external power to shed query

Discussion in 'Electricians' Talk' started by Robert logan, May 20, 2023.

  1. Robert logan

    Robert logan New Member

    Hi guys .
    New here. I want to run some cable to an outside new build shed. Ideally to run a box freezer (permanently on ) and a tumble if and when needed. Cable i have been told is this
    6mm² 3 Core PVC SWA XLPE Armoured Cable
    It can go under or overground ideally over clipped to top of fence (if allowed) the run us pretty much 6 to 8 metres In length. What other items would be needed either end then please? An rcd box inside shed ? And connection to the main fuse board by an electrician. If anyone can post any links to items I'd very much appreciate it. Is there any way you can run a cable from a plug socket in house directly to the shed ( I know you can't put the swa into a plug from what ive read)
    Thank you in advance for any help
  2. Ind spark

    Ind spark Screwfix Select

    Theres a bit more to think about than just running an armoured cable to the shed.
    Glands need to be fitted correctly
    Earthing system needs to be known
    Extraneous parts need to be assessed if there is any.

    Yes you can spur from a socket in the house.

    Best bet is get a sparky In and let him/her do the complete job,not your problem that way.
    arrow likes this.
  3. Robert logan

    Robert logan New Member

    Cheers for reply. I figured there is much more to it. Just thinking if I run the cable from the board and to the shed long enough for electrician to do his bits either end it would save some money on total price.
  4. Ind spark

    Ind spark Screwfix Select

    Yes you could but agree it with them first, last thing you want is for him to say that's the wrong cable.
  5. arrow

    arrow Screwfix Select

    Let the Electrician do the whole job. You could cleat the cable to a standard you think is acceptable and might not be to the Electrician. For him to put his name on it he would then need to redo it costing more time and money than the Electrician starting from scratch.
    Ind spark likes this.
  6. MGW

    MGW Screwfix Select

    We have a number of considerations as already stated, this PDF is a little dated, but gives main points and this one points out the problems with some types of supply a metal shed is like a mobile home or caravan, and really should not have a PME or TN-C-S supply, where with wood or plastic it is not such a problem.

    The ring final can be overloaded at the ends, but not at the centre, so it does depend how far from the consumer unit you want the supply to come from, in the main a fused connection unit (FCU) is all that is required, but you want it to auto disconnect within the allowed time, so it does depend how long the run is, a socket tester with loop upload_2023-5-21_10-31-6.png should highlight most faults, but they cost around £50, and so very quickly you end out paying more to DIY than to get an electrician, plus where I live in Wales job is notifiable so that's another £100 plus vat.

    As to RCD protection, likely you already have it in the house, no point feeding a RCD from a RCD if both 30 mA. The main consideration with a freezer is volt drop, if a refrigeration motor does not reach speed fast enough the pressure builds up and it stalls the motor, the built in overload will auto disconnect, and it will retry as it auto resets, this can happen if you loose the supply and it is returned very fast, as pressure has not had enough time to drop. But if the overload repeatedly trips, the overload will burn out, start up amps can be around 10 amp, so we measure the loop impedance or prospective short circuit current and calculate the volt drop which for sockets should not exceed 5% and lights 3%, fluorescent lights are also affected by volt drop and can also fail to start.

    New inverter drive freezers do not have the problem, and fluorescent lights with electronic ballasts do not have the problem, but not seen chest freezers with inverter drives, most freezers, or any other refrigeration plant will warn "Do not use extension leads" this is why, the volt drop can be a problem.

    The DIY problem is the cost of test gear, it may well be you can do exactly the same job as an electrician, but you can't test before you install, so you just cross your fingers it will be OK, but the electrician can test in seconds.
  7. The Happy Builder

    The Happy Builder Screwfix Select

    If you have an RCD in the shed protecting the freezer, how will you know if the RCD has tripped and a freezer full of food is thawing out?
  8. robertpstubbs

    robertpstubbs Screwfix Select

    If attaching cable to a fence check the type and condition/age of the fence. Fences do have a tendency to deteriorate and get blown down.
  9. Robert logan

    Robert logan New Member

    Fence is all new but thank you for reply
  10. bright_Spark

    bright_Spark Screwfix Select

    Personally I wouldn’t want to clip an armoured to the top of a fence. It would be better literally laid at the base of the fence in the flower bed.
  11. Robert logan

    Robert logan New Member

    I've no idea someone just mentioned you need an rcd separate in the shed. I'm good with tools etc and plumbing and gas etc as used to be a gas engineer but electrics isn't my strong point. I'm happy to drill. Holes and run cables etc and even make some connections if not massively complicated but I'm.not touching main fuse board etc . This is why I'm looking for advice on what mainly I could do. Thanks for reply
  12. Robert logan

    Robert logan New Member

    Yeah I considered that would be lot easier for me too. Thank you

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