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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've not come across this type of kit before, so guessing really, but assuming the "CT" really is of the correct special type that will detect d.c. residual currents - my next guess was what setting did you have the MFT on? - from memory the d.c. trip levels for B-type RCDs differ from the nominal a.c. ones (from even vaguer memory) I think a 30mA B-type need not trip until 60mA d.c. for instance - I don't know if your MFT takes such things into consideration or just created a d.c. residual current of the specified setting (mine is old and doesn't have such features Frowning)

      - Andy.

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  • I've not come across this type of kit before, so guessing really, but assuming the "CT" really is of the correct special type that will detect d.c. residual currents - my next guess was what setting did you have the MFT on? - from memory the d.c. trip levels for B-type RCDs differ from the nominal a.c. ones (from even vaguer memory) I think a 30mA B-type need not trip until 60mA d.c. for instance - I don't know if your MFT takes such things into consideration or just created a d.c. residual current of the specified setting (mine is old and doesn't have such features Frowning)

      - Andy.

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