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RCD TESTING BS7671:2018+A2:2022

sparkiemike

Anybody notice the changes to 643.7.1 and 643.8 when it comes to RCD testing. In the note it says that "Regardless of the RCD type, effectiveness is deemed to have been verified where an RCD disconnects with in the time stated below with an alternating current test rated at residual operating current I△n"

So the minimum requirement is to set your instrument to RCD type AC and carry out the test even if you have a Type A or Type B RCD.

Parents

  • Test button last in case the RCD or RCBO explodes on the initial test.

    Been there done that. 

    Something long and pointed is handy for pressing the test button rather than a finger. 

  • in reply to Sparkingchip

    Yep, test with instrument before using test button. This simulates a real "natural" fault situation. It proves that the R.C.D. is working correctly.

    Z.

  • in reply to Zoomup

    This is one of those cases where there's no right answer ... for example:

    Zoomup said:
    Yep, test with instrument before using test button.

    So, use an instrument with a test method that returns a fault down a protective conductor ... without checking the protective device is working?

    Some devices with RCDs say "Test before use": https://www.screwfix.com/p/british-general-900-series-13a-2-gang-sp-switched-passive-rcd-socket-white/3133j

    Safer not to follow manufacturer's instructions?

    Zoomup said:
    This simulates a real "natural" fault situation.

    Far from it. And the 1x test does little more than "push the button" (the test button for a 30 mA RCD can't generate more than 1.66 times the ampere-turns produced than that generated by the residual current tests - for other values it's 2.5 times).

    • If the fault is "additional protection" (i.e. fault through person worst case) the fault current would return down the general mass of earth, not the protective conductor which (until now) is where we've been told to return the fault current. In dry conditions, the fault current can be anything, but potentially at a rough guess we're concerned about fault currents in excess of 250 mA (or 5x) ... and we aren't doing those tests any more !!!
    • If the fault is due to a fault to PE, whether we are considering ADS or additional protection, then in most installations far more current will flow, from around (or just under) 1 A in TT systems through to possibly many kA in TN systems ... and we aren't simulating that either.
  • in reply to gkenyon

    "So, use an instrument with a test method that returns a fault down a protective conductor ... without checking the protective device is working?"

    The current is only allowed to exist for a very short period of time, as designed into the meter operation. That is a safety feature. Obviously we would take safety into account before carrying out any tests, e.g. warn householders etc.

    Z.

  • in reply to Zoomup

    Isn't it just a simulated, mechanical test rather than an electrical one and not a true trip, in the sense of a truly, operational trip when in service.?

    Jaymack  

  • in reply to Zoomup
    Zoomup said:
    The current is only allowed to exist for a very short period of time, as designed into the meter operation. That is a safety feature.

    That's based on a touch-voltage or touch-current for time that's not guaranteed to protect all adults (never mind children).

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  • in reply to Zoomup
    Zoomup said:
    The current is only allowed to exist for a very short period of time, as designed into the meter operation. That is a safety feature.

    That's based on a touch-voltage or touch-current for time that's not guaranteed to protect all adults (never mind children).

Children
  • in reply to gkenyon

    So we keep others away whilst undertaking any live testing. That is obvious really. I have already said that I warn householders BEFORE I undertake any live testing.

    Z.

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