1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Garage/Shed Consumer Unit RCD tripping continuously

Discussion in 'Electrics UK' started by Spuggy54, 26 Sep 2016.

  1. Spuggy54

    Spuggy54

    Joined:
    26 Sep 2016
    Messages:
    8
    Thanks Received:
    0
    Location:
    Tamworth
    Country:
    United Kingdom
    Hi,
    I'm new to the site and hopefully someone will be able to help. I've recently purchased a property and wanted to sort out the garden electrics. I was a qualified electrician before I retired. There was already SWA cable installed around the garden supporting lights and sockets for two sheds, two pond pumps and two UV filters. The feed was taken directly from a 13A spur from the dwelling ring final circuit. All lights, sockets, pumps, UV filter and any attached devices were working fine.

    I decided to install a small garage consumer unit in my shed to run the aforementioned services. I bought the CU from screwfix. The RCD is rated a 40A 30ma and has two MCB's - 6A and 32A.

    I've reconnected the existing SWA cable feeds to the CU. The feed to the CU is still from the switched 13A spur from the dwelling ring final circuit.

    As soon as I switch on the MCB for each circuit, for either the lights or sockets, it trips out the RCD. The RCD doesn't trip until I switch on the MCB's. One device does work without tripping the RCD which is an aerator pump used in the pond. I've connected the pumps directly to the dwelling's ring final circuit and they don't trip the dwelling RCD. I've checked the L-E, N-E and L-N impedance, using a multimeter, and they are over 500Mohms. I haven't used a megger yet to test the resistances as I don't have one now.

    Hope I've made sense but any advice would be greatly appreciated.

    Regards,

    Chris
     
  2. Sponsored Links
  3. Iggifer

    Iggifer

    Joined:
    8 Sep 2011
    Messages:
    4,637
    Thanks Received:
    586
    Location:
    Warwickshire
    Country:
    United Kingdom
    Do they take out the RCD in the house when they take out the outside RCD?

    Can you not energise the MCBs with nothing plugged in? Or it trips when the loads other than the aerator pump are plugged in? If it's the latter, is your polarity at the spur the same as the CU? Some of people use grey for cpc, lots of people use black.
     
    • Thanks Thanks x 1
  4. motorbiking

    motorbiking

    Joined:
    31 May 2016
    Messages:
    5,847
    Thanks Received:
    665
    Country:
    United Kingdom
    Are you able to swap the mcb/rcds over with some from your main consumer unit - incase its faulty.
     
    • Thanks Thanks x 1
  5. Spuggy54

    Spuggy54

    Joined:
    26 Sep 2016
    Messages:
    8
    Thanks Received:
    0
    Location:
    Tamworth
    Country:
    United Kingdom
    Thanks for the quick responses.
    Iggifer - yep, I can energise the MCB's with nothing connected or switched on. It trips as soon as I switch anything on lights, pumps etc. - other than the aerator pump.
    Motorbiking - I could try this. Actually I still have the original RCD that the previous owner used which I could rig up.

    Something I haven't yet tried which I should do is to connect the lawnmower or similar and see what effect that has.

    I'll get back to you tomorrow hopefully.

    Thanks again.
     
  6. Iggifer

    Iggifer

    Joined:
    8 Sep 2011
    Messages:
    4,637
    Thanks Received:
    586
    Location:
    Warwickshire
    Country:
    United Kingdom
    Sounds like you have a polarity issue to me, maybe the aerator pump does not pull enough load to trip the rcd.

    On a new site recently had a socket circuit that would run a battery charger, but plug in a hoover and it would take out two RCBOs - one or both (can't remember now) neutrals were in the wrong RCBO, but it would run a Makita charger without tripping
     
    • Thanks Thanks x 1
  7. Spuggy54

    Spuggy54

    Joined:
    26 Sep 2016
    Messages:
    8
    Thanks Received:
    0
    Location:
    Tamworth
    Country:
    United Kingdom
    Thanks Iggifer. I'll check it out and let you know.
     
  8. deadshort

    deadshort

    Joined:
    20 Sep 2014
    Messages:
    2,086
    Thanks Received:
    211
    Location:
    uk
    Country:
    United Kingdom
    I would connect a temp lamp across the rcd to see if it trips. I would suspect water in the external wiring. Did the original rcd trip when tested ?

    Welcome, by the way.

    DS
     
    • Thanks Thanks x 1
  9. Spuggy54

    Spuggy54

    Joined:
    26 Sep 2016
    Messages:
    8
    Thanks Received:
    0
    Location:
    Tamworth
    Country:
    United Kingdom
    Cheers. No it didn't trip which is why it is so frustrating as I was trying to improve things. Blinking annoying as nothing is now working except for the aerator pump. I'll give your idea ago but there is an internal light in the same shed as the CU which also trips the RCD.
     
  10. Sponsored Links
  11. deadshort

    deadshort

    Joined:
    20 Sep 2014
    Messages:
    2,086
    Thanks Received:
    211
    Location:
    uk
    Country:
    United Kingdom
    Thanks. I would disconnect all the wiring and test with my test lamp only in circuit. If the original RCD wasn't working you may have had a fault already on the circuit. Have you checked the earthing from the dwelling to the shed ? if the main RCD is not operating, that's odd?

    Regards,

    DS
     
    • Thanks Thanks x 1
  12. Spuggy54

    Spuggy54

    Joined:
    26 Sep 2016
    Messages:
    8
    Thanks Received:
    0
    Location:
    Tamworth
    Country:
    United Kingdom
    The original RCD was working fine. It was situated in the conservatory of the dwelling, fed from a switched 13A spur off the ring final circuit of the dwelling. There was a metal junction box that supported the SWA cable which was the mains feed to the sheds and garden services. All I've done is remove the old RCD and metal junction box, installed a new IP65 junction box in the conservatory which supports the SWA cable feeding the mains to the shed CU via the original switched spur. I haven't changed any of the original load cabling. Just connected to it straight to the new MCBs (lights and sockets) in the CU.

    I've physically checked the earth connections and also with a multi-meter, but I will need to get a megger to check it properly I think. As mentioned, as the devices work when connected to the house ring without tripping the dwelling's RCD, I'm assuming that they they are ok and that it must be a water ingress or earthing type problem in the outside cabling. It's just a bit weird that with a heavy load (lawnmower, pond pumps and filter etc.) the old RCD didn't trip at all. One of the other responses suggested a polarity problem which I will check as well.

    I will use your idea of a test lamp to check out the cabling tomorrow.

    Thanks for your help.

    Cheers.
     
  13. Taylortwocities

    Taylortwocities

    Joined:
    28 Jul 2006
    Messages:
    19,608
    Thanks Received:
    1,992
    Location:
    Oxfordshire
    Country:
    United Kingdom
    Lets see a photo of the wiring inside the shed CU. Maybe there's something that an eagle-eyed person can spot.
     
  14. Spuggy54

    Spuggy54

    Joined:
    26 Sep 2016
    Messages:
    8
    Thanks Received:
    0
    Location:
    Tamworth
    Country:
    United Kingdom
    Thanks for the response. Will get one tomorrow.

    Cheers.
     
  15. securespark

    securespark

    Joined:
    11 Jan 2004
    Messages:
    35,199
    Thanks Received:
    1,129
    Country:
    United Kingdom
    Forgive me, but what's the point of a 6 and 32A breaker on a 13A supply?

    The house RCD may not be tripping because it is faulty.
     
  16. Spuggy54

    Spuggy54

    Joined:
    26 Sep 2016
    Messages:
    8
    Thanks Received:
    0
    Location:
    Tamworth
    Country:
    United Kingdom
    It's a brand new CU in the house but I can check it. The mains feed to the shed is a spur off the dwellings's ring final circuit which the ex-owner installed and as I didn't want to have to install a new armoured cable, decided to use it. Is there a problem spurring off the ring these days?
     
  17. DaveHerns

    DaveHerns

    Joined:
    11 Nov 2009
    Messages:
    2,583
    Thanks Received:
    207
    Country:
    United Kingdom
    Why are you using a 32 amp breaker? What size SWA have you got?
     
Loading...

Share This Page