Earth bonding and LV bathroom electrics

[Rich_W]

I've been reading a lot about earth bonding in bathrooms recently and I have a question.

My bathroom has LV lighting and an LV fan. Neither of these items has its own earth.

The power shower I'm planning to install will be connected to a combined RCD/FCU (as purchased from Screwfix). This will be spurred from the ring main (the recommended fuse rating is 3A, so I'll swap out the 13A fuse supplied with the RCD/FCU).

I'm assuming that supplementary earth bonding will be required in this scenario. If so, would it be appropriate to connect it to the combined RCD/FCU?

Thanks in advance.

 

[Damocles]

If the power shower is entirely hidden from people in the bathroom, then strictly speaking it does not make any difference to your bathroom setup. Supplementary bonding should connect together any source of earth entering the bathroom zones. (a bathroom is split into zones where different regulations apply). Which means metal pipes coming in (water supply or waste pipes) and any electrical equipment which incorporates an earth. If your pump or indeed immersion heater are hidden away in a cupboard or behind panels then they do not count as being inside the bathroom.

 

[Rich_W]

My power shower installation will be hidden behind a panel (accessible from outside the bathroom).

From this, I would assume that I have no electrical equipment in the bathroom which incorporates an earth.

That said, the instructions explicitly state that all copper piping must be cross bonded and connected to an earthing point. However, none of the copper pipes feeding the shower will be accessible from the bathroom.

In this case, I guess the question is: do I actually need to cross bond the pipes which are accessible in the bathroom? Your reply suggests that I do.

On that basis, the easiest earthing point would be the RCD for the shower - would this be an appropriate connection point?

 

[Damocles]

You are allowed to do bathroom supplementary bonding just outside the bathroom (for example in some cupboard or compartment) but it should be accessible for inspection as and when this might be required.

if the manufacturers are instructing you to cross bond things then I amd not going to argue with their recommendations for their equipment. I am only talking about the general wiring regulations.

Electrical equipment includes lights, unless they are not powered by electricity. However if the ceiling is high enough they may be above the zones and thus not count.

The principle behind supplementary bonding of bathrooms has nothing to do with power showers. If somehow the hot tap has become live, and then all wet you grab the cold tap, could get a bit nasty. So the idea is to bond each separate supply entering the room. That way there can never be a voltage between them.

 

[Rich_W]

Thanks for the details - your replies, along with some of my own research have helped me understand the principles behind supplementary earth bonding.

I suppose all I'm trying to do is find a sensible place to which I can earth the incoming metal water pipes in my bathroom.

If supplementary bonding can be routed just outside the bathroom (this is how I have interpreted your response), then I would probably look to use the combined RCD/FCU for the power shower. I take your point about supplementary earth bonding having nothing to do with power showers - I simply mention it because it is the most convenient place into which I can run the cross bonding from the exposed pipework in the bathroom.

Electrical equipment includes lights, unless they are not powered by electricity. However if the ceiling is high enough they may be above the zones and thus not count.

Duly noted, although what I was trying to get across was the fact that my lighting has no earth points to which I can connect - with the exception of the earth in the 240v cable to the LV transformer. Would this be where I should look to include the lighting in any bonding?

Thanks for taking the time to reply

 

[Damocles]

I am not quite sure what you mean by 'use the combined rcd/FCU...for bonding'. You do not have to 'earth' the pipes which you are bonding. What you have to do is join them all together.

Any earthing which happens is incidental and due to them being earthed already. The idea is that you do not care what happens on the other end of any of these pipes or wires coming into the bathroom. So long as they are all connected together inside the bathroom you can not get a shock off any two of them, and there should not be anything else which could conduct electricity into or out of the room.

An electrical earth which comes into the room as part of a circuit is just another earth to be joined together. You should not be thinking of it as a link to the real earth. Particularly since a thin wire might be a much poorer earth than a good hefty copper pipe.

 

[Rich_W]

Cue sound of pennies dropping. All clear now - thanks for bearing with me!