Rcd fault not tripping

[Retroelectric]

Hi
I have only had a quick look at a fault so haven’t gone too far into it.
Lighting mcb tripped out, elderly lady wanted it checked out before it went back on so meggered it, all lights worked but rcd would not trip.
It’s a BG 3+3 split load installed by someone when the heating was done about 8 years ago, no paperwork.
Swapped the second rcd for one I had on board but still would not trip, plugged tester in first rcd and both tripped.
circuits are
Rcd
Cooker
Water heater - 2 twins
Sockets - 4 twins
Rcd
Sockets 4 twins
Garage - swa
Lighting - 4 twins
Is this likely to be a neutral in the wrong bar? No continuity between neutral bars when Rcds are off.
Any ideas where to start first?

 

[freddo]

You can disconnect the outgoing L and N of the RCD and do an RCD test at the terminals if this passes that rules out the RCD. I would expect a neutral in the wrong bar to cause immediate tripping rather than not tripping.

Insulation resistance tests would be where I would start to look for the RCD problem, on all circuits. Don't be mislead by the tripped MCB on the lighting circuit. There is likely another, separate issue causing the RCD not to trip. The MCB could have tripped due to a lamp blowing for example, though you mention all lights are working. How did you carry out the insulation test on the lights? If only the MCB tripped the fault could be between live and neutral conductors.

 

[cireland]

What type of RCD is it?

 

[littlespark]

Could the replaced rcd also have a fault?

The ones rolling about in the van tend to be from old, stripped out boards… unless it’s boxed, new, fresh from the wholesalers.

Does it actually turn off when you turn the switch down? Maybe the internal mechanics are stuck?
Ie, it is sensing a fault to trip off, but nothings physically moving.

 

[Retroelectric]

Hi guys,
Thanks for the replies.
so I popped there today and had another look.
Rcd definitely ok,
Neutral earth on first rcd on heating that has been wired with an immersion on a ring main for some reason, turned off wiring centre and clears fault, both rcds trip as they should.
Traced neutral earth from wiring centre to Oil boiler that you can be unplugged so did this, all clear and rcds working as normal.
Plug the boiler back in and heating circuit does not trip.
Second Rcd does not trip with tester and first rcd takes both out when tested.
No main bonds in place bat incoming water is plastic.
Pme supply that has also has a TT earth stake installed directly from the cutout.
Any ideas what’s going on?

 

[Jock from the north]

Hi guys,
Thanks for the replies.
so I popped there today and had another look.
Rcd definitely ok,
Neutral earth on first rcd on heating that has been wired with an immersion on a ring main for some reason, turned off wiring centre and clears fault, both rcds trip as they should.
Traced neutral earth from wiring centre to Oil boiler that you can be unplugged so did this, all clear and rcds working as normal.
Plug the boiler back in and heating circuit does not trip.
Second Rcd does not trip with tester and first rcd takes both out when tested.
No main bonds in place bat incoming water is plastic.
Pme supply that has also has a TT earth stake installed directly from the cutout.
Any ideas what’s going on?

Hi do yo mean 2 immersion are off the socket ring main or just that there wired in a ring main .

 

[Tom256]

Hi do yo mean 2 immersion are off the socket ring main or just that there wired in a ring main .

Likewise. Not following this at all.
The terminology is not clear and not enough information.

 

[Jock from the north]

Hi
I have only had a quick look at a fault so haven’t gone too far into it.
Lighting mcb tripped out, elderly lady wanted it checked out before it went back on so meggered it, all lights worked but rcd would not trip.
It’s a BG 3+3 split load installed by someone when the heating was done about 8 years ago, no paperwork.
Swapped the second rcd for one I had on board but still would not trip, plugged tester in first rcd and both tripped.

You can disconnect the outgoing L and N of the RCD and do an RCD test at the terminals if this passes that rules out the RCD. I would expect a neutral in the wrong bar to cause immediate tripping rather than not tripping.

Insulation resistance tests would be where I would start to look for the RCD problem, on all circuits. Don't be mislead by the tripped MCB on the lighting circuit. There is likely another, separate issue causing the RCD not to trip. The MCB could have tripped due to a lamp blowing for example, though you mention all lights are working. How did you carry out the insulation test on the lights? If only the MCB tripped the fault could be between live and neutral conductors.

Hi
I have only had a quick look at a fault so haven’t gone too far into it.
Lighting mcb tripped out, elderly lady wanted it checked out before it went back on so meggered it, all lights worked but rcd would not trip.
It’s a BG 3+3 split load installed by someone when the heating was done about 8 years ago, no paperwork.
Swapped the second rcd for one I had on board but still would not trip, plugged tester in first rcd and both tripped.
circuits are
Rcd
Cooker
Water heater - 2 twins
Sockets - 4 twins
Rcd
Sockets 4 twins
Garage - swa
Lighting - 4 twins
Is this likely to be a neutral in the wrong bar? No continuity between neutral bars when Rcds are off.
Any ideas where to start first?

circuits are
Rcd
Cooker
Water heater - 2 twins
Sockets - 4 twins
Rcd
Sockets 4 twins
Garage - swa
Lighting - 4 twins
Is this likely to be a neutral in the wrong bar? No continuity between neutral bars when Rcds are off.
Any ideas where to start first?

Hi its got me stumped would need to see pictures of board .I've had bg boards with cross polarity from rcd to rcd cos there junk .there was a time b and q were selling 10 way dual rcds type ac for 45 pound fully loaded .I can understand first rcd taking out second one but not second rcd not tripping at 30 ma .especially if I think you said you changed it.can you send pics .thanks