Calling All Sparks!

[RF Lighting]

The only reservation I'd have about relying on the current using equipments fixed load in a domestic is when the thing goes wrong and it is replaced - maybe with a full range or double oven.

Exactly. That is why I continue to condemn 32A cooker circuits with 2,5 in them.

If anyone can explain the regs satisfactorily, I may change my mind.

IMO, It is not a problem, as long as there is a device which limits the current draw on the undersized cable, wether it is at the point where the cable size steps down, or at the point of utilisation.

If you have a look in appendix 15 at radial final circuit arrangements, you will see in the right hand diagram, and example of a 2.5mm² spur from a 32A radial circuit.

The 2.5mm² can not be overloaded as it supplies a socket outlet, and the current draw from the socket is limited by the fuse in the plugtop.

Obviously the circuit is open to abuse, but it is no different to a DIYer coming along and wiring his sockets in 1.0mm², and there is nothing you can really ever do to prevent this.

I know they are different regs, but think about how the DNO distribute power. They have a large feeder with a small branch off to each house. The small branch is protected against overload by the company fuse in the service cutout.

 

[securespark]

Yeah, I don't have a problem if the current draw is limited by a fuse, but don't the regs mention "at the point where the reduction in csa occurs"?

 

[ColJack]

Me cry...

I've already said that the regs say there are exceptions to the rule as long as certain criteria are met..

 

[Spark123]

You have to protect the cable against fault current i.e. PSCC or PEFC, in order to do this the protective device must be upstream (although there are a few exceptions to this rule).

You also have to protect the cable against overcurrent, this protection may be downstream of the reduction of cable size or by the load being fixed.