Testing RCDs

[Lemond2008]

Can all the normal tests on an RCD be done with it totally isolated - i.e. straight out of the box?
Sorry - forgot to put. By normal tests I mean trip times and ramp testing.

 

[RF Lighting]

RCDs should always be tested in isolation (with no load / wiring connected)

You will obviously need a line and neutral supply to the RCD to do the tests

 

[Lemond2008]

Do the RCD testers have the facility to be plugged into a normal mains socket to get the live and neutral supply? I want to take one up to a hubby electrician of someone at work for testing, and want to check that it's not more hassle to have it away from my CU.

 

[Spark123]

An RCD tester can be plugged into a socket to test an upstream RCD, why not have the electrician come to your house to do the test?

 

[JohnD]

You sound like you mean, can you plug an RCD tester into a socket, to test a loose RCD in its box? No, you can't, the RCD under test must be connected to a supply.

It is possible to connect the loose RCD to a mains socket using a plug and flex, to make it live, and then connect the Tester to the load side of the RCD, but this is not a good idea if the socket is itself RCD protected, as you will then be testing both of them, and they may both trip at the same time, or one before the other. You would have to use Safe Workshop Practice to jury-rig this sort of test, so your chum could not reasonably be expected to do it on his desk.

Is this an existing RCD currently installed in your house, or a spare new or used one in a box and not connected to anything? Why do you feel it needs testing?

 

[Lemond2008]

'Cos i've now removed the RCD from the CU and put the circuit that was protected by it onto the unprotected side. I had some tripping problems, and the missus was getting fed up with the power going off, and hence why the RCD is now out. I have read on here that it is not unusual for them to be faulty, and so whilst it is out, I would like to get it tested to eliminate that as the cause of the tripping.

 

[rebuke]

So your RCD was tripping, and rather than try and ascertain why (e.g. switching off individual circuits etc), you've just removed it. This seems a very bad idea, as it may have been tripping for a good reason, and I wouldn't want someone to find that reason the bad way...

It is possible for RCDs to go faulty (as with anything), but I wouldn't naturally assume that and just remove it - if I were you I'd either put it straight back in now and get your mate with the RCD tester to come round and test it for you when he can, or I'd go and get a new one (they're not hugely expensive) from somewhere, and put it in - if it still trips, then you almost certainly have a real fault...

 

[david_uk]

If the RCD is tripping, it could be nuisance tripping but there is more than likely a fault in the circuit.

Spent all day yesterday on what looked like nuisance tripping from the RCD. It was intermittant and no pattern to it. The fault was eventually narrowed down to an intermittant short in one section of the downstairs ring. What had happened was a picture hanging nail just happened to be vertically above a socket in the kitchen. There was continuity and IR came out OK, but just sometimes I'd get a neutral to earch short reading. Took a while. Why I got the readings I did, I don't know. However, a new bit of cable cured it.

So if you have RCD tripping, it's most likely to be something that's connected to the circuit, or a fault in the circuit. I wouldn't go down the route of assuming it's the RCD and changing it as a first step.

 

[Lemond2008]

Sorry - one vital point I didn't put originally is that the Press To Test button does NOT trip the RCD out. I have put the RCD back in the CU now, and still the Test Button does not work, but also I have not had any trips. This was one of the reasons I thought it could be the RCD gone weird

 

[rebuke]

If it doesn't trip when you push the test button (assuming it's got power), then it's definitely dead in some way, so no point trying to get someone to test it, it needs replacement - given you're happy removing and reinstalling it, you should be able to order another one for around £30 or so - if you're having trouble finding the right one, let us know any part codes or whatever from it (or post a pic) and i'm sure someone will find it for you...

 

[Lectrician]

RCD's do indeed go faulty, but in 99.9% of the cases, you will find you have a perfectly working RCD and a fault somewhere on the supplied circuits.

This fault may not be a direct danger, but it indicates a problem, and should be inestigated by someone who is capable of fault finding.

There is of course a chance the fault could BE VERY DANGEROUS, especially if associated with a poor earth loop impedance due to a damaged circuit or possibly faulty supply.

If this is a TT system, then you have put everyone in the house in DIRECT danger by removing the RCD.

 

[rebuke]

A fault on a circuit shouldn't stop the test button from working - if the test button isn't causing the RCD to trip, then the RCD is faulty (assuming the RCD is powered at the time)...