rcd ramp test results

[17thman]

hello there.

i was called to an rcd intermittant trip fault. As per normal, i disconnected all loads and tested IR, fine. Then ramp tested the rcd which disconnected at 15ma and 17ma on both halves of the cycle in 9ms and 14ms respectively. I then introduced some of the loads gradually. wash mach, dish wash, ff, kettle so on. could not recreate it. checked continuity of ring and inspected all accessory connections that i could find. Nothing outdoors!! re ramp tested got 22ma and 21 ma at 15 and 17ms. then had chat with customer and then reramp tested and got a trip at 180 degrees at 14ma in 20ms.

So i know that i never get anything over about 23 ma when i ramp test.

What can i deduce from this? A combined intermittant earth leakage from appliances and an intermittantly over sensitive rccb?

There could of course be an intermittant fault in the fixed wiring and an intermittant rccb sensitivity problem. does any body else experience such different ramp test results on retest? I have agreed to change rccb when or if it next trips but a discussion may help me

 

[securespark]

Anything less than 16 ditch the RCD.

RCD tests SHOULD be done in complete isolation, IE disconnect both outgoing tails.

If this is difficult, switch off all MCB's on the RCD and then disconnect the neutral to the busbar.

This isolates all wiring/ equipment from the RCD.

If it still shows a fluctuating ramp test result, then ditch it.

 

[RF Lighting]

Don't forget that a 30mA RCD sould trip at below 30mA

 

[17thman]

yes Rob thanks and to secure(simon, i remember)? I tested RCCB in isolation. can there be a reason for fluctuating ramp test results other than faulty rccb or faulty fluke(calibrated 2 months ago).

fluctuating supply voltage or is this irrelavant across the mechanism? or temperature differences for instance, obviously not in this case, as the interval between test was short.