Bonding

[Madrab]

All - I know that this has probably been done to death but given there doesn't seem to be a real consensus on the subject, depending on who you talk to and given changes in the latest regs and nothing recent on the forum.

As a plumber/gas engineer we are taught as part of the C&G tech certs that bonding (equipotential and supplementary) is required when installing metal pipework and fittings in a home, especially on Gas pipework and any other associated metal pipework/fittings even when RCD's are present and given a lot of external supply pipework is now transitioning to plastic so there's no natural path to ground any more. I think it is also referenced in BS 7671 as a specific requirement for metal work and that then links to Part P using that standard to define a system as being safe.

What is the bottom line, is it needed as a standard and part of the regs?

TIA

 

[mattylad]

As a plumber, are you recertifying your electrical competence part of your training on a regular basis like the electricians are?

AUIU the rules change pretty often as new things come to light and changes to what they do are required.
From what I see there are regular courses required by electricians to keep up to date with all this.
Which is why the recommendations on bonding changed.

 

[flameport]

that bonding (equipotential and supplementary) is required

All bonding is equipotential, that's the whole point of it.
Equi = equal
Potential = voltage.
Keeps two or more conductive parts at the same voltage by connecting them together.

When faults occur within an electrical installation, the main earth terminal and everything connected to it will have a higher voltage until the fault is cleared by the circuit breaker opening.
No bonding installed = metal items which are part of the electrical installation could have a higher voltage than other metal items entering from outside.
This could mean that when a fault occurs the metal case of a toaster has a higher voltage than the kitchen tap connected to metal pipes which enter from underground.
Someone touches both at the same time, they get a shock.
With bonding installed, both parts are kept at the same or very similar voltage = no shock.

Main bonding - connecting conductive parts which can bring a potential / voltage into the building to the main earth terminal.
Typically metal gas / water pipes which enter from underground, and bring Earth potential into the building.
As water and gas supply pipes have been plastic for decades, main bonding is less relevant than it was.

Supplementary bonding - the same principle applied to one location, such as a bathroom.
Relevant when all internal pipework was copper or steel, and most electrical items had exposed metal cases. Mostly irrelevant now due to the massive prevalence of plastic pipes and plastic lights, switches, and everything else.

Then there are all the things which were bonded long ago but never needed to be. Radiators, metal baths, boilers, kitchen sinks, metal window frames and the rest. None of those things could bring any potential into the building and yet a whole pile of dodgy 'guidance' was shovelled out by the usual suspects mostly in the 1970s/1980s implying that unless grotty little green and yellow wires were strung between every metal item in the building, instant death would occur.

is it needed as a standard and part of the regs?

Bonding is needed where it is needed.
It's not a 'shove this in and all is well' - every installation has to be assessed individually.

 

[CountryFan]

Maybe this is of some use? https://electrical.theiet.org/wiring-matters/years/2019/75-may-2019/to-bond-or-not-to-bond/

 

[Madrab]

As a plumber, are you recertifying your electrical competence part of your training on a regular basis like the electricians are?

There are basic requirements and content, as part of the C&G tech training that cover electrical safety and bonding is part of that. Once completed that part of the course then there is no requirement to return to update, if and when any subsequent requirements may change. So no, we don't need to

So as part of 'due diligence' I guess, it's always good to keep up to date with anything that may influence specific decision as part of daily work or how to direct clients on a day to day basis. The default though is always to direct the client to the relevant professional for advise.

The requirements for bonding can seem to 'change' though depending on the electrician asked.

 

[ericmark]

I also find the question of bonding hard to answer, even as an electrician.

So if I have a bit of class II electrical equipment used outside so not within the equipotential zone, and no problem touching the ground and the equipment at the same time.

But with an outside socket I have to connect the earth, so if using class I equipment then the soil and the equipment can be at a different potential. So we are not permitted to connect caravans to a TN-C-S supply, and EV chargers need loss of PEN protection.

In the house there is less of a problem as we are within an equipotential zone, it is where something moves between outside to inside not so bad with water, it can likely carry 100 amps through the pipe, the problem is mainly with gas pipes which, if they are asked to carry 100 amp, they could melt, so just as important not to include some items going outside as it is to include items inside.

So a water supply, and gas supply brought to the home in plastic, with just a short lenght of metal pipe as it enters the house there is not a problem, the other way is to have some insulating block.

But within the home, as long as all metal comming in to the home have been bonded to the electrical earth point, short lenghts of metal used where seen to look better, don't really need bonding.

The old idea was, if a dog was to knock over a standard lamp, in the room your in, you will see it, so even if the bulbs element is resting on the radiator, you will see there is a problem. But if in another room, then you could touch a live radiator as you have no idea what the dog has done.

We went mad on equipotential zone bonding, metal window frames, even door handles, then it was realised if you touch a radiator at 230 volt above true ground, as long as everything else is also at 230 volt, it is like a bird on the power lines, and there is no problem.

The main problem is entering and leaving the building, so as long as around the door nothing is bonded to either the true ground or the PEN, you will not get a shock.

Which leaves things like mobile homes, caravans, boats, porta-cabines, metal garden sheds, and garages etc. So these are not permitted to have a TN-C-S supply.

But this also leaves a problem, if a water pipe is metal and is connected to the PEN, and you put an earth rod in near to it, then that earth rod maybe at the PEN polarity rather than true earth.

I can continue for pages, only safe way, is ban TN-C-S, can't see that happening.

However, short lengths of pipe don't in general need bonding, and we hope that the RCD will pick up and trip when bonding is poor.

But I am stopping, as to list all is near impossible.

 

[JohnW2]

Bonding is needed where it is needed. It's not a 'shove this in and all is well' - every installation has to be assessed individually.

Very good summary.

The one thing you don't seem to mention (but obviously will know) in your concluding statement (quoted above) is that not only is bonding not needed when it's not needed but, worse, if things are bonded that didn't need to be bonded that can, in some situations to lead to an increased risk of electrical shock - not because it is 'bonding' but because it also 'earths' things - and unnecessarily creating extra earthed metal for people to touch (at the same time as touching something 'live') can increase the risk of electric shocks.