Cable ratings from henley blocks?

gesl · Feb 22, 2012

Hi there, I've been to look at a job today were the occupier has recently moved in. Before he bought the house he had a pir done which came back good bar a couple of things that were put right. The supply is pme 25mm tails and 16mm earth 80a bs1361 henley cut out. after the meter the tails go into a pair of henley blocks. out of each block then come one pair of 25mm cables to the rewirable fuse wylex consumer unit, one pair of 10mm cables to a 45a fused supply for a stairlift and one pair of 6mm cables to another fused supply to a shower unit. The old wylex board only has four ways and this is clearly the reason for splitting the supply. What bothers me is that all these cables are effectively protected by the main 80a supply fuse, fine for the 25mm but not sufficeint for the others. I can't find anything in the bgb that says this is ok, but the local guy that did the PIR would surely have picked this up if it were wrong.

I'd appreciate your thoughts.

Thanks

Stu

telectrix · Feb 22, 2012

agree with you there. however, as the 6mm and 10mm cables are a very short, exposed run, it's unlikely that they will cause a problem . i would code it as C3 and recommend a CU upgrade.

gesl · Feb 22, 2012

Thanks telectrix, I suggested a cu change which went down like a lead balloon. The guy is moving his kitchen around (sink, worktops the lot shifted about) and wants extra sockets and existing sockets moved plus an extra light fitted all in the kitchen area. The Stairlift is no more, so I'm thinking the cheap option is to use that supply into a small cu just for the kitchen sockets and lights.

Not ideal but the customers king!

Cheers

Mark_Burgess · Feb 22, 2012

The 45A amp fused supply and the shower fused supply should interrupt in the event of an overcurrent fault before the overcurrent fault would reach anywhere near the 80A.

gesl · Feb 22, 2012

I agree Mark, but reg 433.1.1 that talks about the relationship between Ib In and Iz says that those cables ought to be bigger. I just wondered if anyone knew a deep dark exception to this reg.

Cheers mate.

telectrix · Feb 22, 2012

it's assumed that those cables themselves will not cause a fault , but that a fault on the circuit, sufficient to overheat the tails before the suppliers fuse popped. fed by them will cause that circuit's OCPD to trip. similar logic apples to tails over 3m to be protected at source end.

Deleted member 26818 · Feb 22, 2012

Where there is a reduction in the CCC of a conductor, the Regulations allow a protective device to be placed along the run of the conductor, within 3m of where the reduction occurs.
This is why we have the limit of 3m for meter tails.
The protective devices in the CUs provide the protection for the reduced CCC conductors.