Burying armoured cable in garden - what type of sand?

"sufficiently deep"

That famous NJUG diagram puts LV at least 450mm deep or 600mm deep under carriageways, which doesn't seem like a bad starting point. I'd try to have the trench at least 500mm deep under say a lawn so it's safe from being spiked by garden forks and the like used to aerate the turf. Under cultivated areas obviously much deeper, or something like a flagstone over the top to reduce the likelihood of the cable being hit. If under what's going to be a permanent path or such shallower might be OK.

If you do have issues with sharp stones and the like - I'd probably go for a twinwall duct rather than sand - much quicker and easier to install and probably more reliable as it's not going get displaced when backfilling or by future groundworks like sand might be. Just be careful that the duct's arranged so water can't collect inside it (i.e. no U shapes) - most cables don't like being immersed permanently.

   - Andy.

It's coming back to me that for mine "sufficiently deep" turned out to be dig down until you hit the (ceramic) sewer pipe, and then come back up a bit! But reassuring that (from memory) that was pretty much the same interpretation I made, including, being a cautious chap, running through duct.

Thanks, Andy

AJJewsbury said:

That famous NJUG diagram puts LV at least 450mm deep or 600mm deep under carriageways, which doesn't seem like a bad starting point. I'd try to have the trench at least 500mm deep

GN1 says 500 mm deep. Some of the Part 7 locations have requirements for 600 mm (705, 708, 730), but note also 705 requires 1 m deep under cultivated land.

Also worth remembering that there will be compacting when you back-fill (unless you compact as you go) ...

AJJewsbury said:

Just be careful that the duct's arranged so water can't collect inside it (i.e. no U shapes) - most cables don't like being immersed permanently.

That includes "normal" SWA. If SWA is buried in certain kinds of clay ground, with no ducting, best to try and provide some drainage or similar around the cable, by digging down at least another 200 mm, and back-fill with aggregate first, topping off with 1/4 down or similar, and then 50-100 mm of sand on which the cable is laid.

And don't forget if duct is not being used, cable tiles and/or marker tape above the cable.

AJJewsbury said:

That famous NJUG diagram puts LV at least 450mm deep or 600mm deep under carriageways, which doesn't seem like a bad starting point. I'd try to have the trench at least 500mm deep

GN1 says 500 mm deep. Some of the Part 7 locations have requirements for 600 mm (705, 708, 730), but note also 705 requires 1 m deep under cultivated land.

Also worth remembering that there will be compacting when you back-fill (unless you compact as you go) ...

AJJewsbury said:

Just be careful that the duct's arranged so water can't collect inside it (i.e. no U shapes) - most cables don't like being immersed permanently.

That includes "normal" SWA. If SWA is buried in certain kinds of clay ground, with no ducting, best to try and provide some drainage or similar around the cable, by digging down at least another 200 mm, and back-fill with aggregate first, topping off with 1/4 down or similar, and then 50-100 mm of sand on which the cable is laid.

And don't forget if duct is not being used, cable tiles and/or marker tape above the cable.