Emergency light won't switch off - correctly wired new lights.

[ddelectrical]

Hi, here's a good one - replaced 15 E-lights recently, (tube type replaced with Newlec led type), and noticed one of the old outside Thorn 2D E-lights was on when driving past a few days later. The Thorn lights are all up to spec and function as they should. Went to investigate and it seems that some residual voltage on the switched / maintained line is triggering one light to come on. I connected the switched lines to two of the inside lights and now they stay on but the outside light is off. Enough residual voltage absorbed by the interior lights prevents outside light triggering.

It seems that the voltage threshold for the maintained input is set so low that it can trigger switching from induced voltage. Someone else has had the same problem here I think as there are a few disconnected exit lights that should be on the exit light switch. The system is 19 E-lights in two banks across the whole building. Four outside and the rest indoors. The exit routes E-lights are supposed to be switched / maintained but only one outside light was left connected. Someone has disconnected the faulty ones previously. The wiring system is only a few years old and has been done to a good standard. The earth lines are present to all the E-lights so I would have thought that the residual voltage would be drained sufficiently to avoid nuisance operation.

Still with me? So, the switched live lines show correct switching when operating the exit light switch. There is a very small voltage present on these lines however when the switch is off that is enough to trigger the lights.

There is a split phase supply to the main grid switch position for all the lights. Could it be that the induced voltage in the grid switch enclosure is high enough to cause this? (415 between phases in a small enclosure feeding two single phase systems). The lighting system is all 240V, it has just been wired so the system is supplied from two phases.

Could it be that the main earth impedance for the building is high and causing stray currents? I will go back and check this.

I am considering fitting resistors / filter capacitors to the switched live inputs to see if that cures the problem.

Anyone else had a similar experience? Any clues most welcome.

I have had to leave the switched lines disconnected at the lights themselves as disconnecting the exit lights switch has no effect, (other than disabling the function of the switch).

All the lights perform as they should under test. The charging indicators are showing ok.

I love my job really. Honest.

 

[Rpa07]

When you say they are ON do you mean a faint glow of the LEDs or do you mean it’s fully lit? Clarifying if that’s ok.
And what test kit are you useing for the voltages?

 

[Pete999]

Did you fit a maintained or non maintained type when you replaced the fitting?

 

[Lucien Nunes]

It's unlikely to be anything to do with the earthing or proximity to other phases specifically. If the SL insulation is intact, it's probably the total stray capacitance between PL and SL pulling the SL up high enough to cause the effect, allied with poor design of the fittings that should be tolerant of this. What type of cabling is in use and approximately what total length of SL is connected to one switch?

If the cause is indeed capacitive leakage, a small resistive or capacitive load to N should solve it.

 

[*-jester-*]

My first thought was induction. Especially if the cables run parallel to other circuits for any distance. You could rule this theory out by isolating other circuits.

 

[westward10]

Temporarily replace one of the external ones and see if it still happens.

 

[davesparks]

My first thought was induction. Especially if the cables run parallel to other circuits for any distance. You could rule this theory out by isolating other circuits.

Cables in parallel will suffer from capacitive coupling rather than induction.

 

[ddelectrical]

When you say they are ON do you mean a faint glow of the LEDs or do you mean it’s fully lit? Clarifying if that’s ok.
And what test kit are you useing for the voltages?

They have a two state dim function. They are full brightness in emergency mode and slightly dimmer in maintained mode. They are on in this slightly dimmer state but it is normal. They even auto dim to off when turning off the SL line. (The ones that work properly that is). Very swish!

 

[ddelectrical]

Did you fit a maintained or non maintained type when you replaced the fitting?

They are multi-purpose. Just remove a link for maintained use.

 

[ddelectrical]

It's unlikely to be anything to do with the earthing or proximity to other phases specifically. If the SL insulation is intact, it's probably the total stray capacitance between PL and SL pulling the SL up high enough to cause the effect, allied with poor design of the fittings that should be tolerant of this. What type of cabling is in use and approximately what total length of SL is connected to one switch?

If the cause is indeed capacitive leakage, a small resistive or capacitive load to N should solve it.

The lights are all wired in standard 1mmsq flat pvc 3 core and earth. The circuit length from the switch to the lights is about 15mtrs. Then the three lights in question are radially wired from there over another 10mtrs or so.

As yet I have only used a bar graph led type volt probe as I didn't have enough time to get all the toys out today. I will return with proper gear and get some data.

I did wonder tonight if someone had taken the SL line from one phase and the PL line from another. This needs checking asap. This would introduce 415V into every light fitting.

 

[*-jester-*]

Cables in parallel will suffer from capacitive coupling rather than induction.

Inductive coupling, capacitive coupling or a combination of both can occur. Though inductance coupling is more common.

Electromagnetic Interference - Siemon - http://www.siemon.com/us/white_papers/02-03-22-emi.asp

 

[ddelectrical]

I have come across stray induced voltage many times before but find it is usually controlled by the presence of the CPC. Especially as it lies in the center of flat twin and earth. The old two wire light cable that was around for a while many years ago causes CFL lamps to flash. The igniter part of the control circuit in the lamp harvests a capacitor full of stray charge off the de-energised lines and fires a pulse to initiate the discharge but cannot maintain the plasma as there is no sustaining voltage. The further from the source the more they flash as more cable is coupling to other circuits. Great fun.

The customer was a little concerned about their haunted lights so I said don't worry - exorcisms are all just part of the service!