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

 

[Pretty Mouth]

It sounds like there may be an interconnection somewhere between a circuit on RCD1 and another circuit on RCD2, this could explain why both RCDs trip when one is tested. From the limited description I'd guess a heating system that is supplied from both a FCU on a circuit on RCD1, and a plug/socket arrangement on a circuit on RCD2.

Alternatively, possibly a N to E fault on a circuit that is missing its own earth continuity, but gains earth continuity via pipework when the boiler is plugged in?

Your description really needs to be clearer, you really need to say exactly what you mean if we're to be much help to you.

 

[Tom256]

Your description really needs to be clearer, you really need to say exactly what you mean if we're to be much help to you.

Agreed. Use correct terminology and always explain how you are carrying out the tests.
It would be easy for me to assume your method used is inline with what I might consider to be the method that I would be using in this instance.
The post is too subjective in its content. When reporting use objective language.

 

[littlespark]

I think you're confusing yourself, guys.... OP never mentioned 2 immersions.

He says thers AN immersion, but its wired as a ring for some reason.
OP.... have you tested this circuit as a ring, or just assuming as theres 2 cables at the board? It may be 2 radials... one for immersion, one for something else?

Are you picking up any continuity between outgoing circuits? Where there obviousy shouldn't be.
If testing individual circuits doesnt bring up anything.... need to test between circuits to find any cross-connections.


Photos will help, of course. Board with the cover off if you can.

 

[Retroelectric]

Sorry for lack of info and pictures, I will put some on as I will pop back as this would help more.
Property is an early 70s chalet bungalow and so single sockets and very few of these.
Has had a new cooker circuit installed at some point in trunking.
New ring has been installed upstairs at a guess 20 years ago.
Existing old ring still in place, this appears ring upstairs with spurs taken down to lounge / kitchen.
Immersion heater (1) and heating fused spur (1) are wired as a ring main.
Boiler is wired directly from wiring centre, the plug i removed at the boiler is the internal one where you wire the flex into.

Will carry out some more tests, thought it may have been a ring in the wrong side but no continuity between any circuits with mcb's off, no continuity between neutral bars with rcd's off and no neutral earth / live earth with main switch off until boiler is connected.
New up ring is closed as is heating ring.

 

[Tom256]

Sorry for lack of info and pictures, I will put some on as I will pop back as this would help more.
Property is an early 70s chalet bungalow and so single sockets and very few of these.
Has had a new cooker circuit installed at some point in trunking.
New ring has been installed upstairs at a guess 20 years ago.
Existing old ring still in place, this appears ring upstairs with spurs taken down to lounge / kitchen.
Immersion heater (1) and heating fused spur (1) are wired as a ring main.
Boiler is wired directly from wiring centre, the plug i removed at the boiler is the internal one where you wire the flex into.

Will carry out some more tests, thought it may have been a ring in the wrong side but no continuity between any circuits with mcb's off, no continuity between neutral bars with rcd's off and no neutral earth / live earth with main switch off until boiler is connected.
New up ring is closed as is heating ring.

Still can't say I am following this but here is something to consider.
Fault on boiler internals - N to E of say 1500 ohms what happens on your RCD test L to E? - do the numbers

Knowing how you are testing the devices would really help

 

[Retroelectric]

I’m using megger mgt to test.
Basically all clear on IR until the heating spur switched on.
Disconnected programmer, stat, boiler, pump neutrals from wiring centre. IR all clear apart from boiler and that reading is 0.00
Removed connection plug from boiler and that clears the reading and whole install is clear and rcds working properly.
Plug the boiler in and second rcd fails to trip, even tried loop test on 2 high as that normally takes anything out but just gave me the loop reading, first rcd takes both out when tested from cooker socket.
I have not done insulation resistance between live and neutral on lights as I haven’t removed all the lamps.

Job was just elderly lady wanted me to check the lights as she was scared they had tripped out, normally I would just flick it on as normally a lamp has blown ,but I did IR on live to earth that was clear then put it back on and checked the lights but they were all working.
Had visual look at all the lights and switches an although they were fairly old nothing looked out of place and double insulate flex at pendants, outside lights were dry and all working and mounted in porch.
Checked all connections in cu all ok apart from garage neutral that I tightened up.
Decided to test rcd while I was there from top of lighting mcb but failed to trip so I plugged in on washing machine socket that was on same rcd as lights and it still failed to trip.
I agree pictures would have been more helpful so will take some when I can pop back.
Thanks guys.

 

[Retroelectric]

This is what I mean by boiler plug, something like this