Earth Leakage - Martindale Clamp Meter

[Luckyboy]

Hi all

I recently attended to a call-out to intermittent RCD tripping on a dual RCD board.
Got out my Martindale CM69 TRMS Earth Leakage Clamp Meter and put them around the tails and switched on a circuit at a time, the leakage was significant, hundreds of milliamps, RCD didn't trip.
Measured insulation resistance to all circuits, all above min. 1 mega ohm.
Owner said it trips randomly but started over the weekend when it was raining rather heavily.

Any ideas on why my clamp meter is showing such large leakage with the RCD not tripping?

FYI I have "zeroed" the meter, it is less than a year old and in good condition.

 

[newfutile]

You could check it against known loads like a led lamp,they usually have the milliamp rating on the side of them

 

[binky]

surely you clamp it around the main earth, not the meter tails.

 

[Murdoch]

surely you clamp it around the main earth, not the meter tails.

I would try on both to compare the results - this is what I normally do.

If there are circuits not protected by the RCD's that could offer an explanation

 

[Richard-the-Ninth]

surely you clamp it around the main earth, not the meter tails.

You would have thought so, but you don't, it should go around the meter tails. After all, the RCD doesn't monitor the earth. The idea is the clamp meter detects the difference between L & N

 

[Andy™]

did you actually test the RCD properly or just winging it with a clamp meter whilst hoping for the best?

 

[SPECIAL LOCATION]

surely you clamp it around the main earth, not the meter tails.

That would only show any leakage current via the earth conductor...

It would not identify any leakage via an alternative earth path...
e.g. via an extraneous conductive part.

 

[Luckyboy]

did you actually test the RCD properly or just winging it with a clamp meter whilst hoping for the best?

Well of course, RCD ramp test was OK @ 21ms during 30mA load and trip times for x1/2, x1 and x5 all OK.

 

[Luckyboy]

I would try on both to compare the results - this is what I normally do.

If there are circuits not protected by the RCD's that could offer an explanation

Thanks @Murdoch - 2 DBs, all circuits protected by RCD although I only put the clamp on the meter tails for the DB affected.

 

[binky]

You would have thought so, but you don't, it should go around the meter tails. After all, the RCD doesn't monitor the earth. The idea is the clamp meter detects the difference between L & N

learn something every day

 

[Stevie G]

The Owner said it trips randomly but started over the weekend when it was raining rather heavily. Would look at any outside Light fittings etc, as clue due to heavy rain