Garage workshop electrics & part P

[max_depth]

Thanks
Max

 

[Adam_151]

4mm² XPLE SWA can just manage 40A if the run is short enough, though its close to the limit.

A fact to note here, is that the fact that the submain CU only has a 16A, and a 6A breaker in, is giving closer overload protection to the cable than the upstream breaker, the upstream breaker is providing short circuit protection to the cable, so its important to consider that the effect that changing breakers in the submain has on upstream cabling as well, in your case as I said, it would *seem* as long as the cable is XPLE and not run through any lofts, etc, etc then the 40A breaker can provide overload protection to it

The incommer on the garage cu does not provide overcurrent protection (though I hope as the garage is TT, that it is an RCD?)

Would use SWA with the metalclad sockets instead of PVC conduit

Its notifiable under part p, yes

 

[max_depth]

Adam, thanks for the reply

 

[Adam_151]

Adam, thanks for the reply
I would have thought that it was common sense that if you are installing a circuit, the downstream cable should be rated higher than the mcb supplying the circuit. ie surely the electrician who wired the house should have fitted a 32A mcb or used heavier cable?

Yes, its possible that the cable is still rated for 40A but without knowing the excat de-rating factors involved, its impossible to say, though usually in something like this, the upstream overcurrent device protects against overload, there are many situations where its not like this, consider the service cable to your house, can probably carry 100A - 125A, the fuse at the substation would be much higher than this, but the fuse in your meter box will be a max of 100A, if you want a example that comes under BS7671, then the standard fused spur off a ring main is a good example, cable rated at 20A, breaker at 32A, but the fuse in the downstream fcu is 13A, its seen as good practice to put the fcu directly on the ring, but by no means totally necessary

One reason why you might want a bigger breaker upstream is to ensure good descrimination.

Personally, I'd swap it (the submain breaker in the house CU) for a 32A breaker, and if the disconnection time calcs allowed it, make it a type C

Anything involving swapping breakers or adding circuits is notifiable

 

[ban-all-sheds]

Thanks
Max

What kind of a question is that????

 

[Adam_151]

Why the **** have you editted out your posts We are trying to help, and can't if you edit your posts away

 

[ban-all-sheds]

4mm² XPLE SWA can just manage 40A if the run is short enough, though its close to the limit.

It can only do that by operating at 90°C, so beware of where it is installed, and what it runs into/with/close to, because if other items limit you to 70°C you will not be able to put 40A through it.....

 

[plugwash]

thats core temp though iirc so i'd imagine the sheath temp would be a bit lower.

 

[ban-all-sheds]

And the metal terminals into which the cores are terminated will be mounted in what?