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

 

[telectrix]

if it's buried under a patio or slabs, no need to be 600 deep. i have a run of pond flex in kopex, 6" below patio slabs. been there 9 years, no problems.

 

[richy3333]

I buried a body under slabs once. Think it was an objectionable, old NICEIC assessor

 

[DPG]

I buried a body under slabs once. Think it was an objectionable, old NICEIC assessor

Did you put 'dead body' warning tape above it?

 

[Jeremy Hale]

Depth of buried SWA cable 500mm lay in sand. cover with warning tape at higher level. You may have to make Cabin a TT installation with eath Rod

 

[davesparks]

Depth of buried SWA cable 500mm lay in sand. cover with warning tape at higher level. You may have to make Cabin a TT installation with eath Rod

Why would they need to make the log cabin a TT installation?

 

[Jeremy Hale]

Only if House or main supply is PME

 

[davesparks]

Only if House or main supply is PME

Why would they need to make it TT if the supply is PME?

 

[Jeremy Hale]

See Attached, SWA Armor sheath is earthed at main board. The earth is isolated at outbuilding and eath rod installed to form a TT system with a 30ma RCD covering outbuilding. The supply to SWA cable feeding outbuilding should be protected by a time delayed RCD 100ma
there is a lot on the web about not exporting PME.

 

[DPG]

So are you saying that you believe every outbuilding or garage should be TTd if the supply is TNCS?

 

[richy3333]

@Jeremy Hale nothing attached. Still dont see why it necessarily needs to be a TT system.

 

[telectrix]

only needs to be converted to TT if extraneous parts in outbuilding and cpc of the SWA is < 10mm (or equivalent) for bonding for a PME supply.

 

[davesparks]

See Attached, SWA Armor sheath is earthed at main board. The earth is isolated at outbuilding and eath rod installed to form a TT system with a 30ma RCD covering outbuilding. The supply to SWA cable feeding outbuilding should be protected by a time delayed RCD 100ma
there is a lot on the web about not exporting PME.

That doesn't explain why though, you are just repeating a common misconception without backing it up with reference to the regulations or technical knowledge. Plus you've got it wrong, the SWA doesn't need RCD protection.

Creating a TT earthing system for the outbuilding is only necessary if there are extraneous conductive parts present in the outbuilding and if it is not practicable to install main bonding to them. At this stage in the OPs situation where they have not yet begun work the better options are adding a 10mm earth to the submain or increasing it to a 10mm 3 core SWA,this will give them a 10mm bond at the log cabin to connect to any extraneous conductive parts.

'TTing' as it has become known should be the last option considered as it swaps a very good, low impedance earth connection for what is likely to be a poor, high impedance earth connection. This then leads to a reliance on RCDs which are far from infallible.

 

[Jeremy Hale]

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

 

[Midwest]

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

Think you're digging a trench for yourself here @Jeremy Hale , that link is about using the armouring of swa as cpc.

If you look in the resourcing section, there's some content about this matter. I've read before about permissions from DNO's etc, but never found any such requirements. We have to abide by BS7671, they have other regulations.

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[Jeremy Hale]

Yes you right, as long as its complies with BS7671 and its safe