I pressed the "Press to Test" button on our Wylex RCD in the CU yesterday and it failed to trip! Tried several times, but it would not trip the device.
Switch the RCD off by using the DP switch bult into it - then switched it back on again. After doing this the PTT button works fine. I shall replace the thing anyway - but is this "usual" for such devices? It is only about 3 years old. I must admit I hadn't tested it for some 6 months so is that the possible cause?
Did you try pressing and holding it for a couple of seconds?
Although they should be pretty reliable, they do go faulty. If it's a devices that is being tripped out regularly by lamps popping and things, then it might be passed its use by date.
No - only for about a second I guess. Will try again tomorrow.
dave coughed up some electrons that declared:
Replace it with a reasonable sense of urgency (don't panic, but as soon as practical) - it's got sticky. It'll probably work fine for a while, especially if you keep poking the test button, but it's liable to stick again just when you need it.
Cheers
Tim
This does seem to be the most common failure mode - the trip mechanism is sticking, basically. Is your specimen in a particularly dusty, damp or hostile environment, or was it installed during building work when there was a lot of dust around?
Frequent testing is certainly said to help, but you shouldn't expect such premature failure under normal reasonably clean installation conditions.
Further reading:
together VIA A SUITABLE RESISTOR, to leak 30mA to earth, to prove it is sticking, rather then the test button's contacts being dirty?
(Sorry, not too sure how to calculate the resistor, or wattage of said resistor!) But I assume it can't need to be that higher wattage, as there is one inside every RCD and RCBO!) (That has just made be think to measure the resistance across a (Disconnected!) RCD with the test button pressed to find out :-)
Toby...
Ohms law basically...
V = IR
so R = V/I
If you want to pass 30mA at 240V that would be 240/0.03 = 8000 ohms
To check the power dissipated in the resistor you can use either:
P = I^2 R or P = VA
Both will give 7.2 watts (so a fairly hefty resistor)
See the table at the end of:
Bin it and replace.
No. It ought to work after years of doing nothing.
Well you could, but it would be much better to use a proper RCD tester to check that it trips within the permitted times, and doesn't trip at
15 mA. And if the test button isn't working the thing needs replacing anyway, so why mess about? 230 V / 30 mA = 7.67 kohm, so say a 6k8 resistor. At max mains voltage (253 V) a 6k8 would dissipate 253^2 / 6800 = 9.4 W, but you don't really need 10 W continuous power rating for obvious reasons.
Looking online a 7W resistir is pretty big - is there really one this large inside and RCD/RCBO, or as it is (should!) only be sinking power for a fraction of a second, can it be a lot smaller?
(I don't have an RCD I want to break apart to check!)
Toby...
A hefty resistor of that size could also be called a light bulb, or lamp, or lumenaire, or lantern, or..............
I'm off to bed. :-)
In fact you could stick a bog standard 1/4 watt one in there. The tester will alert you to the failure of the RCD by making a nice "popping" sound (well once at least) ;-)
There are safety issues with a resistor in a plug. Better to use a 15w bulb connected L-E. Not that its ideal, but it would test it.
NT
Test duration is supposed to be limited to 2 seconds max, IIRC. That's so that if there's someone somewhere else in the building who suddenly finds your earth leakage test current, which isn't tripping the breaker, is now going through them for some reason, you limit the shock to 2 seconds.
Actually, if you have any cause to suspect an earth fault, don't do such a test if there are other people on the premises (other than someone watching over you in case you have an accident).
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