Electric hob prewired with 13A plug.

[:::Jerry::::]

Ouch, Oops !... :~(

[Andy Wade]

Only if the designer so decides. The definition of design current (Ib) is the "current intended to be carried by the circuit in normal service."

I can think of two cases where you might be able to use a smaller cable size by setting Ib < In (where In is the device rating). The first is where the circuit is voltage-drop limited, so a lower value of Ib allows a greater circuit length for a given cable size (Zs permitting).

The second case is where a grouping factor (Cg) applies and you've elected to take advantage of the "not liable to simultaneous overload" relaxation. In this case the required cable rating (before application of any Ca & Ci factors) is given by the greater of the two expressions

It >= Ib/Cg, and

It >= sqrt(In^2 + 0.48*Ib^2*(i - Cg^2)/Cg^2).

This can give an It value of less than In/Cg so might just save a step on cable sizing. [See Section 6 of Appendix 4 to BS 7671 for full details.]

[Martin Angove]

Several reasons:

Firstly, your last point, which *is* a bodge when there is a better way.

Secondly the fact that there were no socket outlets near the intended point of use, so we were going to have to wire something up, also this would be a large point load on any existing sockets circuit and so would probably be treated to its own circuit anyway.

Thirdly there was a not-full-utilised distribution board a mere couple of yards away, with a nice knockout on the side perfectly sized for a

32A connector.

Fourthly, if it had been installed somewhere else I didn't want someone plugging it into two phases.

Fifthly the guns were 2kW each and intended to be used at full power, so it wouldn't have been a couple of sockets, it'd have been four or six.

Shame it seems that it never worked once they built a proper (rip-stop) balloon for it.

Erm... come to think of it (look, this was two and a half years ago and my memory's dodgy at the best of times) I don't think it *was* wired for

32A single phase. I think I wired it for 20A three phase. That would have made more sense (two guns per phase) but without going digging into my (unsorted) photo collection (I did take one of the innards) I can't be sure.

Hwyl!

M.