in the figures.

 

[scousespark]

That's got nothing to do with Part P. If somebody did as you said, they would be doing something beyond their level of capabilities. Your example feeds the argument for the scheme operators, when they say that only qualified electricians should be able to work in the domestic field.

It does, indeed, feed the argument that all electrical work should be notifiable, and either self-certified (ideally with some checks) or certified by LABC inspectors or their appointees.

However, I think my point has got everything to do with Part P as it is. That point was that even a job which most/all people would agree is not notifiable under Part P (as it is) could be done badly/dangerously - so whether or not something could be done dangerously is not a helpful criterion in relation to trying to interpret what is notifiable under the present Part P.

Kind Regards, John.

You can't legislate for stupidity.

 

[PrenticeBoyofDerry]

Interesting debate chaps, still think schedule 4 stinks though.
But if that is the way in which it is designed to instruct so be it!
I will still continue to notify all my work that effects the current rating and protection of the circuits when replacing electrical equipment, there is nothing in schedule 4 preventing me from doing this.

 

[EFLImpudence]

Does it cost you £1.50 or £400.00?

 

[PrenticeBoyofDerry]

Does it cost you £1.50 or £400.00?

Cost me £440 to be registered and £1.50 to notify.
I have to fill the documents out anyway, so may as well notify, can do it on-line in two minutes. Add the extra charge on to the bill, in my experience the customer is happy knowing the jobs been notified, whether it's an EIC or a MW. They receive there confirmation letter and every thing is sweet!

 

[JohnW2]

There's no need as it will be stated on the box, 7.5kW @ 240V, i.e. 7500/240 = 31.25A. That's what the shower is. That's not using 240V as the nominal voltage. The MIs are telling you the current.

In that case, the MIs are telling you what the current would be with a 240V supply. However, that doesn't alter/answer my question. When deciding what is the 'design current' of the circuit (to determine BS7671 compliance), what supply voltage does one assume - nominal (i.e.230V), the voltage for which the MIs state the current (i.e. 240V in your example) or the maximum permissible supply voltage (i.e. 253V - which may be approached in practice, particularly if very close to the transformer/substation)? As I said, one has to do a bit of guessing for voltages different from that specified by the MI - but, with your example, it is likely to be at least 32.94A (probably more) at 253V.

So, my question remains - when determining the 'design current' of a circuit in order to determine whether 433.1.1(i) is satisfied, what supply voltage does one assume?

Kind Regards, John.

 

[JohnW2]

However, I think my point has got everything to do with Part P as it is. That point was that even a job which most/all people would agree is not notifiable under Part P (as it is) could be done badly/dangerously - so whether or not something could be done dangerously is not a helpful criterion in relation to trying to interpret what is notifiable under the present Part P.

You can't legislate for stupidity.

You can't legislate to prevent stupidity - but we can, and frequently do, legislate to make many stupid things illegal. Indeed, it's easy to argue that most illegal things are 'stupid' - driving whilst drunk, robbing banks, murdering people ....!! In fact, in context, any electrical work which is so stupid as to be dangerous has been legislated against - it is unlawful per Part P of the Building Regs.

However, that wasn't the point - which was what I stated above.

Kind Regards, John.

 

[EFLImpudence]

So, my question remains - when determining the 'design current' of a circuit in order to determine whether 433.1.1(i) is satisfied, what supply voltage does one assume?

That is quite clear - it is the nominal voltage of 230V.

The total range of actual voltage must have been taken into consideration when this was decided with regard to safety.
As I have said when the nominal voltage was arbitrarily reduced the values used for calculation were adjusted so that the results were exactly the same.

I don't know why you are having such difficulty with this.
It matters not which number we are told to use if the results are the same and safe.

Going back to the shower example, the manufacturers still use 240V to describe their products because, to the uninitiated, it makes them seem more powerful.
Anyway if they state use a 32A CPD we have to do that so it does not matter, in this case, what the nominal voltage is.
We don't have to use it. We just have to take 32A as the design current and fit a 32A CPD whether the conductors can handle more or not

Apart from anything else we have, in previous discussions, deduced that there is a huge built in tolerance for safety in CCC etc.

 

[ban-all-sheds]

You can't legislate to prevent stupidity - but we can, and frequently do, legislate to make many stupid things illegal. Indeed, it's easy to argue that most illegal things are 'stupid' - driving whilst drunk, robbing banks, murdering people ....!!

Actually, whilst wrong, and rightfully proscribed, the latter two are not necessarily stupid.

And sadly we also frequently legislate against things where there would be no need if people were not stupid, i.e. not things like drunk driving, but things which per se would not need to be illegal were people able to be trusted not to behave stupidly.

 

[JohnW2]

So, my question remains - when determining the 'design current' of a circuit in order to determine whether 433.1.1(i) is satisfied, what supply voltage does one assume?

That is quite clear - it is the nominal voltage of 230V.

If it's 'quite clear', then that obviously completely answers my question - but could you perhaps point me towards whatever it is that makes this so clear? Thanks.

My thought was that if a designer knows that the supply voltage of a particularly installation is nearly always over 250V, it might be considered inappropriate ('bad design practice') to calculate 'design currents' of circuits on the basis of what current would be drawn if the supply voltage was only 230V.

The total range of actual voltage must have been taken into consideration when this was decided with regard to safety.

When what was decided? 433.1.1(i) merely requires that In ≥ Ib. Are you saying that it really means (roughly) 1.1*In ≥ Ix, where Ix is the actual current which may be drawn by the circuit?

Anyway if they state use a 32A CPD we have to do that ...

As I've suggested, I'm not so sure I'd agree with that if it resulted in non-compliance with 433.1.1(i).

Apart from anything else we have, in previous discussions, deduced that there is a huge built in tolerance for safety in CCC etc.

Indeed, that (probably large) safety net is always going to exist but, in most other situations, I don't think you would say that this made it OK for a designer to exceed, say, tabulated maximum CCC 'by just a little bit', on the basis that the current was still well within the built-in-tolerance, would you?

Kind Regards, John.

 

[JohnW2]

... i.e. not things like drunk driving, but things which per se would not need to be illegal were people able to be trusted not to behave stupidly.

I think I need some help in understanding that one. If everyone could be totally trusted never to drive whilst drunk, there would be no point/need in it being made illegal, would there?

Kind Regards, John.

 

[ban-all-sheds]

OK - here is one example:

Driving whilst drunk is, per se, something to be forbidden.

Ownership of handguns is not, but has been made so because of stupidity.

 

[EFLImpudence]

So, my question remains - when determining the 'design current' of a circuit in order to determine whether 433.1.1(i) is satisfied, what supply voltage does one assume?

That is quite clear - it is the nominal voltage of 230V.

If it's 'quite clear', then that obviously completely answers my question - but could you perhaps point me towards whatever it is that makes this so clear? Thanks.

Definitions ?

My thought was that if a designer knows that the supply voltage of a particularly installation is nearly always over 250V, it might be considered inappropriate ('bad design practice') to calculate 'design currents' of circuits on the basis of what current would be drawn if the supply voltage was only 230V.

That is what the regulations tell us to do.
Don't accuse me of 'blindly' following the regulations without thinking because I have explained how/why I think this is covered.

The total range of actual voltage must have been taken into consideration when this was decided with regard to safety.

When what was decided? 433.1.1(i) merely requires that In ≥ Ib. Are you saying that it really means (roughly) 1.1*In ≥ Ix, where Ix is the actual current which may be drawn by the circuit?

Nominal voltage. It was only reduced to 230V because it supposedly 'brought us into line' with Europe - as you know nothing changed apart from the tabulated figures.

If the same voltage is used to calculate design current, PEFC, PSCC, CPD rating, maximum Zs allowed etc. it doesn't really matter what that voltage is - the results will be the same.

Do you not accept that if 230V is used the installation will, by default, still be safe at 253V?

Anyway if they state use a 32A CPD we have to do that ...

As I've suggested, I'm not so sure I'd agree with that if it resulted in non-compliance with 433.1.1(i).

It won't.
The regulations do not say "Check and see if it still complies should the voltage rise to 253".

Apart from anything else we have, in previous discussions, deduced that there is a huge built in tolerance for safety in CCC etc.

Indeed, that (probably large) safety net is always going to exist but, in most other situations, I don't think you would say that this made it OK for a designer to exceed, say, tabulated maximum CCC 'by just a little bit', on the basis that the current was still well within the built-in-tolerance, would you?

No, I wouldn't but that is what the regulations do.

Perhaps when formulating the figures and values the powers that be used 260V, to be on the safe side, and then scaled down everything to 230V for our use.

But you knew all that.

 

[JohnW2]

OK - here is one example: Driving whilst drunk is, per se, something to be forbidden. Ownership of handguns is not, but has been made so because of stupidity.

OK, I see your point, but I'm not sure that there is as much difference as you're suggesting ... ownership of handguns would not have to be illegal if everyone could be totally trusted not to do stupid things with them ('stupid things' including failure to take every reasonable step to prevent them getting into the 'wrong hands').

Kind Regards, John.

 

[EFLImpudence]

If everyone could be totally trusted never to drive whilst drunk, there would be no point/need in it being made illegal, would there?

There would be no point but -

There's never going to have been a Council/Parliament meeting where it was proposed that...

"Everything is fine now - the people don't need us any more".