RCD tripping. Give me a clue!

[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