do i have the correct electrics for a 8.5 kw shower ?

[NEIL222]

The electrical wiring for a electric shower is already in place and i wanted to fit one myself
basically i'm not sure if i need to change anything electrical
the cable size is 10mm2
at the consumer unit the shower has an MCB fuse of 40A
at the consumer unit there is a 80Amp 30mA RCCB trip switch
i got the info below from a different site:

Standard Shower Rating (8.5kW)

Watts (kW)
Maximum load from the supply 36.95 A

Maximum size of Protective device 40A
Recommended

Minimum 10mm2
Cable Size to be Used

Protective Device RCBO

if the shower uses 36.96 A would that cause the 30mA RCCB to trip
any help is much appreciated

 

[didthathurt]

10mm cable is good for your needs.

There's no such thing as a

Standard Shower Rating (8.5kW)

the shower you buy will be rated somewhere between 7.5kW and 10.5kW - your plan has to reflect that.

at the consumer unit the shower has an MCB fuse of 40A

That's good for up to 9kW

Protective Device RCBO

An RCBO is a device that combines the functions of an MCB and an RCD in one unit. If you are putting the shower cct onto an RCD protected source in the CU you just need an MCB.

if the shower uses 36.96 A would that cause the 30mA RCCB to trip

The 30mA refers to the sensitivity of the RCD to earth leakage not the power that can safely pass through it, so no, no problem - but that figure of 36.96 A presupposes an 8.5kW shower on an exactly 230V supply.

Do bear in mind there are what are known as supplementary bonding requirements for bathrooms etc. If this means nothing to you I'll post about them if you wish.

 

[NEIL222]

for "didthathurt" thanks that was really helpful
please post me about supplementary bonding

so it looks like im good to fit an 8.5kw shower?

i've read that the earth terminal at the shower unit itself should also be connected to the copper pipe with earth cable, and then the copper pipe is connected by earth cable to the other coppers pipes nearby?

 

[didthathurt]

That's pretty much it. The theory is to ensure that nowhere in the bathroom do you have a situation where a potential can exist between any metal parts you are liable to touch. To achieve this you connect all the metal pipes, somewhere close to the bathroom if you can't do it in the bathroom, to the shower earth, the lighting earth and the earth of any other cct supplying a service in the bathroom. This all needs to be done in 4mm earth bond wire. The only problems normally involve accessing the ccts and physically connecting a 4mm earth bond into a light fitting. Just choose the most accessible.

 

[ban-all-sheds]

for "didthathurt" thanks that was really helpful
please post me about supplementary bonding

http://www.niceic.org.uk/downloads/NL139supp.pdf

http://www.niceic.org.uk/downloads/E169-9.pdf

http://www.niceic.org.uk/downloads/Earthing Bonding guide.pdf

http://www.iee.org/Publish/WireRegs...tumn_plastic_pipes_to_bond_or_not_to_bond.pdf

That's pretty much it. The theory is to ensure that nowhere in the bathroom do you have a situation where a potential can exist between any metal parts you are liable to touch. To achieve this you connect all the metal pipes,

No - not all of them - only those which are extraneous-conductive-parts. Please read the 2nd and 4th links above for clarification.

somewhere close to the bathroom if you can't do it in the bathroom, to the shower earth, the lighting earth and the earth of any other cct supplying a service in the bathroom.

Not "any" - only those supplying appliances in Zones 1, 2 or 3. Please read link 1 above for details on zones.

The only problems normally involve accessing the ccts and physically connecting a 4mm earth bond into a light fitting. Just choose the most accessible.

You only have to bond to the cpcs (earth cores) of the circuits - you don't have to do this at the actual light fittings.

 

[didthathurt]

Thank you BAS. You are 100% accurate - as we have come to expect. I do, somewhat, simplify these matters when I discern that I'm probably dealing with a relative novice as I like to remove the element of doubt as to whether or not a requirement applies.

For example:

No - not all of them - only those which are extraneous-conductive-parts. Please read the 2nd and 4th links above for clarification.

I'd rather someone bonded that one extra pipe, maybe unnecessarily, than missed it out erroneously and learnt the hard way. As just about all metal pipes supplying a bathroom will, somewhere, join a metal fitting that can be touched, I feel advising they all be bonded (which, after all, will probably only be 1 hot, 1 cold and 1 radiator supply) an option that will serve the OP's best interests to the greatest degree.

Not "any" - only those supplying appliances in Zones 1, 2 or 3. Please read link 1 above for details on zones.

Your point on Zoning is valid. However, given that the smallest "shower bath" is around 1600mm x 700mm, and located in a corner, no bathroom less than 3.7m x 4.6m or with a ceiling height greater than 2.25m will have anywhere within in that falls outside of the zones. I don't know about you, but I do, just about, 100% domestic work and see, maybe, 1 house in 50 that has a bathroom exceeding the above. I, therefore, would always advise bonding all ccts (again, we are talking, really, 1 lighting, 1 shower and, maybe, 1 power - eg towel rail - cct).

You only have to bond to the cpcs (earth cores) of the circuits - you don't have to do this at the actual light fittings.

Absolutely. I do find that this will mean accessing the cct at the switch or the luminaire/ bulb holder itself - if I gave the impression (as I think you correctly point out, I did) that this had to be at the bulb holder/luminaire then I agree I should have elaborated more.

That's my logic, BAS. I genuinely respect your views and always read your posts - and those of a number of others - with great interest; do you, and our other eminent knowledgeable pro's, think I disserve such OPs by overly simplifying. I would appreciate your opinions.

 

[ack351]

Did-that-hurt, keep up the good work, far better be safe than sorry

 

[ban-all-sheds]

Thank you BAS. You are 100% accurate - as we have come to expect. I do, somewhat, simplify these matters when I discern that I'm probably dealing with a relative novice as I like to remove the element of doubt as to whether or not a requirement applies.

Simplification is a great idea, and as ack351 said, better to be safe than sorry.

Talking of sorry - apologies, BTW, for the "read this for more info" stuff - it was late and I think I got mixed up who I was replying to..

But I'm afraid I don't agree with simplification to the point of not encouraging people to learn and understand for themselves, rather than doing stuff without knowing why.

For example:

No - not all of them - only those which are extraneous-conductive-parts. Please read the 2nd and 4th links above for clarification.

I'd rather someone bonded that one extra pipe, maybe unnecessarily, than missed it out erroneously and learnt the hard way. As just about all metal pipes supplying a bathroom will, somewhere, join a metal fitting that can be touched, I feel advising they all be bonded (which, after all, will probably only be 1 hot, 1 cold and 1 radiator supply) an option that will serve the OP's best interests to the greatest degree.

The only problem is that if a metal part is not an extraneous-conductive one, bonding it makes it less safe, not more...

As for the zones thing - you are right, not many people have huge bathrooms, but anything built before the war will have ceilings over 2.25m, so a ceiling luminaire and pull-switch might well be out of the zones, so given the aggro of bonding that circuit it's definitely worth checking out.

do you, and our other eminent knowledgeable pro's.

Aww, shucks. There's something I should probably tell you...