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Not testing RCDs at x1 is omitting an essential test

Sparkymania
Hi all


Following the last two weekends posts about RCD testing and trip times, in which I learnt a few things that I would never have known

as they are not documented in most tester manuals, a few more thoughts have come up.


On the hager site where they have "updated guidance on testing" their 30mA RCDs at 250mA they stated 2 things that were wrong.

This same mistake had been made in 2 videos as well.


They state that if you don't have a tester with a VAR that can be set to 50mA at x5 to give 250mA then you can use 300mA setting at

x1.

This is wrong. As I've found out over the last two weekends the tester does an unseen pretest before the main test. 300mA x1 will

pretest at about half 300mA and trip the RCD with the diplay showing "trp" and abort the test.



They also state "The x1 test is no longer a requirement but could of course be carried out".

I can't find anywhere that states it is no longer a requirement.


Regulation 643.8 requires that the instrument used complies with BS EN 61557-6.

There is a ‘Note’ to this regulation but Notes to Regulations only provide guidance and are not regulations.

The Note says: “Effectiveness is deemed to have been verified where an RCD meeting the requirements of Regulation 415.1.1 disconnects

within 40 ms when tested at a current equal to or higher than five times its rated residual operating current”.

Is this reg stating x 1 doesn't need to be done or is this being misinterpreted?


On the new test forms there is no longer a column for x1.

The other sparks I work with now only do x5 tests unless doing a MWC where it still has a x1 entry. However I still do all tests.

A 30mA RCD is supposed to trip when 30mA is detected. How are you going to know if it does that if you don't do a x1 test?

I tested one this week that passed x5 at 16.9ms but failed x1 with >300. When I ramp tested it it tripped at 75mA.

This proves that it needs to be tested at x1 as well, especially when used for additional protection as it must trip at 30mA when

going through the human body, not at the 75mA it was ramp tested at.


Also, as someone pointed out on another post, If someone mistakenly installed a 100mA (non-delayed) unit instead of a 30mA one -

chances are it would pass if only subjected to a 40ms/150mA test - yet it would hardly provide adequate additional protection.



As a side note and for the information to those who replied to my post about this pretest setting of half the selected current:

I don't think it's a half current pretest.

I have tried the VAR setting of 50mA x5 and it works. However, if it did pretest at half current then the 30mA RCD would trip at 25mA

as that is over the ramp test result of 22mA at 0 and 24mA at 180.

It even worked at 55mA without tripping and that would have been 27.5mA if it was half.

It did trip, though, set at 60mA, displaying "trp" so must have pretested at over 22/24mA.

Therefore I think this pretest current is somewhat less than half.

Too knackered after today's work to try to work out what the likly percentage of pretest current is but I bet some here will be able

to.


Any thoughts on this?



  • 0
    I don't see anywhere in 7671 where it specifically says the x1 is not required.

    The references to 40ms at x5 where removed from the section referring to RCDs for additional protection and put in chapter 6 with the note "times five or above" allowing the Hager 250mA nonsense just because BS61008 allows it with no thought of current practices or test equipment. Hager have now changed it back to 150mA from OCT 19. (Sorry. Too knackered to look up the actual regs I'm referring to).


    The OSG suggests that you should still be doing x1 in 11.2 (b) and 11.3 (b) to make sure it trips within the time specified at the rated current of the RCD.



  • 0
    I've read 0.300 as 0.030 in the dim light under the stairs and announced the RCD had failed the test, until the error of my ways were pointed out to me, not that I was expecting to see a 300 mA RCD in the cupboard under the stairs in a house, it is not a common occurrence.


    Andy B.
  • 0
    On your second point, I agree with you that it should be picked up on inspection. Before I even test a board I check ratings and cable sizes, so yes, that would be picked up. I was only repeating a point made by someone else to include it in my discussion, but this can be missed when someone is under pressure from a "haven't you done that one yet" type of boss.


    On your first point:

    I tested the RCBO at the DB with the circuit disconnected to make sure there was no external influence on it.
  • 0
    However, the Hager site still says "The x1 test is no longer a requirement but could of course be carried out". I still assert that they are giving potentially dangerous information for the reason I stated above. "Where did they get this from"? is what I'm wondering.

    Well if BS 7671 no longer says a 1x test is required, I'm not sure we can deduce that it is.


    I might suspect too that either someone from Hager or someone from one of their manufacturer's associations will have had some input to JPEL/64 on this very subject.


    You might also have noticed that all the references to RCDs for additional protection operating within 40ms at 5x IΔn have disappeared from BS 7671.


        - Andy.
  • 0
    I tested one this week that passed x5 at 16.9ms but failed x1 with >300. When I ramp tested it it tripped at 75mA.

    Were you able to definitely establish the cause of the failure? For instance manufacturers have been complaining for a long time that most RCDs returned to them as faulty check out OK on their tests - and they blame installation conditions fooling the test. Things like poor N-PE insulation downstream of the device (even in an switched off appliance) can result in a proportion of the test current returning via N rather than PE - giving an over-estimte of the actual residual current seen by the RCD. Likewise capacitors or inductors can make the trip times appear extended. Were you able to prove 100% that it was the RCD that was to blame?

     
    Also, as someone pointed out on another post, If someone mistakenly installed a 100mA (non-delayed) unit instead of a 30mA one - chances are it would pass if only subjected to a 40ms/150mA test - yet it would hardly provide adequate additional protection.

    But we should be able to detect that kind of error by inspection - just as we would if someone installed a B16 in place of a B6 MCB.


    There was a lot of discussion about this a while ago (probably around the time of the DPC for the 18th) - the initial suggestion was that specific testing of RCDs need not be done at all (which would put them in line with MCBs or fuses) - so we'd just have the "T" button.


        - Andy.
  • 0
    Your right.


    I've been using FormFill Plus for MWC and they have both the x1 and the x5.

    The Excel template that was given to us to use at the start of the 18ed replaced the three columns with  "x1 - x5 - func test" with "x5 - func test - AFDD".

    I should have looked at the model forms at the time to check as this didn't seem right.That makes more sense to just have disconnection time.

    They then sent us updated forms but didn't say they removed the x5 and just put "disconnection time". We were told that the old form was corrupt.

    Nobody has noticed this and are still think it says x5.


    I will have to inform my firm tomorrow about this.


    However, the Hager site still says "The x1 test is no longer a requirement but could of course be carried out". I still assert that they are giving potentially dangerous information for the reason I stated above. "Where did they get this from"? is what I'm wondering.
  • 0
    What RCD test current is stated on both the Minor Works and EIC/EICR model test certificates in BS7671?


    Andy Betteridge

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