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Use of Type B MRCDR with no Neutral

Lee Colin Ingram

We have Type B MRCDR's installed within our MDU/MDA assemblies. The manufacturer/model is Doepke - ELR-3BN+ residual current transformer.

They have been installed on supplies to VFD controlled equipment so we have followed manufacturers guidance.

My question is this.....The VFD equipment does not require a Neutral therefore only the 3 phases pass through the associated residual current transformer. 

We were able to test the device as both a Type AC and a Type A and the device operates, it does not however operate as type B when this is selected on the MFT.

I may be worried about nothing as they are operational.

Please share your thoughts

Parents

  • I had better be honest here, several years ago I attended the Elex Show at Coventry and I stood and had a conversation about RCD testing with Michael Peace, John Peckham and Graham Kenyon, so hopefully having talked about RCD testing with all three of them at the same time, hopefully I am getting it right.

    Michael wrote this IET Wiring Matters article about RCD testing.

    electrical.theiet.org/.../

  • in reply to Sparkingchip

    The IET Guidance Note Three says the test current for a Type B RCD is 2x I delta n  smooth DC.

    A Megger 1700’s series MFT will not do a 2x I delta n  smooth DC test.

    So, for example, to test a 30mA B-type with DC (not that such a test is a requirement, but if we wanted to) .. we'd have to test with at least 60mA d.c. - which would mean setting the MFT at say 100mA x1 ?

       - Andy.

  • in reply to AJJewsbury

    AJ are you a graduate of the Hager School of RCD Testing?

    The test current for a Type A 30 mA RCD to trip in 40 milliseconds is either X5 (150 mA) or 250 mA and you have to ask the RCD manufacturer which is the correct test current, if you ask Hager they say you need to test at 250 mA to get their Type A RCDs to trip in 40 mS, but if you don’t have a 250 mA test on your tester use 300 mA.

    So Hager were telling electricians to use a X10 test to get their 30 mA RCDs to trip in 40 milliseconds.

    But then Hager went on to say that electricians did not need to do a X1 test, so the X10 test was the only test needed.

    https://hager.com/uk/support/regulations-18th-edition/updated-rccb-testing

    So some clarification was required in the 2022 GN3 I posted a picture of above.

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  • in reply to AJJewsbury

    AJ are you a graduate of the Hager School of RCD Testing?

    The test current for a Type A 30 mA RCD to trip in 40 milliseconds is either X5 (150 mA) or 250 mA and you have to ask the RCD manufacturer which is the correct test current, if you ask Hager they say you need to test at 250 mA to get their Type A RCDs to trip in 40 mS, but if you don’t have a 250 mA test on your tester use 300 mA.

    So Hager were telling electricians to use a X10 test to get their 30 mA RCDs to trip in 40 milliseconds.

    But then Hager went on to say that electricians did not need to do a X1 test, so the X10 test was the only test needed.

    https://hager.com/uk/support/regulations-18th-edition/updated-rccb-testing

    So some clarification was required in the 2022 GN3 I posted a picture of above.

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  • in reply to Sparkingchip

    There is a note in that Hager Type A RCD testing guidance:

    Devices pro­duced up to July 2019

     ** Please note: This guid­ance DOES NOT ap­ply to CD285U RCCB with a pro­duc­tion date code after 19219 **

    That means if you go to inspect and test an installation with a Hager Type A DP RCD installed around seven years ago, you will need to take the RCD out of the board to read the date code on the back of it,  if you are intending to test in the way that Hager tell you to do it.

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