Adding another spur to socket for lights?

[EFLImpudence]

Expansion of what? The Universe?

Doesn't that mean a spare way or two in the CU rather than 10mm² lighting circuits?

 

[JohnW2]

No, it wouldn't be. It would be one spur with two sockets.

That's strictly true, but it's what people very commonly describe as 'a spur from a spur', here and elsewhere.

Kind Regards, John

 

[JohnW2]

Why do people get so agitated about what might be changed in the future?

I think it probably depends upon how easily the change can be made.

I certainly don't think that we should 'get agitated about' the possibility that someone might change the installation's wiring in the future - not the least because anything is then possible!

However, if it's just a matter of changing a fuse in a FCU(or FCUs) and then subjecting the circuit concerned to much higher loads than was envisaged at the time of design, then I think it can be argued that one probably should consider that possibility.

KInd Regards, John

 

[mwatsonxx]

Expansion of what? The Universe?

Doesn't that mean a spare way or two in the CU rather than 10mm² lighting circuits?

You tell me.

 

[JohnW2]

You tell me.

I think you first need to tell us what regulation requires provision to be made for 'future expansion'.

Kind Regards, John

 

[ban-all-sheds]

That's strictly true, but it's what people very commonly describe as 'a spur from a spur', here and elsewhere.

People are very commonly wrong about things.

Look at the definition of a spur, and see if either:

a) The concept of a "spur from a spur" fits

or

b) Adding a 2nd socket to an existing spur makes it two spurs.

 

[JohnW2]

Look at the definition of a spur, and see if either: ...
a) The concept of a "spur from a spur" fits . ... or ... b) Adding a 2nd socket to an existing spur makes it two spurs.

I'm not quite sure what answer you are expecting but, in terms of the BS7671 definition, I would say that neither of those is correct.

Kind Regards, John

 

[ban-all-sheds]

Precisely.

 

[JohnW2]

Precisely.

So what description would you suggest?

Even if it's not correct in terms of the BS7671 definition, I think that "spur from a spur" effectively conveys the correct/intended meaning to virtually everyone.

Kind Regards, John

 

[ban-all-sheds]

So what description would you suggest?

What's wrong with "spur"?

Even if it's not correct in terms of the BS7671 definition, I think that "spur from a spur" effectively conveys the correct/intended meaning to virtually everyone.

I don't think it does, because it draws people away from thinking what the real issue is, i.e. the total load on the spur, and leads them to think that it is a topological concern.

 

[JohnW2]

What's wrong with "spur"?

That, alone, would not fully describe what we're talking about. "Two sockets on one spur" would.

I don't think it does, because it draws people away from thinking what the real issue is, i.e. the total load on the spur, and leads them to think that it is a topological concern.

True, but one has to recognise that the vast majority of people think of this issue in terms of the guidance in App 15, not what the regs say about loads on cables, and, when they think is those terms, is does become essentially topological - i.e. since the guidance says that an unfused spur can supply (only) one single socket, one double socket or one FCU, it follows that daisy-chaining any second accessory off the first is effectively what is being 'forbidden' by the guidance (not that guidance can 'forbid'!).

If people did as you would like, and thought about the load on the cable, rather than the 'guidance', things would be different - and, as I recently wrote, they would then realise that not only two single sockets but, theoretically, up to about 8 FCUs (with 3A fuses) on one unfused spur would be compliant with the regs. However, it appears that very few electricians are prepared to 'ignore' the guidance.

Kind Regards, John

 

[EFLImpudence]

So - what, then can it be thought, is the purpose of Appendix 15?

It would appear to 'forbid' (not that guidance can 'forbid'!) acceptable methods and practices compliant with actual regulations.
It cannot even be thought that 15A is somehow considering the special circumstances of the ring final circuit, as 15B 'imposes' the same restrictions to a radial final.

 

[JohnW2]

So - what, then can it be thought, is the purpose of Appendix 15? It would appear to 'forbid' (not that guidance can 'forbid'!) acceptable methods and practices compliant with actual regulations.

I would say that the intended purpose is to act as guidance, but guidance which is non-comprehensive (i.e. does not include all possible arrangements which would/could be compliant with actual regulations).

The unfortunate thing is that it includes the word "only" when saying what may be supplied by an unfused spur, which makes it sound horribly as if it is "forbidding" anything else - so those who don't realise that the Appendix cannot 'forbid' anything, or who realise that but want to avoid the possible hassle of having to justify "contravening Appendix 15" essentially think of it as if it were (and could be) 'forbidding'.

It seems particularly unfortunate that this "only" has the effect of suggesting that one should not supply two single sockets from an unfused spur - since any electrical argument for that is, at best, 'open to debate' in terms of the regs.

Another case, I fear, of a non-ideal choice of wording.

Kind Regards, John

 

[ban-all-sheds]

So - what, then can it be thought, is the purpose of Appendix 15?

It's BS 7671 For The Hard Of Thinking.

 

[ban-all-sheds]

so the hard-of-thinking who don't realise that the Appendix cannot 'forbid' anything, or who realise that but want to avoid the possible hassle of having to justify "contravening Appendix 15" essentially think of it as if it were (and could be) 'forbidding'.