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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?



Parents
  • 0
    some are failing at 150mA. This is making the RCD less effective for additional protection as well as causing problems for testing. They've been sent back as faulty.

    That's exactly why the manufacturers have been complaining - if it takes 250mA to trip within 40ms that the device isn't faulty from the manufacturer's point of view - as it complies perfectly with the product standard.

     
    It says x5 OR above.

    Exactly - so if it passes the 40ms test at 250mA or (as you say) 5A or 50A it's a pass according to the current BS 7671 wording. Simply not tripping at just 150mA is no longer a fail. There's no requirement either in the requirements or testing sections of BS 7671 for a 30mA RCD to achieve 40ms disconnection at 150mA.

     
    Whatever the regs say I think they are wrong about testing RCDs. I also thing that it is a mistake in BS61008 to change the current resquired for 40ms trip from 150mA to 250mA

    Fair enough - if you want to go above and beyond current standards that's fine - but for most of us the standards are what they are (both BS 7671 and BS EN 61008 etc) and complying with those standards is considered sufficient. I might take the view that omitting supplementary bonding in bathrooms is a mistake but at the same time I feel I would be on very soft ground if I went around rejecting installations as faulty when they complied with the current regs on that point.


    (BTW I think it has been suggested that is wasn't a (recent) change in BS EN 61008 etc to allow the 250mA option - but that it's been in the standard for quite a while - it's just that it's only recently that some manufacturer's have taken advantage of it as it were - possibly part of a drive to reduce nuisance tripping on transients and the like.)


    I do think that BS 7671 could be clearer on its requirements for RCD testing - especially on the model forms.


       - Andy.
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  • 0
    some are failing at 150mA. This is making the RCD less effective for additional protection as well as causing problems for testing. They've been sent back as faulty.

    That's exactly why the manufacturers have been complaining - if it takes 250mA to trip within 40ms that the device isn't faulty from the manufacturer's point of view - as it complies perfectly with the product standard.

     
    It says x5 OR above.

    Exactly - so if it passes the 40ms test at 250mA or (as you say) 5A or 50A it's a pass according to the current BS 7671 wording. Simply not tripping at just 150mA is no longer a fail. There's no requirement either in the requirements or testing sections of BS 7671 for a 30mA RCD to achieve 40ms disconnection at 150mA.

     
    Whatever the regs say I think they are wrong about testing RCDs. I also thing that it is a mistake in BS61008 to change the current resquired for 40ms trip from 150mA to 250mA

    Fair enough - if you want to go above and beyond current standards that's fine - but for most of us the standards are what they are (both BS 7671 and BS EN 61008 etc) and complying with those standards is considered sufficient. I might take the view that omitting supplementary bonding in bathrooms is a mistake but at the same time I feel I would be on very soft ground if I went around rejecting installations as faulty when they complied with the current regs on that point.


    (BTW I think it has been suggested that is wasn't a (recent) change in BS EN 61008 etc to allow the 250mA option - but that it's been in the standard for quite a while - it's just that it's only recently that some manufacturer's have taken advantage of it as it were - possibly part of a drive to reduce nuisance tripping on transients and the like.)


    I do think that BS 7671 could be clearer on its requirements for RCD testing - especially on the model forms.


       - Andy.
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