Tracking RCCB nuisance tripping

James · 2006-09-12T16:06:11+00:00

I know this is an old chestnut, I've been googling !This 70s house (live wires are red - not brown) has always beensensitive to tripping.The old washer made it happen a lot. It was replaced with a greatimprovement. (I guessed there were leaky radio interferencesuppression capacitors from live and netral to ground causing this???)An old iron made it happen a lot. It was sent to another house with noproblem there.Well, the problem seems to be back.I've come up with an idea to help locate it and would be grateful forany comments.The house uses a 63A / 30mA Crabtree RCCB with everything exceptlighting and immersion heater on the protected side.This assumes an appliance problem.(I am reasonably electrically savvy.)1. I made up a 2m 13A extension cable with the earth lead disconnectedin the plug.2. I *VERY CAREFULLY* connect appliances to the extension cable.3. I measure current using a multimeter between the opened earth leadand the earth pin in the plug.Checking the washing machine, I measure 2mA. I'm going to work my wayaround everything. Obviously it will be more difficult on hard wiredunits, eg the cooker.I'll try to post measured values.I understand that a 30mA breaker could trip at 50% x 30mA = 15mA, soseveral times 2mA can add up quickly to 15mA.I hope it's an appliance fault as wiring leakage sounds a very painfuland expensive fix.Any comments or pointers to other tracing techniques.I don't have a megger, but could easily do resistance checks with themultimeter.I seem to recall while googling seeing a technique of (power offsituation) strapping together the live and neutral, then measuringresistance to earth. This sounds promising and not too difficult.Is there any way to test to see if the RCCB is too sensitive ?Thanks in advance.James

Sep 12, 2006 22 Replies

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John Rumm 19 years ago

The voltage measured will be a function of the loading on the circuit at any given time. I have a feeling this particular test may just confuse things....

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meow2222 19 years ago

And switching the breakers off will ensure the same zero loading on all circuits.

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Andy Wade 19 years ago

Bear in mind that leakage currents will not necessarily add arithmetically. E.g. your 2 mA from the washing m/c (which seems a bit high) is likely to be capacitive and will add in phase quadrature to any resistive leakage current present. So 5 plus 2 makes 5.4 in this case.

Classic intermittent fault behaviour to a tee...

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