Fault current complies

Does it though? 1.5mm² T&E has a 1.0mm² c.p.c. - which generally isn't sufficient for the energy let-through of even a B type 32A MCB. RCD won't necessarily help unless you can be sure that earth fault current is low (e.g. <575A) as even at 40ms it likely is to be a lot slower than an MCB for fault currents.

   - Andy.

AJJewsbury said:

Does it though? 1.5mm² T&E has a 1.0mm² c.p.c. - which generally isn't sufficient for the energy let-through of even a B type 32A MCB.

Agreed ... also a consideration

(Although, a fuse could be used ... there may well be fuse and circuit-length combinations for which 1.0 sq mm is OK).

considering we allow 1.5mm flex on the downstream side of the same 13A fuse that is in the plug or protecting the 1,5mm spur, there is no real electrical problem in terms of overload or fault, I will take the reduced cpc as a possible issue but only if we are expecting large CPC currents so the copper is pre-heated to 70C before the fault comes on.

M.

mapj1 said:

onsidering we allow 1.5mm flex on the downstream side of the same 13A fuse that is in the plug or protecting the 1,5mm spur, there is no real electrical problem in terms of overload or fault, I will take the reduced cpc as a possible issue but only if we are expecting large CPC currents so the copper is pre-heated to 70C before the fault comes on.

Apologies, but I don't agree.

BS 7671 doesn't "allow" that, because it's outside the scope of the standard.

I agree what you decribe may be mis-use, but as far as BS 7671 is concerned, it's "foreseeable mis-use". We can address that by co-ordinating the final circuit CSA with the OCPD appropriately. The non-adiabatic approach in the referenced standards permits that.

It may be the case, that the non-adiabatic approach, in some circumstances for fixed installations, may lead to a 1.5 sq mm conductor for wiring systems other than MICC, but in my opinion this is a "non-standard circuit", and it's it he designer's lap as to whether it's acceptable for the particular installation.

As others have said ... unlikely in some circumstances for adiabatic in any case.

mapj1 said:

onsidering we allow 1.5mm flex on the downstream side of the same 13A fuse that is in the plug or protecting the 1,5mm spur, there is no real electrical problem in terms of overload or fault, I will take the reduced cpc as a possible issue but only if we are expecting large CPC currents so the copper is pre-heated to 70C before the fault comes on.

Apologies, but I don't agree.

BS 7671 doesn't "allow" that, because it's outside the scope of the standard.

I agree what you decribe may be mis-use, but as far as BS 7671 is concerned, it's "foreseeable mis-use". We can address that by co-ordinating the final circuit CSA with the OCPD appropriately. The non-adiabatic approach in the referenced standards permits that.

It may be the case, that the non-adiabatic approach, in some circumstances for fixed installations, may lead to a 1.5 sq mm conductor for wiring systems other than MICC, but in my opinion this is a "non-standard circuit", and it's it he designer's lap as to whether it's acceptable for the particular installation.

As others have said ... unlikely in some circumstances for adiabatic in any case.