Earth Bonding in Bathroom

[sg31]

I'm in the process of refitting my bathroom. Currently everything is taken back to the bare walls and I'm battening one wall ready for plasterboarding, then I'm going to bond and set the complete room. All the services to the existing bathroom came down behind boxing on this wall.

The existing plumbing is basically speedfit tube and fittings connected to copper in the ceiling void.

Earth straps are connected to the copper and earth cable dangles in long lengths which would reach the WHB and WC.

No provision exists for earth cable to what will be the new steel bath or the new shower.

There is an existing power feed to one wall light which is permanently live (the light itself incorporates the switch) This is 1.5 twin and earth terminating in a standard connector block with an earth cable attached to the earth of the twin and earth of the power cable.

I think that sets the scene reasonably well. The plumber is coming to first fix in the next few days then I want to plasterboard this wall. There are no electrics to do as everything is staying the same except for the new shower. The cable for the shower was first fixed by a qualified electrician and the shower will be fitted after plastering with the connections made by a qualified electrician.

What I need to understand is the earth bonding requirements. I used to know them but I think things might have changed.

I presume I need to keep the existing connection to the permanently live 1.5 twin and earth. Is this adequate or should I provide an earth cable to the new shower cable as the earth to that will be more substantial?. The earth of the 1.5 Tand E strikes me as potentially inadequate.

Do I need to run extra eath cable to the new metal bath and cross bond to the taps.

I presume there should be eath bonding to the wc and WHB taps.

I'm not sure how the speedfit tube affects matters, if at all. In effect the water must provide a way to earth although I suppose it wouldn't if the pipes were drained down.

Can anyone help?

[csearle]

I can help, but I'm just leaving site so will reply properly later. C.

[csearle]

Can anyone help?

Hi SG,

There are two separate ways of mitigating against the added danger of shock in a bathroom. Up and until 2008 the only way available was through “supplementary equipotential bonding” around your bathroom. This involved connecting together all exposed metallic parts entering the bathroom* from without using these (ugly) green/yellow wires. By the sound of it your old bathroom was protected in this way.

Whilst this method is still available it has been largely superseded by another way. This other way simply involves
a) making sure that all electrical circuits supplying your bathroom (often just the lighting) are protected by a 30mA RCD, and
b) ensuring that your protective bonding connecting your gas, water, electricity, oil, etc. is adequate (>=10sqmm csa).

So you have two choices. Either re-instate the supplementary equipotential bonding making sure that all metallic items entering the bathroom walls (including lighting Earth + shower Earth) are connected together using 4sqmm (if mechanically protected) or 6sqmm green/yellow cable, or
ditch all this Earthing and make sure that both your lighting and your shower circuits are protected by a 30mA RCD. In this latter case your electrician needs to ensure that your protective bonding between services is in place and adequate.

Personally I would go with the RCD option given the choice. I realise this is a question likely to raise further questions. Feel free.

Regards,
Chris

* Your steel bath need not be included if it is connected to any (already bonded) metal water pipes entering the bathroom (if they are plastic then it need not be included nor any other metal parts e.g. towel rails not electrically connected to anything).

PS The only things that need “supplementary equipotential bonding" are Earth potentials conducted through the walls of the bathroom.

[pochisoldi]

or
ditch all this Earthing and make sure that both your lighting and your shower circuits are protected by a 30mA RCD.

Is the requirement to remove the bonding required to avoid a "disconnected neutral" to a TN-C-S/"PME" supplied property resulting in causing the earth terminal voltage in the CU (and hence the locally bonded items) to rise with respect to the "local earth" (i.e the route to earth via the water supply), as against the situation where a TN-S fed property where the separate incoming earth back to the substation transformer is pretty much at the potential as the "local earth".

(please feel free to correct/clarify my terminology)

PochiSoldi

[sg31]

OK, thanks for that.

We had a rewire of the house including the consumer unit about 3 years ago by a very good qualitied electrical firm 3 years ago. I'm sure they did everything to proper standards. The CU is one of the new metal types.

The earth bonding was probably left because it was inaccessible behind boxing in and base units and permanent feed to the bathroom wall light was behind tiling.

I'm happy to rip out the earth bonding but will ask the electrician who wires up the new shower to check everything is in order.

[csearle]

or
ditch all this Earthing and make sure that both your lighting and your shower circuits are protected by a 30mA RCD.

Is the requirement to remove the bonding required to avoid a "disconnected neutral" to a TN-C-S/"PME" supplied property resulting in causing the earth terminal voltage in the CU (and hence the locally bonded items) to rise with respect to the "local earth" (i.e the route to earth via the water supply), as against the situation where a TN-S fed property where the separate incoming earth back to the substation transformer is pretty much at the potential as the "local earth".

There isn't a requirement to remove the supplementary equipotential bonding, SEP, around the bathroom, in fact if that is the only method of providing the additional protection then it mustn't be removed. It's just that with more and more installations being protected by residual current devices, RCDs, the SEP can in many cases be safely removed. Clients often don't want to see green/yellow wires, Earth clamps, boxing, etc. in their sleek bathrooms.

Just for clarity the main protective bonding between metal water, gas, electricity, oil, etc. services must be in place.

There is an issue with properties with the Earthing method TN-C-S* and disconnected neutrals, and that is that this system was introduced (like me )in about 1960 (apparently) and the multiple Earth electrodes that were installed at the time immediately began corroding. By the end of the seventies these started failing. Any poor connexions in the neutral wire back to the substation started causing the normal load current to prefer to find its way to the substation via water pipes etc. rather than the poor neutral connexion. Rather than paying to have the Earth electrodes maintained the distributors have found a way of passing the cost over to the home owners. They are in the process of making it a requirement a) to have Earth electrodes interwoven with steel reinforcement in the foundations of new builds, and b) to have every household with Earthing method TN-C-S install (and therefore maintain) their own Earth electrode.

Regards,
Chris

*TN-C-S Earthing arrangement whereby the Earth connexion and the neutral wire are shared (and Earthed at multiple locations) up to the origin of each electrical installation then separated within the building.