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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
    Really
    I've only ever seen an AC s type.

    THe 30ma are AC too.


    George

  • Former Community Member
    0 Former Community Member
    Grobbyman:

    Really
    I've only ever seen an AC s type.

    THe 30ma are AC too.


    George



    Thanks for the reply  George, have a read through a few topics on the old forum using the keywords “neighbours RCD” . The neighbour having an borderline N-E fault and a stuck RCD isn’t something I would discount.

    https://www2.theiet.org/forums/forum/search.cfm


  • 0
    Thanks for that.

    been there today and swapped the S type over for new.

    Made sure both internal RCDs trip without affecting S type.

    New one ramps up to 75mA.

    If it still trips I'll try to persuade the neighbours to let me in.

    As I said, hob and oven both on and no trip on S type.

    Regards
    George

  • Former Community Member
    0 Former Community Member
    Your welcome, it does more often seem to be inductive saws, cement mixers etc that cause these problems! Hope it goes well :)
  • 0
    Nothing else has this week.

    Thanks for your good wishes though, appreciated.


    George
  • Former Community Member
    0 Former Community Member
    Also, looking on the bright side, the existing RCD that is tripping probably as it should do, rather than not operating due to being “blinded” from operating by some theoretical jargon!
  • 0
    Well I returned to the premises on Friday and replaced the MCG AC S type with a Lewden model of the same type.

    Tripping times measured about the same and the new RCD ramps at 75mA instead of 60mA.

    So far no return calls.

    Fingers crossed.

    George
  • 0
    perhaps the rcbos were all allowing say 10mA leakage current through, not enough to trip them but the cumulative current was enough to trip the s-type?

    Edit; oops misread the thread, OP has only two 30mA RCDs, oh well.

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