 | Home > Off Topic > Armoured Cable Advice - routing underground? |
 
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| Ianh Member Since: 17 Sep 2018 Location: Essex Posts: 1997  
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There are flexible steel rods , approx 5 mm in diameter that can have various size drill heads attached and can be run from a reasonably powerful cordless drill to go under drives. The rods can go approx 20ft with good accuracy. They were developed for telecommunication companies so they can feed fibre or copper cables under people’s driveways.
I know they exist and seen videos of their use, but can’t find them on line at present. As said above, with power cables you do need to go the correct depth and use the appropriate armour cable else you are putting people at risk. |
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29th Jul 2023 12:58pm |
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| Mr Fox Member Since: 10 Sep 2011 Location: green & pleasant land Posts: 1037 
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Ian, I've seen these videos too but am struggling to find the auger extensions - although I've only done a quick search and not gone in depth. |
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29th Jul 2023 2:28pm |
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| AmL Member Since: 22 Jan 2016 Location: Devon Posts: 30 
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I agree, it's not good advice but it's not my place to give advice, I'm mealy providing an option that answers the question - how can I get a cable across without digging a trench. The mole doesn't answer the question because you need to dig a pit at each end of the bore, and in this case, one of those will be in the middle of the drive, next to the box he wants to get to. A digger and whacker plate will definitely do the job but it'll leave a big scar across the drive, which he's trying to avoid. Remember, most electric cables, gas and water pipes in a house will be less than 1" from the wall surface, they're at much greater risk than an SWA cable 8"-12" below a driveway. If you want advice, go to an experienced electrician but he'll likely only tell you what the code says. |
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29th Jul 2023 3:52pm |
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| Rashers Member Since: 21 Jun 2015 Location: Norfolk Posts: 3497 
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Believe it, or believe it not, there is actually no minimum depth for an electrical cable buried underground.There are loads of anomalies like this in the IET Wiring Regulations where you think there should be a fixed value, but it is left to the discretion of the installer to install the cable so it will not be damaged and cause harm to persons.
There are the NJUG regulations (National Joint Utilities Group) who publish guidelines. In roads and paths, utilities should be at designated depths. Well that's the idea. The reality is a lot different. By using steel wire armoured cable, there is a certain amount of mitigation. If a shovel goes through the cable, if installed correctly, the armouring should be connected to earth and if the circuit is designed correctly, it should cause the automatic and safe disconnection of the supply. SWA cable should be laid in sand or sifted soil (if it is not being placed within a duct or conduit) and in both cases, a warning tape placed half way between the cable and the surface. Now in reality, if you are putting a cable below the ground in your garden, you won't be doing much of the above 
It's worth remembering that if you are supplying a building outside (in the electrical industry this is known as being outside the equipotential zone) in your garden, and your house has a TN-C-S or PME supply (this is the most common type of electricity supply in this country), you should be isolating the buildings earth before it enters your outside building, providing an earth electrode as an earth reference and a 30mA double pole RCD at the incomer, or you need to extend the equipotential bonded zone by installing a bonding conductor of equal size to that in your house (normally 16mm2 Copper) to your new building from your main earth terminal. Yes, even a shed! Now I realise that everyone is now going to say 'I didn't do that and my shed works just fine'. Yes I agree, I'm just advising what you should be doing  Don't shoot the messenger.
The one thing you must do is make sure the supply is protected by a 30mA RCD (trip switch) if the cabe is going underground and you are supplying a building outside. As for getting under the ground, there are so many variables, but all of the above seem plausible. It just depends on what access you have if you are thinking of pushing a pipe under. Wouldn't it just fill up with muck and become difficult to clear out? You could do what Virgin Media seem to do with their fibre optic cables. Scrape about two inches of soil in your flower bed and cover the cable up. Then get really upset when the customer sticks a spade through their cable. Seen it done dozens of times  |
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29th Jul 2023 7:11pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17371 
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As I said in my post above, if using the pipe technique you need to close the leading end of the pipe while driving it through to stop the pipe filling with crud.
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29th Jul 2023 9:47pm |
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| alwoodley72 Member Since: 14 Mar 2010 Location: salisbury, wilts Posts: 724  
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^^as Rashers says!… I’ve rotavated virgin cable laid under new turf, think you’ve got a long snake at your heels!.. we’ve encountered gas pipes moled in 100 mm from the surface, water pipes that snake around properties rather than running straight to the house, I wouldn’t be worrying about an armoured cable properly connected, running in a straight line..
I’d hire one on the larger bladed stone saws, cut a 100 mm wide trench in the tarmac,clear a trench, lay cable , sand, tape, stone and then some bags of patchmac to finish the job. Leave the tape just under the surface at the far end so that anyone with any nouse will see what’s there in the future. Job done Cheers Alex 98 300 tdi 90 project 94 Range Rover vogue 4.2 lse 79 911 sc 08 130 double cab utility |
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31st Jul 2023 5:21pm |
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