Suddenly I'm getting nuisence trips...

[HDRW]

I replaced the old rewireable fuse box in my house back in December 2004 (obviously!) with a Wylex split consumer unit, with the immersion heater and up and down rings on the RCD side.

All has been well since then, but yesterday evening I had a nuisence trip of the RCD. I turned off the MCBs, reset the RCD and turned on the MCBs, and all was well.

But this morning it happened again! (The name is well chosen, it is a darned nuisence!).

Nothing has changed for many months, the house isn't leaking water (despite the downpours we've been having) and as far as I know there aren't any rodents in the building. The immersion heater is on a timeswitch, and both times the switch would have been off (I checked the timer this morning to confirm that), so I don't think that's the source of the problem.

How on Earth do you set about tracking down the cause of something like this? If it was solid fault I imagine it's just a question of isolating circuits, then going round the dodgy one looking for the problem, but when it's intermittent like this what's the technique?

Cheers,

Howard

 

[Diyisfun]

I had similar after my house was partialy rewired. I phoned the sparks he had no idea. After about 2 weeks, I took all the sockets off & found a live wire was not tight, & was arcing enough to break through the cable.

 

[JohnD]

It sounds as if you immersion is on the RCD, this is not usual. Is the cooker on it too? You may have a build up of small leakages from apploances which add up to enough to trip the RCD.

I would suggest you start by unplugging the washing machine, dishwasher, kettle and any other "watery" appliances as they are the most frequent cause of leakage; and turning off the immersion heater and the cooker with its DP switch. (not just the timer as you may have an N/E fault). Also isolate any outside circuits including garden sockets and lamps, fountaiins, pool heaters, spas and jacuzzis.

You could also try turning off all the MCBs that you can afford to do without, and seeing if the tripping stops (this will only work if it is a P/E fault).


p.s. I have 50p on the immersion heater. They often get a bit leaky with age

 

[LionIrons]

Don't rule out a faulty RCD.
I have seen it twice.

 

[HDRW]

It sounds as if you immersion is on the RCD, this is not usual.

I didn't get where I am today by only doing the usual things! Can it still cause a problem when it's switched off by the timeswitch? It's single pole, so I suppose if the leakage acts between N and E it could, but I'd have thought it would be more persistent than just 2 incidents 12 hours apart.

Is the cooker on it too? You may have a build up of small leakages from apploances which add up to enough to trip the RCD.

There is no cooker - or at least the gas pipe that it's connected to doesn't run through the RCD!

I would suggest you start by unplugging the washing machine, dishwasher, kettle and any other "watery" appliances as they are the most frequent cause of leakage; and turning off the immersion heater and the cooker with its DP switch. (not just the timer as you may have an N/E fault). Also isolate any outside circuits including garden sockets and lamps, fountaiins, pool heaters, spas and jacuzzis.

OK, I don't have most of those, but I can do the ones I have.

You could also try turning off all the MCBs that you can afford to do without, and seeing if the tripping stops (this will only work if it is a P/E fault).

Tricky, since it's intermittent and there are only the 3 MCBs (Immersion Heater plus 2 rings, upstairs and down). I can disconnect the immersion (DP switch downstream of the timeswitch) but I won't know unless it's not that and it trips anyway...

p.s. I have 50p on the immersion heater. They often get a bit leaky with age

OK, 50p it is!

Cheers,

Howard

 

[HDRW]

Don't rule out a faulty RCD.
I have seen it twice.

I must say I hadn't considered that! I do have an RCD tester, so I can have a go with that and see what level of imbalance trips it.

Thanks!

Cheers,

Howard

 

[securespark]

You did not do any tests before changing the board? Suicide!!

You must test the RCD, and not from a socket outlet, but directly from the outgoing RCD terminals, with no circuitry attached (ie DISCONNECT the neutrals and switch off the mcb's.

Do an auto test to make sure it is not tripping on the 1/2 x test and to ascertain whether it is within the parameters on 1x & 5x test. Guess having an RCD tester you know what they are. But also do a ramp test. If it trips at 1/2 rated or less, it is goosed. Again, do this test as above, directly from the RCD with no circuits attached. Personally, I would like to see a minimum of 18mA. Any less and I change it as routine.

 

[HDRW]

You did not do any tests before changing the board? Suicide!!

I did! The readings were all fine then, but that was two and a half years or so ago. There hasn't been a problem until this week.

You must test the RCD, and not from a socket outlet, but directly from the outgoing RCD terminals, with no circuitry attached (ie DISCONNECT the neutrals and switch off the mcb's.

Understood. I assume the functional Earth needs to remain connected, though?

Do an auto test to make sure it is not tripping on the 1/2 x test and to ascertain whether it is within the parameters on 1x & 5x test. Guess having an RCD tester you know what they are. But also do a ramp test. If it trips at 1/2 rated or less, it is goosed. Again, do this test as above, directly from the RCD with no circuits attached. Personally, I would like to see a minimum of 18mA. Any less and I change it as routine.

Right, thanks a lot. I do know what you mean, but I wasn't sure what would be regarded as the limit for an acceptable level - 18mA sounds like a good one!

Cheers,

Howard

 

[HDRW]

OK, someone owes me 50p - it still happened with the Immersion Heater isolated!

I've just done some tests on the disconnected RCD (isn't that a pain to do? Why are the finger-guards on the probes just too wide to allow both probes into the screws without my having a black belt in the use of chopsticks?).

It trips always at 20mA, and often at 15mA (can't get any closer than that - my tester only has 10, 20, 30... and 1/2x, 1x, 5x). So I think it's time for a new one! It would have to be the most expensive item in the box, wouldn't it?

Thanks for all the help, people. I'll report back if changing the RCD doesn't fix it...

Cheers,

Howard

 

[securespark]

If a ramp test trips it at 15mA, then it it goosed.

 

[HDRW]

If a ramp test trips it at 15mA, then it it goosed.

Yes, it's certainly gone South (for the winter? )

I've replaced it, and all's been OK since, touch wood!

Thanks for the advice, everyone.

Cheers,

Howard