I agree if the RCD trips immediately given a good supply and nothing connected to its output terminals, then the unit is duff.

Presumably this is an industrial environment - is there any other electrically  "noisy" equipment about? I'm just wondering about something putting large spikes on the mains - and type B RCDs will be packed with far more electronics than a traditional coil-and-solonoid AC type of yore. Any SPDs about?

     - Andy.

I appreciate your feedback. I used a earth leakage clamp meter to measure the current of the seven motors that make up the machine. When I clamped all three phases (Supply) together, the current was 45 mA. When I clamped all three phases and the CPC together, the current was 390 mA (fluctuating 400 +) I measured each motor separately. The current of the three motors that were connected to inverters was around 15mA when I clamped only the phases, but it increased to around 60 mA when I clamped the CPC as well. The feeder motor, which had a power rating of 1.1kW and was supplied by an inverter, had a different current pattern. It had a low current of 7.7mA when I clamped only the phases, but a high current of 140mA when I clamped the CPC as well.

I appreciate your feedback. I used a earth leakage clamp meter to measure the current of the seven motors that make up the machine. When I clamped all three phases (Supply) together, the current was 45 mA. When I clamped all three phases and the CPC together, the current was 390 mA (fluctuating 400 +) I measured each motor separately. The current of the three motors that were connected to inverters was around 15mA when I clamped only the phases, but it increased to around 60 mA when I clamped the CPC as well. The feeder motor, which had a power rating of 1.1kW and was supplied by an inverter, had a different current pattern. It had a low current of 7.7mA when I clamped only the phases, but a high current of 140mA when I clamped the CPC as well.

When I clamped all three phases (Supply) together, the current was 45 mA. When I clamped all three phases and the CPC together, the current was 390 mA (fluctuating 400 +)

Are there any parallel earth paths from the machine (parallel to the c.p.c. that is) - e.g. any direct connections to metallic water pipes, structural steel or other machines with their own c.p.c.s. I'm just wondering if the c.p.c. currents are a bit of a red herring - either leakage originating from other parts of the installation and finding a path through your c.p.c. or even currents from outside the installations (e.g. diverted PEN currents from TN-C-S distribution systems).

In any event RCDs just see the currents in live conductors, so clamping around just those and ignoring the c.p,c. should be sufficient to see what's happening.

   - Andy.

Hello, yes. The machine has a lot of structural steel, steam pipes etc attached to it.

So if I can disregard the CPC readings the overall leakage current shouldn’t be a problem. I suspect I’m not being told the full story leading up-to the RCD failure. Currently I have the machine locked off, I Will reenergise tomorrow. Thanks Andy 

AMK said:

When I clamped all three phases (Supply) together, the current was 45 mA. When I clamped all three phases and the CPC together, the current was 390 mA (fluctuating 400 +)

Then 390 mA ± 45 mA must be flowing in the CPC - this is similar to my house, but as Andy says The RCD should not care.

If there is anything at all with the 3 phases together, where is the imbalance going? Shouldn't earth leakage through the inverters be pretty symmetrical? I wonder whether there is a somewhat intermittent fault which produces significantly more imbalance at times.

This must be one hell of an ironer. I had imagined a commercial laundry with people and moisture, but 422.3.9 implies a textile factory. What are they making please? Baize?

Hi Chris, the installation is a location where BE2 conditions exist. Are you asking if there’s a Three-phase voltage imbalance, not 120 degrees apart ? The 5.5 kW motor are all leaking 13.5 mA and the 1.1 kW is 7.8 mA. But you are right, it is possible that there is a somewhat intermittent fault that produces more imbalance at times, such as a loose connection, a damaged cable, or a faulty component. Is Baize used for snooker tables ?

Hi Chris, the installation is a location where BE2 conditions exist. Are you asking if there’s a Three-phase voltage imbalance, not 120 degrees apart ? The 5.5 kW motor are all leaking 13.5 mA and the 1.1 kW is 7.8 mA. But you are right, it is possible that there is a somewhat intermittent fault that produces more imbalance at times, such as a loose connection, a damaged cable, or a faulty component. Is Baize used for snooker tables ? And the manufacturer specified RCD fire protection.

AMK said:

Is Baize used for snooker tables ?

Yes indeed and for covering doors. IIRC, the cloth is trimmed during its manufacture which must produce a lot of dust.

P.S. Strictly speaking, snooker is a game which is played on a billiard table.

They haven't let Gregg Wallace into the factory, have they?

Snooker table round our way. Inside the Factory ? Did Gregg Wallace’s lack knowledge when it came to the correct terminology? Sorry the irony and sarcasm is wasted on me.

Oh dear!

Gregg Wallace is a rather endearing bald greengrocer who has turned into a TV presenter.

Neither irony nor sarcasm, but pedantry. Billiards existed long before snooker originated about 150 years ago. However, I can see its popularity, which only really started after the Beeb started showing it on the made-for-TV, Pot Black in 1969. Clearly, viewers had to be able to see the colour of the balls, whereas only the distinction of red and white was obvious in B&W (not that billiards was shown very often). Ted Lowe did his best when he said, "Steve [Davis] is going for the pink ball - and for those of you who are watching in black and white, the pink is next to the green."

Chris Pearson said:

and for those of you who are watching in black and white, the pink is next to the green."

That has been quoted many times.  I still find it funny.

It is almost a Michael Fish moment

public forecasts, on any topic, which turn out to be embarrassingly wrong

October 1987 storm