Minimum depth underground cable

[RickH]

If providing power to an item in the garden via SWA cable, Is the depth required to be only 240mm ?

This is under a lawn ... came across this statement "All ducting must be laid with electrical cable warning tape, which should be installed at a depth of 240mm below gardens and paths"

I have only put in SWA cables at 450mm depth previously but if only 240mm is required will save a lot of digging ....... I can put in a warning tape 150mm above it.

 

[motorbiking]

I think it’s the tape that goes to that depth. I’ve always worked to 450mm

 

[opps]

I too thought that it was 450mm

 

[RickH]

I have always used 450mm for feed to buildings, just came across the comment about 240mm on a search this morning.
Seems I have the extra digging then.

 

[flameport]

There are plenty of recommendations, but there is no required depth.
The depth depends on where the are buried and what's likely to be occurring there, and how likely those activities are to damage buried cables.
There is a vast difference between a domestic garden and a farmers field.

 

[DetlefSchmitz]

I think I've said before. I remember one of the C&G Wiring Reg questions was always (something like):

How deep must you bury a cable:
a) 450mm
b) 100mm
c) as deep as it needs to be
d) 500mm

 

[plugwash]

IIRC BS7671 doesn't specify a specific depth, only that it must be deep enough to avoid any reasonablly forseeable disturbance to the ground.

450mm is a utility standard for "low voltage" (in the IEC sense, that is <=1KV) cables in "Unmade ground, footways & footpaths". Still it seems to me to be at least in the right ballpark for cables in a domestic garden. It gives a reasonable safety margin beyond the length of a garden spade.

 

[JohnW2]

I think I've said before. I remember one of the C&G Wiring Reg questions was always (something like): ...

Do I take it that the expected/'correct' answer was (c) ?

Kind Regards, John

 

[opps]

I think I've said before. I remember one of the C&G Wiring Reg questions was always (something like):

How deep must you bury a cable:
a) 450mm
b) 100mm
c) as deep as it needs to be
d) 500mm

But don't those regs go on to say that less than 450mm is "inadvisable"?

 

[EFLImpudence]

They never used to tell you which question(s) you had wrong so unless you got 100% you wouldn't be sure.

The answer must be in BS7671.

 

[DetlefSchmitz]

Well, I did get 100% one year. The other year they told you how many you got right in each section. So yes, I do know the answer they considered right. Of course if the wording in BS7671 has been developed the question may be different nowadays.

 

[EFLImpudence]

522.8.10
"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. The location of buried cables shall be marked by cable covers or a suitable marker tape.
Buried conduits and ducts shall be suitably identified. Buried cables, conduits and ducts shall be at a sufficient depth
to avoid being damaged by any reasonably foreseeable disturbance of the ground."

 

[JohnW2]

They never used to tell you which question(s) you had wrong so unless you got 100% you wouldn't be sure.

or 0%

Kind Regards, John

 

[JohnW2]

But don't those regs go on to say that less than 450mm is "inadvisable"?

Not that I have noticed (although I often 'miss things' ) - but related publications (e.g. the OSG) may (and often do) 'make up' such guidance, which often confuses people into believing that the same exists "in the regulations"!

Kind Regards, John

 

[securespark]

I got one question wrong in the 17th update and considered it ambiguous. The reply came back that my complaint had been passed to the question compilers and they considered it OK.

The funny thing was, if I'd got 75%, I'd have probably been happy.