Intemittent tripping RCD.

[HappyHippyDad]

Hello everyone..

I have a job tomorrow tracking down a tripping RCD fault.

This would have panicked me a year ago, now I'm looking forward to it and cant wait to get there!

However, from the phone conversation I have discovered the following:

1. No recent DIY work or professional work has been carried out recently.
2. One of the RCD's (dual board) trips every 5-40 minutes, this RCD feeds the kitchen ring, all lights and one other circuit (forgotten which)
3. It does not trip at any regular time of the day (so possibly fridge or other irregulary timed power source)
4. It started approx 3 days ago, nothing 'different' happened at that time. No new fridge, cooker etc.
5. Sometimes trips when different appliances are switched on, sometimes just spontaneously.

Basically the prelimanary detective work has given me little insight into the problem so I will be relying on IR testing and earth leakage clamp meter. I expect/hope that the global IR test will show a poor reading so then it will be a simple job of narrowing the fault down. However..

I do like to try and have a plan for any eventuality, so this is my question:

1. If the IR tests show no fault then where do you go from there?

I know I'm being a bit ----, but I like to play it a bit like a game of chess and think many moves ahead!

My thoughts are (given good IR results):

- homeowner could leave one of the affected circuits switched off and see if RCD stops tripping.
- Check all items that get plugged in for earth leakage.
- Visual inspection of O/S lights for poor IR.
- continuity tests between neutrals of differing RCD's (highly unlikely given fault has only just started occuring)
- RCD tests, including ramp.
- Check for loose connection upstream of RCD.

Have I missed anything that you guys would automatically do/think?

 

[Leesparkykent]

Ramp test the rcd and see what ma it's tripping at.

 

[R G]

I think with the recent posts about this topic , the most valuable test once the preliminary tests of the circuit have been done is the ramp test with appliances connected and without , that would indicate what appliances are faulty , you can keep trying it and unplugging appliances until the readings improve to narrow it down ..

 

[telectrix]

as above. ^^^^.

 

[Doomed]

Had this the other day, eventually traced to a twisted bit of cable on the kitchen ring main - took hours to find - had been happy for years, but after time it started to trip occasionally, then more frequently and then a couple of times an hour, thats when we were called.

 

[HappyHippyDad]

I think with the recent posts about this topic , the most valuable test once the preliminary tests of the circuit have been done is the ramp test with appliances connected and without , that would indicate what appliances are faulty , you can keep trying it and unplugging appliances until the readings improve to narrow it down ..

Thanks Ray,

I'm unsure how having the appliances connected, unconnected affects the Ramp test though? Doesn't the ramp test just show at what mA the RCD is tripping when you put the fault current through it?

 

[VoltzElectrical]

One that got me on an intermittent was not leaving the earth cables connected in the bar testing between cores on IR. The cable cores were clear to each other, but the live was down intermittently to the general mass of earth which I had eliminated by taking the earth cable out of the bar. Gggrrrr.

When the installing electrician stripped the cable back for the outside light, he had ringed the insulation on the live that was touching the brickwork as it came through the wall. Sometimes it would trip every couple of weeks. Sometimes every couple of days. Very frustrating trying to fault find a fault that isn't there when you attend, but get a phone call a week later to say it's tripped again!

You can have this little gem for free, as long as you let us know what it was when you find it dude.

x

 

[telectrix]

if you ramp test with no circuits connected and get, say, 25mA, then with circuits/appliances connected get 10mA, that says there's 15mA leakage.

 

[R G]

On pretesting,one that got me was some outdoor spike lights that are class 2 with twin flex in use , and someone had clipped twin flex around to adaptable boxes ,with the lighting circuit with CPC disconnected at the DB it was all clear , But testing down to the MET it was down , eventually found a buried adaptable box wrapped up in a carrier bag ,

 

[R G]

Thanks Ray,

I'm unsure how having the appliances connected, unconnected affects the Ramp test though? Doesn't the ramp test just show at what mA the RCD is tripping when you put the fault current through it?

Thats the most valuable part really because your testing with the leakage there , as Tel says the readings will tell you which appliance is registering the most when they are isolated ( i.e. the difference ) as you unplug items

 

[Octopus]

Stick an earth leakage clamp meter around the tails, turn off each MCB in turn, noting the reduction in the overall leakage.

This may show something useful and save you hours!

 

[SirKit Breaker]

Hello everyone..

I have a job tomorrow tracking down a tripping RCD fault.

This would have panicked me a year ago, now I'm looking forward to it and cant wait to get there!

However, from the phone conversation I have discovered the following:

1. No recent DIY work or professional work has been carried out recently.
2. One of the RCD's (dual board) trips every 5-40 minutes, this RCD feeds the kitchen ring, all lights and one other circuit (forgotten which)
3. It does not trip at any regular time of the day (so possibly fridge or other irregulary timed power source)
4. It started approx 3 days ago, nothing 'different' happened at that time. No new fridge, cooker etc.
5. Sometimes trips when different appliances are switched on, sometimes just spontaneously.

Basically the prelimanary detective work has given me little insight into the problem so I will be relying on IR testing and earth leakage clamp meter. I expect/hope that the global IR test will show a poor reading so then it will be a simple job of narrowing the fault down. However..

I do like to try and have a plan for any eventuality, so this is my question:

1. If the IR tests show no fault then where do you go from there?

I know I'm being a bit ----, but I like to play it a bit like a game of chess and think many moves ahead!

My thoughts are (given good IR results):

- homeowner could leave one of the affected circuits switched off and see if RCD stops tripping.
- Check all items that get plugged in for earth leakage.
- Visual inspection of O/S lights for poor IR.
- continuity tests between neutrals of differing RCD's (highly unlikely given fault has only just started occuring)
- RCD tests, including ramp.
- Check for loose connection upstream of RCD.

Have I missed anything that you guys would automatically do/think?

Give it a full test properly as per GN3 this way you wont miss anything out, and wont get confused its easy to jump the gun when fault finding and ending up going round in circles. Make sure that there is nowt connected and all fused spurs are switched off.

Con, IR, Zs (at every socket) and then RCD and ramp. If that goes well, then i suggest checking for the obvious and easy first. Loose connections and check the socket to make sure that the plug is snug fit and doesn't move about due to wear, or pull out too easily.

Good luck and let us know how it goes.

Cheers.............Howard

 

[HappyHippyDad]

Give it a full test properly as per GN3 this way you wont miss anything out, and wont get confused its easy to jump the gun when fault finding and ending up going round in circles. Make sure that there is nowt connected and all fused spurs are switched off.

Con, IR, Zs (at every socket) and then RCD and ramp. If that goes well, then i suggest checking for the obvious and easy first. Loose connections and check the socket to make sure that the plug is snug fit and doesn't move about due to wear, or pull out too easily.

Good luck and let us know how it goes.

Cheers.............Howard

Thanks for that Howard, very sensible advice.

Quite frankly I dont think that fault stands a chance now!! I'll give it one hour... tops!! :smile5:

 

[Octopus]

Can't wait for the updates on this one!

I'd be asking about leaks, DIY, outdoor connections, ...........

 

[HappyHippyDad]

Can't wait for the updates on this one!

I'd be asking about leaks, DIY, outdoor connections, ...........

Well you know you'll be getting an update Murdoch, perhaps not over the next few days but it'll come. Plus it'll be an honest one, even if it means I missed something silly, so you may be in for a good laugh!

 

[Octopus]

Well you know you'll be getting an update Murdoch, perhaps not over the next few days but it'll come. Plus it'll be an honest one, even if it means I missed something silly, so you may be in for a good laugh!

Intermittent RCD trips are the worse, especially on upfront or dual RCD boards!

The last one I had was due to accumulated earth leakage across one of the RCD's so virtually any extra load on the circuit may push it over.

Fortunately I had installed a hi integrity board (which is the norm for me these days) so moved the "worst" circuit onto its own RCBO!

 

[telectrix]

don't rely on IR test. i had one last week where a L cable in a socket had a nick in it, pressing against the back box. MCB and RCD both tripped after energising circuit for about 1 minute. IR test on the circuit showed 15Megohms.

 

[HappyHippyDad]

Intermittent RCD trips are the worse, especially on upfront or dual RCD boards!

The last one I had was due to accumulated earth leakage across one of the RCD's so virtually any extra load on the circuit may push it over.

Fortunately I had installed a hi integrity board (which is the norm for me these days) so moved the "worst" circuit onto its own RCBO!

Sensible! Do you find you lose some quotes Murdoch with the higher cost of the 'hi integrity' board and RCBO's?

 

[telectrix]

BG hi integrity board £50.

 

[Octopus]

Sensible! Do you find you lose some quotes Murdoch with the higher cost of the 'hi integrity' board and RCBO's?

The install is designed to fit in the MCB's ways within the hi int board, leaving 2 ways spare by the main switch. All my board change estimates include

"NB: If problems are detected during the fuseboard change additional work may be required. Such issues and associated costs will be discussed with you, prior to being implemented"

So the customer cops the additional cost of the RCBO and remedial works.......

The most recent one was where the house had a borrowed neutral on the lights, with absolutely no way to run a cable or fix it... so combine up and down circuit onto 1 x rcbo and everybody is happy.

My pricing locally is lower than most from what I hear, but I'm happy with what I make doing a CU change as its a good rate for 1 days work. Sure there are a couple of "chuck it in anyway" cowboys, but most of my customers won't let them work in their houses once they have met them!