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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

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  • If the Variable Frequency Drive is varying the frequency of the current will it sometimes produce Triplen Harmonics that will create high neutral currents that will not have anywhere to go?

  • in reply to Sparkingchip

    high neutral currents that will not have anywhere to go?

    Only if things are connected in star - otherwise you just end up with differing line currents but no overall imbalance (like a single phase HV transformer connected L-L under 3-phase overheads with no N).

       - Andy.

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  • in reply to Sparkingchip

    high neutral currents that will not have anywhere to go?

    Only if things are connected in star - otherwise you just end up with differing line currents but no overall imbalance (like a single phase HV transformer connected L-L under 3-phase overheads with no N).

       - Andy.

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