Opinions wanted Re: water pipe Main Bonding

[bhm1712]

Morning everyone,

I'd like to get some second opinions if possible please. As some of you will know, I'm a qualified electrician/electrical engineer but am not registered with a scheme as I'm employed in industry. From time to time I do notifiable work and non notifiable (and indeed do notify when required), but in some cases when time doesn't permit, I bring in a registered domestic Sparks to do the work for me to save me the hassle.

I'm currently trying to have my shower cable and RCD shower unit replaced which is a time consuming job due to the length and route of the cable - so this is one of those times I've asked somebody in to quote. 2 electricians have been so far and both have said they will need to upgrade/change the main equipotential bonding arrangements at the house as they're not satisfactory as they stand. I'm arguing this fact as I believe them to be satisfactory.

The stated reasons for MEB being no good:

1) Water pipe is not bonded within 600mm of point of entry to the house.

2) central heating pipework below boiler not bonded to main earth terminal and not cross bonded to each other.

Last year we had to have a new water pipe as the original one kept rotting through under the front garden. The new water pipe was fitted by Severn Trent contractors free of charge (long story). Ultimately however, the new pipe had to take an entirely different route from the street to the house and a new entry point and stop cock was fitted by them. The new entry point is on the other side of the house to the original and a very good distance from the consumer unit location in the garage. To bond the new pipe within 600mm of entry would have meant installation of around 30 metres of 10mm earth cable and either pulling up much of the upstairs flooring or drilling through walls and mounting the cable on the interior walls of the house etc. Therefore I considered this to be totally not "practicable".

The gas meter for the property remains in its original location in a cupboard off the kitchen and this is bonded with 10mm cable and is accessible at all times. The new water pipe passes through this cupboard on its way to upstairs. Therefore, I extended the bonding from the clamp on the gas meter pipework to the new water pipe. This bonding location is around 4 metres from the entry of the pipe into the house. I considered that this was the most practicable and reasonable solution to get the MEB done.

As for the CH pipes, it's my understanding of the regs that unless the CH pipes can be classed as "extraneous conductive parts" (due to travelling underground etc) then they don't require bonding. I have always cringed at seeing plumbers and sparks cross bonding every single pipe to and from a boiler when it's completely not necessary to do it. The CH pipework is showing me a 0.1 ohms reading between the boilers electrical supply CPC as it's all earthed through the boiler as you would expect.

So in my mind, these two sparks are using the regulations surrounding bonding incorrectly. Does anybody concur?

 

[bernardgreen]

The stated reasons for MEB being no good:

1) Water pipe is not bonded within 600mm of point of entry to the house.

2) central heating pipework below boiler not bonded to main earth terminal and not cross bonded to each other.

1) Provided that the water pipe is and remains copper from entry point to bonding point then electrically the entry point is bonded to the MET.
Any work on the water pipe may interrupt that bonding so the plumber would be required to bridge across any non-conductive piping that is installed.

2) Provided none of the pipes are external to the house's equipotential zone then they cannot introduce extraneous potentials and they are anyway bonded by metal work in the boiler.

In the real world the regulations have to cover the few sparkies who can only follow instructions and do not have the ability to evaluate each situation they encounter. The regulations work and ensure safety for 95% of domestic situations.

Bonding supply pipes as per the regulations is fine when the supply pipes are high impedance to ground ( more than 10 ohms ). But beware and think when the supply pipes are low impedance to ground ( hint, what is the current carrying capacity of 10mm² cable as specified for supply pipe bonding )

 

[securespark]

I would expect the CH pipe reading to be less.

 

[bernardgreen]

I would expect the CH pipe reading to be less.

They would ( should ) be very low impedance to other pipework inside the equipotential zone.

The concern is when bonding MET to pipe work ( or other conductive items ) to items outside the equipotential zone which have very low impedance connections to ground

 

[JohnW2]

Last year we had to have a new water pipe as the original one kept rotting through under the front garden. The new water pipe was fitted by Severn Trent contractors free of charge (long story). Ultimately however, the new pipe had to take an entirely different route from the street to the house and a new entry point and stop cock was fitted by them. The new entry point is on the other side of the house to the original and a very good distance from the consumer unit location in the garage.

From what you say, I can but presume that the new water pipe is metal? I'm a little surprised, since I would probably have expected them to replace with plastic, all the way into the house, these days.

To bond the new pipe within 600mm of entry would have meant installation of around 30 metres of 10mm earth cable and either pulling up much of the upstairs flooring or drilling through walls and mounting the cable on the interior walls of the house etc. Therefore I considered this to be totally not "practicable".

"Practicable" is always a judgemnent, but I'm very inclined to agree with you.

Therefore, I extended the bonding from the clamp on the gas meter pipework to the new water pipe. This bonding location is around 4 metres from the entry of the pipe into the house. I considered that this was the most practicable and reasonable solution to get the MEB done.

Again, a judgdement but, again, my thinking would be the same as yours.

As for the CH pipes, it's my understanding of the regs that unless the CH pipes can be classed as "extraneous conductive parts" (due to travelling underground etc) then they don't require bonding. I have always cringed at seeing plumbers and sparks cross bonding every single pipe to and from a boiler when it's completely not necessary to do it.

Totally agreed. Provided that any extraneous-c-ps are properly bonded (as close as practicable to entry into the property ), there is absolutely no need for any 'cross-bonding' - with the one exception (increasingly uncommon) when 'Supplementary Bonding' is required in a bathroom.

So in my mind, these two sparks are using the regulations surrounding bonding incorrectly. Does anybody concur?

As above, I essentially do concur, and I would probably have done exactly the same as you. The problem, as above, is that there will always be scope for debate, and individual opinions, about "practicable". However, you are free to choose an electrician who takes a more sensible/pragmatic view of interpreting the regs!

Kind Regards, John

 

[EFLImpudence]

1) Water pipe is not bonded within 600mm of point of entry to the house.

The regulation states "As near as practicable to the point of entry".

The 600mm. mentioned relates to internal meters only and does not apply to the point of entry.

Does anybody concur?

Yes.

 

[bhm1712]

I would expect the CH pipe reading to be less.

They would ( should ) be very low impedance to other pipework inside the equipotential zone.

The concern is when bonding MET to pipe work ( or other conductive items ) to items outside the equipotential zone which have very low impedance connections to ground

Sorry my mistake in typing my OP - Reading between CPC and CH pipes 0.01 ohms.

 

[bhm1712]

From what you say, I can but presume that the new water pipe is metal? I'm a little surprised, since I would probably have expected them to replace with plastic, all the way into the house, these days.

The pipework from the new service valve on the road is blue HDPE up until the base of the "hockey stick" within the "insuduct" and it the changes from plastic to copper (about 2 feet below ground level) - reason for this decision unknown. The copper then proceeds up through the insuduct hockey stick and into the property at skirting board level, there is then a stop tap and a further 3 meters of copper before it enters the back of the kitchen cupboard

 

[JohnW2]

The pipework from the new service valve on the road is blue HDPE up until the base of the "hockey stick" within the "insuduct" and it the changes from plastic to copper (about 2 feet below ground level) - reason for this decision unknown. The copper then proceeds up through the insuduct hockey stick and into the property at skirting board level, there is then a stop tap and a further 3 meters of copper before it enters the back of the kitchen cupboard

Fair enough. As I said, I felt sure you wouldn't have been asking the question (since the electricians would then have been even more obviously silly!) had the new pipe entered your property in plastic!

Kind Regards, John

 

[flameport]

1) Water pipe is not bonded within 600mm of point of entry to the house.

From the rest of the thread, as it's already connected in a cupboard 3 or 4 metres from the entry point the worst case would be to extend the existing wire by that amount.
However it's not necessary to do that, the regulation only states 'where practicable' and a few metres of copper pipe between the incoming point and the bonding connection won't make any difference to anything.

2) central heating pipework below boiler not bonded to main earth terminal and not cross bonded to each other.

Not required and as the gas is bonded, the rest of it will be anyway by virtue of the metal gas pipe connecting to the boiler.
If it's a combi boiler the same applies to the incoming water connection.

Additional bonding to the boiler would only be required in the rather unlikely situation of the boiler not having any incoming metal pipe from the fuel supply or water, only supplying metal heating pipes and those pipes were also extraneous, and even then the bonding doesn't have to be connected at the boiler.
Perhaps an electric only boiler which was only for central heating and the pipes were copper.

 

[JohnW2]

Additional bonding to the boiler would only be required in the rather unlikely situation of the boiler not having any incoming metal pipe from the fuel supply or water, only supplying metal heating pipes and those pipes were also extraneous, and even then the bonding doesn't have to be connected at the boiler.

Quite. Even in that (I would say incredibly unlikely) situation, it would be those "extraneous metal heating pipes" that would be required to be bonded, not the boiler itself.

In fact, unless the boiler itself were an extraneous-c-p (sitting on bare soil?!) I can't think of any situation in which the boiler itself would require bonding (unless it were in a bathroom and requiring Supplementary Bonding because, unusually, the conditions for its omission were not satisfied!).

Kind Regards, John

 

[Iggifer]

Just put a clamp on where the new water pipe enters the house, add a bit of 10mm² GY to it, then fix it to something so when they pull it, it doesn't move (and they can't see the end) same the other end. Job's a good'un

If on the off chance they do test it, it'll still read as bonded as your existing bond is still doing the job