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Radio interference of RCD's?

alanblaby
I've got an ongoing problem with a randomly tripping RCD.

It started 3 months ago, lost power in the middle of the night. 3 circuits (sockets/cooker/shower) fed by the one RCD.

Initial thoughts were to faulty appliances. But, the trip has been random, apart from it is usually late at night/early morning.

The trip is usually sometime between midnight and 2am. It cannot be pinned down any closer as the flatowner is in bed!

Once reset, it stays on for a week or more.

So far: All fixed wiring has been tested, and all OK. RCD (old Crabtree, plug in type, 15-20yo) has been changed and

ramp/time tested, 27mA ramp, 18/43 time. Earth leakage with my basic meter gave a 6mA reading.

It went again last night after a month of non-tripping.

I think I've covered all bases, and will now be changing the CU for a metal clad all rcbo board.


So, what do you reckon? I'm stumped now, and thoughts have turned to radio interference causing the RCD to trip. 

It's a long shot, but I cant think of anything else that may cause it.

Any thoughts?
  • 0
    ok. Starter for ten, is there an off peak board?
  • 0
    Or even if it is not, switching of other loads on the same substation causing neutral earth bounce.

    Problem is I suspect when ever you go to measure it the E-N voltage will be respectable.

    Such things have occasionally been harbingers of doom substation faults in the past.


    Unless something has changed radio wise recently, and you do not mention that, I'd put early hours RFI behind a neutral fault, either in the building or outside in the pecking order.
  • 0
    What happened to the TVs and GLS lamps exploding at 'random' times in the day?. Most seemed to happen somewhere around worcestershire and herefordshire.

    or a belligerent teenager with a natural propensity for dabbling with higher frequencies?


    look.... conspiracies exist...so why keep them in the theory box? you just end up wondering whether they continue to be alive or dead.....


    Legh
  • 0

    The trip is usually sometime between midnight and 2am.



    Done any insulation tests?  I've seen faults at times like that (actually it was on a network cable and regularly at about 5am, but same principle) - turned out it was a faulty connector that was responding the the building cooling down after the heating shut off at 18:00 - the timing was surprisingly regular despite the variations in the weather.


    So my first suspicion would be a damaged cable or damp accessory that's within a hair's breadth of shorting to earth, and all it needs is a bit of cooling to contract a bit of metal somewhere, or a slight bit of extra condensation, or even being walked over by a small rodent to tip things over the edge.


    Likewise, look for anything that might turn on automatically at such times - e.g. a frost 'stat set a bit too high.


      - Andy.
  • 0
    I had "nuisance tripping" with a Crabtree Starbreaker  plug in type R.C.D. in a small house once. It sometimes tripped OFF when the cooker oven was turned OFF. I witnessed this myself. Initially I took the cooker off the R.C.D. protected side of the consumer unit. R.C.D. tripping issue then stopped. I found no low insulation resistance readings on the cooker or wiring. I later renewed the R.C.D. I concluded that the inductance of the fan motor was causing a high Voltage spike at turn off, that the R.C.D. didn't like, and that spike caused it to trip off. Perhaps the R.C.D. was on a knife edge anyway. I don't think that I returned the cooker circuit to the R.C.D. protected side of the consumer unit after several visits. Enough was enough.


    Z.

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