Running a Permanent Extension Lead to the Shed in the Garden


Postby MarkA67 » Thu Oct 05, 2017 9:56 am

New here so hope I'm posting in the right place. I'm looking to run a permanent extension lead from the house to the shed which is about 15-20 meters away up the garden. There's a border around the lawn and I was planning to dig a very shallow trench in the soil (an inch or 2 maybe) run the cable through the trench and then bury it back under. Would a normal heavy duty lead work for this? A lot of people seem to say that only "burial cable" should be used as its more resistant to rats, mice etc. However, if things eating the cable was not a problem and I wouldn't run it over with the lawn mower, should it all work OK?

I'm not running any high power items, just a 400w freezer so I can buy frozen food in bulk.
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Postby ericmark » Thu Oct 05, 2017 5:26 pm

Although on a caravan site flex is used every few weeks one wraps it up and moves to another site and in doing so you are inspecting the cable for any problems like the plastic cracking, in your garden on the surface this would not be good as not inspected, you could run it in some conduit under ground with suitable warning tape above, but really simpler to use steel wire armoured cable (SWA) to start with.

You really need a metal box, I used a standard socket back box and a fused connection unit so I had a hole for flex to come in with a grip for flex so in my garage there is a short length of cable with a plug on going into a FCU and then from that it is SWA cable.

You also have to consider size, my chest freezer uses 67W running which is very little but the energy meter when plugged in shows a maximum of 1.5 kW as it starts, and we have to work on that start figure when working out volt drop so calculate at 2 kW to be on safe side, near every freezer says don't use with an extension lead because of the volt drop.

So 20 meters plus volt drop already at socket with 1.5 mm cable likely OK but nothing under 1.5 mm sq cable should be used.
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Postby Mr White » Thu Oct 05, 2017 10:03 pm

The "problem" with your idea is that today, you know where the lead is, next month when you are digging the flowerbeds................
Or worse still some one else is digging the flower beds..........

There is only one way to do the job and that is properly. As has been said you have to use Steel Wire Armoured cable, which can not only withstand a sharp spade, it can withstand the elements and most other "nasty things"

If you are in the UK it comes under building regulation "part P" which in short means you cant do the job on your own. Its not as daft as it sounds because its meant to insure the job is done safely not like some one running an unsuitable extension lead out side and leaving it there......
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Postby LawnMower » Fri Oct 06, 2017 11:49 pm

Yep, steel armoured cable, pref 2.5mm.

Don't forget an RCD (30ma) or an rcbo rated at 16 amps! Ask a qualified electrician to fit one of these if you're not sure how to fit this.

Basically the steel armoured cable will offer better protection against electric shocks being that it is running outside.
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