Need some ideas - RCD tripping but everything tests fine....

[weevilward]

Hi all,
Customer reports sporadic nuisance tripping of RCD. I cannot reproduce it, or fault anything, except SOMETIMES on EFLI test it trips the RCD (megger mft 1553 'no trip' test).
I'm out of ideas here, can anyone help? This is what I've got:
- TT installation (small domestic);
- 30mA RCCB main switch incomer (Crabtree starbreaker);
- all circuits IR test 8MOhm to L&N-earth;
- RCD testing off load and on load all fine, ramp test 23mA off load 19mA with everything on.
- Ze about 160 ohms down the rod, drops to 12 ohms with all bonding connected.

 

[Pete999]

Borrowed Neutral on the Lighting circuit????

 

[telectrix]

intermittent fault caused by something like a fridge or other appliance that has a switching cycle. i.e. it switches on and off through a thermostat or timer.

 

[weevilward]

Borrowed neutral in lights - Nope. Even if there was, all 5 circuits are on the same RCD so it wouldn't show.

 

[weevilward]

intermittent fault caused by something like a fridge or other appliance that has a switching cycle.

I thought that but I've been here ages and cycled everything on / off. What is bugging me is the ELI test tripping it, never seen that before

 

[westward10]

Might need a leakage tester because combined leakage of the circuits maybe occasionally tipping it over the edge which is what your tester maybe doing.

 

[weevilward]

Might need a leakage tester because combined leakage of the circuits maybe occasionally tipping it over the edge which is what your tester maybe doing.

Ramp test with everything on and running 19mA - I've tested loads of RCDs on load like this and never has one tripped out.
I agree the most likely cause at the moment is combined leakage when something starts up, I just haven't been able to reproduce it.
She also says the RCD was 'tripped' after a power cut - I guess indicating that the startup leakage of everything together was >23mA when the power came back in again. But.... I cannot reproduce that either.

 

[weevilward]

Think I'm gonna have to just change the RCD for a new one today and see what happens... 'Tis 5 o'clock after all
I'm not convinced it's a faulty RCD though.
Please keep any ideas coming, I'll post if swapping RCD fixes it.
Cheers guys

 

[westward10]

Has she got any new appliances.

 

[weevilward]

Has she got any new appliances.

No, nothing new/changed in several months, the problem started about 3 weeks ago.

 

[buzzlightyear]

I depends on which circuit it is , any power to out side or lights you will a have to be Sherlock homes on that one .how big is the house .

 

[Ian1981]

Does she use an immersion heater perhaps through a booster/ timeclock?

 

[weevilward]

I depends on which circuit it is , any power to out side or lights you will a have to be Sherlock homes on that one .how big is the house .

Small 2 up 2 down with outhouse. Nothing major really, tested every, inspected everything.

 

[weevilward]

Does she use an immersion heater perhaps through a booster/ timeclock?

Good idea but no. CH and HW fully functioned - 3-way valve, boiler, pump, all sweet.

 

[buzzlightyear]

with rcd tripping do you know what circuit it is tripping the rcd !

 

[marc8]

hi weevilward
had a similar issue turned out to be a wine fridge some years ago, TT system everything on one RCD unit. would not be so bad if it was not in the cellar, every time we tested the circuit we unplugged the fridge to plug in lead light, found a problem on a ring short caused by a mouse, repaired tested time I got home phone call gone again, went back showed house keeper readings on meter IR testing circuit all clear.
anyway customer had all CB's replaced with RCBO units for each circuit & when it went again called me before turning on the RCBO, went in new wine fridge 3 months old causing issue. Maytag replaced no questions asked, did not help client with approximately 4 days of work caused by the fridge.
earth leakage meter very good used one of those a few times very helpful if you can turn on appliances whilst watching the readings.

have also had another fault about 10 years ago TT system same again 30ma trip on mains, IR tested whole house after I managed to take out all of the Neon indicated extension leads must have been 20-25 leads in the house, sh..t loads of electronics plugged in. spent all day on it IR tested could not locate, turned system on again plugged in & RCD down after 10-15 seconds, owner well it must be on a circuit I stripped down the conservatory, kitchen, lounge, heating, immersion, shower. each time I turned the system on I used hoover on each socket circuit & did not matter which one, owner did not believe me thought I was having him on that it was sheer over load of the RCD unit (30ma).
mentioned I would change board agreed price as I had already undertaken all of the testing on the whole house in that day & had results, agreed deduction on my days wages against fuse box change picked my money up next day got phone call my mate will change for less than you.
I lost it & called him c...t, told him good luck with testing his f.....king house, as I would not give him my notes as he did not want to pay for them.

 

[Des 56]

Is the 8 Mohm insulation test for the installation
Have you tried L+N to earth with all appliances connected

At a guess I would go with Tels suggestion,a appliance problem,fridge,freezer,washer, Cent heat pump or valve maybe

If it was in Wales its almost certainly a outside light filled with some of the perpetual rain we have to contend with

 

[Octopus]

Loose connection on incoming supply - had this recently.

Knackered RCD?

 

[buzzlightyear]

just recently had rcd tripping out, told the customer I would pat test several
extension leads tested four ,three failed . possible with yours .
fault found extension lead.

 

[Octopus]

Wonder if the OP has an earth clamp meter? Could just be accumulated leakage!