boiler earthing?

[Stephen]

Hello,

My old (oil fired) boiler had a 4mm^2 (ish) earth wire that ran from the copper oil line back to the CU.

When the (non-oftec) plumber recently installed the new boiler, this was not reconnected. I am having an oftec plumber coming to sign everything off. Should I connect the earth before he comes and for my own safety?

The boiler is earthed but only through the 6A flex.

In my last house the (gas) boiler had all the pipes cross bonded immediately beneath it. None of the pipes going to or from this boiler are. I don't think the CH pipes are earthed anywhere. Should they be?

Thanks, Stephen.

[Andrew Gabriel]

That's the service bonding. Nowadays, it should be 10mm², IIRC.

I would have thought so, but I'm not expert in oil fired boiler matters and any special requirements on them.

They probably are in or adjacent to the bathroom -- that's where it's normally done.

[Andrew Mawson]

boiler

My OFTEC oil installer fitted my boiler but didn't bond the incoming oil pipe, despite me querrying it. My NICEIC electrician certifying the whole electrical installation insisted on 10mm bonding back to the main earth point at the CU. Mind you I can (and actually have in a previous posting) cite several errors of fact on his certificate !!!) The boiler per se is only earthed via the copper plumbing which is bonded and its own electrical connection 2.5mm earth.

AWEM

[John Rumm]

That would be the main equipotential bond for the incoming service (i.e. oil pipe)

All incoming services in metallic pipes should be included in the main equipotential bonding.

For TN-C-S and TN-S installations this is usually 10mm^2 earth single. For TT it can be 6mm^2

See:

The boiler is earthed but only through the 6A flex.

That is fine.

Where is the boiler? Where was it in the last place?

Generally speaking you would expect to see supplementary equipotential bonding in places that pose an special risk (bath / shower rooms, pool / saunas etc). There is no harm in have supplementary bonding between its connections, however there is in many cases no absolute requirement for it. Note that supplementary bonds do not need to be either earthed, or connected back to the main CU earth terminal.

[Stephen]

I remember the electrician who checked the electrics before we moved in said something about the earthing not being to the latest regs. I can't remember if it is 4 mm^2 or 6mm^2, I guess I'll have to measure the diameter of the wire and calculated the area to see. He said it ought to be 10mm^2 to comply with the regs but he thought it was safe nonetheless. Is it worth upgrading it to 10mm^2?

You are quite right. I've just looked; behind the pedestal and under the bath, all out of sight, the bath, basin, and bathroom radiators are bonded.

[Stephen]

My OFTEC chap didn't comment that it's not connected. However since the wire is there I will connect it. I'll have to be careful though as I assume the 10mm micorobore pipe is more easily damaged if I overtighten the clamp.

Thanks.

[Stephen]

It is in the kitchen, exactly where the old one was. Thinking about it it's all copper pipe around the boiler but after 2 metres it turns plastic, so I'm not sure that bonding would do much, except in the immediate area of the boiler.

Is supplemental bonding supposed to be 10mm^2 too? I am not going to do it (unless you tell me otherwise) but I ask out of curiosity.

Thanks.

[John Rumm]

In "special locations" (of which a kitchen is *not* one - part P lumps it in with them, but the wiring regs do not), the question to ask, is are the pipes capable of introducing a potential into the room from elsewhere. In you case it sounds like the answer is "no".

To quote the OSG (16th edtn): "There is no specific requirement in BS

7671 to supplementary bond the following

kitchen pipes, sinks or draining boards

metal furniture in kitchens

metal pipes and wash hand basins in domestic locations other than bathrooms."

Where there is no mechanical protection for the bonding conductors,

4.0mm is commonly used. Where you are bonding a circuit protective conductor, then you should not use a smaller CSA wire than that of the CPC - however domestic wires with CPCs larger than 4.0mm are not common (only 16mm^2 for T&E)