Newbie - Garage RCD Query

Discussion in 'Electricians' Talk' started by MetalDude86, May 27, 2024.

  1. MetalDude86

    MetalDude86 New Member

    Hey guys,

    I am learning as I go so please be patient & take that into account.

    I have this RCD unit in my garage. When something in the circuits in the garage isn't right, it trips the main consumer unit in the house as opposed to just tripping the garage.

    From my quick foray into researching, am I to assume that I need to replace my garage circuit breaker(s)?

    If so, how do I determine how much amperage I need or should I just swap like for like?

    TIA

    20240524_183034.jpg 20240524_183024.jpg
     
  2. arrow

    arrow Screwfix Select

    That is not an rcd unit, although rcbo's could replace the breakers.
    If the garage supply had been wired with armour cable there would have been no need to be rcd protected in the house, assuming it is the rcd tripping.
    A photo of house fuse board would help.
     
  3. spinlondon

    spinlondon Screwfix Select

    As the circuit supplying the garage has RCD protection, installing more RCD protection in the garage, will not guarantee that the RCD in the house won’t trip.
    You may even find, that both the RCDs in garage and house will trip at the same time.
     
  4. WH55

    WH55 Screwfix Select

    As others have said, no need to convert this to RCD unless some very unusual circumstances exist. You have RCD protection and that covers you.
     
  5. Refuse to Bend

    Refuse to Bend Active Member

    If the garage supply had been wired with armour cable there would have been no need to be rcd protected in the house, assuming it is the rcd tripping.
    A photo of house fuse board would help.[/QUOTE]
    Assuming ADS is provided without an RCD.
     
  6. MetalDude86

    MetalDude86 New Member

    Please see the two photos below: the main RCD & armoured cable feed to the garage unit

    Cheers 17168062439635573042757049870877.jpg 17168062673056023426558267312488.jpg
     
    Last edited: May 27, 2024
  7. MetalDude86

    MetalDude86 New Member

    What seems to happen is that when a fault occurs in the garage the rccb protecting the garage now trips (in the house)
    I would have thought (bearing in mind I'm a novice) that the garage wylex would trip, not the house. That's why I was thinking that one of the breakers had perhaps failed 17168065481209117882533216950837.jpg
     
  8. MGW

    MGW Screwfix Select

    The consumer units have neutral bars and it depends how many it has to if MCB's and be changed to RCBO's and is really not a DIY job.

    Where I worked we had the main distribution board with a 300 mA RCD, this fed smaller boards with 100 mA RCD's, which fed local boards with 30 mA RCD's which fed a 10 mA RCD MK socket on the bench.

    Pressing the test button on the 10 mA socket would trip the lot.

    Fitting a consumer unit like this upload_2024-5-27_11-52-8.png with all RCBO's will cure the problem, in fact garage supply could be an MCB with RCBO's in the garage, but with a £270 price tag without fitting do you really want to pay out that much?

    The RCD's fitted in your CU are no longer used, and that size limits size of incoming supply fuse, and makes fitting of solar a problem, so it may well be the best option to change consumer unit.
     
  9. Bazza

    Bazza Screwfix Select

    Does the armoured cable go all the way from the house consumer unit to the garage?
     
  10. spinlondon

    spinlondon Screwfix Select

    The device shown in the picture of the house Consumer Unit, is an RCCB (Residual Current Circuit Breaker) more commonly known as an RCD (Residual Current Device).
    The other devices nest to the RCD and also shown in the picture of the Garage unit, are known as MCBs (Miniature Circuit Breakers).
    RCDs are much more sensitive than MCBs, they will operate with fault currents as low as 17 milliamps, whereas the MCBs in the garage will need 30 amps and 160 amps to operate.
    A milliamp, is one thousandth of an amp.
     
  11. spinlondon

    spinlondon Screwfix Select

    Look at the picture on the Garage Unit, looks like 10mm2 T&E.
     
    The Happy Builder likes this.
  12. arrow

    arrow Screwfix Select

    There is no armour, looks like 10mm t&e getting degraded by uv spanning unsupported from house to shed. All in all the wiring in the shed and the supply cable is an absolute lash up.
     
    The Happy Builder likes this.
  13. Coloumb

    Coloumb Screwfix Select

    Also the supply from the house CU is on a 32a breaker and the shed CU also has a 32a breaker so there is no point having it there tbh as they are both of the same rating. You could have achieved the same by not having a shed CU and fitting a FCU fused down for the lights.
     
  14. spinlondon

    spinlondon Screwfix Select

    Good luck terminating 10mm2 in an FCU.
     
    bright_Spark likes this.
  15. MetalDude86

    MetalDude86 New Member

    Just to clarify: I bought the house in this 'state' / 'setup'

    Everything worked as it should but now I get moaned at in the house if something in the garage trips as it knocks the rccb protected circuits in the main CU
     
  16. Refuse to Bend

    Refuse to Bend Active Member

    If you have established the garage is causing the RCD to trip then it is better to resolve this than by spending on RCBOs which is pointless.
     
    MetalDude86 likes this.
  17. spinlondon

    spinlondon Screwfix Select

    It could be possible to adjust the House CU, so that the MCB is not protected by either of the RCDs.
    Then replace the MCBs in the garage unit with RCBOs, or replace what is labelled up as the Main switch for an RCD.
    However, I would expect most electricians to suggest swapping the house Consumer Unit for a new one.
     
  18. Coloumb

    Coloumb Screwfix Select

    Why would you terminate 10mm in fcu?
     
  19. spinlondon

    spinlondon Screwfix Select

    I wouldn’t, but that’s the size of the cable supplying the garage.
     
  20. Refuse to Bend

    Refuse to Bend Active Member

    It would need to be confirmed the RCD is not required for fault and/or additional protection.
     

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