Gas meter with plastic supply pipe - earth bonding worthless?

[NickVegas]

A 'Sunday challenge' for the qualified electricians....

Can anyone explain why a built-in gas meter housing box

that is located 600mm above a block paved driveway, with a plastic (Polyethylene - MDPE) supply pipe and no extraneous conductive part, could result in a dangerous potential difference between a fault and the metal gas pipework within the property?

There seems to be a lot of confusion regarding it and often the 'external meter box at ground level with a metal pipe that could be covered by earth' is raised (which I can understand).

However, the NHBC technical guidance below states that the gas meter does NOT need to have the internal metal pipework earth bonded:

https://www.nhbc.co.uk/binaries/content/assets/nhbc/tech-zone/nhbc-standards/tech-guidance/8.1/protective-equipotential-bonding-peb-of-gas-installation-pipework-new-june-2020.pdf

The internal gas metal pipework could possibly touch a metal water pipe, but the water supply pipe (if metal) should presumably already have a PEB.

If metal objects (e.g. a gas meter) insulated from the ground need to have a PEB, then why not metal tables, chairs, coat stands, etc. that are on carpet, or metal window frames set within brick walls?

Can anyone think of an example or is it simply an urban myth, similar to how external meters without a PEB are flagged as a defect (when everyone knows that you'd do the PEB inside the building within 600mm of the meter)?

 

[NickVegas]

I've had no replies, so I guess it's due to one of the following:

a). There is a benefit from earth bonding a gas meter that's 2ft above the ground, with no extraneous conductive parts, and insulated from the ground....but nobody knows (or can explain) why

b). There's no point in ever doing it, but it's a 'nice little earner' to install a metre or two of 10mm earth cable, scare the client about 'better to be safe than sorry', don't rock the boat.

I'm veering towards option b).

 

[LastManOnline]

I've had no replies, so I guess it's due to one of the following:

a). There is a benefit from earth bonding a gas meter that's 2ft above the ground, with no extraneous conductive parts, and insulated from the ground....but nobody knows (or can explain) why

There is no benefit in bonding a gas meter that's installed as you describe above. I cannot explain why its still done.

 

[NickVegas]

There is no benefit in bonding a gas meter that's installed as you describe above. I cannot explain why its still done.

Thanks LastManOnline, I agree with you.

As for the explanation, that's a trickier one.

Ove the last half century the UK has become a world leader in risk aversion and blame apportionment/management.

Nowadays we all yearn for decisions to be made by committee (no personal liability) and don't want to be responsible or accountable for anything. Any misfortune encountered must be someone else's fault and never our own.

Consequently, even when there is not a risk, if it's thought that there might be a risk people will err on the side of paranoid to avoid accountability.

(For example, after an investigation of 243 petrol station fires around the world over an 11-year period that had been attributed to mobile phones, not one of them was actually found to have been caused by a handset...but the law in the UK states that we cannot use a mobile phone on a petrol station forecourt)

So, I think the explanation is 'accountability denial', which results in the client incurring unnecessary extra costs.

 

[westward10]

You use of mobile telecommunications equipment at fuel filling stations goes back a long way, before the devices we all have today. The hose on a fuel dispenser is conductive and when removed from the dispenser it breaks the loop, it is possible that powerful telecommunication equipment such as that used by the armed forces could induce a spark at the point of the loop breaking and this is why you do not see military vehicles generally using stations reserved for the public. I suspect this fear passed onto devices the general public use although the chances of them being powerful enough are zero. The ban on mobile phones is now viewed in other ways, that it can cause distractions etc.... in what is a dangerous environment.

 

[NickVegas]

You use of mobile telecommunications equipment at fuel filling stations goes back a long way, before the devices we all have today. The hose on a fuel dispenser is conductive and when removed from the dispenser it breaks the loop, it is possible that powerful telecommunication equipment such as that used by the armed forces could induce a spark at the point of the loop breaking and this is why you do not see military vehicles generally using stations reserved for the public. I suspect this fear passed onto devices the general public use although the chances of them being powerful enough are zero. The ban on mobile phones is now viewed in other ways, that it can cause distractions etc.... in what is a dangerous environment.

Thanks westward10, I didn't know the history behind it, but it probably made sense for higher power military telecoms equipment.

As you say, for low power smartphones it's zero risk.

The 'mobile phones could cause distraction' argument sounds more like blame management to me.

"We've enacted legislation for a non existent risk, people will blame us and say we're fools....let's think of another reason for the legislation"

 

[LastManOnline]

There seems to be a lot of confusion regarding it

Thats a very fitting description of bonding in most sparks experience

However, the NHBC technical guidance below states that the gas meter does NOT need to have the internal metal pipework earth bonded:

https://www.nhbc.co.uk/binaries/content/assets/nhbc/tech-zone/nhbc-standards/tech-guidance/8.1/protective-equipotential-bonding-peb-of-gas-installation-pipework-new-june-2020.pdf

That guidance document hits the nail right on the head. End of

If metal objects (e.g. a gas meter) insulated from the ground need to have a PEB,

They don, t. Never did.

then why not metal tables, chairs, coat stands, etc. that are on carpet, or metal window frames set within brick walls?

Technically a metal window frame could be an "extraneous part". But it's resistance to earth would likely be so high (this can be tested) that it does, nt provide a danger under fault conditions

 

[NickVegas]

Thats a very fitting description of bonding in most sparks experience

That guidance document hits the nail right on the head. End of

They don, t. Never did.

Technically a metal window frame could be an "extraneous part". But it's resistance to earth would likely be so high (this can be tested) that it does, nt provide a danger under fault conditions

Thanks LastManOnline.

Your views agree with my initial thoughts on the matter.

I'm not a qualified electrician and so I wanted to check if I'd missed something.

Thanks for confirming that I hadn't.

 

[Lister1987]

I think it's a simple case of "Can you verify the pipe goes into the ground at any point of its run (and when in the ground, tht type of type used?) even with plastic inserts? If no then they Bond it.

When ypu test the pipe; does it show as extraneous?