RCD Tripping when light is switch off

[hutch6447]

Hi, right been to a 3 storey house that has been turned into offices the problem is first all the circuits are protected by 1 RCD the actual fault itself is when you switch the light on in the basement its fine when you turn it off it trips the RCD then everything is off, so I have narrowed it down to the circuit that has the fault on it an isolated it so the rest of the installation is fine.

The circuit that has the problem is a 6A Lighting circuit with 3x lighting points and 2 way switch and an emergency light the occupier said that the in house contractors changed a few lights and did something else.

The bottom switch you can turn that on/off all day and its fine the switch upstairs going on is fine and sometimes it lets you turn it off but other times you turn it off and it trips the RCD, I have tried a new switch that didnt work had a look behind the lights and it seems ok and apparently it all worked fine before the contractors change the lights so to me rules out damaged cable but will do another insulation resistance test on circuit anyway.

Anyone had this problem before? Thanks

 

[Chr!s]

Is it a Double Pole switch, if so if possible replace with a single Pole.

 

[hutch6447]

yes it is a double pole switch I will try that there has to be leakage somewhere.

 

[Chr!s]

yes it is a double pole switch I will try that there has to be leakage somewhere.

There's probably nothing wrong with the cable, just a bit of capacitance, just make it single pole.

 

[ackbarthestar]

A double pole 2 way lighting switch. Do they exist?

My bet would be if there was any discharge lighting on the circuit it might cause transient voltages generating an induced voltage on the cpc.

 

[hutch6447]

Its not the switch thats the problem, going t try a few things with the emergency light it has to be the fittings!

 

[Spazz]

Do a full IR test between L/E and N/E when the switch is on and off, it is some leackage there somewhere and sounds like the leakage is in the switch somewhere or even in the wiring between the 2 switches.

Try turning the light one down then coming back up and try the top one. If it only trips in 1 position then its that switch. If it trips in both positions then its the cable between the switches.

Good Luck

 

[Chr!s]

A double pole 2 way lighting switch. Do they exist?

My bet would be if there was any discharge lighting on the circuit it might cause transient voltages generating an induced voltage on the cpc.

Has he said it's two way?

Is it two way?

Is it Double Pole?

 

[Spazz]

The circuit that has the problem is a 6A Lighting circuit with 3x lighting points and 2 way switch and an emergency light the occupier said that the in house contractors changed a few lights and did something else.

Like he said - 2 way switch so yes it is a 2 way switch - then yes it has to be a double pole!

 

[Chr!s]

Like he said - 2 way switch so yes it is a 2 way switch - then yes it has to be a double pole!

I see now , though a two way aint double pole is it, single pole two way!

 

[Spazz]

You are right - double pole is an intermediate switch or a main switch or FSU for example
2 way is a light switch.

 

[ackbarthestar]

or two ganged single pole 2-way.

double pole is where two poles are switched at the same time, ie phase and neutral as you would find on an isolator

Edit : an intermediate might fill the part but is still only switching or crossing over one pole.
That would then mean there is another single pole 2-way switch soemwhere.

 

[Chr!s]

or two ganged single pole 2-way.

double pole is where two poles are switched at the same time, ie phase and neutral as you would find on an isolator

Edit : an intermediate might fill the part but is still only switching or crossing over one pole.
That would then mean there is another single pole 2-way switch soemwhere.

Yes that is what i was alluding too, are both poles switched, i.e Neutral and Line.

 

[ackbarthestar]

Switches are generally designed to disconnect the two poles together or the phase a fraction before the neutral.

If there are transient back emfs generated while switching a single pole device then the neutral and/or cpc could carry a current back to the DB

 

[MarkieSparkie]

Sounds like there is a high standing leakage on one or more of the final circuits and that the switching transients are combining with that to push the leakage over the tripping threshold of the RCD. Solutions:-1) Identify the leakage source(s) and remove or reduce if possible. 2) Remove over all RCD protection and RCBO individual final circuits. 3) Wire a snubber across the offending switch contacts.