Which RCD type does NOT trip with voltage spikes?

Discussion in 'Electricians' Talk' started by rogerk101, Aug 10, 2020.

  1. rogerk101

    rogerk101 Screwfix Select

    I have a rental home with a single standard Hagar RCD (it came with the house, so I don't know what type it is).
    When I installed a wet underfloor heating system, I installed a 'smart' eco circulating pump. Each time the circulating pump turned on, it caused the RCD to trip. I replaced the circulating pump with an old classic Grundfoss pump that I had as a spare, and everything works just fine.
    I'm pretty sure the 'smarts' in the eco circulating pump are generating voltage spikes and associated current 'leaks' that are causing the RCD to trip, because the UFHC supplier sent me a replacement 'smart' pump and it behaved exactly the same way, tripping the RCD whenever it turned on.
    Which RCD type would be most tolerant to spurious voltage spikes caused by a 'smart' pump motor, but still be within regs?
  2. MGW

    MGW Screwfix Select

    There was a RCD called the X-pole silly name as when I try to find it all I get is pictures of girls dancing on internet, however it was claimed they trip at 90% to 100% instead of normal 50% to 100% and they are not affected by spikes, and have a warning window which shows when the leakage is getting high.

    However these were advertised many years ago, and things have generally moved on. In general it is not tripping which is the problem with using the wrong type of RCD, not tripping when they should not, but I have to admit I have never checked the leakage when fitting a new RCD on an existing circuit, I know I should, but I have not got a clamp on ammeter that will measure 9 mA which is considered as the maximum leakage permitted due to capacitive and inductive linking which can't be checked using an insulation tester as they use DC.

    So it is likely many others have done the same, so if you have one item that has just 2 mA leakage through the suppressor network that is enough to tip the balance, in hind sight we now know the twin RCD consumer unit was not suitable for many installations, and either a high integrity unit, or all RCBO, the likely cure is to change one RCD for either a 100 mA version or an isolator and fit RCBO's fed from it, only reason to fit 100 mA RCD is if some circuits need better than type A RCD's.

    However since all homes are now protected by RCD's you should not really have new equipment which will cause it to trip.
    Jord86 likes this.
  3. rogerk101

    rogerk101 Screwfix Select

    Thanks for your input.
    As you point out, the different RCD types available all seem to make them MORE sensitive to current imbalances caused by spurious voltage spikes; not less, which is what I want.
    If anyone else knows of an RCD type that might suite my needs better, please let me know.
  4. MGW

    MGW Screwfix Select

    My old house had two RCD's for whole house, they seemed to have batches of tripping, would go couple a years no trips, then one a week for maybe a month, then another couple of years with no trips. Mothers house had two RCD's and four RCBO's the kitchen was all RCBO protected. I did not have them trip other than when testing them. This house all RCBO's and have a water leak which has tripped a couple (14 in all) but main circuits no affected, glad I went all RCBO.

    It would depend on the consumer unit, with my old house it was two of the old Wylex fuse boxes with the fuses changed for MCB's and two RCD's fed the two boxes, so until the fuse boxes are changed to a consumer unit there is no way RCBO's can be fitted. When the consumer units came out they would often not take the longer RCBO's however today there are some short versions, the Wylex short version is type A and switches the neutral so suitable for a TT system.

    So it depends on the make of consumer unit and what will fit, but if you can fit RCBO's then swapping the RCD on affected side for an isolator and fitting all RCBO's will likely cure the problem, however it seems modern RCD's are less affected by spikes, can't see how one can find out which is which.

    I know in the early years I have gone to a house and the RCD was tripping, I measured the insulation resistance and it was OK, I used a RCD tester and the RCD showed as OK, so in desperation since I had a spare RCD I changed it, and the new one also tested as OK and did not trip all the time, left me scratching my head wondering why, I suppose a ramp test may have found a difference, but my meter did not have a ramp test.

    So today I have a box full of MCB's and RCD's and I know they are all good, but also unlikely I will every use them, I must I know dump them, but loathed to dump good gear.
  5. sparky steve

    sparky steve Screwfix Select

    You may find this helpful?
  6. MGW

    MGW Screwfix Select

    Found x-pole this one is a RCBO X-pole.jpg note the little red arrow, it seems this gives a warning before the device trips that it is near the limit.

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