Main Earthing conductor

[ban-all-sheds]

I misread the original post - I thought the proposal was to have the earth for connected to the gas pipe, and at another point on the gas pipe have the MET connected.

I have no idea why - sorry...

But I'm not sure I can see a real difference between these two:

The issue will be with 542.4
In this (and in Guidance Note 3) there is a requirement to be able to disconnect the MAIN EARTHING conductor at the MET.

You can with both arrangements.

if at some point, for whatever reason, someone disconnects the earth rod, then the gas becomes the main earth and anyone testing the main earth will still see it as to earth..

That applies equally to both. Once the cable is disconnected from the rod there's no difference at all between L & R.

There are various sections of the 17th edition that refer to this but 542.4.1 specifically mentions that protective bonding conductors shall connect to the main earthing terminal .

He's got a MET, and the gas bonding conductor is connected to it..

 

[dingbat]

AAAaargh!

Will you all (exception Bas) stop using the expression 'main earthing conductor', please?

There is only one.
It is called the earthing conductor.
It used to be called the 'earthing lead'.
It was not called 'main' anything because, back then, there were no bonding conductors to get it confused with.

As the gas service pipe will quite possibly have a lower resistance to earth than a four-foot rod banged in, either arrangement in the drawings may well contravene 542.2.4, in that, effectively, it is using the gas service as an earth electrode.

In any event, if you try and do anything other than what Joe Spark expects to see, you are only going to have future recurrences of this discussion. Keep it simple.

 

[ColJack]

you don't disconnect from the rod to test, you take the wire out of the MET and test it that way..

removing it from the MET and you still have the gas pipe connected.

 

[electronicsuk]

you don't disconnect from the rod to test, you take the wire out of the MET and test it that way..

removing it from the MET and you still have the gas pipe connected.

In this situation it would be up to the spark to realise that the gas bonding would provide parallel paths. It wouldn't be hard to disconnect the earth conductor temporarily from the clamp onto the gas pipe.

 

[holmslaw]

..

 

[riveralt]

AAAaargh!

Will you all (exception Bas) stop using the expression 'main earthing conductor', please?

There is only one.
It is called the earthing conductor.
It used to be called the 'earthing lead'.
It was not called 'main' anything because, back then, there were no bonding conductors to get it confused with.

Main earthing conductor - never heard of that phrase

But I'm not sure I can see a real difference between these two:

He's got a MET, and the gas bonding conductor is connected to it..

BAS I think this is another one of those guidance issues that could possibly be done by other means.

This a TT earthing system. The introduction of the gas pipe into this system by directly, as opposed to indirectly linking it to the earth rod via the MET, probably would have the same affect as a secondary earth rod. In other words it should result in a slightly lower Ze and thus Zs.

The only issues are that, I've been taught that additional earth rods should not be linked but taken straight back to the MET and the reference to 542.2.3 metalic pipes for gases shall not be used as an earth electrode.
Furthermore, it becomes a bit more cumbersome to measure Ze having to remove main protective bonding from more than one point.

I can understand your logic and that of the OP and I cannot argue a case again it (you know I would if I could) - but it just doesn't feel right and anytime I came across it I would change it to that described in the OSG.

I'm still not sure whether the OP describes the connection on the supplier side or the consumer side of the meter

 

[holmslaw]

..

 

[ColJack]

technically speaking it's a CPC.. albeit for the distribution cables..

 

[ban-all-sheds]

That would be because there is no real difference between you're L and R pointless sketches - think MET.

All I have done is not to draw the actual MET - I have shown the cables joining at the place where it would be.

If I show the MET on the drawing how does that change what is connected to what, and where?

If I show the MET will L & R differ in a way in which they do not when the MET is not shown?

 

[ColJack]

If I show the MET on the drawing how does that change what is connected to what, and where?

when they are all connected it doesn't.

If I show the MET will L & R differ in a way in which they do not when the MET is not shown?

yes.. now you can disconnect the earthing conductor to test it in isolation from the gas pipe without having to know that the earthing conductor connects to the earth rod via the gas pipe, or having to trace it out to find it.

 

[ban-all-sheds]

As the gas service pipe will quite possibly have a lower resistance to earth than a four-foot rod banged in, either arrangement in the drawings may well contravene 542.2.4, in that, effectively, it is using the gas service as an earth electrode.

Err - the one on the left is the way it's usually done - compare it to the figures in Chapter 2.1 of the OSG..

 

[ban-all-sheds]

This a TT earthing system. The introduction of the gas pipe into this system by directly, as opposed to indirectly linking it to the earth rod via the MET, probably would have the same affect as a secondary earth rod. In other words it should result in a slightly lower Ze and thus Zs.

The existence of the MET is not in question - I just didn't bother to draw it the first time around, but drawing it doesn't change what paths to earth exist. The only difference that I can see is that the one from CU to earth rod might be a different length, but it's hard to imagine that it would be a significant difference.

In neither L or R is the gas pipe a secondary earth rod - as soon as you apply main equipotential bonding to extraneous conductive parts where they enter the property they become connected in parallel to the earth rod.

The reference to 542.2.3 metalic pipes for gases shall not be used as an earth electrode.

That's what I originally thought was happening, but it's not.

I'm still not sure whether the OP describes the connection on the supplier side or the consumer side of the meter

That's also irrelevant, really. Obviously it's a real concern, but what I mean is that in relation to whether the connection between the rod and the pipe goes via the MET or not it is irrelevant - neither of these would be right:

 

[ban-all-sheds]

In this situation it would be up to the spark to realise that the gas bonding would provide parallel paths.

How would he know? What would give him grounds for suspicion?

The fact that there's no direct cable from the MET to the rod, and the one from the MET to the gas pipe doesn't stop there?

In any event, if you try and do anything other than what Joe Spark expects to see, you are only going to have future recurrences of this discussion. Keep it simple.

Furthermore, it becomes a bit more cumbersome to measure Ze having to remove main protective bonding from more than one point.

Can't argue with that, and I agree it shouldn't be done, but I'm not convinced that it actually breaks any regulations....

 

[too old to learn]

To the op, I think you would agree that the majority agree with my original advice, and you obviously don't like that advice.

actually I do agree with your advice and I have mentioned to him that he should replace this cable with two new cables. one directly to the earth rod to the MET and then one from the MET to the Gas pipe (well actually he can keep the one connected to the gas pipe since its all ready there)

and to confirm, it is on the consumers side of the gas pipe as per the regs.

I just wanted to know if there is actually a reg stating this and there appears to be not.

Many thanks to all for information supplied

 

[holmslaw]

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