Kitchen ring circuit

[sparkymaz]

If a ring main is needed to be installed with one leg of the ring passing through a stud wall with thermal insulation (Inst. method 103#) the current carrying capacity is 13.5A. To comply with regs on a ring final circuit, the current carrying capacity has to be at least 20A for a 32A breaker. Can i protect this circuit on a 20A breaker and still comply with regulations? My thinking is that if you devide 32 by 20 (which is 1.6 (call this the 'factor')) then you need each leg to be capable of carrying at least 12.5A.

Im sure im not the only one to come accross this so any help would be much appreciated.

 

[lister]

why is the stud wall insulated? (internal wall so no heat loss- common area so no real need for any major sound proofing?) easiest solution would be to remove insulation in the section you run cable (i would) rather than have a kitchen ring on 20a as this would normally be biggest load.
rather than downgrade the mcb i personally would sooner upgrade the cable or alter the reference method ie, singles in conduit through stud wall section.

 

[Spudnik]

I think that most internal stud walls should be insulated.

Something to do with soundproofing.

Not 100% sure tho.

 

[sparkymaz]

yeah i know what your saying with changing the installation method. all walls are insulated now days. The biggest pain in the arse for us all i reckon. Its just hyperthetical really. Got my elecsa assessment soon. but when doing a new installation, say the main cable route has thermal insulation exceeding 100mm in thickness, (ref 101, table 4D5). This means 16mm would have to be used for a 9.5kw shower. Seems excessive to me but hey i dont write the regs.

Also, the thermal insulation would be installed after the 1st fix on the electrics. Just seems that we are going in the direction of using 4mm for ring mains, as on a new installation when are we ever going to avoid any insulation at all? even if we do, how do we know it aint gonna get crammed with insulation when we have finished the 1st fix? Is it feasible to create a system where we can keep the main cable routes free of insualtion by building a compartment within the joist layouts. Or would this contravene building regs with inadequate insulation?

Would love to hear your guys thoughts