Which MCB For Garage?

[neerday]

I've changed my old fusebox for a new consumer unit. I labelled all the wires and put them into the correct mcbs in the new unit with the socket rings, and garage on an rcd. Don't have an electric shower and the general advice seemed to be not to put the cooker on the RCD. I selected the mcbs according to the size of fuse which was in the original fusebox. No problems - everything seems to work as before and the mcbs seem to isolate the correct circuits.

My question is to do with the size of MCB needed for the garage. The fuse was a 30 amp one so I've put it onto a 32 amp mcb. The wire to the garage is 2.5mm 3-core armoured cable. The garage has its own little fusebox with a 5 amp fuse for the lights and a 30 amp fuse for the sockets which are in a conduit round the wall. Is this size of mcb OK for the job even though its just a single wire to the garage?

Also - I see that the earth for the garage is the 3rd wire in the armoured cable plus the armouring all joined together. It's quite a long way to the garage (about 100 feet) so is this a good enough earth or is there anything else I could/should do?

Thanks.

 

[securespark]

CHANGE IT TO A 20A!!

2.5 is not rated to 32A.

 

[Adam_151]

2.5 is not rated to 32A.

90 Degree XLPE is (unfortunaly his CU won't like conductors at 90!)

I guess this is how the problem came about... DIYer picks up 2.5 xlpe in B+Q, sees makers rating on it, and thats as far as the design stage gets

Had the same thing there when we moved in, 6mm² T+E left CU from a 32A breaker, didn't realise until spark came and moved CU up a few feet and needed to extend T+E, that the SWA was only 2.5mm²

 

[ban-all-sheds]

Also - I see that the earth for the garage is the 3rd wire in the armoured cable plus the armouring all joined together. It's quite a long way to the garage (about 100 feet) so is this a good enough earth?

The only way to be absolutely sure is to measure the loop resistance at the furthest point.

2.5 is not rated to 32A.

90 Degree XLPE is (unfortunaly his CU won't like conductors at 90!)

But at 30+m of cable he shouldn't be drawing much more than 15A....

 

[securespark]

Apologies: I should have been more precise.

Yes, XLPE may carry the load, but not at that distance.

 

[Qedelec]

Aside from the qestion of the garage MCB, dont you think its iresponsible to assume the installation is safe just because it works. Changing a CCU is notifiable for a very good reason. When did you qualify as an electrition?

 

[neerday]

When did you qualify as an electrition?

Not notifiable in West Lothian so far as I'm aware.

If I were an electrician I wouldn't ask these questions eh? The reason for asking was that I felt that 2.5mm single was likely not rated to 30A. Now I know I'll fit a lower rated mcb. However the 30A fuse has been there since before I owned the house.

In terms of safety I feel quite sure that it's just as safe as before and likely (because of the RCD) a little safer. After some 30-odd years as an electronics engineer I feel that I know my own boundaries and limitations.