Light fault 'tripping' RCD on the ring circuits.

[binky]

With respect, you are wrong. RCDs trip quite happily on neutral to earth leakage. You can prove this quite simply in the home!

If that was the case 16th edition boards would be forever tripping for lighting faults, which they don't. RCDs do not monitor what is upstream of them, only what flows through them. They are not reliant on any CPC to operate as they only monitor live and neutral. Stick your finger in the live, you cause an imbalance and they trip, likewise the neutral, albeit the leakage is provided by electricity flowing through you to earth.

 

[Murdoch]

With respect, you are wrong. RCDs trip quite happily on neutral to earth leakage. You can prove this quite simply in the home!

Yes but only when the neutral for the circuit passes through the same RCD as the live for the circuit.

Which in this case can’t happen as the op has confirmed that only the sockets are protected by the RCD

Time to get my coat

 

[Geoff1946]

With respect, you are wrong. RCDs trip quite happily on neutral to earth leakage. You can prove this quite simply in the home!

Please explain how an RCD can trip for a neutral to earth fault UPSTREAM of it's supply.
We all know how it works for a fault downstream; no argument there.

 

[C15JON]

RCD (Residual Current Device) devices are designed to monitor the balance of current flowing through live and neutral conductors in a circuit. When a fault occurs, such as a neutral-to-earth fault, it creates an imbalance in the currents between the live and neutral conductors.

In a properly functioning circuit, the current flowing through the live conductor should be equal to the current flowing through the neutral conductor, resulting in a balanced system. However, in the case of a neutral-to-earth fault, some of the current intended for the neutral conductor is diverted to the earth conductor, causing an imbalance.

The RCD continuously compares the current flowing through the live conductor to the current returning through the neutral conductor. If it detects a difference, it assumes that leakage is occurring, indicating a fault such as a neutral-to-earth fault. This triggers the RCD to trip and disconnect the circuit, preventing potential electric shocks and fire hazards.

 

[Geoff1946]

Spot on!
BUT you are missing the point that the circuit under discussion is connected to the supply BEFORE the RCD.
Hence no current is, or can, flow through the RCD without some additional connection to its downstream side..

 

[C15JON]

I take your point, @Geoff1946, nicely explained. I need to go sit in a dark room with a damp flannel over my face and think about this because I"ve seen it happen...

 

[Murdoch]

Having 7 socket circuits to a single RCD isn’t a great set up to start with

Extreme Earth leakage from “other” circuits can trip RCDs protecting other circuits.

Post 5

 

[binky]

I take your point, @Geoff1946, nicely explained. I need to go sit in a dark room with a damp flannel over my face and think about this because I"ve seen it happen...

The only way I can think of it happening is multiple faults, which is possible with damp. Somehow damp in the light/ outside wall is firming a connection to the socket circuit. As the OP is on an earth rod, it's possible the resistance to earth is hundreds of Ohms, so fault maybe finding an easier earth path via sockets somehow. Not a job I would like to fault find - proper head scratched

 

[Feenster]

Northern or Southern Ireland?

Just south of the border with NI.

 

[Feenster]

Where is your neutral connected to earth

The neutral ground bond is in the inverter itself. When replacing the 7 MCBs and 1 RCD with RCBOs I will move the neutral ground bond to the distribution panel.

 

[Fleeting]

Just south of the border with NI.

Being in Southern Ireland it would be illegal unless you are an REC to interfere with your consumer unit.

 

[SPECIAL LOCATION]

Have you ramp tested the RCD to see how sensitive it is?

remember that although a 30ma RCD MUST operate with faults greater than 29ma.. [approx 7watt load]
they can also operate with anything from 16ma... (Must NOT operate at 15ma). [approx 3.5watt load]

Did you do any continuity / insulation resistance tests on the lighting circuit that you found water ingress at a fitting?

Do you have any other outdoor wiring / accessories connected to any of the socket circuits?

Have you done any insulation resistance tests on all of the socket circuits supplied via the RCD?

It could be an accumulation of multiple problems; Natural leakage, Deteriorating wiring that you have not yet tested or identified, Oversensitive RCD... etc.. etc...

Without some more factual test results there is a significant amount of guesswork trying to establish the actual cause..

However, from past experience the majority of RCD tripping faults have a correctly operating RCD.. But if an RCD is faulty, generally it fails to trip at all, or will not mechanically reset ON... Over-sensitive RCD faults tend to be the minority of problems!

This thread is yet another example of the inconvenient consequences of cheap single RCD installation -vs- bit more expensive but far more reliable full RCBO installation..... Although it may comply with BS7671 it is a pain in the bum and can be very time consuming trying to track down intermittent RCD faults.

 

[SPECIAL LOCATION]

I have an offgrid set up with no mains connection at all.

Being in Southern Ireland it would be illegal unless you are an REC to interfere with your consumer unit.

Is that true of off-grid installations with no mains connection?

I would have thought that a CU on an off-grid arrangement is purely a private matter, as it has no relevance to any external supply networks??

 

[Fleeting]

Is that true of off-grid installations with no mains connection?

I would have thought that a CU on an off-grid arrangement is purely a private matter, as it has no relevance to any external supply networks??

Didn't see the top line in #1. Not 100% sure to be honest.

 

[poni]

Being in Southern Ireland it would be illegal unless you are an REC to interfere with your consumer unit.

is it not the same in the UK? (part P)

 

[Fleeting]

No in the UK there are no legal restrictions on people carrying certain electrical works although some of it must be notified there is nothing stopping the home owner from doing this.

 

[Feenster]

Without some more factual test results there is a significant amount of guesswork trying to establish the actual cause..

Yes I agree with that. I need to do a few tests, but getting the time is the difficulty at the moment.

 

[Feenster]

While having a few moments today I turned off each of the MCBs for the lighting/radial circuits. There are 3 MCBs for lights with 2 radial circuits on each. On one circuit there was a voltage of 7.2V between Live and Neutral/Earth with the MCB off, 6.2V on the next and 1.8V on the last. Should this be the case? E/M induction?

 

[Murdoch]

While having a few moments today I turned off each of the MCBs for the lighting/radial circuits. There are 3 MCBs for lights with 2 radial circuits on each. On one circuit there was a voltage of 7.2V between Live and Neutral/Earth with the MCB off, 6.2V on the next and 1.8V on the last. Should this be the case? E/M induction?

Induced voltage from adjacent cables.

 

[Geoff1946]

If you are using a cheap DIY type multimeter it will have high impedance input.
This makes readings from open circuit wires meaningless as it will detect capacitive and inductive coupled voltages. Even strong radio signals can be picked up under some conditions.