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Voltage at light fitting that is turned off

Discuss Voltage at light fitting that is turned off in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

Thank you all for your replies. All were very helpfull. I understand now that it is probably induced/capacitance voltage and that the only way to get around the problem is to use a resistor/snubber. Could anyone point me in the right direction of the size that I would need or a calculation to work it out.

Am I right in guessing that it is Ohms law? I have the voltage (74), but I have no current and therefore no way of working this out at the moment.

many thanks again
 
Depends on the lamp spec (ie min current), I'd go for a 2K7 Ohm resistor, if you've got to buy some then buy a set of standard values. If you think about it you do have a current, the spec of the lamp is 7W (at 230V).
 
Do you have a dimmer on the lights? I fitted led's back when they were still very new and the dimmer actually lets a little voltage past and the lights never went all the way off. Could only be seen at night though but it was twinkling.
 
joking appart what would be an idea is to do a complete test on the circuit r1r2 ,r2rn etc etc this voltage could well be caused by a fault or underlying fault so could be well worth checking
 
Do you have a dimmer on the lights? I fitted led's back when they were still very new and the dimmer actually lets a little voltage past and the lights never went all the way off. Could only be seen at night though but it was twinkling.

Hi Joe, no dimmers on this circuit or any circuits in the house for that matter. No electrical control gear anywhere either.



It is definitely a capacitance building up (if thats the right way to think about it) on the strappers. I have done all tests possible (R1+R2, R2/R1/RN, Meggered at 1000v between all conductors on the 2way intermediate strappers. Removed all LED lights from the circuit and Meggered the complete circuit again. Disconnected the earth bond to the gas/water to see if I was getting anything from those. Tested for voltage on the water pipework in the house (altough all plastic apart form airing cupboard).

I have litterally been over this with a fine tooth comb, and this is the only thing that it can be. I would like to resolve the issue of the capacitance but it is a no-no as the house is now finished and chasing walls is out of the question.

I even removed the strappers and common from the switches at both ends of the 2way, and connected one strapper (black) to the live, and then tested for voltage at the 2nd 2way switch. I was getting 105v on the common (brown) and 60v on the 2nd strapper (grey).

I then isolated the circuit, put it all back together, and put a 2K2 resistor between the switch live and neutral (at the switch) this stopped the 74v which I had at the fittings, the only problem was it glowed red hot when the switch was on and suppling the fittings. Obviously it can't withstand the 240v running constantly through it.

Could anyone give me a clue on working out the size of resistor that would be needed?
It needs to be able to allow the 74v through it to neutral, but not allow the 240v to do the same.
So would a high resistor i.e 1M or above do this?


God my brain is fried......Please help.....
 
What rating of resistors did you buy? That 2K2 resistor is going to be dissipating about 25W when the lighting is full on. It should be rated at 250V and around 35W to be safe. Perhaps I should have stated that.
 
I was in RS and in a hurry, so I brought some 1k and 2k2 both of which are rated at 3w! No wonder it was getting a bit warm. I'm going to look at the RS website now to see if I can find the ones you recommend.

many thanks for your advice, much appriciated
 
I'm probably barking up the wrong tree entirely, but have come across induced voltage problems before, which seem to have been caused by a disconnected cpc, 90-100V in one case. Have you checked the cpc?
 
I'm probably barking up the wrong tree entirely, but have come across induced voltage problems before, which seem to have been caused by a disconnected cpc, 90-100V in one case. Have you checked the cpc?

Thanks for the advice Jeremy, but these have all been checked and cheaked again. Getting the voltage on the brown/grey when not connected to anything is definitely pointing to the conductance.
 
Limited choice on the packaging front. I'd probably go for this given your 2K2 Ohm choice: Buy High Power RESISTOR 50W 2K2 Vishay RCH50S22000JS06 online from RS for next day delivery.

Easy to solder some leads on for use and wrap in heatshrink for use. Should be easy enough to incorporate in the box(es).

Hi, I managed to get hold of these and they seemed better than the first lot I got hold of, I wired one up to a plugtop to see how hot they got. It lasted for about ten minutes, didn't get too hot, but then burnt it's self out.
Speaking to someone at the wholesaler and they have suggested that I could put an SES lampholder with a oven lamp in the ceiling void which will take the excess voltage out of the switch live.

Good Idea??

I'm not too sure. It would probably work but I dont fancy leaving something like that in the celing...

Is there any other suggestions that anyone can come up with?
 
Burnt out? What did you use as a heatsink?

Errrmmm?? Nothing....

I just left it on the floor, to do it's merry business. It expanded slightly on the back, then it cracked and stopped working.

I really have no idea with this. I wouldn't have thought it needed a heatsink as surely it would have said it needed it on the paperwork?
 
Data from the spec:

Power at 25°C50W with heatsink, 5.5W without heatsink
Resistance Tolerance±5%
Temperature Coefficient≤1Ω ±250ppm/°C, >1Ω ±150ppm/°C
Operating Temperature-55°C → +125°C
Thermal Resistance1.0°C/W
Limiting Element Voltage1285Vac
Overload Voltage2500Vac (Max.)
Dielectric Withstand Voltage3.5KVac
Insulating Resistance10000MΩ
Length50 mm
Width29.4 mm
Height15 mm
 
This is getting silly.

The customer has low energy lighting, 2 X 7W was mentioned. To stop the slight glimmer a loading resistor is suggested which if we go with the first suggestion of 2K2Ώ which will dissipate about 19.5W of waste heat. Near three times the lighting load.

It’s making a mockery of “energy saving”.

Would it be possible to fit a single halogen somewhere in the circuit? At least it would do something useful.
 
This is getting silly.

The customer has low energy lighting, 2 X 7W was mentioned. To stop the slight glimmer a loading resistor is suggested which if we go with the first suggestion of 2K2Ώ which will dissipate about 19.5W of waste heat. Near three times the lighting load.

It’s making a mockery of “energy saving”.

Would it be possible to fit a single halogen somewhere in the circuit? At least it would do something useful.

Thank you Tony, that is exactly what I have been thinking.

So talking to another wholesaler we came up with this; wiring a 25a modular contactor/relay in the smallest possible enclosureand placing this in the ceiling void.
Wring the switched live to A1 then link that to the top terminal 1, wiring the light from the bottom terminal 2, then wiring the neutral to A2 then linked to the light fitting.

This will enable the contactor coil to take the 74v constantly without pulling in the contacts, and when the switch is live this will then pull in the coil and the contacts switching the lights on.

Any thoughts on this??

I know putting it in the ceiling void isn't the best idea, but there is no other place to fit it as the house is finished. But it's alot better then sticking a pigmy lamp in the void as mentioned before!!
 
It would work and your loading would come down from 33.5W with the resistor to 21W. You could use an octal base relay, they are only 5W.
 
Thanks you brain boxes ,i have been in the trade for 50 years and only the other day came across this induced/ghost voltage for the first time ,thought i was going mad ,you have proved me wrong just seniel i expect ,no sterile, Regards Ronky
 

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