Rcd tripping when lights turned off

[sidekick]

Have been to check site where consumer unit with 5 circuits. 4 of those circuits feed various light and sockets in one stable barn with a lot of flourecent strip lights and outdoor school flood lights. The 5th circuit is on 16A mcb and feeds a second consumer unit via armoured cable in a second stable barn.
The second consumer unit has only 2 circuits. 1 feeding only 1 socket and the 2nd on a 6a mcb feeding x 7 flourecent strip lights, x 2 Ansell flood lights and x 1 security camera.
No problem was apparent until the x 1 security camera was installed. Now when the flourecent strip lights are turned off the rcd trips.
Have done full test and inspection on all cables and found no faults.
Both consumer units have 40A 30ma RCD as main switch so no discrimination straight away but other than that can't find anything wrong.
Could it be accumaltive earth leakage. Any ideas anyone.

 

[polo1]

Have you tried with the cctv power supply removed; is it the rcd on the second db that trips or both; have you ramp tested the rcd(s)? It might just be coincidence that the problem has started when cctv installed.

Regards

 

[sidekick]

Have you tried with the cctv power supply removed; is it the rcd on the second db that trips or both; have you ramp tested the rcd(s)? It might just be coincidence that the problem has started when cctv installed.

Regards

Spent some time connecting and disconnecting circuits and fittings to try and reproduce the trip and could not as it is only happening periodically. Usually on an evening when all lights have been on. Did manage to reproduce the trip once when all lights were on and outside flood lights. It was the RCD in the second Consumer unit which tripped mostly, occasionaly the first one. Found a loose earth connecting the two and replaced the second RCD which seemed to trip if i just tapped it. Now problem still there but appears always to be first RCD now tripping.

 

[dim_bulb]

Could you not remove the rcd on second board with main switch? As you have rcd upfront.

 

[sidekick]

Could you not remove the rcd on second board with main switch? As you have rcd upfront.

I could. however, that would not help with the problem as it is the first bosrd rcd which trips. i'm still thinking its an accumalative earth leakage issue and wondering if changing first rcd to 100ma will stop the tripping.

 

[Farmelectrics]

Could be a ghost

 

[Hawk]

You could put each circuit on RCBO's and do away with the rcd's. This would mean that the faulty circuit would trip and not everything.

Earth faults aren't uncommon in fluorescent lighting because of control gear. Are they old fittings? Also is there just one switch controlling the lights?

 

[PEG]

Only a thought,but had similar problem years ago on a equestrian yard and someone had put a bank of flourescents live feed switched neutrals.It tripped rcd everytime they were switched off. Or,its a ghost..

 

[sidekick]

You could put each circuit on RCBO's and do away with the rcd's. This would mean that the faulty circuit would trip and not everything.

Earth faults aren't uncommon in fluorescent lighting because of control gear. Are they old fittings? Also is there just one switch controlling the lights?

All fittings less than 3 years old and all on one pull switch with 2 way pull switch other end of barn. There is an outside flood which has a dawn to dusk censor but does not go off.

- - - Updated - - -

Only a thought,but had similar problem years ago on a equestrian yard and someone had put a bank of flourescents live feed switched neutrals.It tripped rcd everytime they were switched off. Or,its a ghost..

Thanks. Not in this case though. All connections checked.

 

[Lordy9099]

Hello,

Have you checked the connection on the floodlights and fluorescents and check for a loose connection, it could be a hot problem, try turning the outside floodlights off with its MCB and then keep trying with the other MCB and trace what circuit is causing the problem, then remove that circuit from the main RCD on the second DB then put the circuit at question on its own RCBO. Are they on a ring or radial?

 

[Lordy9099]

Sorry just re-read the post and there is a 6A MCB powering 7 fluorescents and 2 floodlights and a security camera? What wattage are the Floodlights, it could be that they are drawing more than 6A when the fluorescents and the floodlights are all on. Check the wattage of all the fluorescents and the floodlights and the Amps that the camera uses, then report back, you may need to change the MCB to a higher Amperage or Put the Fluorescents on there own with the Floodlights and Camera on there own too.

Callum

 

[eollou88]

I would definitely separate the fluorescents onto addition circuit


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[Lordy9099]

Hello,

Correct, all that on one 6A MCB will be very close if not drawing more than 6A, what wattage are both outside lights, I would put them on there own and the fluorescents on there own

 

[BlueToBits]

The 6A MCB won't influence the tripping RCD. The non-functioning dusk dawn sensor on the floodlight may be waterlogged which may be worth closer investigation.

The RCD may be tripping when the lights are switched off due to an induced high voltage spike from one of the chokes causing a breakdown of insulation resistance somewhere in the circuit of one one or more of the fittings. It could be a pain to find as this spike could be several 1000 volts and difficult to replicate. An alternative solution attempt may be to fit a fast electronic relay triggered by a zero volt detector and switch circuit that switches off the lights only when the supply voltage sine wave crosses the 0V line. I would only try this as a last resort
Something like this, but check if suitable for inductive load and Pf rating first:
RGS1A23A25KKE - CARLO GAVAZZI - SSR, 230VAC, 25A, AC CONTROL MODULE | Farnell United Kingdom

 

[sidekick]

Sorry just re-read the post and there is a 6A MCB powering 7 fluorescents and 2 floodlights and a security camera? What wattage are the Floodlights, it could be that they are drawing more than 6A when the fluorescents and the floodlights are all on. Check the wattage of all the fluorescents and the floodlights and the Amps that the camera uses, then report back, you may need to change the MCB to a higher Amperage or Put the Fluorescents on there own with the Floodlights and Camera on there own too.

Callum

x 7 fluorecents at 35w each and x 2 floods at 70w each. Not sure about camera yet but no where near 6a total

 

[sidekick]

I would definitely separate the fluorescents onto addition circuit


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thing is now that RCD changed and switches etc. for some reason that board is ok now but the RCD on the board up stream keeps tripping

 

[Sean Mayes]

Have been to check site where consumer unit with 5 circuits. 4 of those circuits feed various light and sockets in one stable barn with a lot of flourecent strip lights and outdoor school flood lights. The 5th circuit is on 16A mcb and feeds a second consumer unit via armoured cable in a second stable barn.
The second consumer unit has only 2 circuits. 1 feeding only 1 socket and the 2nd on a 6a mcb feeding x 7 flourecent strip lights, x 2 Ansell flood lights and x 1 security camera.
No problem was apparent until the x 1 security camera was installed. Now when the flourecent strip lights are turned off the rcd trips.
Have done full test and inspection on all cables and found no faults.
Both consumer units have 40A 30ma RCD as main switch so no discrimination straight away but other than that can't find anything wrong.
Could it be accumaltive earth leakage. Any ideas anyone.

I know this is an old problem and things have changed since then, I read the posts and yes the value of the system is probably being reached, my advice would be: to separate the circuit and have them on their own feeds.
RCD's work on a out of balance between the live and neutral (nothing to do with spurious earth leakages the earth cable is there to speed up the imbalance) (value of imbalance for the RCD to activate being 30mA) which is probably created when you switch the live off.

1. Upgrade the Distribution Board, you are not allowed to run three different circuits of the same circuit, it works, but not within the regs. you need 6 way metal clad board use the four ways, 1 circuit 1 socket, Circuit 2 Fluorescent lights, Circuit 3 Flood lights, Circuit 4 security camera, 2 x spare capacity. Thing is when electricians go to price jobs to have things done properly costs money the client wants cheap, if we wire cheap we cause problems. Just coming of any old feed to supply something is not always a quick fix. Where are the end of lines for circuits? what is your EFL readings for each circuit?
2. containment, switches, wiring to each separate supply use. Can easily be tested and identified then.

Sean

 

[kingeri]

Eh?

 

[Gnasher]

Non functioning photocell??

Is it possible that this is wired incorrectly, switching neutral.
Possibly switching the neutral and causing a neutral path via the resistor.
Or just a resistor fault affected by temperature.

If it's faulty take out of circuit and wait and see.

 

[westward10]

This maybe totally irrelevant but is the outside flood an led. Fitted some in a warehouse last year and had to return because they tripped the mcb when switched off

 

[123]

Given the thread is nearly 4 years old, I'd like to think the original issue has been sorted by now lol

 

[westward10]

Given the thread is nearly 4 years old, I'd like to think the original issue has been sorted by now lol

Oh yeah didn't notice what a hairpin

 

[marconi]

I did not notice the date either. I was just about to type in these questions to the OP:

Could you tell me the following information so I can think about the problem?

1. What is the supply type? TN-S, TNC-S or TT and is equi-potential bonding present.
2. What is the wiring method for the two switching scheme? 2 wire or 3 wire?
(See https://www.tlc-direct.co.uk/Technical/DataSheets/MK/WiringDiagrams.pdf - the first or third circuit)
3. Has 3 core and earth cable been used to connect the two 2-way switches and are the core colours new or old?
4. How have the core colours been used to connect together the two 2-way switches?
5. How long is the cable run between the two 2-way switches?
6. Is the CPC connected throughout the two way circuit cabling and terminated in the switches?

These were needed by me to inform some thinking on whether there was a way of linking the cause - switching off a set of FLs - to the outcome - a residual flux in the RCD thence trip by considering:

a. what happens electrically when a FL is switched by a SP contact.
b. what happens electrically when a distributed set of FLs are switched off by a SP contact.
c. what effect does the timing of the switching in the voltage cycle have on transient voltages/currents.
d. what way could b or c above change the potential of a weak main earth - if that is the case -and thence the CPC have on the currents in the circuit and line and neutral through the RCD.
e. what way could b or c above change the currents in the two way switched circuit including in the CPC.
f. the effect on leakage current to CPC and neutral due to the way the 3 cores have been allocated and are physically arranged in the 3 core and CPC cabling between switches for Neutral and 2 Strappers (2 wire scheme) or the PL and SL Straps and the Common/Browbar (3 wire scheme).
g. Is there a 'better' allocation to minimise any troublesome interconductor current.

I write this as some idle amusement for me over the next few days but others might want to ponder too. I am not going to 'mark', comment or arbitrate on anyone's contribution.

 

[Gnasher]

This maybe totally irrelevant but is the outside flood an led. Fitted some in a warehouse last year and had to return because they tripped the mcb when switched off

Ha Ha so it is.

I wonder if it was ever sorted?

Would be nice if whoever asks questions would always repay the help given with the answer.