Tight fit or room to spare?

[LeighSawczyn]

Does 6mm2 SWA fit into 25mm Blue MDPE Pipe. The idea being to protect the cable from damp soil or water ingress when it is buried, not for mechanical protection. No tight radii to worry about just a 10-15m straight run.

 

[Pete999]

SWA shouldn't get moisture ingress unless you have damaged it during installation, why go to the trouble of putting it in pipe?

 

[trev]

Does 6mm2 SWA fit into 25mm Blue MDPE Pipe. The idea being to protect the cable from damp soil or water ingress when it is buried, not for mechanical protection. No tight radii to worry about just a 10-15m straight run.

Measure the diameter of the cable. If it's less than the alkathene then it will fit. If it isn't it won't

 

[ruston]

Jewsons sells the proper gear, you wouldn't want someone thinking it was a water pipe.

 

[LeighSawczyn]

If it's there for the long haul then why not add a barrier, anything that slows down corrosion is a good thing as far as I'm concerned, what if it got a scratch in the sheath whilst laying it and the armour corroded? I don't fancy going back to it for free.

 

[Knobhead]

What corrosion? There won’t be any if the outer serving isn’t damaged. Best way to be sure is carry out a sheath test.

 

[Leesparkykent]

If it's there for the long haul then why not add a barrier, anything that slows down corrosion is a good thing as far as I'm concerned, what if it got a scratch in the sheath whilst laying it and the armour corroded? I don't fancy going back to it for free.

I agree that it's prob best to put it in a duct, due to sharps/stone in the backfill material but put it in a proper cable duct as Ruston says you wouldn't want people thinking it's a water pipe. Plus if you put it in a a proper cable duct it would be easier to replace should some one have to at any point in the future, you would have a hell of job trying to replace a SWA through a bit of 25mm poly pipe lol

 

[LeighSawczyn]

So I carry out a sheath test which tells me the sheath has been compromised, then what? I guess I rip it up and put into some MDPE pipe? I'm more a prevention is better than cure guy TBH.

 

[driverman]

So I carry out a sheath test which tells me the sheath has been compromised, then what? I guess I rip it up and put into some MDPE pipe? I'm more a prevention is better than cure guy TBH.

Use Polyduct from builders merchants like Jewsons. i think it is something like 32/38mm Dia. but will do the job easily. use marker tape above it though.

 

[LeighSawczyn]

Good point leesparkykent & ruston. Could leave a plumber in a spot of bother if he tried to tee off for a water supply haha. Mind you the yellow warning tape above should be a clue.

 

[ruston]

Use Polyduct from builders merchants like Jewsons. i think it is something like 32/38mm Dia. but will do the job easily. use marker tape above it though.

Cheap as chips too.

 

[ruston]

Not uncommon to see all the services in one trench though.

 

[Leesparkykent]

And we are talking about a plumber lol

 

[Darkwood]

Sheath test???? What voltage and nature of the installation are we discussing here!


Not sure where or how you were trained but swa is good for direct burial and if not exposed to corrosive chemicals or mechanical hazards then will be good for many decades, there is really something wrong with your installation methods if you manage to damage the outer sheath to the extent it lets moisture through to the armour, unless your using mechanical means to back fill and compact the ground.
Is there an inherent risk of damage during or after its been buried?

Having said this ducting is commonly used where the costs of servicing, replacing the cables would be high in the event of a failure, in this case use the correct cable duct, depth, burying methods and hazard marker tape or is this for a little garden number - supply to a shed/garage.

 

[driverman]

Good point leesparkykent & ruston. Could leave a plumber in a spot of bother if he tried to tee off for a water supply haha. Mind you the yellow warning tape above should be a clue.

Generally...Black ducting is used for electric cables. U/G cables are black including DNO's mains cable. However years ago and still in use is the old plastic water pipes which are also black. So take nothing for granted. Do the job right first time

 

[Darkwood]

Good point leesparkykent & ruston. Could leave a plumber in a spot of bother if he tried to tee off for a water supply haha. Mind you the yellow warning tape above should be a clue.

Most plumbers cannot read big words!!!

 

[Knobhead]

Sheath test???? What voltage and nature of the installation are we discussing here!

What difference does the voltage make? A sheath test should be done on any UG cable to confirm the integrity of the serving. The only exception I would make is for tarred hessian serving as it is designed to allow leakage of circulating currents.

 

[Marvo]

Does 6mm2 SWA fit into 25mm Blue MDPE Pipe. The idea being to protect the cable from damp soil or water ingress when it is buried, not for mechanical protection. No tight radii to worry about just a 10-15m straight run.

The 25mm dimension of polyethylene pipe usually refers to the outside diameter so internal it will be a ball-hair over 20mm. I assume you're using a 2-core in which case it'll be around 17mm dia so it's going to be a tight squeeze and probably won't be an easy pull for 15 meters but it should be possible if you pull the cable through the pipe first with a fishtape then put it in the ground afterwards. I'd personally go with a larger duct like a 40mm because I hate struggling with stuff like that and I'd plan the job for a warm day when it'll be easier to get everything rolled out nice and straight.

 

[ruston]

Aye,that water pipe is a pig at the best of times off the roll.

 

[Darkwood]

What difference does the voltage make? A sheath test should be done on any UG cable to confirm the integrity of the serving. The only exception I would make is for tarred hessian serving as it is designed to allow leakage of circulating currents.

Was questioning to lead the posts the correct way, I don't deal or have experience with HV so would be out of the conversation but if he's talking about running a 6mm 3core to his shed under his back garden then its all usually manual backfill and wouldn't warrant a sheath test as most domestic sparks don't have the appropriate tester to do so, no column on their test sheets for it either... wasn't questioning the testing of the sheath but the circumstances of the install if he's doing a sheath test as this tends to be past your domestic set ups thus curiosity got me, not often a test mentioned on here.

I bet you can drop this conversation into the forum and 90% of the guys who have buried cable on here will not have done a sheath test, I've not done it often myself but thats more to do with the fact I don't bury many cables. I questioned him because of his strange question at the beginning of using a blue pipe as a sheath - its one of them things that ring alarm bells, so had to clarify exactly what kind of install he's doing, he seems to do a test that most on this forum will never have even done yet asks a weird question to boot when standard ducting would be the way to go, even if he had a 10mm clearance he would not get that swa though that pipe as both would have natural bending in them from storage and the friction would be high over 15m length.

@OP - I wouldn't be going anything less than a 50mm duct to drag a 6mm swa through, it will also allow for future issues to be easily rectified if needed to change the cable.