Main earthing by gas pipe.

[miLarKey]

Hi,

I have recently carried out a periodic test and inspection on 1960s purpose built flat. The means of earthing was via the main gas pipe connected by earth clamp before the gas meter.
Is this acceptable under BS 7671 2008? I had a Ze reading on 0.19 ohms.

 

[KINKY]

542.2.4 says no

metallic pipe work used for water supply maybe used if precautions are taken against its removal

 

[miLarKey]

Cheers, I didn't think so.

 

[Deleted member 9648]

Hi,

I have recently carried out a periodic test and inspection on 1960s purpose built flat. The means of earthing was via the main gas pipe connected by earth clamp before the gas meter.
Is this acceptable under BS 7671 2008? I had a Ze reading on 0.19 ohms.

Are you serious??
Just to clarify Kinky's post ,it is not acceptable to use a public water supply pipe as a means of earthing.Only private pipes may be used as an earth electrode with the precautions stated above.

 

[sparkylad]

Hi,

I have recently carried out a periodic test and inspection on 1960s purpose built flat. The means of earthing was via the main gas pipe connected by earth clamp before the gas meter.
Is this acceptable under BS 7671 2008? I had a Ze reading on 0.19 ohms.

Thats a wind up isnt it , surely ?

 

[Burnt Fingers]

Thats a wind up isnt it , surely ?

Possibly not - owned a house in Leeds from the Victorian era where main earth was gas pipe - clamped on the customer side of the meter too....

 

[Spudnik]

Found a fair few that have been earthed via incoming gas pipe.

Very old houses though.

 

[WayneL]

Hi,

I have recently carried out a periodic test and inspection on 1960s purpose built flat. The means of earthing was via the main gas pipe connected by earth clamp before the gas meter.
Is this acceptable under BS 7671 2008? I had a Ze reading on 0.19 ohms.

Surely that's a wind up, though.

If the DNO gave him TN-C-S now, with the regulation 0.35 Ze, and he bonded that gas pipe (as you do) - most of the installation's current is going to be flowing down that gas pipe.

Or am I missing something??

 

[sparkylad]

Wayne the tncs will probably [but not always] be less than 0.35 ,and there will always be the case of parrallell paths to extraneous conductive parts in the event of a fault to earth, so i dont think that is a major issue. the issue is not having a suitable earthing facility at present. Must say though that if the op has to ask the question then maybe he should consider some training, cos its a fundamental part of I & t to know the answer.

sparkylad.

 

[Deleted member 9648]

Wayne the tncs will probably [but not always] be less than 0.35 ,and there will always be the case of parrallell paths to extraneous conductive parts in the event of a fault to earth, so i dont think that is a major issue. the issue is not having a suitable earthing facility at present. Must say though that if the op has to ask the question then maybe he should consider some training, cos its a fundamental part of I & t to know the answer.

sparkylad.

My thoughts exactly.....If you have to ask whether it is acceptable to use a gas pipe as a main earth you do not have sufficient knowledge to be carrying out a PIR.

 

[Baal]

It's a rather frightening post, what else is overlooked when fundamentals are missing....

 

[WayneL]

Wayne the tncs will probably [but not always] be less than 0.35 ,and there will always be the case of parrallell paths to extraneous conductive parts in the event of a fault to earth, so i dont think that is a major issue. the issue is not having a suitable earthing facility at present. Must say though that if the op has to ask the question then maybe he should consider some training, cos its a fundamental part of I & t to know the answer.

sparkylad.

Yeh, my point was that it seemed awfully low - surely that's not the kind of reading I'd get if I did a Ze test on my gas pipe.

Let's take a good TN-C-S system with a Ze of 0.19 ohms - are you telling me that a bonded gas pipe would offer the same impedance back to the transformer as the supply neutral conductor connected to the star point?

Either there is another means of earthing or he's measured it wrong...... or it's a wind up

I wasn't talking about an earth fault, by the way.

I was talking about the normal operating current taking this path as oposed to travelling down the neutral(of higher impedance)

 

[sparkylad]

Oh. Got you now wayne ..sorry , yes I get the point you are making, and yes the op unfortunately does not inspire great confidence in his I & T ing prowess so he may well indeed missed some other means of Earthing or Bonded Extraneous part such as a mettallic water pipe etc.

 

[Monkey1984]

Your sure that is the main earth to the flat?

Have you tried to do a Ze on the remaining earths in the MET? I can understand older houses having relied on the use of a Metal pipe for an earth but a 1960s flat? What floor was the flat on and was there a communal cupboard with the main incoming supply for the building in there?

 

[Des 56]

Yeh, my point was that it seemed awfully low - surely that's not the kind of reading I'd get if I did a Ze test on my gas pipe.

Let's take a good TN-C-S system with a Ze of 0.19 ohms - are you telling me that a bonded gas pipe would offer the same impedance back to the transformer as the supply neutral conductor connected to the star point?

Either there is another means of earthing or he's measured it wrong...... or it's a wind up

I wasn't talking about an earth fault, by the way.

I was talking about the normal operating current taking this path as oposed to travelling down the neutral(of higher impedance)

It could be that he was measuring a gas bond with a common pipe to other flats and the reading of 0.19 was via the other flats gas bond to their met

 

[Monkey1984]

This was my thinking - That's why I am wondering where the main incoming supply is. Whether there is one main supply cable split to individual meters for each flat or if they all have individual cables. Round my way especially its unusual to get flats that all have an individual supply cable coming into them. They normally have one massive supply cable that feeds meters for each flat (That probably makes very little sense to people reading but its clear in my head!).

 

[chiplard]

A gas pipe or water pipe should not be used as a means of main earthing for one common sense reason, the same reason the behind the BRB regulation. Irrespective of whether you get a good Ze measurement or not you can't guarantee that this will always be the case because water/gas companies can and do disrupt/upgrade their supply pipe. ie to plastic pipes

 

[andyb]

Possibly not - owned a house in Leeds from the Victorian era where main earth was gas pipe - clamped on the customer side of the meter too....

Them Victorians eh!
They were probably working to the 1st or 2nd edition of the regs where this was acceptable.

 

[Burnt Fingers]

Lol, but was rewired in 1968 by YEB using the same regs I fear. Meter board was held against wall of cellar by a 4" x 4" chump of wood jammed in there.

 

[KINKY]

Possibly not - owned a house in Leeds from the Victorian era where main earth was gas pipe - clamped on the customer side of the meter too....

Had similar thing in my house. There was no earthing conductor.

Only path to earth for the entire property was via the bonds to gas & water mains.

Gas bond was after the meter andf the incoming water was plastic.

o dear