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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

  • RCD testers are designed and manufactured to BS EN 61557-6 Effectiveness of residual current devices (RCD) in TT, TN and IT systems for testing electrical installations. The standard requires that the instrument be able to verify correct disconnection of the supply in the event of a fault but it does not provide requirements for extensive product standard testing.  Subsequently, not all instruments will be well suited to carrying out anything more than the most rudimentary of tests. 

    electrical.theiet.org/.../

  • 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.

  • Lee, what tester and settings did you use for the tests?

  • 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.

  • The comments about Hager and their 30 mA Type A RCDs partly explains how we ended up with this regulation and the guidance in GN3 I posted above as recommendations for testing RCDs.

    It then begs the questions, why was the Type B test being done and what were the settings on the tester?

  • in reply to Sparkingchip

    There is another question as well, was the VFD running during the test and what was the frequency of the current if it was running?

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