RCD Nuicance tripping (HELP)

[simbo1]

Have a senario where a 30mA trip cuts out whenever a Commercial dishwasher starts the electric pump in its initiation cycle.This equipment is on a radial circuit insulation tested and sound, the Dishwasher has been checked by the installers with no faults. If this cicuit was isolated and set up with a 100mA RCD is this likely to cure the problem?It is accepted that a 100mA RCD affords only indirect or fault protection. However it is assumed that this is still better than overcurrent protection alone.

 

[IQ Electrical]

It might stop it tripping but what is the purpose of the RCD in this situation ie. why was it used/specified?

 

[Sintra]

If the RCD is installed for additional protection then 30mA is the max that can be used. I would suggest that there may be a fault on the appliance if all the tests on the RCD prove satisfactory.


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[davelerave]

low IR on dishwasher pump anyhow-i wouldn't call that fault-free

 

[bugsy]

There are two pumps on dishwashers, drain pump and circulation pump from what your saying it sounds like the drain pump causing the problem, If this fault has recently occured I would suggest changing the drain pump

 

[Chr!s]

Place one lead of your insulation tester across the Line and neutral, the other too earth. Ensure on off switch is in the on position and the door is closed, carry out test, disconnect one by one until the fault is found

 

[davelerave]

why would you need to troubleshoot-if the fault is obvious

 

[Chr!s]

why would you need to troubleshoot-if the fault is obvious

Well i would see it as god practice, if the IR was low, as you say you could disconnect the pump straight away, though some dishwashers the motor circulates as well as drains, if this is the case why is it only tripping when it drains?, could be a leak on the drain hose.

This would also show up other possible faults, if the IR still remained quite low this may be an indication of other possible faults like the element on the way out.

 

[mogga]

Fault on the appliance sounds most likley if circuit tests out OK then its the Appliance simples

 

[simbo1]

Thank you all for your input thus far. It might be better if I can provide info that may shed a little more light on this problem.
The installation is in a School canteen/Kitchen by others, looks very neat and professionally set up.
The whole system comprises of 2 boards one RCD protected one not, spare capacity on both.
The circuit is radial I have done IR and tested RCD inc, ramp tested, all ok. Did not have Dishwasher connected during IT test as I'm a little nervous of over energising the electronics on the control panel. Wrongly?
The equipment manufacturers have been out three times and tested dishwasher to death apparently, all ok. so I assume IR in machine ok.
On starting the DW goes through a heat cycle for a couple of minutes, all ok. Then a motor cuts in (sound of water spraying / being pumped ) then pop. could the combined effect of heating and the initial surge of the motor induce a trip?
Once again thanks for your help.

 

[davelerave]

if equipment is compatible with 30ma protection

i'd prob swop out rcd as precaution


confirm IR

and recheck dishwasher with nothing else on rcd

 

[Engineer54]

The problem is, that when a single RCD is looking at several circuits, then normal leakage currents are always going to accumulate. It could well be that the RCD is nearing it's limit and when this DW is going through it's cycle it reaches a point where that normal leakage is high enough to trip the RCD out!!

You will need a mA clamp meter to fault find further, if this is the case. Ramp tests will not tell you what leakage is passing through the RCD with any accuracy, or tell you what other individule appliances are contributing to the overall leakage the RCD is sensing...

 

[davelerave]

shouldn't be hard to clear up this mystery-even if you don't have mA clampmeter


if there is 'standing leakage' on the rcd -he can rcbo the final circuit