Does armoured cable to Garage need to be buried?

[chivers67]

Maybe he's running 25mm!

Any cable buried needs electrical tape or cable covers unless in a duct or conduit. 522.8.10 Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, a cable buried in the ground needs an earthed metal armour or metal sheath (or both). Any cable needs to be buried at a sufficient depth to avoid being damaged by any reasonable foreseeable disturbance of the ground. So number 4 for me from BS3036s question, though in this instance 500mm sounds a reasonable depth.

I guess it depends if there's a chance anyone would want to extend the house, run a soil pipe of any other service near the front.

He says that as it's armoured he need only hide the cable just under the gravel, with no warning tape on top of it.

He's incorrect.

https://www.tlc-direct.co.uk/Products/FMPT103.html

 

[Roy22]

How is this electrician proposing to fuse down the swa, given you wrote " splitting the heavy supply cable to Consumer Unit"? is there room for a switchfuse in the meter cupboard? Hope he wasn't expecting to just join it directly to the cu tails.

He said there was room in the Meter Box to put a splitter (it had a name which I forget) and that he'd run 4mm2 armoured. Now you mention it, it did cross my mind this wouldn't fuse the armoured run before the garage box, except for the 100A main fuse(!) What should he do there? Think he was looking for a way to avoid running a cable indoors under floorboards and all that upheaval.

 

[chivers67]

Henley block? There should be some kind of down rated fuse or small enclosure

Something like this with a smaller fuse.

Edit for the little extra cost go for 6mm at least

 

[yorkspark]

View attachment 256123 As posted, should look something like this when done correctly!
Tails split using henley blocks, then a switchfuse or 1way cu installed with the swa correctly terminated using the correct glands.

Note - Pic for illustration only!!

 

[Roy22]

Henley block? There should be some kind of down rated fuse or small enclosure

Something like this with a smaller fuse.

Edit for the little extra cost go for 6mm at least

Yes! Henley block was what he said.

 

[flameport]

Nothing in BS7671 states that cables must be buried or otherwise. Cables must be suitable for the environment they are installed in.

Meter cabinets are for meters and DNO equipment only, they are not intended for other devices such as switchfuses or grotty little consumer units.
Cables require overcurrent protection, so just connecting in with 'henley blocks' won't do, and you can't connect armoured cable directly to such things anyway.

4mm² will be useless for charging an electric vehicle.

 

[JohnW2]

522.8.10 Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, a cable buried in the ground needs an earthed metal armour or metal sheath (or both).

... that is, of course, what we are talking about. It is also very oddly worded, since it would take very very little of a 'conduit or duct' to offer the "equivalent degree of protection against mechanical damage" to the (extremely little) protection against mechanical damage afforded by a metal sheath!

... Any cable needs to be buried at a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground. So number 4 for me from BS3036s question, though in this instance 500mm sounds a reasonable depth.

As I recently wrote, it is a non-explicit requirement which requires judgement. Opinions will obviously vary, but I can certainly see an argument that disturbance that would represent a significant to threat to SWA (at any depth) was probably not "reasonably foreseeable" in gravel trench varying in width from 4" to 13", particularly since one digging (or similar) is not someone one would normally do in a gravel-filled trench. If there was ever any need to excavate the trench, one would normally 'scrape out' the gravel fairly gently, very probably by hand with such a narrow ditch.

Any cable buried needs electrical tape or cable covers unless in a duct or conduit.

That is, indeed, what 522.8.10 says, and even if the cable is "in a duct or conduit", the duct or conduit is required to be "suitably identified".

However, if it is decided (per above argument) that "just under the gravel" is deep enough for the SWA, then, pragmatically speaking, anyone seeing marking tape would have seen the cable itself in the absence of that tape.

Whatever regs may say, marking tape is really only of any practical value if it can be installed a very appreciable distance above the cable since, otherwise, by the time one encounters the tape (e.g. by digging) one will already have damaged the cable.

I do think that this is yet another of those situations in which a bit of common sense is needed.

Kind Regards, John

 

[EFLImpudence]

522.8.10 actually states:

"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."

which is slightly different.

 

[Roy22]

Regarding an Electric Car charging point, I did casually raise this, not because I plan to get one (currently managing without any car) but as a future benefit whilst he was running a proper supply to the garage. His reply was to the effect that he didn't want to get involved in that, basically he didn't seem happy to be answerable for installing one of those and would rather someone else was. This response surprised me somewhat, it was only a casual afterthought enquiry and I'd assumed it was no harder a task than than the one he was doing.

Does it require any extra certification/skills? Or does this suggest an inexperienced, albeit qualified, Electrician?

 

[JohnW2]

522.8.10 actually states:
"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. ...." ... which is slightly different.

Yes, it does say that, but I think that those of us quoting bits of the reg have not bothered to include "suitable for use as a protective conductor", since it doesn't appear relevant to this discussion.

Given that the armour of SWA is "suitable for use as a protective conductor" (always as a CPC, sometimes also as a bonding conductor), in the context of this discussion, what exactly is it that you are suggesting is "slightly different" from what?

Kind Regards, John

 

[EFLImpudence]

No, I meant the regulation was slightly different than that previously written by Chivers.

However, you did write:

... that is, of course, what we are talking about. It is also very oddly worded, since it would take very very little of a 'conduit or duct' to offer the "equivalent degree of protection against mechanical damage" to the (extremely little) protection against mechanical damage afforded by a metal sheath!

I agree it is oddly written but does -
"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."
just mean it has to be equivalent to - as adequate as - the protective conductor?

Although that isn't really mechanical protection, is it?

 

[JohnW2]

.... I agree it is oddly written but does -
"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." just mean it has to be equivalent to - as adequate as - the protective conductor? .... Although that isn't really mechanical protection, is it?

I'm not sure of your point - the "equivalent adequacy' surely explicitly relates to ('adequacy of') 'mechanical protection' (red above) (of which a protective conductor, per se, does not necessarily provide very much at all), doesn't it?

If it were intended to say something different from that, then 'equivalent' to what do you think that "equivalent protection against mechanical damage" was intended to mean?

Kind Regards, John

 

[EFLImpudence]

Yes, maybe, but a metal sheath provides no mechanical protection and as you have said neither really does the so-called armour.

 

[EFLImpudence]

"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 more I read it the less it makes sense. What do the two commas indicate?

What about -

"A cable buried in the ground shall incorporate an earthed armour or metal sheath, or both, suitable for use as a protective conductor except where installed in a conduit or duct which provides equivalent protection against mechanical damage."

 

[EFLImpudence]

Or -

"Except where installed in a conduit or duct which provides equivalent protection against mechanical
damage, suitable for use as a protective conductor, a cable buried in the ground shall incorporate an earthed armour or metal sheath or both."