Seprate earth

[malcolmsanford]

In the original post he states a 100 A supply as I've always understood for this size incomer 25mm tails should be used (approx 114 amps) for 100A main fuse ,16mm has a rating of around 87 amps clipped direct .
ie in the op 100A main fuse to henley block separate tails to 63A 30mA Rcd

Did you read or do you know regulation 434.2.1 this regulation leads you nicely onto 434.2.2 which is the one relevant to this scenario. which I posted on my OP ? Providing the OP can adhere to the points within these regulations, which if fitting a small sub board by henly blocks the chances are he will, then he can reduce the CSA size of the tails from the henly block to the sub board.

In fact sections 433 and 434 are pretty good reads in general when providing overload and fault protection. Both these sections will give guidance as why he can fit smaller tails from the Henley block to the sub board.

 

[edexlab]

Hello Malcom I have to confess that i like most electricians do not know the regs to the same level as yourself
I remember reading a previous post you made on this subject awhile ago and did read some of the regs involved as it was something I knew could be done but did'nt know the whys and wherefores etc ie you see it in meter cupboards all the time.
Anyway I reread the regs mentioned and I do see the point being made, although I think you'll agree that sizing any tails by the service fuse and subsequently any sub board connections being the same csa is a common practice and that it is ok to do so, of course you are right it would be easier to do it with a smaller csa.
I would like to hear your take on 434.2.1 (ii) " reducing risk of fault to a minimum" in this case I'm thinking the only option you have is to physically protect the conductor ie some mechanical protection like trunking , as I don't think that tails whether you say double insulated or insulated and sheaved can comply with this on their own
If this is correct then its a ---- up between installing 25mm csa or try and protect the smaller csa conductor

 

[malcolmsanford]

My take on it is, the note underneath it which is "protection of wiring against external influences". What sort of external influences are you going to encounter on a short length of tails from an henley block to a small Garage/Shower enclosure, not too may I would imagine. Of course like every job you do you have to assess what those influences are, but I would imagine there would be very few instances in a domestic situation where you would need to consider any extra protection for those tails due to influences in Chapter 52.

I always had with me lengths of 10mm double insulated tails which with places like TLC you can buy per metre. or you use to. The double insulation in 95% of cases would give you both extra protection against the event of a fault on the cable and external influences.