Power to the man cave.....

Discussion in 'Electricians' Talk' started by slt1976, Jun 30, 2020.

  1. slt1976

    slt1976 New Member

    Morning all. I'm after some advice regarding running power out to a new man cave that is soon due to land.

    The run from my existing CU/incoming mains to the new CU that will go in the cabin is 20 meters. I intend to run a small ring (1 x 32A), lighting (1 x 6A) and provision for a hot tub that will be external to the cabin (so 1 x 32A to feed a rotary isolator). So max current pull is 70A

    As a bit of background. My dad is a retired sparky. Spent his life in a prison doing electrics. On the right side of the bars I hasten to add. The bottom line is everything he does has to be 110% safe. By his own admission he is out of touch with what 18th edition may mean and wanted me to try to get confirmation before we go and buy anything.

    He has suggested splitting the incoming tails into a Henley block and running a 2 way board with an RCD in it at the head end (simply because they are much cheaper than a fused switch). This connection will obviously be done by an electrician. I would then feed out to the shed (see question below on cable), all of which is above ground clipped to a fence. This will run into a 4 way board in the cabin with RCBO's.

    My questions....

    1 - Is the head end connection OK? I am assuming it will need to run into a compliant small metal CU.

    2 - I've used an online calculator (Doncaster cables site) and it is confirming 16mm SWA. It also shows 10mm Tuff Sheath as an option. Would this be OK? I planned to use 3 core with one core exporting the earth (TNCS earth on incoming). I used 5% for the volt drop calc.

    3 - Is exporting the earth OK? My dad seemed to think a 20M run on 10mm or 16mm would be OK but was not sure on the regs with one of the RCBO's being for a hot tub. Or do I now end to rod it at the cabin and provision the earth here?

    4 - Probably the most contentious one. As my old man is more than competent I was intending to get him to do most of it with the exception of the connection of the tails in to the new switch. If everything is left exposed/open for inspection and test would most sparkies be happy to certify it when they do the connection?

    Many thanks in advance for any help or advice and apologies for a very long winded post. I just wanted to put as much info in as possible.
  2. Comlec

    Comlec Screwfix Select

    Good luck with finding a registered CPS electrician to sign off your work.
  3. slt1976

    slt1976 New Member

    Ok. My aim here was to seeek advice so that by design it is compliant. Not yet connected and open to inspection by a registered CPS electrician. As opposed to a DIY lash that just gets thrown in regardless.

    Thanks for your help....
  4. Bazza

    Bazza Screwfix Select

    There are several design issues from your first post that shout “red flag”.
    Contributors don’t design this sort of thing on line for you. That is the job for the electrician who will need to NOTIFY and CERTIFY the work. The certificate Basically says I certify that the work that I have DESIGNED, INSTALLED &TESTED complies with BS7671.

    So, find your electrician now. Have him tell you what is needed, and what you can do. (Most electricians don’t like digging trenches!)..

    He/she can then complete and do the required paperwork.

  5. Bob Rathbone

    Bob Rathbone Screwfix Select

    Use a 2 core cable and do not export the earth, earth the SWA at the new metal CCU in the house, fit an all insulated CCU in the shed (controversial) it's not in the house, non conducting is better as shock risk is higher and also damp with corrosion. Back to the cable, do not terminate the swa at the shed end, use a grip gland for mechanical security, fit a 30mA RCD and an earth electrode to get a clean earth for the hot tub. Take a look at some recent hot tub issues on here regarding electric shocks from the water and you, and your dad will understand why I suggest a TT system. Yes it is notifiable work :) certificates will be required.
  6. Coloumb

    Coloumb Screwfix Select

    If the earth type is TNS or PME it's better to export the earth as it will help with a compliant Zs thus touch voltage won't get higher than 50v. The RCD will then provide additional protection rather than the only protection.
  7. Comlec

    Comlec Screwfix Select

    You should seek advice from a local electrician. Someone who can visit and assess the existing installation and provide a design for the proposed addition. To help with the design process you should have the manufacturers' instructions for the equipment you are going to install.

    If you live in England or Wales then this will be notifiable work under Part B of the building regulations. You will have three options
    1. Do the work yourself. You must notify the LABC before starting any work and pay their fees.
    2. Engage the services of an Electrician who can self-certify such work
    3. Engage the services of a Third Party Certifier before you begin any work

    Good luck with your project
  8. So that would be Fire Safety then!
  9. slt1976

    slt1976 New Member

    Thank you everyone for your comments and suggestions. Totally understand that it's notifiable under part P. As I suspected the Earth is the item that's the most contentious. I do plan to get a local electrician in prior to doing anything and appreciate all the help and advice on here.
    Bazza likes this.
  10. Comlec

    Comlec Screwfix Select

    Maybe instead of being a smart a$$e you could just have pointed out the typo and corrected it.

    If you live in England or Wales then this will be notifiable work under Part P of the building regulations.
  11. Bob Rathbone

    Bob Rathbone Screwfix Select

    Thanks for the input Coulomb, I do understand the the issue of exporting the CPC to zones outside that protected by the equipotential bonding is a contentious issue. Only if you provide local equipotential bonding will the touch voltage be controlled, without bonding, the touch voltage will be the difference between the CPC potential and the real earth that the user stands on. Under fault conditions this may exceed 50V for longer than 0.3 seconds Take a look at the requirements for swimming pools, a spa is no different. Even at 50 volts, a person who is wet and in good contact will receive a shock, that while it may not kill, could be a cause of distress.
  12. Maybe or most definately I would not have mentioned it if you had not been such a smart A on another thread and answered my question as to how my advice was wrong not to solder wire going into plug tops regs or not.
    Comlec said:
    True but the OP is wiring up an extension lead

    He is putting on loads of plugs and wanted to tin the ends, my advice was the same as seneca which was not to tin the ends.
    Why would you say seneca's advice to not tin the ends was pertinent and my advice to not tin the ends was not pertinent.
    Could you explain please as we both gave the same advice.

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