Burried SWA for a log cabin

[Gringoking88]

Hi all,

Hope someone can give me clarity around the need to bury an SWA cable please.

I've been asked to install an 4mm SWA from the main DB to a "to be built log cabin" at the end of the garden about 50m away, it will need to run along a fence for most the route (or underground).

I called NICEIC to clarify and they advised I cant clip it to the fence incase it falls down, cant leave it on the surface due to rodents and have to bury it for the entire length. My question is reg 522.8.10 says "burried cables shall be buried to a sufficient depth to avoid being damaged...." what do you guys call a sufficient depth and whats your thoughts about rodents chewing through SWA armour???

Basically what do you guys do in these cases??...

Many thanks,

M

 

[Des 56]

you may need permission From DNO to export PME.

They would not give you that permission
If the pme is taken to a shed it will be the electrician himself taking on that responsibility, if the circumstances comply with whats required by our regs then the liability is reduced

 

[davesparks]

Agreed however there are recommendations as attached document READ MORE HERE and you may need permission From DNO to export PME.

Well yes you would need permission to export PME, but that is not what is being discussed here. The subject here is extending the equipotential zone of an installation fed from a TNCS supply.

 

[Gringoking88]

I've never seen a rodent chew through SWA, but then I ain't seen everything. I've also never seen a fence blown down and damage a SWA.
You'd also best not clip cables in sheds in case they fall down or put light fittings in rooms under bathrooms in case the bath floods if going by the logic of the advice given.

LOL I was wondering how a mouse or even a rat could chew through SWA, the rubber possibly, but the wire armour, hummmmm.
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I usually ignore the Niceic warnings about the imminent collapse of a fence and clip it along the fence (also it must be the case that Welsh rodents don't eat cable sheathing as much as the English rodents,that is if this particular fear is indeed as frequent a occurrence as some would have me believe)
My reluctance to embrace the "don't clip it to a fence" outrage is probably because in the mines they were in full view,especially to the rodents who resided underground,they somehow seemed not to have the taste for cable sheathing that their their above ground kin must have acquired in later years,thats if you believe all these alarm bells that are always being rung about the subject

Where it has to be buried it would be 2 spades depth with a sand base,lay marking tape above the cable,if vehicles are to be driven near or over the run, in this case a duct of sorts would help protect that cable

I agree and dont get the entire fence argument, however, down south we do have the biggest badest rodents.

To be honest, I dont really get the point of marking tape either, if your digging shoving a spade into a flower bed, I dont see how you would see or even notice tape, never mind how you would manage to put a spade threw the wire armour, is that even possible, maybe I'll test it.
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Hi gringoking88,

Got a bit confused for a moment because you have DIY on badge but you where able to call niceic help line. Your profile shows your quals so not sure if you are DIY.

Anyway I totally agree with des 56 I quite often clip to fences. Don’t see a problem as long as it’s not rotten or about to be replaced. I always ask the customer I am dealing with what there preferences are.
Buried or clipped.

As a side issue 50 meters 4mm. Hope the load isn’t too high.

Without doing any calcs I think you would struggle to get under adequate voltdrop for anything over 20amps.

Reason I mention it is I have just done calcs for a 10 mm SWA over 50 meters.

May be worth checking.

I'm registered with the NICEIC as a DI.

I agree, hadnt acually done the calcs yet, but after doing so I will go with a 6mm on a 32 amp mcb, given volt drop, I think it should be fine, the client only wants a ring main and a light circuit.
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As some if the others have said 4mm is not sufficient due to voltage drop. 6mm may just be ok if minimal sockets and lighting in cabin, otherwise 10mm.

Thats exactly what I thought, all they want is a ring main and a lighting circuit, tbh 20 amp radial would be fine and 6 amp lighting.
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Based on a similar job I have just calculated for 50 Meters. It was 10 mm SWA.

I don’t know your total load after diversity so cannot give you your definite sizing.

You will have to work it out on your figures.

Hi,

Total load would be minimial, a ring and a lighting circuit, thats it.
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Thanks all for the replies, love the banta btw!

 

[Bobster]

The problem with rodents and light spade damage to cables aren't immediate.

Once the outer sheath is broken, water ingresses around the armour, it rusts and corrodes away quite quickly. Now, if the circuit is using the armour as it's CPC, this kind of damage can unknowingly remove the CPC protection.

Hence burying surrounded with sharp sand, not just led in the ground where rocks could pierce the outer sheath.

 

[davesparks]

I was wondering how a mouse or even a rat could chew through SWA, the rubber possibly, but the wire armour, hummmmm.

To be honest, I dont really get the point of marking tape either, if your digging shoving a spade into a flower bed, I dont see how you would see or even notice tape, never mind how you would manage to put a spade threw the wire armour, is that even possible, maybe I'll test it.

I agree, hadnt acually done the calculatios yet, but after doing so I will go with a 6mm on a 32 amp mcb, given volt drop, I think it should be fine, the client only wants a ring main and a light circuit.

Rodents can chew through the outer sheath of SWA, once the sheath is broken the cable will fail as moisture gets in and rots the armour.

Correctly placed marker tape should alert anyone who is digging to the presence of a cable, it should be sufficiently far above the cable that it is noticed before you reach the cable.
Finding something like that when you are digging is very obvious as it always gets tangled on the spade and you probably feel it first before seeing it.
You don't need to cut through the cable with a spade to damage it, once the outer sheath is damaged the cable is compromised. Plus of course people use other things thna just a spade to dig, a fork will go straight through.

It sounds like you are intending to install a 32A MCB for the submain with a 32A MCB for a final circuit fed by this submain, that's a pretty poor design.
I don't see how you have come up with 6mm as suitable when there is a lighting circuit connected to it? I would have thought 10mm would be the minimum.

 

[Midwest]

Some manufacturers will not indemnify their swa cables being lain in water logged ground. They should be lain in a nice piece of ducting.

 

[Gringoking88]

Sorry all, I was being a dunce 20amp radial sockets and 6 amp lighting circuit.

 

[HappyHippyDad]

Sorry all, I was being a dunce 20amp radial sockets and 6 amp lighting circuit.

Super, so now you know that you need to use 10mm as 6mm will not be sufficient due to voltage drop (approx 8.3V with 6mm SWA).

 

[richy3333]

Whats a DI? In Scotland we are either registered Approved Contractors or nothing. I thought DI was a plumbing thing for wiring up boilers and the like?

 

[Spoon]

Whats a DI? In Scotland we are either registered Approved Contractors or nothing. I thought DI was a plumbing thing for wiring up boilers and the like?

DI stands for Domestic Installer

 

[Spoon]

It’s short for d1ck

Thats Detective, silly....

 

[Pete999]

DI stands for Domestic Installer

Or disaster immanent JOKE

 

[davesparks]

Whats a DI? In Scotland we are either registered Approved Contractors or nothing. I thought DI was a plumbing thing for wiring up boilers and the like?

DI usually refers to the NICEIC domestic installer scheme, it is their part P competent person scheme which allows electricians to self certify for the purpose of part P.
Approved contractors doing domestic work will have the DI scheme added to their membership.

One key difference between DI and approved contractor is that a sole trader can become a DI but usually cant become an approved contractor (AC requires two people on the registration normally, a qualified supervisor and a principle duty holder)

 

[telectrix]

Glennsparks is AC and he's a sole concern.

 

[davesparks]

Glennsparks is AC and he's a sole concern.

Oh, maybe they've relaxed the rules a bit. They told me I couldn't register as an AC as a sole trader a few years ago.