3 rcbos tripping at different times

[mick b]

My mates asked me to go and help find some faults at a house. Rcd tripping so he put 3 socket rings on 3 separate rcbos. Now he says they are all tripping at different times. . Says he's tested ir and it's about 6 meg on one ring. If they are separate why would they trip. . Good Ze in board . Correct polarity circuits not linked in any way ?

 

[Cadgey123]

If there is 3 new RCBOs and it's still tripping.

Are they ring final circuits? Do you have the correct legs of each ring circuit?

Maybe dig deeper into the route cause in the field. Disconnect items from each socket

 

[Octopus]

Fault on incoming supply

 

[mick b]

Fault on incoming supply

My first thought. Asked him to remove earths and test ze . Said it was fine. Had a similar problem and the earth had gone but it was coming in through the water pipe

 

[Octopus]

My first thought. Asked him to remove earths and test ze . Said it was fine. Had a similar problem and the earth had gone but it was coming in through the water pipe

Faults can occur on live and neutral too!

 

[Stspark]

With assumed correct ZE and voltage tests what else could an incoming supply fault be?
I'd be looking at the installation. As suggested above, are the correct r1 + rn's with the corresponding rcbo? Are the rcbos connected up correctly? Has full 3 step ring final continuity tests been completed? Is there a number of appliances leaking to earth?

 

[Colin Jenkins]

My mates asked me to go and help find some faults at a house. Rcd tripping so he put 3 socket rings on 3 separate rcbos. Now he says they are all tripping at different times. . Says he's tested ir and it's about 6 meg on one ring. If they are separate why would they trip. . Good Ze in board . Correct polarity circuits not linked in any way ?

Hello Mick B.

I think there are two faults present, and STSpark (above) has identified one of them. If there are three ring circuits, but any of them have been cross-connected in the past, the single RCD up front would not see this condition. Installing three separate RCBOs now means a cross-connection will trip at least two of the RCBOs as soon as a load is switched on. It is likely that two of circuits have got cross connected somehow, probably from the original installation It's best to do the basic ring circuit three-step continuity checks on all three circuits to see if this is what's amiss. It's on page 98 of the IET On-Site Guide.

Now consider the 6M Ohms insulation reading on one ring circuit. It is probably this reading that caused the original RCD to trip. Whilst the reading appears to be satisfactory, remember that the insulation tester voltage is 500 volts d.c. and that 230 volts a.c. mains has a different searching characteristic. Also, the 6M Ohm reading may vary with time, temperature and/or connected load. It would be wise to inspect every socket and accessory on this circuit, looking for damaged insulation. If these are flush accessories, the plate-fixing screw sometimes traps a cable inside the metal box. I recently replaced a faulty flat pvc + cpc cable that was reading L-E 299M Ohms +, L-N 299M Ohms + and N-E 9M Ohms. The RCBO was tripping intermittently on this - sometimes OK for weeks, sometimes only for a few hours. It's ok now.

Regards,

Colin Jenkins.

 

[Octopus]

With assumed correct ZE and voltage tests what else could an incoming supply fault be?

loose connection in the service head?
fluctuating voltage L-N

If a TT supply is the tripping coinciding with the wind?

 

[mick b]

Thanks to all who have given their advice. I am going on Monday to see what's going on. It's a good starter to strip it down and check each ring as you said. Can I let you know what sorts it . Always nice to hear differing views on faults . It's a learning curve even for the older generation

 

[Octopus]

Thanks to all who have given their advice. I am going on Monday to see what's going on. It's a good starter to strip it down and check each ring as you said. Can I let you know what sorts it . Always nice to hear differing views on faults . It's a learning curve even for the older generation

I'm very confused now - in an earlier post you said your friend had tested the Ze?

If all 3 different RCBO's are tripping at different times, IMHO this does point at an "external" influence.....

 

[Stspark]

Thanks to all who have given their advice. I am going on Monday to see what's going on. It's a good starter to strip it down and check each ring as you said. Can I let you know what sorts it . Always nice to hear differing views on faults . It's a learning curve even for the older generation

Well Mick B, is it sorted?

 

[mick b]

Yes . When I got there two of them had not tripped for 3 or four days. The one that was tripping had a laptop tripping it. And a light in the conservatory was down N/E. on a spur . Got rid of them two and alls good . Not sure what was going on with the others, he may have got confused , but yes all good. Sometimes people lose the plot a bit . He seemed more relaxed with two heads to find the problem