armoured cable depth

31 May 2016
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United Kingdom
I'm digging a trench for an armoured cable to run power to my man cave / garden room.

how deep do I go? and is it ok to run it diagonal across the garden?

I'm getting an electrician to do the final connection and certification. but want to make sure I do the rest right.
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Has the electrician told you what size cable to get before you bury it?
2.5mm armoured. but I have lots. was going to dig 400mm down and put warning tape at 250mm
What is the armoured cable length? And the design current?
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but I have lots.

Having "lots" will not increase the safe current carrying capacity of the bit that you use.

Depending on the length of the cable and the amount of power you want to use in the man cave 2.5mm² may be too small.

Ask the electrician what size cable is needed. will give you an idea of what he should be recommending.

While you have the trench open lay in a duct for ELV cables ( data, phones, alarm, door bell etc etc )
The man cave has :
1 strip light in the shed bit
1 3 x LED light.
1 3 X LED outside lights

5 double sockets 2 with USB powering a tv and a play station. On an internal ring, with the lights on a 5A FCU. Currently the whole thing is on a temporary extension lead cable with a plug on the end and a 13A fuse which has never tripped. I'm tempted to put another RCD at the man cave end. Is there a benefit of having a local RCD?

Armoured cable will be 5-6M and the waterproof junction box installed by the sparkies is on a 2.5mm Spur (so 20A) So, I'd say 20A design - fused at 13A will be plenty.

According to the calculator - I'm good for up to 4Kw & 8M?

Any links to to the type of duct suggested? - drain pipe?
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I'm surprised a sparkie is putting that lot on a spur rather than taking it back to the consumer unit.
Personally I would go for at least 6mm², then you have future proof if you want to put a heater/kettle/tumble dryer etc in there later on.
Run a duct in then you can pull in what the elecrician determines.
Twinwall ducting is what you need, like this

Depth depends on what is above it. As a general guide

Screenshot 2016-08-05 09.13.35.png
I'm surprised a sparkie is putting that lot on a spur rather than taking it back to the consumer unit.
Indeed... These are the same sparkies who replaced an FCU with a standard light switch (my other thread), creating a 30A lighting circuit running on 1.5mm cables.

I also have an outside pair of sockets on the ring (also installed by the sparkies) - would I be better extending that ring to a pair of armored 2.5mm cables - i.e. a ring.

I have enough cable to do two runs.. but to be fair even with a fan heater, tv and PS4 on - the 13A fuse has never blown. I'm also not 100% sure the single 2.5mm cable doesn't run directly back to the consumer unit. I didn't see it go in.. I will check, as there are some direct single lines - they said its a "20A supply"

@Taylortwocities Do I have to do anything to stop rain water running in to the ducts?
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Armoured cable is designed for outdoor environments, including bring totally immersed. You don't need to worry about water!
The best way to run this sort of feed (IMO) is to have a separate switch fuse from the supply head with the SWA terminated there. At the distant end that is where an RCD (may be more than one, may be RCBOs) are located. This limits circuit-specific faults to the remote loacation (aka man cave). Even a digger run through the SWA would only blow the switch fuse for the cable itself.
This means that the main house is independent of happenings in your personal place.
many thanks for your help.. btw on the tumble dryer idea.. did you miss the bit where I said this was a man cave :D tumble dryer ffs ;)
OK Sauna, hot tub, sunbed, running machine.....Requirements change. My study became a nursery and is now a double bedroom. My attached garage is now split into a music room, utility and a WC......

It's a lot cheaper to create a margin for changes in requirements at the start, rather than have to re-engineer it all in 5 years time.

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