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RCD Testing x5 150mA (or higher for Hager RCCB)

sparkiemike
Following on from John Peckham's recent post, I have recently installed several of Hager's consumer units with their new 100A 30mA Type A RCD (CD285U)


When testing the RCDs I noticed the trip times were much higher than previously experienced. Hager have said that RCCB needs to be tested at 250mA https://www.hager.co.uk/news-exhibitions-case-studies/18th-edition/updated-guidance-rccb-testing/97806.htm


In addition, if you have a Fluke you may notice that when carrying out a earth loop test (in no trip mode) the Fluke will fail to get a reading and trip the RCD. Apparently Hager have had a several reports of this and when I called could not explain it.
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    Given that they could have chosen any resistor value for the self test, and parts with a 5% tolerance cost pennies and 1% tolerance only a bit pricier, even laser trimmed 0.1% are not that dear; I'm sure there is a deliberate  intention to set the 'self test' current a bit high, or perhaps to be more charitable, it may be to  make sure the same design can be used for  110V as well as 230.

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    mapj1:

    So a test current of 70mA at 230v then ( R= 230V / 3.3k ohms)

    as I said, neither 30mA nor  5 times it, just something to make it trip.

    Presumably those are marginal for use at 110V as well as 230V, although at 30mA test current would be only just about OK.

    Of course a good 30mA RCD fires at about 20-25mA so really it is fine.




    Note to self. Always tighten up the cage clamp screws before testing the resistance of the internal test circuit of an R.C.D. or the loose terminal clamps may not actually connect to the fixed terminals, and the screw heads may be completely electrically isolated, thus provide a false test result of open circuit.


    A Schneider DIF263300 2P 63A 300mA-A (Type A) R.C.D. reads 0.364kOhms across the test circuit with the button pressed in.


    Z.


     

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    Sparkingchip:

    It begs the question as to why the manufacturer chose to go for the higher design parameter or did they just turn out that way?


    Andy 




    With regard to RCDs I think Hager's interpretation of  536.4.202, 531.3.3 and 415.1.1 means they are offering consumer units with RCDs that are 100A -  Type A -  30mA (in a two module form factor). Whereas Wylex and MK seem to have taken a different approach with Wylex offering boards with a 80A  - Type A - 30mA and can't see boards from MK with type A. (other manufacturers are available ?)


    I am guessing that there may have been some design limitations to achieve the characteristics Hager wanted (i.e. 100A - Type A - 30mA - two module form factor), which meant that the trip time and trip current are on the thresholds of the BS EN 61008-1.


    It would be interesting to test some other manufacturers RCD (100A - Type A - 30mA - two module form factor) and compare results.

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    It begs the question as to why the manufacturer chose to go for the higher design parameter or did they just turn out that way?


    Andy
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    So a test current of 70mA at 230v then ( R= 230V / 3.3k ohms)

    as I said, neither 30mA nor  5 times it, just something to make it trip.

    Presumably those are marginal for use at 110V as well as 230V, although at 30mA test current would be only just about OK.

    Of course a good 30mA RCD fires at about 20-25mA so really it is fine.
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    Having just tested 2 Wylex R.C.D.s, a WRS40/2 and a WRS80/2 they both read 3.3kOhms for the test circuit with the test button pressed.


    Z.
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    davidwalker2:

    I have always assumed that pushing the test button on an RCD or RCBO injects a fault current of 30mA.  I am now wondering if that is so, and that it is actually 150mA


    David




    Ah well usually it is neither  - for RCDs that may run on 110V or 240, the test resistor is set to be well over 30mA even at 110V.  Actually  for RCDs with a real test resistor inside that gets put between outbound L and inbound N, or v/v if you have a general purpose meter with a resistance range covering K ohms, then you can measure it on the bench, meter probes in the appropriate L-N and press the test button.


    Usually more like 100mA 2,2 k ohms ish.

    note that on some electronic RCDs and RCBOs, the push button goes to an on board microcontroller that in turn fires the trip, so only testing the mechanics can move, and  not the current sensing aspect at all, so metered tests do have a purpose.

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    I thought it needed a MCB upfront of it and I wasn't expecting to see it connected into the main switch as it is



    Those sorts usually have a one-shot thermal fuse in them (that if broken, cause a red bar to appear the window). This allows it to be used without MCB as long as the upstream device is "good enough". For example the Wylex SPDs that come in their CUs don't need protection if the upsteam fuse is <= 125A.


    As an aside - I'm surprised by the orientation of that Hager SPD - if it had been manufactured with L,N below and E above, all three connection leads could have been substantially shorter, and for transients, the inductance of the leads has a large effect on the voltage that is passed through. For example, a typical type 2 SPD might achieve down to 1.5Kv across its terminals, but add in 1m of L+E leads, and that might increase to 3kV at the other ends of the leads. So rather than 1.5K reaching equipment, 3kV reaches it. It looks like maybe 30cm of unnecessary cabling there, which might be letting through another 0.5Kv.
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    There is a note in the BEAMA RCD guide


    TABLE 4 – STANDARD VALUES OF BREAK TIME AND NON ACTUATING TIME

    For RCCBs and RCBOs of the general type with I∆n≤ 0,030 A, and RCBOs of the general type incorporated in or intended only for association with plugs and socket-outlets, 0.25 A may be used as an alternative to 5I∆n


    Does that mean Hager are wrong supplying these RCDs for anything other than plug and docket circuits?


    Andy
  • Former Community Member
    0 Former Community Member
    Have a look at this it may be of some help.
    https://youtu.be/c0dPUf_aZ4E

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