Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 37 replies
  • Subscribers 32 subscribers
  • Views 7549 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

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
    John Hill

    Agreed, but as Sparkingchip pointed out, the model forms just say "disconnection time (ms)", It does not specify a multiplier.

    Therefore I would now record the highest trip time of either the x1 or x5 tests.

    Looking further last night, someone on another forum had said the same thing and I think that's the best way.
  • 0
    John Hill TMIET:

    This issue came up on the 18th edition course. The testing procedure for rcd's hasn't changed, it's just the requirement to record the 1x IΔn value that has been removed.



    It may be the case where RCDs are specified for additional protection that the specific requirement in BS 7671 to test and record at x5 is not stated.


    However, RCDs may also be used for ADS to achieve a disconnection time in accordance with Chapter 41.


    In a TN system, the disconnection time is 0.4 s (or 5 s for distribution circuits and some larger-rated circuits), and therefore the x1 test would meet the requirement - is there any need to conduct a x5 test?


    In TT systems, a disconnection time of 0.2 s may be required. The x1 trip time could be within "spec" and greater than 200 ms - would you omit the x5 test if the x1 test was below 0.2 s? I've occasionally come across x5 tests which are a longer trip time than x1. if you look at Table 3A, it's actually the x2 test which is required for ADS in circuits requiring 0.2 s disconnection time.


    Very pertinent on circuits protected by an RCD larger than 100 mA (say to prevent nuisance-tripping with a downstream RCD), where 0.2 s disconnection time is still required.

    On a 30ma device for additional protection you still need to test at 1/2 x IΔn to rule out nuisance tripping, 1x IΔn to confirm normal operation and the 5 x IΔn value is recorded. If for some strange reason the device does not trip out within the required time at 1 x IΔn then it would be recorded as a C2 in the observations and would need to be repaced, regardless of the 5 x value.



    Agreed for Additional Protection and where a disconnection time of 0.3 s (300 ms) or less is required, with 30 mA and 100 mA RCDs.


    The conclusion of all this, is that probably the x5 value is most pertinent to record with 10 mA, 30 mA and 100 mA RCDs, but with RCDs with a greater residual current rating, it may not be safe (or if there's a high earth electrode resistance, perhaps not possible) to get the x5 reading !



    This of course assumes it's correct to test the functionality of the RCD with the associated protective conductor. Certainly the test to BS 61557-6 is really a manufacturing test for the RCD stand-alone, not really a performance requirement for RCDs in an installation. Consider the two following cases, are you happy with the statements based on the previous sentence:
    • Most 30 mA RCDs provide additional protection, and for additional protection we cannot assume there is a protective conductor ... we are protecting against (among other things) accidental failure of basic protection (e.g. cut 2-core lawnmower cable where there is no protective conductor).

    • Where the RCD is required for ADS, it is feasible to rely on the earth fault loop impedance, or Ze+(R1+R2), being low enough to achieve the relevant residual current for x1 or x2 (or x5) based on the disconnection time required, as discussed above, if the RCD is tested with an instrument to BS EN 61557-6, using the "up/down" method (as one test equipment manufacturer calls it)?

  • 0
    Whether a requirement or not I feel the times 1 must always be done and x5 if for personal protection, naturally that would also include the x1/2 nontrip too. I always as amatter of course do a ramp test my tester on say 30mA starts with 15mA then 18, 21, 24,27 in steps. Having two basic trip points (x1 & x5) I feel gives a good indication of reliabillity and the ramp gives a clue of what realistically it might trip at. Obvioulsy the tester is not foolproof and neither are RCDs foolproof but it often gives you an extra chance IMHO
  • 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.
  • 0
    If one was seeking clarity on testing RCDs, it would seem prudent to refer to IET Guidance Note Three. Certainly with additional protection 2.6.19 requires a test to ensure the RCD trips within 40ms when a rest current of 5xIdeltan is applied. So the 250mA lark isn’t even acknowledged. With respect to other RCDs the operating times have to be established where they are relied on for disconnection for compliance with Chapter 41. Other than these two circumstances, instrument tests are not required.

    The inclusion of Table 2.9 which sets out operational tripping times for various RCDs along with the requirement to test on both sides of the AC cycle could be taken to infer that nothing has really changed from the 17th. Not exactly unambiguous! Maybe the authors were eager to get it to the publishers so screw clarity!
  • 0
    Sparkymania:

    John Hill

    Agreed, but as Sparkingchip pointed out, the model forms just say "disconnection time (ms)", It does not specify a multiplier.

    Therefore I would now record the highest trip time of either the x1 or x5 tests.

    Looking further last night, someone on another forum had said the same thing and I think that's the best way.


    Oh yes they do!


     Andy Betteridge 


  • 0
    Thing is this:

    If the change was to reduce nuisance tripping then fair enough. But this is a major change. It should have been introduced across manufacturers and coordinated with advice about using the VAR x5  on testers. Those without this facility would just have to upgrade with new testers having a 250mA selection.

    How many sparks know about this issue? I only know about it due to someone saying on one of my posts "and what about the Hager issue".

    I then responded asking "what issue" to which they explained.


    This is not the way to go about making changes like this. Anyway, they have now changed it back to 150mA so was the nuisance tripping issue that much of an issue if no one is going to push it to become common practice for all manufacturers to make the change and for people to be informed so as to avoid  confusion?
  • 0
    Sparkingchip.


    I thought you were referring to the fact that they didn't just say x5 in the column on the schedule of test results.

    When I checked after your first reply I found that it just says "disconnection time (ms)".

    I thought that's what you meant.

    I checked both the minor works and the column in the schedule of test results.

    I don't understand when you say "Oh yes they do!"
  • 0
    Have a look at page 127 Guidance Note 3. Column 23 has been completed with figures that exceed those required for additional protection. It is clear from column 8 that the mcbs are providing the necessary automatic disconnection although circuit 10 would appear to rely on the RCD as Zs measured exceeds the permitted Zs stated in column 8. Small wonder sparks are bewildered at the RCD testing requirements!
  • 0
    The test results sheets ask for the rating of the RCD IΔn mA and the disconnection time in mS.


    That is what you need to record, it is the 5Δn disconnection time test result that you don’t need to record on the certificates.


    Andy B

Community Rules & Guidelines