Where is supplementary bonding required

Connections are made on the metal pipes near the point at which they enter your home, i. Main Bonding is there to protect you. A fault current amps , but if is easy to understand in volts think of it in that way instead, will always try to find a path down to earth, literally to the ground. The current will always take the easiest path to ground; the idea of Main Bonding and Supplementary Bonding is to create an alternative path for the current to flow that is an easier path than along one of your heating pipes, along your arm, through your body, down your legs to the wet kitchen floor and to ground.

By using a thick copper cable, you are creating a path that is more inviting to any fault currents and will divert any fault currents from your body or places where it should not go, as the current flows down to ground.

Protective equipotential bonding is different from supplementary bonding. Supplementary bonding is the practice of connecting two conductive simultaneously accessible parts together to reduce the potential difference between the parts. It should be noted that the term extraneous-conductive-part is hyphenated, which means it is a single term which has a specific meaning. It can sometimes be difficult to determine if a part meets this requirement, therefore it is sometimes easier to break the definition down into three separate parts.

Earth potential is generally assumed to be 0 volts introduced by the general mass of Earth more commonly known as the planet we stand on. With a couple of minor changes in terms of wording there is bound to be some confusion, but what exactly has changed since the previous edition?

Table Practically speaking, nothing has changed regarding this Regulation except for the addition of the above statement, but it will undoubtedly make people question whether protective bonding is required at all. So, the part has to be conductive, for example a metallic water pipe, and not part of the electrical installation and essentially able to introduce Earth potential.

This would usually mean a conductive part going outside the building and touching the ground or going to another building. If this can be verified by visual inspection, the part does need main protective bonding.

If an installation pipe is constructed from a plastic type material such as medium density polyethene MDPE which is most commonly installed, it is unlikely to be considered an extraneous-conductive-part, but this must be verified.

Another cause of confusion is regarding the terminology of the pipework installation. The gas regulations describe the service pipework as the pipe that comes in from the road to the meter. The pipe from the meter to the property is called the installation pipe.

BS regulations are with regards to the installation pipework and not the service pipework. It should be verified if parts are deemed to be extraneous-conductive-parts before there may be a requirement to connect them to the MET. The best way to determine whether a conductive part is likely to introduce Earth potential is visual inspection. If it is not possible to determine by visual inspection alone, then a measurement of resistance to Earth can be obtained to determine if the conductive part in question is to be considered an extraneous-conductive-part.

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.

Yes as David Z points out we only have to consider "reasonable use" These conductive parts are extraneous to the bathroom not the whole building.

So can they introduce a potential to the bathroom, ""accessible extraneous-conductive parts,within a room containing a bath or shower"? The question has to be asked can this metallic pipe introduce a potential in to the bathroom equipotential zone? Or do we have an equipotential zone in the first place? Or do we need to establish by supplementary bonding an equipotential zone?

Other parts listed in All plastic pipe in the bathroom and no supplementary bonding is required. Different circuits with mixed disconnection times with some circuits not RCDed and all plastic pipe?

Or did JPEL get the regulation right in the first place? I think some are missing the point. Where there are no e-c-ps to the building then having no main bonding IS protective equipotential bonding according to Therefore in the bathroom supplementary bonding may be omitted if the other conditions iv , v and vi are met but things still have to be verified.

The note under In the circumstances being discussed it might be possible for this 'R' to be between ohms and 23k ohms.