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Discuss Power to an Outside Office - Spur from Ring Final? in the Electrical Wiring, Theories and Regulations area at ElectrciansForums.co.uk.

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  1. Marcus Vaughan
    Offline

    Marcus Vaughan Regular EF Member

    Location:
    Sheffield
    Hi All,

    Just looking for some reassurance on a job I've looked at today. My status is that I am trying to stay within the realms of 'Minor Works' until I get a bit of experience under my belt. Conscientious decision - but everywhere I go it seems that notifiable work is needed as well. Anyway......

    So - a customer has asked me to supply power to an outside office that's about to be built (when it stops raining), and has asked if I can take the supply from a nearby external supply he has spotted (actually supplies a pond). I've done my homework, read around the subject.

    TNCS
    Pond Supply = 2.5mm but spurred from B32 Ring Final.
    Tested (live) Zs near the pond at 1.28 ohms so already a bit naughty.
    Ring Final IS RCD protected.
    The outbuilding has no extraneous conductive parts.
    Not sure on the demand for the office but its pretty small, it has its own 'garage unit' (apparently) so suspect a B16 for sockets and B6 for lights.
    New building is a gnats whisker from the man house and ring final.

    It needs a new circuit - doesn't it?

    I'm clutching at straws because the consumer unit is a long way from the new building, and running a new circuit will be a fair amount of work for a few sockets and a light.

    I'm toying with taking another fused spur from the same ring (if Zs is low enough), through the walls and into the new building.

    What then though - I understand you need a double pole isolator in the new office - but do I ignore the 'garage' consumer unit or use it? Maybe run a 4mm from the house ring final spur to the garage unit? Not ideal, but if Zs (or Zdb) in limits at the garage unit.....

    I'll be interested to hear your thoughts and opinions.....
     
  2. Spoon
    Offline

    Spoon Trusted Advisor

    Location:
    Lancashire
    Is this "Office" just for the person of the house? e.g. it's only going to have 1 or 2 PC's in it and maybe a heater, maybe TV?
     
  3. Marcus Vaughan
    Offline

    Marcus Vaughan Regular EF Member

    Location:
    Sheffield
    Yes. I’d say so. Biggest demand likely to be the heater.

    Can’t see the 13 amp fuse blowing in the spur...
     
  4. Spoon
    Offline

    Spoon Trusted Advisor

    Location:
    Lancashire
    If you are going down this route then just make sure you state the max 13A supply in your quote and explain this to the customer.
    Got to C.Y.A. if the customer decides to put 3 heater into the place then whinges..
    Are the cable calcs ok for Zs and other rubbish?
     
  5. Marcus Vaughan
    Offline

    Marcus Vaughan Regular EF Member

    Location:
    Sheffield
    It's the cable calculations I'm looking at now. It's a bit close to the mark with the B32. It's probably best if I do dead tests instead of live Zs Tests through the main board RCD...

    I like the idea of stating the max 13 amp. on the quote though. Makes sense.
     
  6. Murdoch
    Offline

    Murdoch Electrician's Arms

    Location:
    Woking
    In such cases you should ALWAYS state the design load on your estimate or quote - CYA applies!:)
     
    • Like Like x 1
  7. Taylortwocities
    Offline

    Taylortwocities Electrician's Arms

    Location:
    Oxfordshire
    If you are running the supply from a 13A FCU, then what is the point of this second CU?

    You won’t get any discrimination, and the source ring final is already RCD protected, so you don’t need another one!

    This needs a separate circuit. Sorry if this is outside your experience/ability.
    Park it and walk away.
     
    • Agree Agree x 1
  8. Marcus Vaughan
    Offline

    Marcus Vaughan Regular EF Member

    Location:
    Sheffield
    Yeah. I might give the customer a choice.
    60 metres of SWA and labour (and an RCBO)
    Or 4metres of Twin and Earth.
    I wonder what they'll go for?
     
  9. 123
    Offline

    123 Electrician's Arms

    I'd say there is every chance of the fuse blowing. Heater/PC/Printer/TV/Fridge/Vacuum Cleaner etc etc.

    Also I find modern Fused Spurs (of pretty much any brand) are pretty garbage if anything like 2-3kW is the load for long periods of time
     
  10. Murdoch
    Offline

    Murdoch Electrician's Arms

    Location:
    Woking
    Hold on ................ 60m of SWA or 4m of T&E ................ can you explain

    And I would NOT be recommending anybody that they try and run a garden office off a 13A spur......................
     
  11. Marcus Vaughan
    Offline

    Marcus Vaughan Regular EF Member

    Location:
    Sheffield
    Thanks. I know I wouldn't get discrimination.....
    I was thinking the Zs might creep up too high for ADS if I didn't use the garage unit....but then again it's not really a sub main, it's a spur from a ring final. It all sounds like a bit of a hash up..

    Your honest reply is appreciated!
     
  12. 123
    Offline

    123 Electrician's Arms

    Zs shouldn't be an issue as that part of the circuit will be protected by a BS1362 13A fuse.
     
  13. Marcus Vaughan
    Offline

    Marcus Vaughan Regular EF Member

    Location:
    Sheffield
    New circuit from the consumer unit on one side of the property to the other- probably around the outside (there is no easy route). Or 4m from the ring final through a wall...

    I might have exaggerated with the 60m.....not really looked at the new circuit options properly yet. Cc
     
    • Like Like x 1
  14. Murdoch
    Offline

    Murdoch Electrician's Arms

    Location:
    Woking
    If they can afford a new garden office then they should really put in a proper dedicated supply .........................
     
    • Agree Agree x 3
  15. Marcus Vaughan
    Offline

    Marcus Vaughan Regular EF Member

    Location:
    Sheffield
    Good point!
     
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