A cable wit a CCC of "less than 20A" protected by 32A OPD upstream and 26A downstream, with a 'design current' of at least 20A, quite probably 26A? How may one (and/or who/what says that one may) "do that"?
Kind Regards, John
Spur of a radial....
- Thread starter martygturner
- Start date
Kind Regards, John
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You wouldn't - but that is not the only configuration for a spur.
I'm not sure that I understand - are you perhaps thinking of just one single socket (or FCU). If a double socket is being fed, I can't see what 'configuration' would allow one to use cable with a CCC of "less than 20A".
Kind Regards, John
I am thinking of many of the usual reasons to have a spur - lights, fans, etc. where a smaller cable would be adequate without overload protection.
You know as well as I that 433.1.204 is still written for BS3036 30A fuses so with a 32A MCB things are different.
For a double socket you wouldn't have smaller than 2.5mm² so, in that example, your belief that 433.1.204 applies to the spur is irrelevant.
If 433.1.204 applies to unfused spurs then a T&E cable with a CCC of 20A is not allowed, is it? It has to be 2.5mm². Are you saying that an unfused spur of 1.5mm² T&E would not be adequate for a light (assuming fault current requirements are met)?
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No, but it's quite possible you would have 2.5mm² installed under a method that gave it a current rating of at least 20A, but less than 26A. For example method 100, 102 or method A.
Just like any other cable, you mean?
Hmmm. Are you suggesting that one might feed lights or a fan etc. from a 32a ring final, using very small cable (adequate for the load - hence now very probably 1.0mm²), without an intervening FCU? Whilst I cannot deny that if you could successfully argue that the load was such that it was unlikley to result in an 'overload' that it would then be technically compliant with the regs, but I have never heard of anyone (other than a DIYer who didn't understand the issues or regs) doing that, have you?
That's what I meant, since I thought we were talking about sockets on spurs.
That is definitely not my 'belief'. As I said, I just don't know, since the reg is not written sufficiently clearly - and i can see that the reg can be interpreted in either way..
For whatever reason, that reg does not allow 1.5mm² T+E, but it does allow 2.5mm² or 4mm² T+E whose CCC has been reduced to 20A by installation method and/or 'de-rating factors'.
If you were confident that the light was 'unlikely to create an overload', then 1.0mm² T+E (or even 0.5mm² T+E, if it existed) would be more than (electrically) "adequate". However, we are talking about 'regulations', not electrical "adequacy".
Kind Regards, John
Then you agree with me so how can the regulation apply to the spur?
Is it not the case that very often the fuse in a plug is not really necessary?
Ok.
Why then does it say "with or without unfused spurs"? Does that not signify that the spur has nothing to do with the ring regulation?
Yes, but people always bring up the installation method but that would have the same effect whatever one does.
The 1.5mm² would not be allowed anyway if the installation method prevented it so how can that be the reason for its prohibition?
Well, we are talking about you thinking that is what it might mean when clearly there are instances where it does not.
Are you saying that you agree with me that, whilst (given the 'caveat') what you suggested would, strictly speaking, be compliant with regs, virtually no-one would ever do it?
... I don't really understand the connection. 'The regulation' essentially exists to over-ride others in certain circumstances, so I can't see that one can make any assumptions such as you have done.
I don't know if it is 'very often', but the fuse is theoretically unnecessary IF (and only IF) the load is not considered likely to cause an overload - since the cables connected to plugs would very rarely (if ever) have a CCC of 20A, let alone 32A.
As I keep saying, that can be read either way - yours is one interpretation, the alternative is that the entire of the paragraph which follows (with is prohibition of <2.5mm² and <20A) applies to both the ring and any spurs from it. Given the total (logical) inexplicability (at least, to me, of the 2.5mm² minimum) I wouldn't dare to even guess what the intended meaning of the reg is/was!
As above, goodness only knows why 1.5mm is not allowed, at least in the ring itself, if not also spurs.
For what it's worth, the diagram ('guidance') in Appendix 15 shows an FCU spurred from the ring with 2.5mm² cable. Since 1.5mm² would clearly suffice (electrically), that might possibly suggest that (for whatever reason) the "2.5mm²/20A minimum" is meant to apply to spurs, as well as the ring, mightn't it?
I don't think that "clearly" and the reg in question can be spoken of in the same breath!
Kind Regards, John
I would certainly agree that none of the past couple of pages of 'discussion' above are anything that really needs to be even thought about, let alone 'worried' about!
As for 'upgrading the RCBO', I personally wouldn't 'worry' much about that, either. Regulation-wise, I personally would not think that adding one socket (to many) would invoke a need to bring the entire circuit up to the requirements of currents regs. In electrical/safety' terms, I'm still trying to find some 'chapter and verse' about the actual implications, in practice, of the different types of residual devices - although I do know that I have lived comfortably (with no 'worry') whilst 'being protected by' Type AC RCDs for probably 30+ years!
Kind Regards, John
Are you talking regulatory-wise, or about a 'need' which you feel yourself?
Kind Regards, John
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