Light off socket circuit, which bit can be 1mm T&E?

[securespark]

Did they ever?

In the 14th metric and 15th Eds., it was allowable to use 1 milli for "power" circuits like an immersion.

I'm sure a later edition said that the CSA for cables used on "power" circuits should be a minimum of 1.5.

 

[plugwash]

Really?

The default position is that the protective device protecting a wire should be rated less than or equal to the cable, but there are some exceptions to this.

There is a exemption allowing ring circuits with or without spurs to be wired with smaller cable than would otherwise be required. This is what allows a ring to be wired in 2.5mm²

There is also an exemption that you can have the protective device "downstream" of the reduction in wire size as long as adequate "short cuircuit" protection is provided for the wire. Some would argue that the 32A breaker will provide adequate short-circuit protection for the spur feeding the FCU (it probably will but doing the calculations to prove it can be a pain).

Similarly there is an exception that if the load is "unlikely to cause an overload" then the cable can be smaller than the protective device. What devices are "unlikely to cause an overload" is somewhat open to interpretation. Some might argue that this means you don't need a fuse at all.

However, there is also the consideration of the light fitting itself and what overcurrent protection is appropriate for it. IIRC BS7671 specifies a maximum protective device rating of 16A for supplies to BC, ES, SBC and SES lampholders. I don't think there is an explicit maximum specified for other types of lampholders or integrated fittings, but I would be reluctant to put a light fitting on a supply fused at over 16A.

 

[EFLImpudence]

I'm sure a later edition said that the CSA for cables used on "power" circuits should be a minimum of 1.5.

It still does for "non-sheathed and sheathed cables" but not for "non-sheathed and sheathed flexible cables".

Do you think harrypotter's light wiring is a power circuit?

 

[securespark]

Up to the outgoing side of the FCU, no?

 

[EFLImpudence]

Up to the outgoing side of the FCU, no?

It's all far from clear - and even farther from sensible.