Rccb test button not working

Discussion in 'Electricians' Talk' started by mattymtyuk, Aug 9, 2018.

  1. mattymtyuk

    mattymtyuk Member


    Hi all, can someone please clarify this for me if I press the test button on rccb 1 nothing happens, I press test on 2 and it trips out, is rccb 1 faulty? Or is it only 2 that should trip on a test?

  2. Pollowick

    Pollowick Well-Known Member

    Both should trip when tested. If RCCB1 is not doing that then there is potentially a fault which could be either the detection circuit or the fault load that is put in place when the button is pressed. Which ever it is, the RCCD needs replacement - an electrician could run a test in a few minutes to confirm and replace if required.
  3. mattymtyuk

    mattymtyuk Member

    Thanks so it’s a faulty rccb and if I replace it it will be ok, I’m a bit puzzled as to how or why this is happening, house was rewired 3 years ago, had an extension wired in 6 months ago and never had any issues, I’m wondering if the rccb would trip if a fault on the circuit was detected or is the whole switch faulty or just the test function is faulty?
  4. Pollowick

    Pollowick Well-Known Member

    You will not know what is faulty without testing. There are very complex testers which slowly ramp up the current to find te trip point. And there are also some basic ones which put a fault load on that will cause a 30mA imbalance and that will trip it.

    Get you electrician back and he can test and replace if required - maybe source an exact replacement so he does not have to which will mean you are only paying for the short time he is there rather than him driving to the wholesalers and back too.

    Also, check the warranty on the device. Some have 10 year and others just one or two.
  5. MGW

    MGW Well-Known Member

    The button tests the mechanical action, it seems over time the devices can stick, and using the test button checks if stuck, however it does not test speed so it only does a part test.

    I have found some times something as simple as strain caused by a wire pulling on terminal can stop them working, simply slacking off screw and tightening again has cured the problem, but to test it needs a special meter, the meter costs more than getting an electrician so in real terms this is not a DIY job as simply not worth buying the meter needed to test it. New one may work, but question is will it work within 40 mS, and I can't use a stop watch to measure that, it needs a proper tester.
  6. mattymtyuk

    mattymtyuk Member

    Thanks for the help everyone, it’s all fixed now, hit it a few times with a screwdriver handle and it’s freed up whatever was stuck and now works not exactly to 18th edition or whatever regs applies but it’s working fine now ‍
  7. HappyHacker

    HappyHacker Active Member

    The test button puts a small resistor between the outgoing live and the incoming neutral to create an imbalance on the sense coil of the RCD effectively simulating an earth fault on the load side. If the fault is with this circuit and the RCD otherwise works you still should replace it as you have no means of simply testing it in the future.

    It is recommended that the RCD is tested every quarter (I think it is changing to twice a year in the 18th edition of wiring regs). Testing makes sure it is not stuck and by making the mechanism move reduces the chance of it working slowly due to partial stickiness.

    I recently tested a customers RCD with the button and it did not work so tested it with an RCD tester and it still did not work so it got replaced. I took it to pieces and it was full of tiny dead ants or spiders, it was difficult to tell as they were very small and dried out.
  8. peter palmer

    peter palmer Well-Known Member

    I've seen a few RCDs that don't trip first time after they have been in a few years, get it to trip and its fine after that but will probably seize up again after a year or so, hardly the life saver they purport to be.
  9. Bob Rathbone

    Bob Rathbone Well-Known Member

    Ah, yes percussive maintenance. But the device is unreliable and needs to be changed.
  10. unphased

    unphased Screwfix Select

    That is why we are supposed to press the button regularly to avoid the thing sticking and failing to operate when called upon in a real need situation. How many bother?
  11. peter palmer

    peter palmer Well-Known Member

    Why would it be a joke spark from kent(y) loads of things work again when you **** them.
  12. Sparkielev

    Sparkielev Well-Known Member

    Just because the test button works doesn't mean it"s working right
  13. chippie244

    chippie244 Well-Known Member

  14. Mgreen201

    Mgreen201 New Member

    like sum1 hass said this happens due to not being regularly tested . the working just sieze any springs lose there tention .

Share This Page