Swa underground.

[Shift]

I've just run some 2 core 10mm Swa to my garage but not yet connected at either end. I've only used Swa in factory installs before and never needed to bury any underground. I planned on using the steel wire armouring as the earth as I have done previously and I know Swa is ok to bury but a sparky at work said it's not recommended and I should have used 3 core as the armouring can rot eventually. I cant find anything in the regs that states I cant use the armouring as the earth when it's buried underground.

 

[Spark123]

There is nothing wrong with using the armour as the earthing as long as it complies with either table 54G or the adiabatic equation, //wiki.diynot.com/electrics:earthing_supply_types_and_bonding:swa_earthing .
Just to check you are using 70degC PVC??

 

[breezer]

by the time it rots we will all be long dead

 

[Shift]

I thought he was talking b******s but like to make sure before I tell him.

 

[ColJack]

did you bury it properly in a trench, 12 inches underground at least and with warning tape on it??? ( all things I vaguely remember reading in a regs book but not exactly sure on the specifics.. )

as long as the outer sheath is not damaged in the ground and that suitable boots are used at the ends and the ends are indoors in a dry environment, I don't see a problem with the armor "rotting" however, there are specific tests to be carried out if the armor is used as the sole means of earthing...

I personally would have gone for 3 core... but it wasn't my choice was it...

 

[ricicle]

Just to check you are using 70degC PVC??

Yes, as XLPE will need the adiabatic done on it

 

[ricicle]

did you bury it properly in a trench, 12 inches underground at least

Surely you mean 18 inches

 

[securespark]

12 inches

A bit more than that!

 

[Spark123]

A 90degC XPLE 2 core 10mm² SWA does not comply with table 54G, it should therefore needs to be checked for compliance using the adiabatic.

 

[ricicle]

Secure 123

 

[Spark123]

lol, should type faster I know.
Do you have any extraneous conductive parts in the garage, if so what type of supply do you have and what size bonding?

 

[ColJack]

depth not specified in the regs... just that it is at a suitable depth to avoid disturbance of the soil.. standard spade / garden for is 12 inches is it not???

also i did say I was not sure of the specifics..

 

[securespark]

May I point out the bit in bold?

This from the 16th Edition (1992 - yellow):

522-06-03
Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, a cable buried in the ground shall incorporate an earthed armour or metal sheath, or both, suitable for use as a protective conductor, or be of insulated concentric construction.

Buried cables shall be marked by cable covers or a suitable marking tape. Buried conduits or ducts shall be suitably identified. Buried cables, conduits and ducts shall be at a sufficient depth to avoid being damaged by any reasonably forseeable disturbance of the ground.

Sorry, I've edited this post by mistake - What a Berk!

 

[Shift]

Sorry for slow response, major breakdown,anyway bought the cable from tlc didn't realize there are different types of swa and I've been using the stuff for many years anyway Tlc's site says xlpe, I presume they mean xple as in the charts so my cable doesn't quite comply. Can I run a seperate earth as it's not buried yet or have I wasted my money. How are you supposed to do an adiabatic equation without knowing the values!!!

 

[plugwash]

I cant find anything in the regs that states I cant use the armouring as the earth when it's buried underground.

there are a number of issues with using armouring as earth, the first three apply to this case the others are for general info.

as others have mentioned there is the armour CSA issue, needs to be checked out using the adibetic for this size of cable.

there is also the EFLI issue, you must get the EFLI low enough and since steel is less conductive than copper this may be a problem.

there is the issue of badly terminated glands (this is the reason i always advise diyers to use 3 core)

also there is the issue of possible damage, the inner cores are proabblly stretchier than the armouring and generally have more slack too so it is not unheared of for the armour to be ripped out of the gland while the inner cores stay connected. Pretty unlikely on a domestic but can be an issue in rough industrial environments.

finally you mustn't do it if your wiring a marina (i belive seeing that reg out of context is the reason some sparkies belive it is forbidden)