Circuit Breakers Ask questions and find answers to many subjects relating to electrics and electrical work

[ECRyder]

I am wiring an electric shower to an existing consumer unit (new circuit breaker type). There is a spare slot for one. I think I need a 35 amp one because the supply is only 40 amps. This is for a 8.5 kw shower. Are alll circuit breakers the same standard size and for any consumer unit??? Or do I need to name the consumer unit to get the correct circuit breaker because that required circuit breaker may be specific to that consumer unit?

[sparx]

If you need to ask these questions you are clearly not a registered electrician, therefore doing this work is illegal! It is controlled work under part-P of building regs. because all below:
1)Installing a new circuit.
2)In a room containing a shower.
3)Altering the characteristics of the supply.

Please go to top of page, click on 'projects', look in list for 'Part-P'

NB a 8,500W shower will draw 36.95A @ 230V so will trip anything less than a 40A mcb.
Why is supply only 40A?
Most MCB's will only fit the correct make/model consumer unit, some may be similar and can be made to fit but if so done will break manufacturers type approval and void guarentee.

If you have already notified LABC of your intention to do this work and paid their fee (doubtful) how will you test the circuit and issue the required certificate?

sorry, but this has been the case for over 5 Years now so can't condone / abet law breaking.
regards

[ericmark]

Sparx is correct. There are provisions under Part P for DIY but in real terms this is to allow commercial electricians to do odd job on a house or break into the domestic market it is not for true DIY'ers.

To answer your question however consumer units are type tested and as such only components recommended by the manufacture can be used.

Distribution units which are not type tested can only be used where only competent persons (Electricians) have access. So not allowed in houses.

In practice there are some consumer units that will take other makes of MCB, RCBO, Isolators, RCDs etc. But often the buzz bars don't make proper contact and there have been a number of fires as a result and of course if not installed correctly insurance firms can refuse to pay out and it could result in manslaughter charges.

So this is not a DIY job. And one would be foolish to invalidate insurance so also would be foolish to DIY.