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Swimming pool 3 phase motor trips occasionally on earth leakage RCD

CliveS
We have a new 4 kW 3 phase pump motor at the local pool which has a new variable speed drive unit attached and occasionally it trips out on the RCD which I assume is 30mAmp .  The connections are star inside the motor but not earthed which should have stopped it tripping.

We are not sure what to do, we could run the motor flat out and delta connect the windings possibly or some suggest disconnecting the RCD as the circuit is completely separate from normal wiring.  Would this option contravene any of our regs?
  • 0
    CliveS:

    We have a new 4 kW 3 phase pump motor at the local pool which has a new variable speed drive unit attached and occasionally it trips out on the RCD which I assume is 30mAmp .  The connections are star inside the motor but not earthed which should have stopped it tripping.

    We are not sure what to do, we could run the motor flat out and delta connect the windings possibly or some suggest disconnecting the RCD as the circuit is completely separate from normal wiring.  Would this option contravene any of our regs?


    What type is the RCD? It probably needs to be at least A, but the manufacturer's instructions should specify.


  • 0
    does it trip while running, or just at start up ? How much current flows in the CPC when it is running ?

    Ii is likely that the VSD is designed with RF interference filters (well it should be if it is CE marked) and these will include capacitance from L-E as well as N-E. This leads to s standing current imbalance even when nothing is wrong.
  • 0
    Removing the RCD is not sensible without chacking the cable type and routing, the maker's instructions, and the type of earthing used on the site.

    However some types of RCD are over sensitive to short term events, others are less so.
  • Former Community Member
    0 Former Community Member
    CliveS:

    We have a new 4 kW 3 phase pump motor at the local pool which has a new variable speed drive unit attached and occasionally it trips out on the RCD which I assume is 30mAmp .  The connections are star inside the motor but not earthed which should have stopped it tripping.

    We are not sure what to do, we could run the motor flat out and delta connect the windings possibly or some suggest disconnecting the RCD as the circuit is completely separate from normal wiring.  Would this option contravene any of our regs?


    Hi Clive, how is the vsd controlled, as a manually set control or some sensors etc? 


    I’m a bit worried where you say “but not earthed which should have stopped it tripping” What do you mean by this?


    A clear photo of the RCD and any other items may help for further info.


  • 0
    CliveS:

     occasionally it trips out on the RCD which I assume is 30mAmp .  

    If it trips every time I would suspect an issue with the selection of RCD, an occasional trip suggests the RCD is doing its job and there’s a fault causing it to trip.


    It could be “hanging on the edge” of tripping, but ripping the RCD out without knowing why it’s tripping is foolhardy.


    Why were the new controls installed to what was presumably an existing pump?


    Andy B.
  • 0
    Thanks Chris,Andy and Mike

    The pump starts and runs up to maximum speed and records 5.9 amps on the Variable Speed Drive VSD..  Sometimes it will run for days without tripping and sometimes for only an hour.  We always run the duty pump flat out to get the circulation so I was wondering if we should disconnect the VSD and connect the motor delta which should cure the problem as the RCD is an old AC model.

    Regards

    CliveS
  • 0
    Clive, you said at the beginning that the motor has the VSD attached. If it is only IE2, you will be obliged to use the VSD. I think that you need to "upgrade" the RCD.
  • 0
    You might have to check manufacturers info for the inverter drive??

    I agree with others the type of RCD may not be correct, recently a client had issues with a new refridgeration system that has an inverter drive for the compressor, they were getting tripping of the RCD and loss of freezer stock, the blamed the electrical contractor who had fitted a Type A RCD.


    When I got involved, nothing in the refridgeration companies details, but hidden away on a paragraph of the Danfoss manual, indicated if an RCD was being used with the invertor it actually MUST BE a type B RCD. Contractor fitted a Type B and never any issues since.


    Cheers GTB
  • 0
    Running a VSD thru an RCD is often problematic.


    Most contain filters on the front end which create a deliberate current to earth. The manufacturers documentation will often require that a specific kind of RCD is used or maybe even no RCD at all.


    Also bear in mind that the RCD can't 'see' the output (motor) side of a VSD - it can only protect the input side. This is why "but not earthed which should have stopped the tripping" didn't have any effect.


    As to whether the motor should be in delta or star, well, that depends.... let us see the motor rating plate.
  • 0
    Hi Adrian 

    The motor is Certikin Hurricane [!E2] model CP4005-M 4cv/3kW IP55, 230/400volt 50Hz 10.8/6.2 amp 3 phase,  2850rpm  6s 0.81.

    The VSD is Invertek Optidrive E3 model ODE 3-240095-3FA ; 380-489 volt 3 phase,50Hz 11.5 amp with output 0-500V,3ph,0-500Hz, 9.5 amp 5HP.

    The instructions do mention a type "B" RCD but as the motor is not self starting after a power outage we would prefer to run the motor without the VSD which would avoid the cost of changing the RCD and the motor would automatically start; if the regs permit.

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