doubled cable on a radial

[Ducksy]

Hey guys I see this now and again on my rounds....8.5kw method C on 2 x 2.5mm cable......does it state anywhere in the regs that it a radial must be a single cable Or is it acceptable ? the very least i think its lazy not using 6mm but as always I'm well off from the more experienced guys think

Thanks

 

[markythesparky]

Sounds like a guess. If its not in BS7671 and you can tget information from the manufacturer then you will be guessing.

Although 2.5mm is rated around 27A (clipped direct and depending on its run), the ring will not necessarily put equal load on each cable and hence the 32A device. In your case the cables may well be the same length and therefore in theory should split the load equally. But this does not take into account resistance at the terminations. again this is an unknown. in the event that one side comes free, a 32A MCB will be just enough to protect the cable. In your sitaution it will not be and you will have a fire.

You cant back yourself up in a court case with guesswork. If you go by BS7671 then you will not have unknowns and you will not be guessing. No one will be able to argue.

 

[amlu]

how about just treating that radial as a ring, with single accessory connected at the end of it?
if its sits on its own 32a breaker should be up to the regs?

 

[markythesparky]

Would be better and obviously safer.

BUT.... 8.5Kw / 230v is 36.96amps.

Still think this is an option?

 

[decolad69]

What next? I'll wire my shower in 4x 1.5mm all the same length and taking the same route arty:

 

[Guest55]

unorthodox but no problem at all using 2 feeds to a fixed equipment so long as they're the same length ( for load balancing reasons ) and both cables are wired into the same terminals at the CU ( for identification purposes )

 

[Guest55]

just to add to my previous comment , of course the combined CCC of the feeds must exceed the Ib as per usual , but theres no issues with the principle of multi feeds.

 

[Knobhead]

Sweet would you say that the cables CSA totals 5mm.....as it could be the case the CCC is not sufficient.

You will find (not in the regs) that a parallel feed has a higher CCC than it's sum CSA. The main reason it's used in industry so much. Plus I'd rather pull in two smaller cables than one big one.

 

[Guest55]

You will find (not in the regs) that a parallel feed has a higher CCC than it's sum CSA. The main reason it's used in industry so much. Plus I'd rather pull in two smaller cables than one big one.

agreed , better conductor heat dissapation when split over more than 1 cable.

 

[Richard Burns]

BS7671 says that if the conductors share current equally then you must sum the CCC for each cable (433.4.1BRB)

 

[Engineer54]

While these smaller cables are not normally used in parallel single point supplies, the same principles still apply!! So in fact, those 2 X 2.5mm cables, will carry more current than a 6mm cable using the correct installation method!! So long as all the required criteria for a parallel supply is adhered too, then no problem!! lol!!


Parallel supply/feeders are more commonly used with the larger sized cables, where they can significantly increase CCC with reduced size of cables, and can generally be run over longer distances, than the use of a single much larger sized cable!!