RCD tripping. Give me a clue!

[Marvo]

Yep, but if there happens to be 9mA leakage and your ramp test shows a pass at 22mA then you will leave a non-compliant RCDin service thinking it's okay.

 

[Piratepete]

Forget the torque driver, an earth leakage clamp meter would be more important.

You can't use an inline ammeter to check leakage current because it will only tell you what's going down the CPC, not what's being lost down parallel paths. The RCD doesn't monitor the CPC current so the test would be meaningless.

Good point! Can you recommend a suitable meter.

I accept that the RCD is looking at an imbalance between L and N. Isn't that difference also reflected in the main cpc?

 

[Marvo]

I think many of the UK guys seem to use a Dialog earth leakage clamp meter which I believe is very reasonably priced. I'm sure someone will chip in with the exact model number for you.

Not all fault currents flow down the CPC, for example if an appliance has an IR fault and happens to be in contact with the kitchen sink then the fault current or a good portion of it will flow to earth through the water pipework and/or the earth bonding.

 

[Guest111]

A common one is fridge and freezer compressors,these can test out OK but when they have run for a while and heat up they reveal a fault,that can be a real pain to find.

 

[BigTom83]

Do you not think 1.47 Mohms is a low reading?

Doesn't GN3 state 1Mohm is acceptable reading but anything less than 2Mohms requires further investigation.

Not sure why your testing with everything plugged in? Not sure what this achieves?

The chances are 1.47 Mohms is probably due to it reading through an appliance.

Remove the appliances, lamps, etc. and retest IR on each circuit, see if the readings improve (I guess they will).

If they do try PAT testing each appliance, if one looks dodge exclude it from circuit for few days see if that helps.

Trial & error only way forward if it's an appliance at fault

 

[Piratepete]

Yep, but if there happens to be 9mA leakage and your ramp test shows a pass at 22mA then you will leave a non-compliant RCDin service thinking it's okay.

You have to remember why I did the ramp test, which was to see if it was over sensitive rather than insensitive.
You've made me think though - I'm wondering why my assessors have never pulled me up for not switching off all unecessary circuits (eg.lights) when I do an Auto RCD test with my MFT. I tend to use the cooker circuit and switch off the ring(s) - doesn't do fridges any good! Is it because the standard auto test doesn't include a ramp test? When the tester leaks 30 mA does it take account of existing leakage?

 

[Marvo]

When the tester leaks 30 mA does it take account of existing leakage?

Nope, the tester isn't that clever. If it applies a 30mA leakage test the actual leakage seen by the RCD will be the test leakage plus any other leakage from circuits and appliances.

Ideally you should disconnect all circuits and all loads from the RCD when ramp testing it.

It's good you're beginning to think about the bigger picture, it might help if you draw some circuit sketches of the possible fault paths and testing procedures.

 

[Engineer54]

Good point! Can you recommend a suitable meter.

I accept that the RCD is looking at an imbalance between L and N. Isn't that difference also reflected in the main cpc?

Here you go.....


TM-EL9809 High Resolution AC Earth Leakage Clamp Meter

Both units are rebadged Di-log units, the above is an upgraded unit.
You'll get 5% discount on this model from the forum sponsor test meter too!!


Amprobe AC50A