Stroma Certification Scheme Gas and Electric in same underground duct

[Michaelwgroves]

I need to run gas and electric in underground duct in garden. This is not the supply side, it is the customer side.
Wetpants says his regs say "should be 25mm apart for maintenance" I would argue "should" is not "must". Also it mentions for maintenance. You can't maintain a cable 2ft under in ducting, so from the gas side I think I'm okay.
I recall our regs have similar requirements, but can't find it in blue book. But is there anything specific about running in duct, I can't find anything, other than supply side ?

 

[snowhead]

The Gassafe Registered engineer who will be connecting up the pipework will tell you exactly what can and can't be done.
You are limited to whatever he/she says.

If your wetpants guy is Gassafe registered and suggesting 25mm apart as the only issue then I'd suggest he / she has never buried gas pipe before. You need to find one that has.

Is your ductwork going to be multicoloured to indicate it contains 2 different services?

 

[Michaelwgroves]

The Gassafe Registered engineer who will be connecting up the pipework will tell you exactly what can and can't be done.
You are limited to whatever he/she says.

If your wetpants guy is Gassafe registered and suggesting 25mm apart as the only issue then I'd suggest he / she has never buried gas pipe before. You need to find one that has.

Is your ductwork going to be multicoloured to indicate it contains 2 different services?

Wetpants is GSR, he has not done this before, but that does not make him incapable. He can not find anything in his regs that says otherwise. Neither can I in the BBB.
I don’t know anyone with a gas appliance in their garden, so this is a bit unusual. So trying to find a GSR with this experience I suspect will be tough.
I prefer my GSR’s view that this needs more research before he is happy to progress.

Your multicoloured duct made me giggle,

 

[R-fur]

Your multicoloured duct made me giggle,

People have been killed cutting through water pipes that had cables in them, they weren't giggling.
Use a gasfitter that is LPG registered, there are lots of private gas pipes between LPG tanks and houses

 

[plugsandsparks]

I do commercial gas and electrics.
One trench is OK, you can either separate the services by width or depth or both.
e.g Dig 12 inch trench 500mm drop in duct for cable. bury with tape to 375mm , then gas pipe at 375mm opposite side of trench. Gas guy will have his regs for pipe size, pressure and what the ground and buildings are to get the correct distance from buildings and depth of cover so above is just an example. Gas pipe is always better with no joints underground, so MDPE pipe is often used as you can have no joints for a considerable distance. Plenty of diagrams on internet as the utilities have been doing this from day one. It makes sense for them and i do not see why just because its consumer side you would want to do it in anyway different.

 

[Michaelwgroves]

People have been killed cutting through water pipes that had cables in them, they weren't giggling.
Use a gasfitter that is LPG registered, there are lots of private gas pipes between LPG tanks and houses

I find that hard to believe, please can you share evidence of your claims?

It's natural gas, not LPG, I'm not sure if it makes a difference.
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I do commercial gas and electrics.
One trench is OK, you can either separate the services by width or depth or both.
e.g Dig 12 inch trench 500mm drop in duct for cable. bury with tape to 375mm , then gas pipe at 375mm opposite side of trench. Gas guy will have his regs for pipe size, pressure and what the ground and buildings are to get the correct distance from buildings and depth of cover so above is just an example. Gas pipe is always better with no joints underground, so MDPE pipe is often used as you can have no joints for a considerable distance. Plenty of diagrams on internet as the utilities have been doing this from day one. It makes sense for them and i do not see why just because its consumer side you would want to do it in anyway different.

GSR is recommending tracker pipe so there are no joins, maybe same as MDPE?
I'm leaving pipe sizing etc to him.
As you mention, gas needs 375mm, electric only needs 250mm. So I could put electric trunking on top of gas trunking, but still seems overkill for garden service.
Has anyone come across anything in regs that say's I can't put both in same duct?

 

[R-fur]

When I worked for a DNO I personally attended an incident where a gas man had to change an isolation valve, he had dug down to the yellow plastic pipe in the garden and was applying a 'squeeze' on the pipe to stop the flow of gas. Unfortunately the pipe contained the electric service which exploded burning the gas man. Fortunately he was not badly hurt and made a full recovery.
Incidents like this are well documented in the utility industries but I dont have any 'evidence' to hand for you.
There is little difference between underground pipe for LPG or natural gas, my point was that LPG private service pipes are very common so a gas fitter registered for LPG is more likely to have experience of installing underground gas pipes.

 

[Michaelwgroves]

When I worked for a DNO I personally attended an incident where a gas man had to change an isolation valve, he had dug down to the yellow plastic pipe in the garden and was applying a 'squeeze' on the pipe to stop the flow of gas. Unfortunately the pipe contained the electric service which exploded burning the gas man. Fortunately he was not badly hurt and made a full recovery.
Incidents like this are well documented in the utility industries but I dont have any 'evidence' to hand for you.
There is little difference between underground pipe for LPG or natural gas, my point was that LPG private service pipes are very common so a gas fitter registered for LPG is more likely to have experience of installing underground gas pipes.

I must admit I never considered LPG before you mentioned it, that changes a lot as I can now see it could be much more common. I was not thinking outside of the box, as could not see any further than natural gas.
I do know another GSR who does a lot of LPG, I’ll see what he thinks.
But so far no comments on electrical regulations?

 

[mattg4321]

I wouldn’t run gas and electricity through the same duct unless there was no other option.

What colour duct would you use?

 

[R-fur]

It is unusual to run gas pipe in ducts due to the danger of gas build up in the void. Electric cables can be run in ducts. The duct helps to prevent damage and enables easy replacement but the cable has to be deratted due to the air in the duct preventing thermal dissipation.
Personally I would lay the gas pipe and an electric duct in the same trench keeping them about 100mm apart. Depth 450mm.

 

[mattg4321]

The yellow gas ducting I’ve seen is perforated to stop the gas build up

 

[Michaelwgroves]

That’s starting to make sense, looks like Gas ducting is perforated.
seems best solution is lay tracpipe in bottom of trench with tape above, then duct above this?

 

[Michaelwgroves]

I thought I should give an update on this as it appears I now have a validated answer.
I have spoken with Tracpipe technical and reviewed their manual. It appears as long as the the duct cross section area is less than 0.01M2, it does not require ventilation. Mine is 0.007, so I am fine on this part.
Manual also says pipe should "ideally" be 25mm away from electric cable. But if not practical, the polyethylene cover will provide adequate protection.
There is also no requirement for domestic premises to use coloured duct.
The only thing I need to do different, is lay duct 375mm below ground for gas, rather than only 240mm required for cable.