When is supplementary bonding not required

A resistance test can be carried out between the conductive part in question and the MET. The test needs to be carried out with a continuity tester with a voltage range of between 4 and 24 volts and with a test current of mA. The test should be carried out between the MET and the conductive part in question. The first problem is that the test can only be carried out when the other installations, not forming part of the electrical installation, are complete which means it will not always be possible to determine until the later stages of a project.

Another problem would be that any class 1 electrical equipment connected to the pipework such as a boiler, motorised valve, or pump would create a conductive path to the MET which could indicate a low reading.

In most cases, for example at the design stage, the installation will not yet have been built. In which case, the designer will have to consider both scenarios with and without the protective bonding connected. The prudent option would be to install the protective bonding conductors at first-fix stage as it is likely to be more difficult and expensive to do at a later stage. It would also likely involve damage to the building fabric or be required to be installed surface mounted, which would not be desirable for most clients.

However, it is important to remember that by connecting to the main earthing terminal, in some circumstances, fault currents can be exported throughout the installation which would not be there if protective bonding had not been applied.

This can cause an electric shock risk for persons outside of the installation in contact with the general mass of Earth and earthed equipment such as pipework, for example an outside tap or metal class 1 electrical equipment. It should be noted that even though the incoming service pipe may not be metallic or appear not to be in contact with Earth, there may be fortuitous connections with Earth throughout the installation which may or may not be apparent by visual inspection. For example, the incoming water pipe may enter the building in plastic pipe but in another part of the installation the metallic pipework could exit the building and enter the ground or be connected to earthed plant such as a metal pump, therefore introducing Earth potential.

That is why it is important to ascertain where the extraneous-conductive-part enters or possibly exits the building. I inserted the insulated joint immediately after the water stop valve as I have an overhead supply and do not want my neighbors diverted neutral currents flowing to earth via my bond in the event of the PEN becoming open circuit.

I am thinking that it would be helpful if the words "or all circuits in the building are 30mA RCD protected" should be added to the condition that allows omission of supplementary bonding. Or perhaps main bonding should be applied even if the incoming pipework is plastic and then is connected to metal pipework or a plastic insert is in place?

Zoomup Posts: Joined: 20 February Not bonding again. This might be a looooooong thread. I remember doing a housing development about 15 years ago where supp bonding was all the rage.

We ran a nice bit of 4mm earth from the light and clamped all the plumbers copper tail pipes that were poking out the floors or walls. When we went back for snagging nearly all the clamps had been removed and all the earth wire cut off tight to the floor or wall so impossible to attach anything to. The 'plumbers' said the clamps and yellow cable ruined the look of the new bathrooms , so they removed them as they felt they were unnecessary.

Hmmmm Oh well. My hot water was once like this, as a conventional cylinder with immersion, plus a header tank set-up. The none-original header tank was polypropylene, and at all the places there after that hot and cold pipes met, there was ceramic sinks and tiles But I suppose some odd fault with the immersion heater and its CPC could have raised the voltage on the hot taps to be different to that on the cold, and main bonding alone, without the bathroom end bonded would not help.

Its OK now we have a gas boiler and multiple paths to earth for it. Then there is the edge case of is the worst case shock of 50V not quite tripping an RCD low enough for bathrooms?

That I think is a red herring as an RCD system with an earth impedance that bad would be unusual. Lets consider this a bit further, because the wording of the BBB is not at all helpful, and may even need "adjustment".

So by Chris's reading every metal item in the bathroom would need supplementary equipotential bonding, even the bathroom cabinet and otherwise all plastic connected metal taps. There is no danger from any of this metalwork as none of it can give you a serious shock, and if the current is a bit higher it can trip the RCD which gives you a safe condition.

This is the "normal" and intended condition. It seems to me that John's scenario is very unlikely, and in fact has another error in that the submain traveling alongside a metal pipe so that it could contact under reasonable fault conditions makes that pipe an exposed conductive part, and it should be earthed. We need to remember the "reasonable" condition when considering such faults, and "intended" use, so complex multiple fault conditions are excluded. An SWA submain presents no risk, and neither does a normal sheathed cable, as both have mechanical protection, and unsheathed cables unless enclosed are not permitted.

Reasonable fault conditions, I think not, unless the pipe can exceed the cable temperature limit and the cable is in direct contact with the pipe, in which case the pipe should be earthed as it is effectively an exposed conductive part. There is another possible scenario which is a pipe connected to another circuit which is not RCD protected and has an earth fault, but the normal disconnection time and possible earth voltage drop should make this sufficiently safe.

In my view we need a new term for otherwise unconnected metalwork, pipes etc, because they are not exposed or extraneous conductive parts, yet manage to cause confusion. It is possible to make odd metalwork an exposed conductive part with poor installation practice! You will note that none of the above is affected in any way by whether there is main bonding, any piece of pipe may simply be isolated by plastic plumbing.

Originally posted by: davezawadi It seems to me that John's scenario is very unlikely, and in fact has another error in that the submain traveling alongside a metal pipe so that it could contact under reasonable fault conditions makes that pipe an exposed conductive part, and it should be earthed. Alcomax Posts: Joined: 12 November In my view we need a new term for otherwise unconnected metalwork , pipes etc, because they are not exposed or extraneous conductive parts, yet manage to cause confusion.

Ah yes but you need to read all the paragraphs of the Regulation. Bathrooms are a special location because here are enhanced risks, that is the purposes of special locations or installation, in this case greater areas of skin exposed, wet skin and immersion in water.

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This enables us to offer the highest levels of professional service to you. Thats exactly what I'm asking. Thank you for an honest and straight answer. A known earth within the room. Would you not expect an exposed conductive part to be earthed? Your question was asked perfectly well. The situation you are describing will only come about once in a blue moon. Certainly I have never came across a bathroom or shower room with an exposed conductive part and extraneous conductive parts within touching distance.

But that is not what you posted. To me as you quoted the ohms thing which is what is measured between exposed conductive parts and extraneous conductive parts you were asking about that. You then seem to be complaining that people are not answering a completely different question about what makes a conductive part extraneous.

Which question are you asking? First time on this forum so apologies if I'm not being clear. My question is who actually carrys out the testing to see if supplementary bonding to extraneous conductive parts in a bathroom is required when there is full RCD protection. Your opening post says exposed when really it should say extraneous. To answer your question If these 3 points are met then I do not need to worry about supplementary equipotential bonding in the bathroom.

You seem to be confused about the actual requirements Supplymentary bonding is not required for extraneous conductive parts unless they are within touching distance of exposed conductive parts and the resistance between the two is greater than ohms Main equipotential bonding is. Many electricians will have automatically ensured that main protective bonding is in place as this is required for all ADS protected circuits, not just bathrooms, and the same applies for all the circuits in the installation that they meet the disconnection times.

These should be in place before you start considering bathrooms, it is at this point that any testing for extraneous conductive parts would have been undertaken.

Then when considering bathrooms 30mA RCD protection is required; ensuring this is also included would then mean that supplementary bonding in the bathroom could be omitted. Testing for extraneous conductive parts again in the bathroom would not be necessary because it has already been done. This is not to say that some electricians would assume all main protective bonding is in place and that ADS times are met and so state that 30mA RCD protection is all that is required.

So to answer the question you intended to pose, the testing for extraneous conductive parts would be done earlier and not necessarily in the bathroom as it is the point of entry into the installation of the extraneous conductive part that is the point requiring bonding.

The testing would still be completed, just not in the manner you propose. Paignton pete - Esteemed. Reaction score 2, Post reply.