Depth to bury armoured cable in concrete with vehicles passing over?

[HappyHippyDad]

I will/may be burying 16mm SWA in concrete to route it to an outbuilding (for the kiln I have just been chatting about!). This will be getting driven over by cars. Is there an ideal depth for this? Also, does the SWA require any further form of protection?

 

[telectrix]

i'd put it in rigid ducting 12" deep with sand, then the ducting takes the weight of the traffic and you have the option of rewiring should it ever become necessary.

 

[HappyHippyDad]

i'd put it in rigid ducting 12" deep with sand, then the ducting takes the weight of the traffic and you have the option of rewiring should it ever become necessary.

Pretty deep then! A lot of concrete for me to drill out. Makes sense though.

 

[telectrix]

suppose you could go shallower. not likely to be dug up. the concrete will only be a few inches anyway, then hardcore or just plain earth.

 

[ruston]

Maybe you could use a mole under the existing concrete if you can dig a pilot trench at either side.

 

[HappyHippyDad]

Maybe you could use a mole under the existing concrete if you can dig a pilot trench at either side.

The thought of that scares me silly! ?

In fact, I'm thinking of passing the job purely based on the trench. There looks to be pipework all over the place, some of which may be under the trench. It would only be perhaps 120mm wide and perhaps 3m long but the thought of hitting a pipe does worry me.

Also, how to cover the trench whilst the concrete is setting to allow traffic to pass over?

Perhaps a builder would do this sort of thing and I could contract it out?

It's a bit outside my role. I'm used to changing consumer units and wiring up conservatories!

 

[loz2754]

Good idea.
I would prefer to get the customer to hire a contractor to dig and backfill.

 

[brianmoooore]

Important not to embed the cable directly in concrete. When, not if, the concrete cracks, it will put a shear on the cable. Applies to pipes and cables.

 

[SparkySy]

I would agree with all of the above get a contractor in to do the groundwork and definitely put a duct in if only for future adaption.
Or get a mole service to do the hole, at least the above should have all the necessary insurance for that type of work! Plus if they hit something it's their problem!
Sy

 

[HappyHippyDad]

10-12" deep, cable located in rigid pipe. Contractor to deal with trench responsibilities. Job done! ?

 

[UNG]

10-12" deep, cable located in rigid pipe. Contractor to deal with trench responsibilities. Job done! ?

And don't forget the cable warning tape so if someone digs in the future they get a warning before getting down to the duct / cable and doing damage

 

[Marvo]

Pretty deep then! A lot of concrete for me to drill out. Makes sense though.

12 inches isn't very deep.... if the cable is running under a road in the same direction as traffic we usually go around a meter deep in duct to reduce 'cable creep' caused by cars and lorries especially. If the cable is running across the path of the traffic then creepage won't be an issue so we'd usually go around 600mm deep (2ft). If it's a private driveway then 600mm regardless of direction would usually be good.

Also we wouldn't use concrete for fill, if the substrate is sandy and prone to water errosion we might mix a small ratio of cement in with the fill (maybe a 10 or 12 to 1 ratio of fill to cement) to give it some extra stability against future water errosion. As per UNG don't forget the yellow and red hazard tape above the cable.

If the distance is only 3 meters and the ground is free from rocks and boulders we regularly mole it ourselves by digging a hole or more like a pit either side of the road and using a rigid 25mm hose with decent water pressure inside a 40mm HDPE duct and basically work the hose and the duct backwards and forwards through the sand/soil until it finds its way through. This method has saved us a lot of money in the past, so much so that we bought a cheap petrol driven water pump and a 1 kilolitre water tank specially for this purpose, but it's far from guaranteed though. I'd guess we've had about a 75% sucess rate and there's been several occasions where it's not worked and we ended up getting a proper moling company in so make sure you cover that eventuality when you quote.