Nuisance tripping

ceejay · Dec 6, 2010

I have been investigating a nuisance tripping fault that happens about once every 2 days and even when only the new boiler and the fridge are connected, it still trips.

I have put an RCD SWITCHED FUSED SPUR to feed the fridge and the main board switch still trips but not the fridge SWITCHED FUSED SPUR.

Any ideas as to what else could be tripping it, i have never heard of a boiler tripping an RCD. There is a mains powered smoke detector feed from the upstairs lighting circuit.

ceejay · Jan 10, 2011

Thanks Trix and Simon.

No it's not a 17th edition split board and they now connect the fridge to the other ring but the only problem is that the RCD protects all circuits in the house. I have had more info today that it seems to trip abour 15 - 25 mins before the boiler is due to come on for the heating,

Rcd test results are as follows:
1/2 x 0 deg = no trip
1/2 x 180 deg = no trip
1 x 0 deg = 55ms
1 x 180 deg = 48ms
5 x 0 deg = 26ms
5 x 180 deg = 17ms
Ramp test = 24 mA

All connections have been tightened up.

telectrix · Jan 10, 2011

it's got to be down to cumulative leakage. the only way forward is: A. replace RCD with 2 pole isolator and fit RCBOs. B. earth leakage clamp meter if you could borrow one

ceejay · Jan 10, 2011

I've never used an earth leakage clamp meter, Would i need to test everything that is plugged in or just the white goods? I also don't fully understand cumulative leakage.

telectrix · Jan 10, 2011

cumulative leakage is when you get say 10mA on one circuit or appliance, say 8mA on another, maybe 15mA on another. each is insufficient to trip the RCD, but when all are on together, the total leakage exceeds the 30mA trip current of the RCD.and it trips. and, not having used the earth clamp meter myself, i can't comment on it's use. other guys on here can help you with that. as i see it, you put the meter on each earth or cpc in turn and read the leakage of each circuit. hope this helps., Tel.

SimpleSimon · Jan 10, 2011

Everything has earth leakage but so minimal that usually it's inconsequential. However, cumulatively (a collection of items) would add the total earth leakage to 30mA or more causing the RCD to trip.
Using an earth clamp would determine where the leakage is coming from. Trix's idea of using RCBO's is the best way to sort this most likely the earth leakage is nothing to worry, often happens on start up motors for fridges.

nickblake · Jan 10, 2011

no an earth leakage meter clamps round the cpc of the circuits and checks for any current flowing though it so if you can get hold of one test each circuit and add the total load up and see if it exceeds 30 ma or find a circuit that has a high earth leakage that could exceed the ma rating of the RCD but agree with telextrix it could be cumulative leakage ( were small leakage on each circuit adds up to more than the rated Ma of the RCD , and its a dam fine word too

sparx24 · Jan 10, 2011

As said by others cumulative ie lots of small adding to make large means say 5 circuits with 5mA leakage each would be enough to cause RCD to trip, hence rcbo's on each circuit would not trip as each only 'sees' 5mA unbalance.
Problem with using eareth leakage clamp meter as suggested around cpc is it won't show leakage via other routes such as damp walls etc .
Easiest way is to clamp around L&N tails (but not earth), this will indicate the actual reading your RCD is seeing, so by turning on/off circuits and also devices on circuits you can monitor where leakage occurs.
It is better if this can be done on each individual circuit but rarely room inside cons.unit safely.

pushrod · Jan 10, 2011

You can use an earth leakage clamp meter to test individual appliances. You just need to make up a test lead of a couple of meters of thick flex with a plug and socket on the ends. You then very carefully cut away 10" or so in the middle of the sheath (being careful not to nick the insulation on the cores) . You then just put your test flex in between the item being tested and the socket and put your clamp meter around the live and neutral or just around the earth. You get the same reading each time. Very useful way of quickly identifying dodgy appliances that are giving some but not 30mAs worth of leakage.
I always keep my lead with the test meter.

telectrix · Jan 10, 2011

pushrod said:
You can use an earth leakage clamp meter to test individual appliances. You just need to make up a test lead of a couple of meters of thick flex with a plug and socket on the ends. You then very carefully cut away 10" or so in the middle of the sheath (being careful not to nick the insulation on the cores) . You then just put your test flex in between the item being tested and the socket and put your clamp meter around the live and neutral or just around the earth. You get the same reading each time. Very useful way of quickly identifying dodgy appliances that are giving some but not 30mAs worth of leakage.
I always keep my lead with the test meter.

bit more technical than using a hammer on the fridge