Digging a trench. Line it?

[105.4]

I’m currently digging a trench across my driveway to allow electricity feed to an EV charger. The trench is 350mm-400mm deep.



Will I need to line it with a membrane before the electrician turns up on Wednesday?

If so, will it require a special sort of membrane, or will pond liner suffice?

Sorry for the stupid question, but I’m not a builder or a structural engineer.

Thanks in advance.

[Tymb]

No, should be using SWA cable if direct buried which will be fine.
Make sure bottom of trench is free of sharp stuff and backfill around cable is the same.
Can use sand to line and cover cable.
Electrician should be able to supply some marker tape, I’d normally put it about 150mm above cable.
Under drives with all the hassle of lifting them my preference always used to be to stick some duct in as you never know what else you might want to get under there in the future.
Something like this
https://www.drainagesuperstore.co.uk/product/under...
Pretty much any smooth bore pipe will do just don’t use blue or yellow.

[sherman]

I would drop a conduit in the trench for the wire and leave a few extra pull strings for any extra wires needed in future.

Pond liners will hold water in your trench and most likely corrode your wires.

[105.4]

@tymb
@sherman

Thank you both

My thinking of lining the trench with a membrane mirrored your own. IE; likely to hold water in the trench as opposed to allowing the water to drain away.

It’s a funny kind of ground here. Soil, sandstone, coal, (in abundance around here), then a really thick clay, interspersed with backfill of old brickwork, (our property was previously an old milking shed). With the thick clay at the base, the ground will need all the help it can get to soak-away any heavy downpours.

Your ideas of using a conduit is a good one, and one that I hadn’t considered. A trip to Wickes / B&Q / Homebase tomorrow for 7.5 metres of white drainpipe is now planned. I’ll email the electrician this evening to update him on this.


I assume that the cable that is going to be used will be the same as the stuff in this photo that previously powered a hot tub on the property?



The feed for the EV charger will be coming out of the garage via the same route as that old cable, (once that old cable has been retracted).


Many thanks to you both

[Tymb]

Yes that looks like Steel wire armoured cable.
You have the steel wire around the outside, sometimes used for the earth.
That looks like it might be a 3 phase cable in your hand so if you are going for a single
phase charger your new cable will be a bit smaller probably with only 3 or possibly 2 cores depending on
how car chargers are earthed.

[paulrockliffe]

What's the regs for buried cable? Does it not require a deeper trench?

[BlackZeD]

[skeeterm5]

I would line the trench with pea gravel, put warning tape over the cable and then cover with pea gravel before filling the trench.

[105.4]

paulrockliffe said:

What's the regs for buried cable? Does it not require a deeper trench?

The EV charger installers told us 350-400mm.
The trench is dug to 370-380mm.

[105.4]

BlackZeD said:

Bugger

That’s disappointing.

Thanks Zed.

[g7jtk]

I would sleeve the cable then pea gravel before back filling

[105.4]

g7jtk said:

I would sleeve the cable then pea gravel before back filling

I’ve ordered 10m of this stuff to sleeve the cable with.




Why line the trench with pea gravel though? To help with drainage? How necessary would this be, (on a scale of 1-10)?

Would a couple of inch below the cable and a couple of inch above be sufficient?

[105.4]

skeeterm5 said:

I would line the trench with pea gravel, put warning tape over the cable and then cover with pea gravel before filling the trench.

Would a couple of inches above and below be sufficient?

Cheers

[No ideas for a name]

105.4 said:

I’ve ordered 10m of this stuff to sleeve the cable with.




Why line the trench with pea gravel though? To help with drainage? How necessary would this be, (on a scale of 1-10)?

Would a couple of inch below the cable and a couple of inch above be sufficient?

Ducting for mains should really be black. Green is for comms/cctv. Of course, the electricity doesn't know any different.

I have some black you could have if you are anywhere North Midlands-ish.

[105.4]

No ideas for a name said:

Ducting for mains should really be black. Green is for comms/cctv. Of course, the electricity doesn't know any different.

I have some black you could have if you are anywhere North Midlands-ish.

Thank you very much for the generous offer

Yes, we are in the North Midlands, (Chesterfield / Worksop). Unfortunately my Wife text me about ten minutes ago to say that she’d collected the green ducting from Toolstation.

I did wonder why almost all of the ducting / sleeving I was seeing online was black. Personally I didn’t think that was a particularly good idea, black ducting in dark earth / clay as it wouldn’t be very obvious when you’d dug down to it.

We’ve got the green stuff, plus some red / white hazard tape to wrap it in, plus the cable will be protruding above the ground where it exits the garage and where it starts to climb up the house wall to the charger.

With all of the measures we’ve put in place, I think it should be ok?

Thank you all for your advice. With each titbit of experience you’ve added, you’ve collectively been a great help

[jrb43]

I think “foreseeable disturbance” is your friend: people don’t routinely dig up your drive in the way that you would a flowerbed. I am planning a similar project and thinking SWA in conduit and surrounding warnings/clues is reasonable at <600mm. Of course your electrician may hold a different view: keep us informed.

Can I ask what you used for the trenching?

[105.4]

jrb43 said:

I think “foreseeable disturbance” is your friend: people don’t routinely dig up your drive in the way that you would a flowerbed. I am planning a similar project and thinking SWA in conduit and surrounding warnings/clues is reasonable at <600mm. Of course your electrician may hold a different view: keep us informed.

Can I ask what you used for the trenching?

“Foreseeable Disturbance”…..yes, that’s the phrase I was looking for. And like you have planned, a multitude of warning signs should be enough to cover our backs.


The trench is 7.5m long and at its base, around the width of my hand.





I’ve been using this;



Available from ScrewFix for £160 and it’s performed very well. I was going to rent something similar for the weekend, but the costs of doing so were around £80. I figured I could buy that, use it, then sell it whilst losing less money than the cost of renting one.

I’ve also been using a pickaxe and a couple of gardening trowels for my Wife and I to dig out the trench once the earth was broken up.

I was originally using a trench shovel, but it was digging the trench too wide for our requirements.

I did a couple of hours on my own on Saturday evening, then my Wife and I had most of yesterday on it, followed by a couple of hours this morning. A couple of hours were wasted getting through a sunken, horizontal concrete fence post buried 350mm under the driveway.

As you can see from the bags in the driveway, we’ve removed around two tons of earth digging this trench.

HTH?

[jrb43]

Super helpful, thank you. I hadn’t considered nearly 2 tonnes of spoil…

Hope it all goes well

[jrb43]

Super helpful, thank you. I hadn’t considered nearly 2 tonnes of spoil…

Hope it all goes well

[Caddyshack]

105.4 said:

BlackZeD said:

Bugger

That’s disappointing.

Thanks Zed.

I had to bury mine at 600mm.