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Up front S type RCD tripping

Grobbyman
Rural setting. Two adjacent houses from the same pole.

The one I've been called to has had intermittent tripping problems on the 100mA S type RCD, it's TT, since just before christmas.

Seems to be no rhyme or reason and consumer unit 30 mA RCD's (two) not affected.

Called in on Friday and tested the upfront and tripping times good, ramp tested at 60mA.

Disconnected the only circuit not covered by the consumer unit RCD'd (garage) and asked them to keep an eye on it.


Called Friday night and told me it's tripping again.


Asked next door, who are in the process of rebuilding, whether anything new about christmas time.


Seems they got a new induction hob with boost facility then.


Turned it on, pressed the boost and low and behold next doors S type tripped.


Seems to do it everytime.


Doesnt affect the premises RCD's (30mA's).


Any explanations?


Had a look at the pole can't see anything amiss.


Regards


George
  • 0
    Grobbyman:

    Rural setting. Two adjacent houses from the same pole.

    The one I've been called to has had intermittent tripping problems on the 100mA S type RCD, it's TT, since just before christmas.

    Seems to be no rhyme or reason and consumer unit 30 mA RCD's (two) not affected.

    Called in on Friday and tested the upfront and tripping times good, ramp tested at 60mA.

    Disconnected the only circuit not covered by the consumer unit RCD'd (garage) and asked them to keep an eye on it.


    Called Friday night and told me it's tripping again.


    Asked next door, who are in the process of rebuilding, whether anything new about christmas time.


    Seems they got a new induction hob with boost facility then.


    Turned it on, pressed the boost and low and behold next doors S type tripped.


    Seems to do it everytime.


    Doesnt affect the premises RCD's (30mA's).


    Any explanations?


    Had a look at the pole can't see anything amiss.


    Regards


    George 


    I had this happen once. I arranged for a P.M.E. earth terminal to be installed and removed the S type up front R.C.D. and replaced it with a D.P switch. The consumer unit has R.C.B.O.s.


    Z.


  • 0
    What is the earth resistance of the earth electrode (s)?


    Have you tightened every termination from the supply to the hob and everything inside the consumer unit?


    Do you have an earth resistance clamp meter? What is your total standing earth leakage on the tails? Then the total earth leakage with the hob powered up?
  • 0
    Grobbyman,

    Are the "consumer unit 30 mA RCD's (two) not affected." single pole or double pole RCD's? could be a N - E issue/borrowed neutral from circuits? Seen this a lot before with the main RCD tripping and nothing downstream does.
  • 0
    No, both double pole.

    Both operating normally.

    Still doesn't explain why next doors hob is causing the trip.

    Thanks anyway.

    George
  • 0
    Tried to get there today John, but snowed under (not literally) at the moment.

    THat was my next move, checking the hob had been installed properly.

    Still having difficulty understanding why it would trip next doors s type and not trip the jobs premises RCDs.

    Still, many things confuse me
    George

  • 0
    Think I may have trouble getting UK power to one the village.

    worth a try though.
  • 0
    I had something slightly similar. A lighting circuit in a garage tripping the 100mA S Type front  end RCD on the house. The 30mA RCD in the garage from a different supplier did not trip. All IRs etc good and no significant earth leakage. There was a faulty new HF Fluorescent in the garage which was slow to start failing completely a couple of weeks after installation and a newly installed S type RCD with possibly dodgy filtering, the manufacturer replaced it but never admitted the original was faulty and no more problems. I never found out if the new RCD cured the problem as I replaced the dodgy fluorescent at the same time.
  • 0
    Thanks for that.

    may take another s type just to give it a try.


    George
  • 0
    Are both houses TT, and is there any shared metal ?

    I assume the induction hob is doing two things, one is to inject some current into that houses CPC from the live, and the other will be to introduce a voltage drop in the neutral back to the transformer.

    The tripping house may be seeing its neutral to earth voltage twitching in step with the inrush of the cooker, either because the earth is  shared with the two properties, or becauuse the supply neutral is shared ?

    If it too has things with capacitance N-E this may make the RCD think it sees in imbalance.


    How much wiring is there between the type S and the 30mA RCDs that do not trip, and how high is the leakage (can you measure L-N imbalance with a clamp meter around both)  with the installation running before it is tripped - any chance of a partial N-E fault  due to water ingress or  pinched wire or something getting it uncomfortably close to that 60mA.

    Mike.

  • 0
    No shared metal.

    Seperate oil tanks and sewage tanks.

    Both TT as far as I know, although the neighbours place now has an underground from the pole so could be PME.

    I like (perhaps not the right word) the neutral dipping idea.

    I wondered if the neutral connection on the overhead could be loose.

    Large start up current from the neighbours new job causing the s type to see a neutral dip and then trip.

    Feasible?

    George

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