Bonding a power shower

[RegB]

My old power shower is worn out so I'm now swapping it with a newer version of the same make (Mira Event XS). It has a built-in pump but no heater, using domestic hot water, and draws 150 watts.The pipes and cable enter directly from the wall, so are not exposed. Access to these is via a crawl space. I've noticed the cable goes straight to the CU to a 16amp MCB but there's no RCD protection so I intend to add that. My main concern is about supplementary bonding of the shower unit. The water pipes to it are plastic and the exterior of the shower unit itself is also entirely plastic. Obviously there's an earth in the main cable, running back to the CU but there is no supplementary bonding in evidence. Does anyone know if such bonding should be added? There are no other electric appliances in the bathroom apart from the light.Many thanks for any advice. Reg

[jj4091]

As long as your shower is corectly earthed & in the situation you describe, then there is no requirement for supplementary bonding.

[sm1thson]

In the situation you describe there isnt a need to bond the pipes, although all bathroom circuits should be bonded, so technically I think the earth from the shower circuit should be bonded to the earth from the lighting circuit –although I cant see that would actually achieve much in terms of offering any useful protection [edit]in the situation you describe.

when 17th edition comes out (if they dont change things) all bathroom circuits will need to be RCD protected with no need for bonding anyway, i would be bearing that in mind if i had your bathroom.

(note i may be wrong about any of the above)

[Qedelec]

The reason for bonding the lighting to the shower circuit is to lower the cpc resistance (circuits in parrallel) but I have never been convinced the reduction in trip time would be significant.

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[dingbat]

Qedelec wrote:

The reason for bonding the lighting to the shower circuit is to lower the cpc resistance...

Er, no, it isn't.

Supplementary bonding does not form part of any individual circuit protection. It is required purely to reduce the potential difference between any combinations of exposed and extraneous conductive parts in the location concerned.

Think of it as re-establishing a new 'earth' potential remote from the Main Earthing Terminal; that is, at the MET all main bonding and CPCs are at the same potential as the means of earthing. By the time the CPCs and pipework arrive at a remote bathroom, each will have a slightly different 'earth' potential due to differing resistances. Link 'em together and all are again at the same potential (near as makes no difference).

[sm1thson]

dingbat wrote:

exposed and extraneous conductive parts

in the case of the OP the earthed parts of the power shower arent exposed (i presume) so, according the regs, is this exempt from needing bonding to the lighting circuit? (genuine question, i dont know the answer, as i said i was under the impression it was all circuits entering the bathroom)

[dingbat]

sm1thson wrote:

dingbat wrote: exposed and extraneous conductive parts in the case of the OP the earthed parts of the power shower arent exposed (i presume) so, according the regs, is this exempt from needing bonding to the lighting circuit? (genuine question, i dont know the answer, as i said i was under the impression it was all circuits entering the bathroom)

The regulations require that local suplpementary bonding be provided, connecting together the terminal of the protective conductor of each circuit supplying Class I and Class II equipment in zones 1, 2 or 3 plus any extraneous conductive parts in these zones.

Even in a bathroom with all plastic pipework and all Class II equipment the current regs still require that circuits are supplementary bonded.

(For what it's worth, the only reliable way of killing yourself electrically in a bathroom is by your own stupidity, but, desirable though that outcome may be, we still have to mitigate against it!)

[RegB]

Many thanks to everyone for the replies. I really appreciate you taking the trouble. Thanks. Reg