3 Phase RCD

loadz

Hi

I was asked if there was any unit available to monitor earth leakage. We have a 3 phase, 3 wire RCD which is supplying a motor controller on a ship ( i am not sure of what exactly it contrtols ) as it might have other things in its circuit. They are getting nuisance tripping and they think it might be the controller so we would like to monitor it for earth leakage. For example when it tripped , at what stage of the sign wave it was and so on. Do any of you guys know of any such monitor.

Rgds

Bruthal

loadz wrote: »

Hi

I was asked if there was any unit available to monitor earth leakage. We have a 3 phase, 3 wire RCD which is supplying a motor controller on a ship ( i am not sure of what exactly it contrtols ) as it might have other things in its circuit. They are getting nuisance tripping and they think it might be the controller so we would like to monitor it for earth leakage. For example when it tripped , at what stage of the sign wave it was and so on. Do any of you guys know of any such monitor.

Rgds

I dont see the stage of the sign wave making much difference to show what the cause is, what causes that is one of the phases leaking current to earth, you could get a meggar and switch the power to that circuit off and meggar each outgoing phase from the RCD to ground and see if any are showing a fault, use the meggar at 250v or around that. Its an electricians job anyway to test it. If you find which phase it is then disconnect the motor and retest to see if its the motor.

M cebee

i would try to confirm it's the motor controller causing the nuisance

brightspark

A lot of inverters (I assume that's what you mean by motor controller) have by design a large earth leakage, I recommend that you check the specs of the controller to see if it really should be protected by the RCD

M cebee

i would think they're a potential nuisance alright

difficult to say from here -rcd may be 100 or 300 ma type

-afaik wiring rules etc. don't apply to boats

DublinDilbert

You could get a 1ohm shunt resistor and place in series with the earth line from the inverter. Then pop on a voltmeter with peak hold across it. You cold also do the same with the motor.

Bruthal

DublinDilbert wrote: »

You could get a 1ohm shunt resistor and place in series with the earth line from the inverter. Then pop on a voltmeter with peak hold across it. You cold also do the same with the motor.

Or put ammeter in series with the earth maybe. More or less the same thing. Resistor idea is probably better though if ammeter is fused. But for a test purpose it would work.

Bruthal

One good thing about DDilberts 1 ohm resistor setup is the voltage reading across it if there is any will be the amps reading also.

If there is 0.2v on the voltmeter then the current will be 0.2 amps.

DublinDilbert

The shunt is good cause you can stick a scope on it too, just make sure the minus connection ofthe scope is no grounded to the scope frame.