Tails sizes for CU

[frediaz]

I guess this is going to be an easy one to answer. I am buying a consumer unit, 14 way split 100A + 80A 30mA RCD. What size (csa) should the tails be? 25mm (97A) or better? 35mm (119A)

It is a PME installation so I am asking the electricity supplier if I need more than 10mm2 csa on the main equipotential bonding conductor.

By the way, whose regulation is it that the Consumer Unit has to be 3m or less from the meter?

Thanks in advance

 

[JohnD]

it is the rating of the supplier's fuse that limits potential current, not the size of the CU.

Do you know what fuse is in there? The markings on the fuseholder are only a guide.

 

[frediaz]

No, the meter has not been installed but the supply is already there. Do I need to ask the company that connected the electricty supply or can I see it inside the box?

 

[JohnD]

you will probably see a black or grey service head with a fuseholder on it, at the end of the incoming cable, below where the meter will go.

25mm is usual for tails in new domestic installations.

also, where did you get those cable ratings? According to my tables, 25mm PVC unarmoured single-core copper, single phase, is 114A clipped direct or 101A in surface-mounted conduit or trunking.

If in conduit in a thermally insulated wall it goes down to 80A

 

[frediaz]

By the way, without looking at the service box (I am not there at the moment), the electricity company told me they would give me 100A, I guess that's what they did. The cable ratings, I got them from the supplier. I tried to see the ratings on table 4.7A of the IEE wiring regs but it only goes up to 16mm2 cable.
No, the cables are not within insulation material only the part that goes through the cavity wall so I imagine that there's hardly any derating because of this.