Supplementary bonding in a bathroom (sorry!)

7 Apr 2006
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United Kingdom
I have searched through the archived threads looking for a definitive answer to a question thats really bugging me. To be honest though i'm now more confused than ever!!!

Imagine the scene

25mm2 Meter Tails
16mm2 Main Earth Conductor
10mm2 Main Equipotential Earthing conductors (connected to the gas and water mains)
4mm2 Supplementary bonding between all pipes on the combi boiler(including the shower supply pipe) which resides in a airing cabinet in the bathroom

Here comes the question, does the shower have to be seperately bonded back to the incoming water main/CU or does the supplementary bonding suffice to keep it all at the same potential?

If it does need to be seperately bonded do i use 10mm2?

I really have managed to confuse myself into a frenzy about this.
I was really confident that the supplementary bonding i've already done would suffice but after reading through the archives i'm now totally confused and wonder if the shower needs to be bonded back to CU.

Please help
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sup bonding does *not* go back to the met, it is done in the vicinity of the bathroom to keep all cpcs of circuits supplying equipment in zones 1,2 and 3, and all the metalic items that are capable of intrudcing a potential*, are kept at the same potential

*This is important, its not blindly all pipes for example... a sixth inch piece of copper connected to the houses plastic pluming system under the floor and rising to the taps does not need to be bonded because it can't introduce a potential
Thanks for taking the time to reply to my dumb question!!! :)

So just to be clear (sorry its saturday night and this is all i can thing about!!!!)

In my example the shower would require no further bonding other than the supplementary bonding i've already carried out?
If you have already included it in the bathroom sup bonding then that is correct, but if you are meaning that you have sub bonded it with the boiler stuff, then it'll still need bonding in the bathroom.

Sorry.... just read your post again, got a totally wrong image in my head because the airing cupboard here is no where near the bathroom

As the airing cupboard is in the bathroom, its not really two lots of bonding but one bigger bonding thing, so make sure you include all the earths of the circuits supplying stuff in the bathroom (inc boiler), all metal pipes that could introduce a potential into the bathroom, etc
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Honestly i can't thank you enough for trying to help me out with this!!!

Although now i'm getting confused again....

i'm sorry if i seem dense, its just i've had 3 different sparks say 3 different things so my head is just blown!!!

Yes the shower is bonded to the boiler and all the metal pipes leading from the combi boiler (there are no plastic pipes in the bathroom at all).

I was under the impression that as the combi boiler supplies all the water and heating in the house then by doing sup bonding across all the incoming and out going pipes i was effectively bonding the whole bathroom (especially as the boiler is basically in the bathroom).

One point as well, when you say "earths" including the boiler. Do you mean i'm supposed to link from the boiler's cpc?

See i am really confused....
Let's start again.

You need to bond together all pipework within the bathroom (hot, cold, flow, return, metallic wastes, exposed structural metalwork etc.....) to all cpc's of any electrical equipment within the bathroom (lighting, shower, shaver point, heater(s), heated towel rails, immersion heaters, boilers etc....) When I say all cpc's, I don't mean literally every single cpc, rather, one from each circuit present. If you have a pullswitch, light fitting and shaver point all fed from the same circuit, then you only need bond at one point.

Use a minimum of 4mm2, make all connections accessible (unless sweated), preferably without breaking the conductor, or if you do, use ring crimp connectors.

As has been said, Supp Bonding does not return to the MET. It is purely and simply intended to bring all metalwork within the bathroom to the same potential. If you and the metalwork you are in contact with are both at 230V, there is no PD, and therefore no shock risk.
I beleive Brian Scadden refers to it as a Faraday cage effect. I'm not convinced these are the same but you get the idea.
Thank you!!!!

Really thanks to both of you for taking the time to make it clear
securespark said:
Let's start again.

Use a minimum of 4mm2, make all connections accessible (unless sweated), preferably without breaking the conductor, or if you do, use ring crimp connectors.

Sorry to jump in but what do you mean by "sweated"?
davas said:
Sorry to jump in but what do you mean by "sweated"?

Similar to soldering, attaching a cable to a lead pipe or cable sheath, but the lead melts a tad and 'interminages' with the solder, but if the pipe is copper and not lead, then the its soldered because the copper itself doesn't melt (having a melting point of 1083.4 as opposed to 327.5), well thats how I understand it anyway
So if i solder a bonding connection to a copper pipe then it does not have to be accessible?

a) does the joint need to be viewed by a building inspector/electrician signing of my notified work or would me saying that it's soldered be enough for them?

b) how would you solder it? would you solder the earth wire connection to the clamp ir is it soldering the clamp to the pipe that is the important bit?

you are correct if the joins to the pipes are soldered then they don't need to be accessible for inspection.

btw you don't wan't to use lead free solder to solder to anything with lead in it contamination in lead free solder will often stop it flowing properly and making a bad joint (especially if the solder has one of the newer safer but cr*ppier fluxes rather than good old rosin).

i belive lead free solder has been required for normal plumbing soldering for a while and is now required in commercilly manufactured electronic equipment but you can still get tin/lead solder if you know where to get it
it will be copper pipes only plugwash so lead-free will be ok i guess.

All - what is the definition of accessible?

I am boxing in (and subsequently tiling) most of the pipework so will any bonds there need to be soldered or is ripping off a box unit considered "accessing"
I don't belive there is any actual definition giving in the regs but the general principle i'd advise working to is that if something is required to be accessible then the means of access should be obvious and not involve damaging anything.
Take a couple of photo's of the bonding showing the connection and then where it is located then you can prove it has been done should there be a que erie at a later date.

<edit> if you write the word que erie with out the space it comes out as four stars. This seems a bit over politically correct to me.

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