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.

 

[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!

 

[Deleted member 9648]

TBH if I have these sort of problems with a single RCD install I don't waste a great deal of time if IR tests with everything connected are good. Advise to change to RCBO's. Whatever you do nuisance tripping is almost inevitable with such an install, even if you find a problem chances are something else will trip it before long and then you'll be back again for SFA because "I've already paid you once to fix it". A single RCD don't comply any more anyway!

 

[D00DY_T00DY]

Could be anything. Gremlins I bet.

Once had the moulded plug on an oven extractor being the cause of the problem once.

Eliminate the impossible whatever's left; how ever improbable must be the truth.

Better get your deer hunting cap on OP

 

[The Ghost]

Just a wild stab in the dark here. Found by changing the switch/strapping cables around on the two way lighting this cured such a problem as the earth was close to the permanent live when I swapped it to the other side of the three core + E problem disappeared. So it was two cables away so to speak, hope that is clear?

 

[Rpa07]

Just a wild stab in the dark here. Found by changing the switch/strapping cables around on the two way lighting this cured such a problem as the earth was close to the permanent live when I swapped it to the other side of the three core + E problem disappeared. So it was two cables away so to speak, hope that is clear?

Did you hear a little voice in your head to do that @Vortigern? Stab in the dark but nice result!

 

[The Ghost]

I hear the singing in the wires @Rpa07

 

[bigspark17]

Id go for accumulated leakage, if youve tested the rcd then changing it wont do anything unless you put a faulty one in. Id price for a board change 100ma TDelay main switch and all 30mA rcbo's. The current design is no good for the modern day electrics with circuit discrimination required and so many leaky electronic devices, the system needs an upgrade.

 

[weevilward]

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

Hi Buzz, no I don't, it's not happening often enough to see. I've IR'd the circuits individually and the RFC sockets shows 8M so it's most likely something on this circuit.

 

[weevilward]

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

I don't have a clamp meter but ramp testing with and without everything on shows a cumulative leakage of 4mA difference - this is effectively doing the same as a clamp meter in this case?

 

[weevilward]

Just a wild stab in the dark here. Found by changing the switch/strapping cables around on the two way lighting this cured such a problem as the earth was close to the permanent live when I swapped it to the other side of the three core + E problem disappeared. So it was two cables away so to speak, hope that is clear?

That is a niche fault, Vortigern! I'll have a look at the strappers, but I can't make it trip by operating the 2 way switching, and it has no effect on the ramp test in either position.

 

[weevilward]

Id go for accumulated leakage, if youve tested the rcd then changing it wont do anything unless you put a faulty one in. Id price for a board change 100ma TDelay main switch and all 30mA rcbo's. The current design is no good for the modern day electrics with circuit discrimination required and so many leaky electronic devices, the system needs an upgrade.

You are right Bigspark, it is a pants installation at the moment, I will recommend this but she is on a budget, so 5 RCBOs and a Type S main switch (plus labour) is most likely not going to go down well.... I'll see what she says.
So far the 'swapped' RCCB hasn't gone again, but I am not holding out great hopes!
Cheers for the advice & opinions everyone.