I have a house where the CFL's flicker at intermittent times (visible at night in the bedroom ceiling fixture) when the switch is off. The voltage reading at the light socket with the switch in the off position is 63 volts. Has anyone experienced this before and what was the cause. I have checked the house ground and it is fine. Many of the circuits are 12/2 without a ground. I'm wondering if someone tapped off these old circuits with grounded wire and this ground is carrying some voltage. Please let me know what you think?
CFL flicker with switch off
- Thread starter Jan
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Bad switch???? Or is it a dimmer switch???
walkerj
Senior Member
- Location
- Baton Rouge
Could the switch be a lighted switch?
ptonsparky
Tom
- Occupation
- EC - retired
What are you checking voltage to? Get a cord and go all the way back to the service entrance, ensure a grounded connection and take a new voltage reading.
How close is the house to a high voltage primary?
Switched neutral? MWBC with intermittent neutral connection?
Hallucinogens? Torn retina?
How close is the house to a high voltage primary?
Switched neutral? MWBC with intermittent neutral connection?
Hallucinogens? Torn retina?
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
091219-0801 EST
NuVision bulb, 23 W.
1 megohm series resistor no flash. Insufficient current to overcome leakage in the bulb.
100k in series. Flash rate about 1/3 Hz.
10k in series. Flash rate fast. Estimate 3 to 5 per second based on the 100k test.
Internally there is a rectifier, probably bridge, and a capacitor input filter. Probably there is a voltage level on the capacitor of Vt where below this level little current flows and the capacitor exponentially charges. Then at Vt the voltage is high enough to trigger the driver to the fluorescent tube to cause the capacitor to be discharged. This is somewhat equivalent to an RC oscillator using a neon bulb.
It appears one can make a useful flashing light with the 10k resistor.
As suggested a pilot lamp type switch might be the cause.
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NuVision bulb, 23 W.
1 megohm series resistor no flash. Insufficient current to overcome leakage in the bulb.
100k in series. Flash rate about 1/3 Hz.
10k in series. Flash rate fast. Estimate 3 to 5 per second based on the 100k test.
Internally there is a rectifier, probably bridge, and a capacitor input filter. Probably there is a voltage level on the capacitor of Vt where below this level little current flows and the capacitor exponentially charges. Then at Vt the voltage is high enough to trigger the driver to the fluorescent tube to cause the capacitor to be discharged. This is somewhat equivalent to an RC oscillator using a neon bulb.
It appears one can make a useful flashing light with the 10k resistor.
As suggested a pilot lamp type switch might be the cause.
.
Ohmy
Senior Member
- Location
- Atlanta, GA
We've experienced this with fan remotes and dimmers.
Any chance the circuit is under the control of a X10 device? I've seen that flickering with a plug-in X10 lamp module - they pulse low-voltage when "off" to sense if you have turned the light's switch on-off-on. Its just enough voltage to make CFLs flicker in a dark room. Doesn't sound like this applies here, just throwing out another possible source for the low voltage other than a pilot lamp in the wall switch.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
091221-1714 EST
With an OAC5 solid-state relay and my previously mentioned NuVision bulb the flash rate is about 0.1 Hz and only the lower half of the tube flashes. Simpson resistance reading, very slight meter movement on the 10k range.
I checked the leakage resistance on a Crydom D1210 and with a Simpson 270 it was about 8k. However, the flash rate was not as high as I expected and the brightness not as high as when a straight 10k resistor was used.
Note: the lower current AC X-10s have a Triac output.
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With an OAC5 solid-state relay and my previously mentioned NuVision bulb the flash rate is about 0.1 Hz and only the lower half of the tube flashes. Simpson resistance reading, very slight meter movement on the 10k range.
I checked the leakage resistance on a Crydom D1210 and with a Simpson 270 it was about 8k. However, the flash rate was not as high as I expected and the brightness not as high as when a straight 10k resistor was used.
Note: the lower current AC X-10s have a Triac output.
.
I'm Stumped by this one
I'm Stumped by this one
This one has me stumped. Here's what I know:
1. replaced 2- 3w switches to the lvrm light, they are not lighted or dimmers. Light still flickers. I have gotten a range of voltage readings from 6v to 69v and the flicker can be seen at 59v. These reading occur with the switches in the off positions. The circuit breaker for this light also has the dnrm light on it and the dnrm CFL doesn't flicker, it's voltage reading is zero.
2. There are 2 lights upstairs that also flicker, the hall and mst bdrm. These 2 lights are on a different breaker from the lvrm. The voltage readings also fluctuate on these 2 lights. There is another CFL in the second bdrm that is on this same breaker and it has not flickered it's voltage reading is zero.
3. These voltage reading have been taken inside the fixture sockets and in the wirenuts in the box and they read the same.
4. I have noticed the 3 lights flicker at different frequencies. The last time I was there the lvrm flickered every 13 sec, hall every 7 sec and mbdrm every 30 sec.
5. If the breaker is turned off the flickering stops.
6. I have not been able to determined is this is happening at specific times. I have asked the owners to record when it happens.
7. There is no x10 or radio frequency devices in this apartment. There are 3 apartments in this building and they each have there own meters and panels.
As I said, "I'm Stumped", I'm hoping someone can think of something else I can check. Thanks Jan
I'm Stumped by this one
This one has me stumped. Here's what I know:
1. replaced 2- 3w switches to the lvrm light, they are not lighted or dimmers. Light still flickers. I have gotten a range of voltage readings from 6v to 69v and the flicker can be seen at 59v. These reading occur with the switches in the off positions. The circuit breaker for this light also has the dnrm light on it and the dnrm CFL doesn't flicker, it's voltage reading is zero.
2. There are 2 lights upstairs that also flicker, the hall and mst bdrm. These 2 lights are on a different breaker from the lvrm. The voltage readings also fluctuate on these 2 lights. There is another CFL in the second bdrm that is on this same breaker and it has not flickered it's voltage reading is zero.
3. These voltage reading have been taken inside the fixture sockets and in the wirenuts in the box and they read the same.
4. I have noticed the 3 lights flicker at different frequencies. The last time I was there the lvrm flickered every 13 sec, hall every 7 sec and mbdrm every 30 sec.
5. If the breaker is turned off the flickering stops.
6. I have not been able to determined is this is happening at specific times. I have asked the owners to record when it happens.
7. There is no x10 or radio frequency devices in this apartment. There are 3 apartments in this building and they each have there own meters and panels.
As I said, "I'm Stumped", I'm hoping someone can think of something else I can check. Thanks Jan
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100112-1932 EST
There is a high resistance leakage path from the supply to the flickering lights. The resistance of the leakage is in the range of of the values I mentioned in previous posts.
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There is a high resistance leakage path from the supply to the flickering lights. The resistance of the leakage is in the range of of the values I mentioned in previous posts.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100113-1028 EST
Jan:
Remove all the CFLs on a circuit where they flash. At one of the sockets measure the voltage between the two leads supplying the socket with a high impedance meter, 10 megohms input impedance. What is the voltage reading when the circuit is off? Install a 15 W incandescent. Now what is the voltage? Should be zero. I expect without the 15 W you might read close to full line voltage.
Is it a safety hazard? Probably not.
If you have a substantial voltage reading with no 15 W bulb, then start looking for the source of the leakage current.
If the source is capacitive coupling, then the flashing might occur with .03 mfd of capacitance. My experiment on one bulb. 0.03 is 30,000 pfd. At 20 pfd per foot of Romex it would take 1500 ft to get this much capacitance.
My Fluke reads 92 V of 123 V at 400 pfd. That would be about 20 ft of Romex with one wire hot and the other floating and the floating connected to one meter input with the other meter lead to neutral.
200 pfd 67 V, 100 pfd 40 V.
.
Jan:
Remove all the CFLs on a circuit where they flash. At one of the sockets measure the voltage between the two leads supplying the socket with a high impedance meter, 10 megohms input impedance. What is the voltage reading when the circuit is off? Install a 15 W incandescent. Now what is the voltage? Should be zero. I expect without the 15 W you might read close to full line voltage.
Is it a safety hazard? Probably not.
If you have a substantial voltage reading with no 15 W bulb, then start looking for the source of the leakage current.
If the source is capacitive coupling, then the flashing might occur with .03 mfd of capacitance. My experiment on one bulb. 0.03 is 30,000 pfd. At 20 pfd per foot of Romex it would take 1500 ft to get this much capacitance.
My Fluke reads 92 V of 123 V at 400 pfd. That would be about 20 ft of Romex with one wire hot and the other floating and the floating connected to one meter input with the other meter lead to neutral.
200 pfd 67 V, 100 pfd 40 V.
.
Jnas480
Member
- Location
- Eastern CT
It seems like it is sharing same neut from different circuit.
1.Does it read 63 volts with a digital meter or with solenoid meter.
2.When you are reading it with a meter, have another person shut one breaker off one by one, until there is no more reading on meter. (This will tell you if the Neut is being shared by different circuit)
Good luck
1.Does it read 63 volts with a digital meter or with solenoid meter.
2.When you are reading it with a meter, have another person shut one breaker off one by one, until there is no more reading on meter. (This will tell you if the Neut is being shared by different circuit)
Good luck
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100113-1917 EST
Jnas480:
A shared neutral is unlikely to have anything to do with the problem.
The effect is the result of leakage current to the CFL. There is a rectifier and capacitor input filter in the CFL. Leakage current causes a gradual increase in the capacitor voltage. When the voltage is high enough the bulb conducts causing a light flash and discharge of the capacitor. Then the cycle starts over.
This like an oscillator using a neon bulb, capacitor, charging resistor, and a power source.
In an earlier post I indicated experiments you can run to demonstrate the flashing of a CFL. All CFLs may not exhibit this characteristic.
.
Jnas480:
A shared neutral is unlikely to have anything to do with the problem.
The effect is the result of leakage current to the CFL. There is a rectifier and capacitor input filter in the CFL. Leakage current causes a gradual increase in the capacitor voltage. When the voltage is high enough the bulb conducts causing a light flash and discharge of the capacitor. Then the cycle starts over.
This like an oscillator using a neon bulb, capacitor, charging resistor, and a power source.
In an earlier post I indicated experiments you can run to demonstrate the flashing of a CFL. All CFLs may not exhibit this characteristic.
.
kbsparky
Senior Member
- Location
- Delmarva, USA
Easy fix:
Change out one of those CFL bulbs with a standard incandescent. It doesn't need to be much wattage, but it will provide sufficient resistance to stop the flickering.
Change out one of those CFL bulbs with a standard incandescent. It doesn't need to be much wattage, but it will provide sufficient resistance to stop the flickering.
Jnas480
Member
- Location
- Eastern CT
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
With a high-impedance meter, no doubt. What does it read with the CFL in, and with an incandescent in?
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100114-1800 EST
Post #1 did not say that the CFL was removed, but rather that the switch to it was off and the meter read 63 V. I doubt the voltage was stable if the bulb was flashing.
With a 47 k resistor for leakage to a NuVision CFL I get about a 1 second flash rate. A Simpson 270 in AC and 50 V range reads a fluctuating 20 to 25 V. Similar with Fluke 27.
I can not get a slow flash rate at the present. Two different GEs don't flash with a series 10 K. A NuVision flashes several times per second.
I suspect that different brands or year to year model differences may produce flashers or not.
.
Post #1 did not say that the CFL was removed, but rather that the switch to it was off and the meter read 63 V. I doubt the voltage was stable if the bulb was flashing.
With a 47 k resistor for leakage to a NuVision CFL I get about a 1 second flash rate. A Simpson 270 in AC and 50 V range reads a fluctuating 20 to 25 V. Similar with Fluke 27.
I can not get a slow flash rate at the present. Two different GEs don't flash with a series 10 K. A NuVision flashes several times per second.
I suspect that different brands or year to year model differences may produce flashers or not.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100115-0847 EST
Starting from post #1. "Most wiring is 12-2 with no ground".
Suppose we have an unswitched neutral, then electrically the neutral is essentially at ground potential. The hot wire is switched, and there are two wires in the cable, a switched hot and neutral. This is not a three-way circuit. Any other hot wires are spaced somewhat more than the distance of hot to neutral in the cable of interest. Thus, the capacitance from some other adjacent hot to the switched hot of interest will be less than 20 pfd per foot.
With all loads on the switched circuit removed what is the high impedance voltage (10 megohms input impedance) from the off state switched hot to neutral? Same question but with the switched hot wire disconnected from the switch and measured from the hot wire, and separately from the switch terminal?
Assuming virtual no voltage from the switch terminal, then what is causing leakage to the floating hot wire?
Some readings on a Fluke 27 and Simpson 270 for different series capacitors. The Fluke input is 10 megohms with maybe 27 pfd shunt capacitance. The Simpson 270 was on the AC 250 V range and is 5000 ohm/volt or 1.25 megohms on this range.
pfd Fluke Simpson
0 4.8 0
100 42 7
200 68 13
300 83 15
400 92 25
500 100 29
600 104 34
1000 113 50
Source voltage was 123 V.
If in post #1 the CFL was not present, then the voltage read might imply a 200 pfd coupling if the leakage was capacitive.
From my previous experiment with capacitance in series with the CFL, if the leakage is from capacitance coupling, then a rather large capacitor is required relative to what can be expected from wiring. However, different CFLs might react with far less capacitance.
In a 3-way circuit with a three conductor cable and the switches in an off condition there is capacitive coupling of a hot wire to a floating wire. With newer Romex and thinner insulation, thus wires are closer together, the capacitance per foot may be somewhat greater than 20 pfd/ft, but not 10 times larger.
.
Starting from post #1. "Most wiring is 12-2 with no ground".
Suppose we have an unswitched neutral, then electrically the neutral is essentially at ground potential. The hot wire is switched, and there are two wires in the cable, a switched hot and neutral. This is not a three-way circuit. Any other hot wires are spaced somewhat more than the distance of hot to neutral in the cable of interest. Thus, the capacitance from some other adjacent hot to the switched hot of interest will be less than 20 pfd per foot.
With all loads on the switched circuit removed what is the high impedance voltage (10 megohms input impedance) from the off state switched hot to neutral? Same question but with the switched hot wire disconnected from the switch and measured from the hot wire, and separately from the switch terminal?
Assuming virtual no voltage from the switch terminal, then what is causing leakage to the floating hot wire?
Some readings on a Fluke 27 and Simpson 270 for different series capacitors. The Fluke input is 10 megohms with maybe 27 pfd shunt capacitance. The Simpson 270 was on the AC 250 V range and is 5000 ohm/volt or 1.25 megohms on this range.
pfd Fluke Simpson
0 4.8 0
100 42 7
200 68 13
300 83 15
400 92 25
500 100 29
600 104 34
1000 113 50
Source voltage was 123 V.
If in post #1 the CFL was not present, then the voltage read might imply a 200 pfd coupling if the leakage was capacitive.
From my previous experiment with capacitance in series with the CFL, if the leakage is from capacitance coupling, then a rather large capacitor is required relative to what can be expected from wiring. However, different CFLs might react with far less capacitance.
In a 3-way circuit with a three conductor cable and the switches in an off condition there is capacitive coupling of a hot wire to a floating wire. With newer Romex and thinner insulation, thus wires are closer together, the capacitance per foot may be somewhat greater than 20 pfd/ft, but not 10 times larger.
.
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