Gas and Electric Cable Separation

[AdamCH]

I'm having some building work done which means a gas pipe needs to be relocated to the other side of a wall that has a run of cables along it.

Can pipe and cable be run together with less than 25mm separation if the gas pipe is enclosed in something like a PCV waste pipe or the cable is run in PVC conduit or trunking?

 

[RF Lighting]

Don't see why not. Unless it's a requirement of the gas regs, there's no need to sleeve the pipe either.

Infact thinking about it, I don't think you'd be allowed to sleeve the pipe as it would fill with gas in the event of a leak, causing a bigger issue.

 

[AdamCH]

If I'm reading it right the onsite guide seems to say that separation can be reduced if the gas pipe is PVC wrapped or a insulating barrier is interposed.

The waste pipe wouldn't be sealed - I'm thinking just slit down it's length and pushed on over the pipe.

 

[RF Lighting]

I don't see what it would achieve.

Insulated sheathed cables inside PVC trunking is more than enough IMO.

Remember the OSG is just a guide. There is no requirement in BS7671 to do anything like that.

 

[AdamCH]

Thanks

Trunking it is.

 

[PrenticeBoyofDerry]

Remember the OSG is just a guide. There is no requirement in BS7671 to do anything like that.

There is a gas requirement though, BS6891 and in BS7671 (528.3.4)

8.16.2 Separation of installation pipework from other services
Where installation pipes are not separated by electrical insulating material, they shall be spaced as follows:
a) at least 150 mm away from electricity meters and associated excess current controls, electrical
switches or sockets, distribution boards or consumer units;
b) at least 25 mm away from electricity supply and distribution cables.

So even though mentioned in the OSG, it should not then be assumed that this is guidance only!

 

[AdamCH]

Question really is what counts as "electrical insulating material". If running the cables through trunking counts then that's the easiest for me in this case.

 

[PrenticeBoyofDerry]

Question really is what counts as "electrical insulating material". If running the cables through trunking counts then that's the easiest for me in this case.

It would count, but then you would need to consider any de-rating of current carrying capacity of cables within trunking.
If the separation gap cannot be achieved, I would personally lag the pipe with pipe insulation.

 

[AdamCH]

What I don't really understand is what the regulation is trying to achieve - it just electrical insulation or is it to protect the cables if the pipework gets hot or is it to protect pipes if fire melts cable insulation?

OSG says electrical insulation for cables/domestic pipework but non combustible insulation for the meter & associated fittings.

So not quite sure what it's aimed at & why insulation that melts is okay.

 

[JohnW2]

What I don't really understand is what the regulation is trying to achieve - it just electrical insulation or is it to protect the cables if the pipework gets hot or is it to protect pipes if fire melts cable insulation?

Who knows. I suspect that it's the result of a person (more likely, a committee) who haven't really thought it through, and think that "it sounded like a good idea".

As far as electric insulation is concerned, there will be at least two layers of that betwen live conductors and 'the outside world'. If it's deemed safe for a human being to touch that, what is the additional problem with a gas pipe?

As for the thermal side, by the time a gas pipe has got hot enough to melt the insulation of nearby electrical cables, I think one has much bigger things to worry about than the cables! In any event, the regulations/guidances do not say anything about thermal insulation.

Kind Regards, John

 

[Adam_151]

What I don't really understand is what the regulation is trying to achieve

I assume its aiming so that cables are either supported away from gas pipework or that theres something rigid in between, so that should it suffer mechanical damage from furntiture etc, that the cable doesn't fault to the pipe and blow a hole in it. That would be my best guess anyway

 

[PrenticeBoyofDerry]

As I understand it, it is to prevent any mutual damage arising when operational work is carried out on either service.

 

[JohnW2]

As I understand it, it is to prevent any mutual damage arising when operational work is carried out on either service.

Do you really believe that? ... do you think PVC wrapping of the gas pipe (which appears to be an acceptable 'solution') would present such damage?

Kind Regards, John

 

[Adam_151]

Just throwing this story into the discussion: http://www.theiet.org/Forums/forum/messageview.cfm?catid=205&threadid=22798

 

[PrenticeBoyofDerry]

Do you really believe that? ... do you think PVC wrapping of the gas pipe (which appears to be an acceptable 'solution') would present such damage?

I don't believe it would! But my understanding of this standard is that is the reasoning behind it.