RCBO problems

[BLBelfast]

Got a call out today to a house. The fella told me everytime he plugs something into the ring main it trips the RCBO. So upon investigation I found a neutal to earth fault on one cable. The cable could not be replaced without great damage so I split the ring into two radials. Thing is the RCBOs are still tripping when something is plugged in with any sort of load at all. HELP please

 

[Marvo]

If there's no other neutral to earth faults it will probably be a crossed neutral or borrowed neutral issue.

Did you test the RCBO itself?

 

[BLBelfast]

I changed the 32A for two 20A when i split the ring and both keep tripping. They are ok till anything is plugged in and i tried at least 8 different items and the only thing that didn't trip them was my socket tester. Completely stumped.

 

[IQ Electrical]

I changed the 32A for two 20A when i split the ring and both keep tripping. They are ok till anything is plugged in and i tried at least 8 different items and the only thing that didn't trip them was my socket tester. Completely stumped.

There's a neutral problem there then.

 

[Marvo]

Yep, a neutral fault, crossed or borrowed. Go through all the neutrals again and find the one (or more) in the wrong place.

The RCBO will only trip with a load because if there's zero current flow there will also be zero imbalance between the live and neutral currents. Only when there's a load will a current imbalance occur which will exceed the 30mA (I'm guessing) leakage detection threshold.

 

[marty1234]

I dont think it a crossed neutral try swaping over the rcbo to see if there is a fault in The rcbo .if neutrals wher crossed over it would trip out when you tryed to switch it on with out any load on .I had same problem last week it would trip out when i tryed my martindal tester in it very little load i changed rcbo and worked ok . Both rcbo brand new fitted same day one with a fault give it a try

 

[BLBelfast]

Thanks for your help.Yeah 30mA. I really doubt it is the RCBO as that is three different ones it happens on. And now the ring is split it happens on two different circuits.

 

[WDMDL]

Daft one, but are the circuit Neutrals actually connected to the N LOAD terminal on the relevant RCBO, not straight to the busbar with the tail?

eg Has someone before you changed MCB to RCBO without fully understanding how they work?

And if functional earth type RCBO, is that connected correctly?

Simon.

 

[telectrix]

you say you have split the ring. i take it you have isolated the fault from the ring. if so, take both radials ( all cables) out of CU terminals and IR test again.

 

[SimpleSimon]

If you've isolated the suspect and turned them into radials it's funny that it shows on both.
Check RCBO is wired correctly. Also how long was the RCBo fitted?

 

[BLBelfast]

Daft one, but are the circuit Neutrals actually connected to the N LOAD terminal on the relevant RCBO, not straight to the busbar with the tail?

eg Has someone before you changed MCB to RCBO without fully understanding how they work?

And if functional earth type RCBO, is that connected correctly?

Simon.

Yeah definetly connected properly. These ones, type B have no functional earth.

you say you have split the ring. i take it you have isolated the fault from the ring. if so, take both radials ( all cables) out of CU terminals and IR test again.

Did that and it is coming in at 4 M ohms.

If you've isolated the suspect and turned them into radials it's funny that it shows on both.
Check RCBO is wired correctly. Also how long was the RCBo fitted?

I replaced the 32 RCBP as I split the ring into two radials. So they are brand new and it happens on both. The client said it has been getting steadily worse this last year and now he has been using extension leads rub from his kitchen ring. Another thing is he has alot of computer equipment darted throughout the house but again it is not just that that is tripping it it is every thing you plug in.

Was round for an hour there today and still no further joy. His bill is mounting up and I am no wiser. Bit embarrassing.

 

[IQ Electrical]

If you got no less than 4Mohms on all IR tests then the RCBO's should not be tripping unless they are connected incorrecly or you have a crossed polarity fault at an outlet.

 

[SimpleSimon]

If it's only when things are plugged in that this happens yet 4M ohms between conductors? I can only think reverse polarity. Take all socket covers off n check. If theyre fine it's gotta be in a jb somewhere.
So a year ago it first happened?

 

[BLBelfast]

If you got no less than 4Mohms on all IR tests then the RCBO's should not be tripping unless they are connected incorrecly or you have a crossed polarity fault at an outlet.

This is why I am stumped. There is no other option than using the RCBOs though.

If it's only when things are plugged in that this happens yet 4M ohms between conductors? I can only think reverse polarity. Take all socket covers off n check. If theyre fine it's gotta be in a jb somewhere.
So a year ago it first happened?

It happened when he first got the CU upgraded to the new regs. He was told that it would be more sensitive so expect more trips. The tripping got worse up till this last month where it was impossible to use that ring main.

 

[telectrix]

it's going to be one of those simple things that make you want to kick yourself for not spotting it straight away, i'll bet. got to go down the road of splitting the ring, down and down, plugging into each section till you narrow it down to one small section. make up a thermos of coffee before you start!

 

[WDMDL]

If the RCBOs are tripping, there is an imbalance somewhere. It's not looking like a fault to earth, so is it an interconnection (Borrowed Neutral)?
Try this one:
Safely isolate the supply.
Disconnect the (now 2 radials) L and N from CU and bunch the lot together. Connect to one side of tester
Link L and N busbars in CU. Connect to other side of tester.
Test first on a continuity range. If it shows no connection, test at 250V.

While 4Meg is acceptable, and in theory it would take something as low as 7.67kOhms to trip the RCD, it is pretty low for a small domestic and will be worth investigating.
At this stage, it will be worth pulling every socket frontplate to inspect, if you haven't already. IR test as you go, both the cables and the socket outlets themselves.
Apart from the kitchen ring, do the other circuits have RCD protection?

Simon.

 

[telectrix]

does sound a bit like a neutral/cpc crossed somewhere.

 

[BLBelfast]

If the RCBOs are tripping, there is an imbalance somewhere. It's not looking like a fault to earth, so is it an interconnection (Borrowed Neutral)?
Try this one:
Safely isolate the supply.
Disconnect the (now 2 radials) L and N from CU and bunch the lot together. Connect to one side of tester
Link L and N busbars in CU. Connect to other side of tester.
Test first on a continuity range. If it shows no connection, test at 250V.

While 4Meg is acceptable, and in theory it would take something as low as 7.67kOhms to trip the RCD, it is pretty low for a small domestic and will be worth investigating.
At this stage, it will be worth pulling every socket frontplate to inspect, if you haven't already. IR test as you go, both the cables and the socket outlets themselves.
Apart from the kitchen ring, do the other circuits have RCD protection?

Simon.

Thanks for your advice. I have taken every plate of and tested as I went. Thats what is killing me. I already spent hours investigating all I could think of.

The ring main, cooker, shower, kitchen ring are all RCBO protected. The lights and the rest are on the other side of the split board protected by RCD. I have tried sticking the circuits into an MCB on the RCD protected side and it still trips out the RCD.

The fact he has a few bits of computer equipment shouldnt affect the installation should it? Also the fact it got steadily worse has anybody got a bit of experiance with that sort of problem?

Thanks for everyones input. Will be back on friday for another hair pulling out session and will let youse know the outcome.

 

[LukeD]

I hate to say this.... But i love "Mystery Threads" like this !!!

may i make one suggestion ? Take a "fresh set of eyes" to have a look . some times you get into a mess with issues like this and some bugger comes along and "spots" it in seconds !

 

[nickblake]

It will be some thing stupid and you will kick yourself for not finding it , you said the 2 RCBO's tripped then as i know the guys have said it sounds like a crossed neutral or an inter connection between the ring legs , what i suggest is do an R1R2 test from the board joint the Earth and live to gether and test every socket on the ring , you should get a reading only on one leg as you have split them ,check both legs , then do the same but R2and Rn test all the sockets again you should only get reading on one leg , if you get reading on both legs then you know you have a crossed neutral , double check the IR readings too