Digging a trench. Line it?
Discussion
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.
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
@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feed for the EV charger will be coming out of the garage via the same route as that old cable, (once that old cable has been retracted).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
@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
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?
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 I have some black you could have if you are anywhere North Midlands-ish.
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 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.Can I ask what you used for the trenching?
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?
Mr Pointy said:
You don't need to sleeve that mains cable & the reason for putting it in a duct is so that you can pull other cables through if necessary - eg a network cable to connect the charger to a current transformer. What diameter is the green conduit? Unless it's at least 50mm you'd be better off laying it in separate for any future cables - or use one for the mains & run another spare if your 10m coil is long enough.
The green conduit is 52mm.Fracking is an on / off thing around here. The imminent change of Government may see fracking back on the table, (along with the localised Earth tremors associated with it). If the cable is in conduit, it reduces the chances of the cable becoming damaged via circumstances beyond our control.
Added to which, if the driveway is ever dug up, the cable encased in conduit is another layer of protection.
Is the above overkill? Perhaps. But at under £40 and an extra 15 minutes work, I’d consider it to be a value for money insurance, although I could understand why some may disagree.
With any job, I’d rather do it once and do it right, than run into problems ten years down the line and wishing I’d done things differently. Especially when that ‘differently’ costs so little time and money.
JuanCarlosFandango said:
Isn't there a risk the conduit will fill with water/silt? Or does it not matter?
Potentially, yes. Although I would consider that risk to slight, and even if it does, for any negative effects of it doing so to be even smaller.It’s almost a Catch 22 situation, but one in which I consider it to be better for the cable to be ran through a flexible conduit.
The last two replies from ‘theboss’ and ‘biggiless’ highlight the issues perfectly.
What I know about the building game could be written on the back of a postage stamp, so I’ll make the assumption that both of you know what you are talking about.
But yet both of you have differing opinions on what would be the best option.
I’m not suggesting that either of you are wrong. In fact both of you are probably right. It’s just that it’s a 50-50 coin toss as to which option is best.
I’m told that it is armoured, (SWA) cable that is going to be used. Even so, I am going to stick with running it through conduit with gravel above and below to help aid drainage.
In some ways I’ll be making a good decision. In other ways I’ll be making a poor decision.
What I know about the building game could be written on the back of a postage stamp, so I’ll make the assumption that both of you know what you are talking about.
But yet both of you have differing opinions on what would be the best option.
I’m not suggesting that either of you are wrong. In fact both of you are probably right. It’s just that it’s a 50-50 coin toss as to which option is best.
I’m told that it is armoured, (SWA) cable that is going to be used. Even so, I am going to stick with running it through conduit with gravel above and below to help aid drainage.
In some ways I’ll be making a good decision. In other ways I’ll be making a poor decision.
A quick update
The trench was finally dug to a depth of 400mm…..right up until a couple of feet away from the wall of the house where I encountered the foundations of the property 200mm below the ground.
A quick chat with the electricians and their suggestion, (in writing), was to dig out the foundations of my property so that the cable could be routed at the required depth right up to the wall
Now I’m no structural engineer, but this seemed like a foolish idea to me.
As the requirement is the bury the cable 400mm below the surface of the ground, and the ground cannot be dug any deeper, a simple solution was the raise the level of the ground a couple of feet away from the house wall by placing bricks on the driveway and covering them with dirt. Anyone who was so inclined in such a situation could easily just kick the bricks / dirt out of the way once the electrician has come back tomorrow to install the charger
The armoured cable was run through the 52mm conduit. Below the conduit is 50mm of small, smooth pebbles, with another 50mm placed on top. Above that is well packed-down earth, with a long line of bricks just below the surface to make it obvious that there’s a trench / live cable underneath.
I’ve temporarily capped the ends of the conduit off with plastic bags to stop the conduit filling with water. Once the electrician has finished installing the charger, I’ll cap those off properly with expanding foam.
The final problem is how to get rid of around 750-800kg of rubble. I did phone a couple of local skip companies, and the best price I’ve got is £130+VAT for a 24 hour rental of a 2 yard skip, which is extortionate IMO, and the local tip will only take 50kg.
I’m imagining something along the lines of The Great Escape with what the PoW’s did with all of the dirt from Tom, Dick & Harry
The trench was finally dug to a depth of 400mm…..right up until a couple of feet away from the wall of the house where I encountered the foundations of the property 200mm below the ground.
A quick chat with the electricians and their suggestion, (in writing), was to dig out the foundations of my property so that the cable could be routed at the required depth right up to the wall
Now I’m no structural engineer, but this seemed like a foolish idea to me.
As the requirement is the bury the cable 400mm below the surface of the ground, and the ground cannot be dug any deeper, a simple solution was the raise the level of the ground a couple of feet away from the house wall by placing bricks on the driveway and covering them with dirt. Anyone who was so inclined in such a situation could easily just kick the bricks / dirt out of the way once the electrician has come back tomorrow to install the charger
The armoured cable was run through the 52mm conduit. Below the conduit is 50mm of small, smooth pebbles, with another 50mm placed on top. Above that is well packed-down earth, with a long line of bricks just below the surface to make it obvious that there’s a trench / live cable underneath.
I’ve temporarily capped the ends of the conduit off with plastic bags to stop the conduit filling with water. Once the electrician has finished installing the charger, I’ll cap those off properly with expanding foam.
The final problem is how to get rid of around 750-800kg of rubble. I did phone a couple of local skip companies, and the best price I’ve got is £130+VAT for a 24 hour rental of a 2 yard skip, which is extortionate IMO, and the local tip will only take 50kg.
I’m imagining something along the lines of The Great Escape with what the PoW’s did with all of the dirt from Tom, Dick & Harry
Job done, well, except for getting rid of the rubble. I’m going to be tight and take it to the several local tips over a couple of week period.
The charger is an EVEC somethingorother
All I know is that it can charge two EVs at a time.
Trench? What trench?
Oh dear ! The bricks covered with dirt that were creating a raised hump in the driveway so that the cable was 400mm under the surface of the ground seem to have been stolen. I’ve no idea how that might have happened.
I’m sorry, but there was no way that I was going to dig out the foundations of the house just to lay a cable. That seems ridiculous to me.
At least now I can get the scrap Citroen shifted, which will no doubt temporarily please ‘er indoors’.
The charger is an EVEC somethingorother
All I know is that it can charge two EVs at a time.
Trench? What trench?
Oh dear ! The bricks covered with dirt that were creating a raised hump in the driveway so that the cable was 400mm under the surface of the ground seem to have been stolen. I’ve no idea how that might have happened.
I’m sorry, but there was no way that I was going to dig out the foundations of the house just to lay a cable. That seems ridiculous to me.
At least now I can get the scrap Citroen shifted, which will no doubt temporarily please ‘er indoors’.
Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff