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Apologies for headline trying grab attention

So can someone help on this scenario.

Plant room prob 7Mx7M square ish. Loads of HVAC, pumps etc as you would expect and a ring final circuit.

Socket been damaged somehow and went to replace socket.

After replacing socket just for peace of mind we test that circuit. IR ok elip ok polarity etc.

Test RCBO and with cables disconnected as per GN3 all ok.

Just testing further and left loop tester on high current and the RCBO did not trip unusual so we got out RCD tester and couldn't get the RCBO to trip from socket. Yet with cables disconnected works as should.

So what going on and ae replaced RCBO and same ?

But circuit looks ok all in tact all tests on circuit as expected.

So unplug everything thinking maybe some item plugged in causeing problem but NO joy still.

Anyone ?
 
Hi - 2 thoughts - confirm again that N and E are separated so the rcd trip current returns via E to the earth bar and doesn’t rejoin N before the rcd - and if it’s an AC type rcd possibly loads are putting DC back through it and desensitising it. Good hunting :) .
 
Might seem daft but are you sure the socket is fed from that rcbo?

Also as mentioned above, possible dc locking of the coil due to inverters or other equipment in plant room passing dc into mains.
 
Definitely correct circuit and confirm the ring is complete and figure 8 test all good.

All in right place all through circuit L,E and N.

The dc from other stuff good shout so ill try turning off other stuff see if makes a difference.

Its all sockets on that circuit we even tried testing at the Type B rcbo 32A direct on terminals cables connected wont trip but connected out of RCBO and operates as should.

Now also question was would people class this as a defect as to gn3 i done tests correctly its only further testing thrown this issue up ?
 
HAve you tried reversing the phase of the test current ie using the 0 and 180 deg positions?

And measure the N-E voltage at the RCBO output and socket. Most RCD testers do a pre-check of voltages and also check that the E/cpc will not rise above 50V when the test current is injected.

Is it a single or double pole RCBO?
 
Last edited:
Check N-E IR of the ring at the RCBO but disconnected from it with all socket switches in the on position and all loads unplugged.

Check ring continuity and compare readings of L-L N-N and E-E.

Does the ring supply equipment which is equipotential bonded to MET?

What is earthing system please?

What happened to cause damage to the socket and what was the effect of the damage?
 
Was I.R. testing done with all cpc and bonding connected at met? Was just thinking if there is a neutral to earth fault affecting the operation of the RCBO then this should show up on an IR test if done in this way
 
'We' think you have a 'double-grounded neutral' problem when the N is linked to E before and after the RCBO. Because disconnecting the ring from RCBO enables it to detect earth faults, the ring is likely to have an N_E wiring fault which your tests or way of testing has not yet discovered.
 
In theory there could be something still connected that you have overlooked, that has a high DC resistance N-E hence does not affect the IR reading, but a low enough AC impedance to affect the test. But that would require a very large capacitance so is not very likely.

What type of wiring system is used in the RFC? In a plant room, there may be heavy, noisy loads on cables run along with the RFC, that affect the operation of the tester by induction when the cables are connected to the RCD.
 
'We' think you have a 'double-grounded neutral' problem when the N is linked to E before and after the RCBO. Because disconnecting the ring from RCBO enables it to detect earth faults, the ring is likely to have an N_E wiring fault which your tests or way of testing has not yet discovered.
[/Q
In theory there could be something still connected that you have overlooked, that has a high DC resistance N-E hence does not affect the IR reading, but a low enough AC impedance to affect the test. But that would require a very large capacitance so is not very likely.

What type of wiring system is used in the RFC? In a plant room, there may be heavy, noisy loads on cables run along with the RFC, that affect the operation of the tester by induction when the cables are connected to the RCD.

Low resistance,
Very big capacitor
Power factor correction device is bouncing around my head?
 
Ok to clarify few points made.

Socket front only damaged knocked. So replaced.

IR tests all ok checked and re checked single pole mcb from MG isobar 4c tp&n DB.

Turned off everything in board now except this circuit and still got the fault. 10 outlets across room nothing in any of them.

All bar anyone we try the switches in off position. No fused spurs etc on ang of them.

N- E IR CLEAR as this was our best guess.

Now dont know if this has always been like this as we stumbled across it.
 

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