Electrical Question

Installing power cable from consumer unit to workshop - type and size of swa needed?

The job: I will be posting a job soon for someone to install a power cable from my consumer unit to my new workshop - for average DIY mains use and general lighting - much less than 16A.

The problem: The run from the house wall to the workshop is 30m. Due to the lack of time and somewhat reduced finances, I wanted to do the trench digging and burying of SWA cables (the others are CAT5e) myself, so my chosen tradesman can just wire up each end.

The question: Can one of you experienced electricians tell me what size and type of SWA I need? Obviously I need 2 cores for L&N, but the selection of SWA available doesn't seem to include an earth core - so how does that element work? Is it recommended that I dig the trench, then get a tradesman to do the wiring (including dumping the cable in the hole) and then fill it in and landscape it later? Or can someone definitively tell me what cable I can use?!

Many thanks for any advice.

Thanks REEL Electricians - it's a shame you're hundreds of miles away! I was looking at 6.0mm 3 core, so that should be future proof enough.

1 Answer

Best Answer

For the cable you can purchase 3 core swa which has an earth as well as 2 line conductors. You still need to earth the sheath when terminating.
2.5mm swa 3 core is the minimum size cable you can bury direct in the ground and carries 28 Amps at its max.
4.0mm swa 3 core carries 36 Amps max.
30 metres will not not affect the volt drop as you allowed 5% of 230 volts which is 11.5volts.
Both cables above would, roughly depending on ambient temperature, have a volt drop between 500mv to 600millivolts on 30 metres so will not affect cable in a big way.
Bury cable below 500mm and cover with yellow hazard warning tape.
If you select 4mm you have options in the future to add onto your electrical installation without re digging hole out to replace cable.
Also you could run sockets and lights via a simple garage board terminated at the end of the swa.
Please note all outdoor circuits in domestic properties must be protected by an RCD and tested regularly.
Hope this helps

Answered 4th Sep 2013

REEL Electricians

Member since 2 Sep 2013

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