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.

 

[Octopus]

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?

I would recommend you buy one as a matter of urgency .... Then one of the first tests you can do is establish the leakage........

 

[Octopus]

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.

The price won't go down well, but how much food is in her freezer..... This would go to waste if it trips and she's not around......

 

[Pete999]

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.

Do you mean a type S 100mA RCD as the main switch?

 

[weevilward]

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.

Nasty customer, marc8, well avoided...
Thanks for th advice, I am going to invest in an earth leakage meter - any recommendations?

 

[Octopus]

^^ how much are you prepared to spend?

 

[weevilward]

^^ how much are you prepared to spend?

Decent quality but don't wanna throw money away unnecessarily. I'm 95% domestic, been getting by with just my Megger MFT1553 for last 10 years!

 

[weevilward]

Do you mean a type S 100mA RCD as the main switch?

Or upfront before CU. I know this is a bone of contention on forums - some people say normal main switch and all 30mA RCBOs is fine, others prefer to fit time delay 100mA as well. Don't especially want to go off topic here....

 

[weevilward]

Or upfront before CU. I know this is a bone of contention on forums - some people say normal main switch and all 30mA RCBOs is fine, others prefer to fit time delay 100mA as well. Don't especially want to go off topic here....

Pretty sure crabteee starbreaker don't do a 100mA type S main switch so it'd have to be upfront before CU

 

[westward10]

Or upfront before CU. I know this is a bone of contention on forums - some people say normal main switch and all 30mA RCBOs is fine, others prefer to fit time delay 100mA as well. Don't especially want to go off topic here....

I would go for this as it offers double pole isolation whereas the rcbos do not.

 

[Octopus]

Decent quality but don't wanna throw money away unnecessarily. I'm 95% domestic, been getting by with just my Megger MFT1553 for last 10 years!

Maybe start a thread asking for recommendations?

Doing domestic, a earth clamp meter is essential...

 

[weevilward]

I would go for this as it offers double pole isolation whereas the rcbos do not.

Ok thanks Westward

 

[Deleted member 9648]

Maybe start a thread asking for recommendations?

Doing domestic, a earth clamp meter is essential...

I don't have one, useful, probably invaluable but not essential. I do a lot of fault finding jobs as well.

 

[Deleted member 9648]

I would go for this as it offers double pole isolation whereas the rcbos do not.

So does a main switch.

 

[weevilward]

So does a main switch.

Uh-Oh look what I've started now......

 

[buzzlightyear]

So far the 'swapped' RCCB hasn't gone again

what's the betting he will have to go back!