Replacing an electric shower

[Adam_151]

Thanks Guys, I think the answer is replacing my 32amp MCB with a 30m/a RCDO 40amp single module. The cable is 6mm, so with this setup I can install a 8.5kw shower no problem and it will be safe.

With the RCDO does it just click in the same slot on the CU as the MCB? or does it require any wiring?

Make sure you do your calcs for 6mm² on a 40A, its getting towards the upper end what 6mm² can take, so make sure you do your derating factor calcs, while you are at it, make sure you can meet disconnect time (0.4 sec) and voltdrop requirements. The problem with disconnect time, is that depending on your CU, RCBOs might only be available in C curve, and even though its RCD protected, the primary preotection agaisnt indirect contact on a TN installion should be the overcurrent device (IIRC)

The RCBO fits into the MCB space (though some of them are double width), you connect a neutral flyload to the neutral bar, both phase and neutral from the circuit go in the top of the RCBO, and there will be a thin earth wire from the RCBO that goes into the earth bar along with the circuit earth

 

[ban-all-sheds]

Ones which aren't double width are a lot taller, and may foul all the neutral and earth wires at the top of the CU.

You need to find out what sort of RCBOs your CU takes and see if one will fit.

And I must re-emphasise what Adam said about Type Cs - if you're on a TN-S supply you probably won't be able to fit one. TN-C-S has a lower Ze so you're more likely to be OK.

Check the data tables in the OSG or BS 7671.