Capacitors To Stop Fluorescent Lights From Flickering

[chownah]

I put a large capacitor in parallel with my electrical light to stop it from flickering when it was off....it worked fine...and apparently it passes very very little current. Elkangorito wanted the techinical discussion out of the thread where it started so I'm starting this thread to keep peace in the family.......let the discussion begin.

[PETERTHEEATER]

I put a large capacitor in parallel with my electrical light to stop it from flickering when it was off....it worked fine...and apparently it passes very very little current. Elkangorito wanted the techinical discussion out of the thread where it started so I'm starting this thread to keep peace in the family.......let the discussion begin.

You only have ONE electric light Chownah? A bed-sitter right?

Is the light incandescent or fluorescent?

If it flickers when the control switch is OFF, maybe the switch is faulty. More details would help.

[gcad]

If the light is flickering when off, the entire electrical installation might have low power factor. If this is the case then one capacitor across a single light is only a band-aide fix. If you have multiple fluorescent lights you should put capacitors in all of them. I wouldn't be surprised if the low power factor is the fault of the supply authority because I doubt a domestic installation with a couple of fluoros would cause any significant power factor degradation. On that note, is this for a house or something else?

[chownah]

I have only fluorescent lights in the house and I have two in the bedroom both on the ceiling....these were the ones that flickered and kept me awake. I have already installed the capacitor and it works fine....I only installed on one light but it solves the problem for both of them so why should I install more. I think the problem is caused because both of the lights and a switchable outlet in the bedroom are all wired for dual switches and the result is a nice, neat, compact, perfectly straight run of multiple wires running across the upper surface of the ceiling and all these wires being in close proximity are exciting each other when there are transient fluctuations in the supply and possibly in the neutral.

Edit: By the way these all have instant on ballasts which are the really efficient ones so I think they are high power factor although I only incompletely understand the importance of the power factor.

Chownah

[Crossy]

Flickering when switched off is very often the result of having the switch in the neutral, a potentially hazardous situation.

Putting a cap. across the fitting is shunting the tiny leakage current that causes the flicker, treating the symptom rather than the disease, kind of like taking aspirin for a broken leg (fixes the pain, not the bone).

Before stick capacitors all over the place, which in reality are going to have little noticeable effect on your bill unless you have a LOT of fluorescent lights (if you do have a lot, then using electronic ballasts will save more than adding PF correction), check how your fittings are wired (get out the neon screwdriver).

[chownah]

Flickering when switched off is very often the result of having the switch in the neutral, a potentially hazardous situation.

Putting a cap. across the fitting is shunting the tiny leakage current that causes the flicker, treating the symptom rather than the disease, kind of like taking aspirin for a broken leg (fixes the pain, not the bone).

Before stick capacitors all over the place, which in reality are going to have little noticeable effect on your bill unless you have a LOT of fluorescent lights (if you do have a lot, then using electronic ballasts will save more than adding PF correction), check how your fittings are wired (get out the neon screwdriver).

Looks like you might have posted over me....did you see my previous post?

Recap...only one capacitor needed to solve the problem...already using electronic ballasts...

I've checked all the fittings and the wiring and the switches...its all good...by changing some of the circuit runs (its a complex system with three dual switch circuits) I was able to get either one or the other light to flicker...and with one capacitor I fixed the problem for both. You seem to think that this fix is inadequate...in what way is it inadequate?...cheap (a few baht for the capacitor and a few minutes to install it) and effective....does not draw appreciable current....what's inadequate?

Chownah

[Crossy]

Flickering when switched off is very often the result of having the switch in the neutral, a potentially hazardous situation.

Putting a cap. across the fitting is shunting the tiny leakage current that causes the flicker, treating the symptom rather than the disease, kind of like taking aspirin for a broken leg (fixes the pain, not the bone).

Before stick capacitors all over the place, which in reality are going to have little noticeable effect on your bill unless you have a LOT of fluorescent lights (if you do have a lot, then using electronic ballasts will save more than adding PF correction), check how your fittings are wired (get out the neon screwdriver).

Looks like you might have posted over me....did you see my previous post?

Recap...only one capacitor needed to solve the problem...already using electronic ballasts...

I've checked all the fittings and the wiring and the switches...its all good...by changing some of the circuit runs (its a complex system with three dual switch circuits) I was able to get either one or the other light to flicker...and with one capacitor I fixed the problem for both. You seem to think that this fix is inadequate...in what way is it inadequate?...cheap (a few baht for the capacitor and a few minutes to install it) and effective....does not draw appreciable current....what's inadequate?

Chownah

Whoooaaaa!, now we have more info IF you had flicker caused by a switched neutral it would be inadequate!!

I suspect that your electronic ballasts are charging up from leakage or capacitive coupling (as you surmise), once enough charge has accumulated you get a flash.

I assume you've used a 220V AC rated cap (one meant for PF correction), in which case nothing is inadequate

I'm not sure of the mechanism that's stopping the flicker, and it's interesting that putting a cap on one light stops all of them.

[chownah]

Flickering when switched off is very often the result of having the switch in the neutral, a potentially hazardous situation.

Putting a cap. across the fitting is shunting the tiny leakage current that causes the flicker, treating the symptom rather than the disease, kind of like taking aspirin for a broken leg (fixes the pain, not the bone).

Before stick capacitors all over the place, which in reality are going to have little noticeable effect on your bill unless you have a LOT of fluorescent lights (if you do have a lot, then using electronic ballasts will save more than adding PF correction), check how your fittings are wired (get out the neon screwdriver).

Looks like you might have posted over me....did you see my previous post?

Recap...only one capacitor needed to solve the problem...already using electronic ballasts...

I've checked all the fittings and the wiring and the switches...its all good...by changing some of the circuit runs (its a complex system with three dual switch circuits) I was able to get either one or the other light to flicker...and with one capacitor I fixed the problem for both. You seem to think that this fix is inadequate...in what way is it inadequate?...cheap (a few baht for the capacitor and a few minutes to install it) and effective....does not draw appreciable current....what's inadequate?

Chownah

Whoooaaaa!, now we have more info IF you had flicker caused by a switched neutral it would be inadequate!!

I suspect that your electronic ballasts are charging up from leakage or capacitive coupling (as you surmise), once enough charge has accumulated you get a flash.

I assume you've used a 220V AC rated cap (one meant for PF correction), in which case nothing is inadequate

I'm not sure of the mechanism that's stopping the flicker, and it's interesting that putting a cap on one light stops all of them.

When the problem started (right away....the first time I turned them on) and after I had checked all the switches, connections, and wiring pattern, and swapped out all the ballasts and lights, I decided that it was the wire run causing the problem and started studying up (on the internet) about inductive and capacitive coupling and decided that a capacitor might do the trick...I then contacted an electrical engineer who thought I had a good chance of being right and he emailed me what specs he thought the capacitor should have....I've been going through my old emails but haven't found it yet and I can't remember off the top of my head what the specs were but it seems to me that you need a higher voltage rating because 220V is rms (root-mean-square for those wondering what rms means) and you need to handle peak to peak voltages and also have some safety factor as well and especially since higher voltage capacitors are cheap and readily available you might as well go overboard on the voltage rating for safety.....seems like mine is rated for about 500 volt or maybe even 800 volts but can't remember and I'm hoping I can find the email and then we'll know exactly what I used.

Chownah

[Tywais]

can't remember off the top of my head what the specs were but it seems to me that you need a higher voltage rating because 220V is rms (root-mean-square for those wondering what rms means) and you need to handle peak to peak voltages and also have some safety factor as well and especially since higher voltage capacitors

If they are rated for 220VAC there is no problem (takes into account the peak already) - usually have some over range available. Just make sure they are not DC rated capacitors and especially electrolytic or they will blow up sooner or later.

[Crossy]

..... seems like mine is rated for about 500 volt or maybe even 800 volts but can't remember and I'm hoping I can find the email and then we'll know exactly what I used.

Chownah

It would be interesting, obviously someone else has seen this before.

I suspect you have a paper cap rated at over 650V (220 * [root 2] * 2)= 622V

A 600V cap would 'probably' be OK, 800 or 1kV to be safe, the ones intended for Power Factor correction are ideal.

[Gary A]

I have my desktop computer chassis connected to an earth rod. I just checked the hot wire to the chassis and got 218 volts. I checked the neutral to the chassis and got 11 volts.

[Crossy]

I have my desktop computer chassis connected to an earth rod. I just checked the hot wire to the chassis and got 218 volts. I checked the neutral to the chassis and got 11 volts.

Sounds reasonable, cetainly within acceptable limits

Meanwhile I've posted the flickering lights / capacitor question on the IEE / IET forum, if anyone can explain they can

[elkangorito]

I agree with what Crossy said about a bandaid vs a fix.

Also, besides being a possible problem re switching the neutral, a high floating voltage on the neutral may also cause the flicker. In such a case, earthing the neutral via an MEN link will eliminate this problem.

[chownah]

I agree with what Crossy said about a bandaid vs a fix.

Also, besides being a possible problem re switching the neutral, a high floating voltage on the neutral may also cause the flicker. In such a case, earthing the neutral via an MEN link will eliminate this problem.

Can you explain how it is that a capacitor in series with a fluorescent light on a dual switched circuit could pose a neutral switching problem? I really can't see it at all.

Using the term "bandaid" usually implies some inadequacy...can you say what the inadequacy is?

[Ijustwannateach]

You may also be saving money by doing this... Capacitors offset the the natural self-inductance of the fluorescent light tubes and give you a better overall power rating (puts the circuit in phase)- so you don't have as much wasted current (and money).

[elkangorito]

I agree with what Crossy said about a bandaid vs a fix.

Also, besides being a possible problem re switching the neutral, a high floating voltage on the neutral may also cause the flicker. In such a case, earthing the neutral via an MEN link will eliminate this problem.

Can you explain how it is that a capacitor in series with a fluorescent light on a dual switched circuit could pose a neutral switching problem? I really can't see it at all.

Using the term "bandaid" usually implies some inadequacy...can you say what the inadequacy is?

In actual fact, I was in error in relation to your first post about this subject since you actually placed the cap across the supply (in parallel). I cannot see how a capacitor in series with a fluorescent light on a dual switched circuit could pose a neutral switching problem. But a cap in series with an inductor, if the series C-L circuit is at or near resonance (or unity power factor), can create a higher than usual current in the circuit, which in turn will lead to greatly elevated voltages across circuit components.

The fix is inadequate because it does not address the real problem, which is either a switched neutral or a floating voltage on the neutral. The capacitor is simply a mask.

You may also be saving money by doing this... Capacitors offset the the natural self-inductance of the fluorescent light tubes and give you a better overall power rating (puts the circuit in phase)- so you don't have as much wasted current (and money).

Unfortunately, this is not true. Whilst increasing the Power Factor for an individual piece of equipment may improve its efficiency (reduced internal losses - heat), it will not save the average consumer money. The kilowatt hour measures kilowatts, which takes into account the Power Factor of the installation.

Eg. A 22kW 220v single phase motor has a Power Factor (P.F.) of 0.6. Using the equation P=E x I x Cos#,

I= (22 000) divided by (220 x 0.6)

= 167 Amps.

Since the motor will always absorb 22kW, at a P.F. of 0.8, the current is reduced to 125 Amps but the same power is being used. The kilowatt hour meter will still see 22kW.

[Tywais]

The fix is inadequate because it does not address the real problem, which is either a switched neutral or a floating voltage on the neutral. The capacitor is simply a mask.

One other thing that can potentially cause it is if you have 'lighted' switches where leakage from the lamp can get through to the fixture.

[chownah]

I agree with what Crossy said about a bandaid vs a fix.

Also, besides being a possible problem re switching the neutral, a high floating voltage on the neutral may also cause the flicker. In such a case, earthing the neutral via an MEN link will eliminate this problem.

Can you explain how it is that a capacitor in series with a fluorescent light on a dual switched circuit could pose a neutral switching problem? I really can't see it at all.

Using the term "bandaid" usually implies some inadequacy...can you say what the inadequacy is?

In actual fact, I was in error in relation to your first post about this subject since you actually placed the cap across the supply (in parallel). I cannot see how a capacitor in series with a fluorescent light on a dual switched circuit could pose a neutral switching problem. But a cap in series with an inductor, if the series C-L circuit is at or near resonance (or unity power factor), can create a higher than usual current in the circuit, which in turn will lead to greatly elevated voltages across circuit components.

The fix is inadequate because it does not address the real problem, which is either a switched neutral or a floating voltage on the neutral. The capacitor is simply a mask.

So, am I safe, since its in parallel and not series?

Also, why would someone make a C-L series circuit in house wiring?...is this only a theoretic thing?....or should people worry about this.

Also, the fix is perfect...it solved the problem completely with little cost or effort and there is no danger in the circuits involved due to its configuration...at least that I can see......can you see some danger with this configuration? Please remember that the real problem was the flickering of the light that kept me awake...it has stopped completely....the real problem has been fixed.

[Ijustwannateach]

I agree with what Crossy said about a bandaid vs a fix.

Also, besides being a possible problem re switching the neutral, a high floating voltage on the neutral may also cause the flicker. In such a case, earthing the neutral via an MEN link will eliminate this problem.

Can you explain how it is that a capacitor in series with a fluorescent light on a dual switched circuit could pose a neutral switching problem? I really can't see it at all.

Using the term "bandaid" usually implies some inadequacy...can you say what the inadequacy is?

In actual fact, I was in error in relation to your first post about this subject since you actually placed the cap across the supply (in parallel). I cannot see how a capacitor in series with a fluorescent light on a dual switched circuit could pose a neutral switching problem. But a cap in series with an inductor, if the series C-L circuit is at or near resonance (or unity power factor), can create a higher than usual current in the circuit, which in turn will lead to greatly elevated voltages across circuit components.

The fix is inadequate because it does not address the real problem, which is either a switched neutral or a floating voltage on the neutral. The capacitor is simply a mask.

You may also be saving money by doing this... Capacitors offset the the natural self-inductance of the fluorescent light tubes and give you a better overall power rating (puts the circuit in phase)- so you don't have as much wasted current (and money).

Unfortunately, this is not true. Whilst increasing the Power Factor for an individual piece of equipment may improve its efficiency (reduced internal losses - heat), it will not save the average consumer money. The kilowatt hour measures kilowatts, which takes into account the Power Factor of the installation.

Eg. A 22kW 220v single phase motor has a Power Factor (P.F.) of 0.6. Using the equation P=E x I x Cos#,

I= (22 000) divided by (220 x 0.6)

= 167 Amps.

Since the motor will always absorb 22kW, at a P.F. of 0.8, the current is reduced to 125 Amps but the same power is being used. The kilowatt hour meter will still see 22kW.

You're probably right- but doesn't the power meter run on use of current (i.e., how would it "know" how much power was used?)

[h90]

What I don't understand here:

When the light is off and flickers and you measure both/all three wires going to the light, power, neutral and if there ground against a real ground (often I can measure just against my body and get results, else just put some not insulated copper in the land).

neutral and ground should a complete zero.

on the power there might be something but this must be very minimal else might be open parts of the wire are together with another in a wet wall or something like that.

Not sure if all I wrote make sense, please correct me if you find nonsens in my posting

[Crossy]

OK chaps, the IEE / IET forum have come up with the goods

I'm not sure if non-members can access the forum so I'll post the reply here, a credible explanation as to WHY the lights flicker and the correct solution (which is a parallel capacitor as installed by our OP here)

mapj1 has posted a message entitled Fluorescent lights flicker when off.

Message Posted on: Monday April 02,2007 03:07:19 PM

Connecting a capacitor accross the lamps will reduce the 'off voltage' the lamp sees caused by the capcitive voltage division. see here where this very quesstion has come up in the past (and I replied then too, I must make a decent web page with this on...).

http://www.theiet.org/forums/f...key=y&keyword1=flicker

http://www.theiet.org/forums/f...key=y&keyword1=flicker

"It is the capacitance accross the switch wiring this causes a few uA to slowly charge the reservoirs of the CFL electronics (as these contain a bridge rectifier and a reservoir cap), then once the reservoir is full enough, the lamp driver starts briefly, and runs out of charge almost immediately, and the cycle repeats. - the effect is worse on a 2 way switch circuit because it is so long. The easy fix is a capacitor accross the L-N terminals of the affected fitting. Anything from a few 10s of nF to 1 Uf may be required, depending on the wiring length involved. Obviously the cap needs to be mains rated."

Its not a power factor problem per se, but such capacitors do have the advantage of automatically being mains rated, so fit for the purpose.

regards Mike.

You can view the message at http://www.theiet.org/forums/forum/message...1&forumid=1.

[elkangorito]

I agree with what Crossy said about a bandaid vs a fix.

Also, besides being a possible problem re switching the neutral, a high floating voltage on the neutral may also cause the flicker. In such a case, earthing the neutral via an MEN link will eliminate this problem.

Can you explain how it is that a capacitor in series with a fluorescent light on a dual switched circuit could pose a neutral switching problem? I really can't see it at all.

Using the term "bandaid" usually implies some inadequacy...can you say what the inadequacy is?

In actual fact, I was in error in relation to your first post about this subject since you actually placed the cap across the supply (in parallel). I cannot see how a capacitor in series with a fluorescent light on a dual switched circuit could pose a neutral switching problem. But a cap in series with an inductor, if the series C-L circuit is at or near resonance (or unity power factor), can create a higher than usual current in the circuit, which in turn will lead to greatly elevated voltages across circuit components.

The fix is inadequate because it does not address the real problem, which is either a switched neutral or a floating voltage on the neutral. The capacitor is simply a mask.

You may also be saving money by doing this... Capacitors offset the the natural self-inductance of the fluorescent light tubes and give you a better overall power rating (puts the circuit in phase)- so you don't have as much wasted current (and money).

Unfortunately, this is not true. Whilst increasing the Power Factor for an individual piece of equipment may improve its efficiency (reduced internal losses - heat), it will not save the average consumer money. The kilowatt hour measures kilowatts, which takes into account the Power Factor of the installation.

Eg. A 22kW 220v single phase motor has a Power Factor (P.F.) of 0.6. Using the equation P=E x I x Cos#,

I= (22 000) divided by (220 x 0.6)

= 167 Amps.

Since the motor will always absorb 22kW, at a P.F. of 0.8, the current is reduced to 125 Amps but the same power is being used. The kilowatt hour meter will still see 22kW.

You're probably right- but doesn't the power meter run on use of current (i.e., how would it "know" how much power was used?)

The kilowatt hour meter measures Watts, which is the product of voltage, current & P.F. Each KWH meter has a voltage coil & a current coil. Due to the position of the coils, eddy currents will be induced in the aluminium disc, causing it to rotate.

OK chaps, the IEE / IET forum have come up with the goods

I'm not sure if non-members can access the forum so I'll post the reply here, a credible explanation as to WHY the lights flicker and the correct solution (which is a parallel capacitor as installed by our OP here)

mapj1 has posted a message entitled Fluorescent lights flicker when off.

Message Posted on: Monday April 02,2007 03:07:19 PM

Connecting a capacitor accross the lamps will reduce the 'off voltage' the lamp sees caused by the capcitive voltage division. see here where this very quesstion has come up in the past (and I replied then too, I must make a decent web page with this on...).

http://www.theiet.org/forums/f...key=y&keyword1=flicker

http://www.theiet.org/forums/f...key=y&keyword1=flicker

"It is the capacitance accross the switch wiring this causes a few uA to slowly charge the reservoirs of the CFL electronics (as these contain a bridge rectifier and a reservoir cap), then once the reservoir is full enough, the lamp driver starts briefly, and runs out of charge almost immediately, and the cycle repeats. - the effect is worse on a 2 way switch circuit because it is so long. The easy fix is a capacitor accross the L-N terminals of the affected fitting. Anything from a few 10s of nF to 1 Uf may be required, depending on the wiring length involved. Obviously the cap needs to be mains rated."

Its not a power factor problem per se, but such capacitors do have the advantage of automatically being mains rated, so fit for the purpose.

regards Mike.

You can view the message at http://www.theiet.org/forums/forum/message...1&forumid=1.

I wonder if the same effect could be negated by earthing one side of 'capacitive' circuit wiring? I assume that in this situation, the neutral is not earthed.

[pkrv]

Have you tried replacing the starter? When these fail it causes the light to flicker (you may have a faulty one from new?)

[Gary A]

I just let mine flicker. I must not hurt anything because in almost three years all I have replaced was one starter. And no, it didn't stop the flickering. I have five ceiling circular tube lights.

[Crossy]

Have you tried replacing the starter? When these fail it causes the light to flicker (you may have a faulty one from new?)

If you have electronic ballasts you don't have starters, they are peculiar to regular inductive ballasts.

Note that the lights in question flicker when they are switched OFF!

[Crossy]

I just let mine flicker. I must not hurt anything because in almost three years all I have replaced was one starter. And no, it didn't stop the flickering. I have five ceiling circular tube lights.

If you have starters you have a different problem from Chownah who has electronic (starterless) ballasts which are the devices addressed by the IEE forum posts.

Do be sure you don't have switched neutrals (actually check the neutral is just that, neutral). Letting the tubes flicker is unlikely to cause damage, it's just annoying.

[elkangorito]

So, am I safe, since its in parallel and not series?

Also, why would someone make a C-L series circuit in house wiring?...is this only a theoretic thing?....or should people worry about this.

Also, the fix is perfect...it solved the problem completely with little cost or effort and there is no danger in the circuits involved due to its configuration...at least that I can see......can you see some danger with this configuration? Please remember that the real problem was the flickering of the light that kept me awake...it has stopped completely....the real problem has been fixed.

Yes, you are safe (perhaps. See below).

Someone could make a series L-C circuit by accident or the wrong size cap could be used in a 'capacitor start-run' motor.

I've thought about this situation a lot & here are my thoughts;

1. The capacitor in this instance, was used because an assumed induced voltage was apparent. It was also suggested that the capacitance created by the cables was a part of the problem (must have been a long cable run!). By adding more capacitance in parallel to this already (assumed) capacitive circuit, would simply add to the total circuit capacitance. The only possible way (that I can see) how adding a capacitor to the circuit would fix the problem, is to absorb more current & thereby not allow the otherwise extra current to go to the lamp &/or electronics. The only other possibility is that the extra capacitance changed the phase angle between the cable voltage & the line current & somehow this played a part with the electronic ballast.

2. Induced voltages in cables can only occur if some cables are parallel to others & these parallel cables MUST have current flowing through them to induce a voltage in the 'secondary' cable. Is this the case? BTW, for this to occur, the cables must be in close proximity to each other for quite a distance & the 'primary' current must be ample (not milliamps). Otherwise, there are many cables (20 or more) bunched together.

3. A floating neutral may have a voltage upon it if it's not earthed & this voltage can be quite high...perhaps tending towards 100 volts. Is the neutral earthed at any point?

4. I think that this possibility has been eliminated but is the neutral definitely NOT switched?

5. A fluorescent tube takes about 400 RMS volts to 'strike' to normal operation. Does an electronic ballast need to initially produce this voltage to perform this function? If so, the capacitor will need to be able to handle this 'peak-to-peak' voltage, which is about 440 volts. Is this capacitor rated as such if the tube still needs this voltage to 'strike'?

I'm sorry but I don't completely buy the 'capacitor fix' theory...yet.

[Crossy]

I'm sorry but I don't completely buy the 'capacitor fix' theory...yet.

This is a relaxation oscillation, similar to the old neon timebase, (search google for neon timebase) but basically the voltage rises when the lamp is off, as the impedance is many megohms. Once threshold is reached the lamp lights, but the source impedance is far too high to sustain action for more than a brief flicker, so the volts on the capacitor plummet and the light goes out, and back to high impedance state. Capacitor starts to fill again....

Now leaping forward from 1931 to the present day, and AC mains, the high impedance supply is the capicitance of the wiring, 100p/metre for 1mm T+E, so ~30 Meg ohms for every metre, so say 10m, say 3meg.. say 100uA of charging current, and the old neon is now replaced by a rectifier and oscillator circuit of the electronic ballast. The reservoir capacitance downstream of the bridge in the lamp will need to reach say 50V to start, and will be perhaps 100uF, so flicker rate of half a second, say. result irritating flicker, worse when tube is warm as strike voltage is lower.

If you set this up on the bench with nothing other than an open ended length of cable (as if to go to a switch , but dont fit one) and the electronic ballast, by varying the length of the cable, and therfore the charging current, you can alter the flicker rate.

If it is 10m or so of wire in the switch circuit, then a permanent fix is either to place low current resistive load (perhaps 100K or so - best made up of two resistors in series, to prevent a single failure), or a nanofarad or 10 of suitibly mains rated capacitor in parallel with affected device, to pull the voltage accross the lamp firmly down when off. If you prefer ready made componenents you might find a switch suppressor accross the lamp (not the switch -that would increase the leakage) is all you need. I'd suggest building these into the lumiaire if there is room, or a proper joint box, as dangling live components in the breeze will attract the wrath of the rightous (though its OK inside washing machines and TVs..).

I suppose if you were feeling cheapskate then the parallell capacitance could just be an extra long cable feeding the lamp.

Rest assured this is a well known problem, and need not indicate wiring fault. (though in switched neutral, rather than switched live, the effect can be much worse, as now the total capacitance to earth adds to rather than reduces the leakage current.)

If this makes no sense, come back to me

[elkangorito]

I'm sorry but I don't completely buy the 'capacitor fix' theory...yet.

This is a relaxation oscillation, similar to the old neon timebase, (search google for neon timebase) but basically the voltage rises when the lamp is off, as the impedance is many megohms. Once threshold is reached the lamp lights, but the source impedance is far too high to sustain action for more than a brief flicker, so the volts on the capacitor plummet and the light goes out, and back to high impedance state. Capacitor starts to fill again....

Now leaping forward from 1931 to the present day, and AC mains, the high impedance supply is the capicitance of the wiring, 100p/metre for 1mm T+E, so ~30 Meg ohms for every metre, so say 10m, say 3meg.. say 100uA of charging current, and the old neon is now replaced by a rectifier and oscillator circuit of the electronic ballast. The reservoir capacitance downstream of the bridge in the lamp will need to reach say 50V to start, and will be perhaps 100uF, so flicker rate of half a second, say. result irritating flicker, worse when tube is warm as strike voltage is lower.

If you set this up on the bench with nothing other than an open ended length of cable (as if to go to a switch , but dont fit one) and the electronic ballast, by varying the length of the cable, and therfore the charging current, you can alter the flicker rate.

If it is 10m or so of wire in the switch circuit, then a permanent fix is either to place low current resistive load (perhaps 100K or so - best made up of two resistors in series, to prevent a single failure), or a nanofarad or 10 of suitibly mains rated capacitor in parallel with affected device, to pull the voltage accross the lamp firmly down when off. If you prefer ready made componenents you might find a switch suppressor accross the lamp (not the switch -that would increase the leakage) is all you need. I'd suggest building these into the lumiaire if there is room, or a proper joint box, as dangling live components in the breeze will attract the wrath of the rightous (though its OK inside washing machines and TVs..).

I suppose if you were feeling cheapskate then the parallell capacitance could just be an extra long cable feeding the lamp.

Rest assured this is a well known problem, and need not indicate wiring fault. (though in switched neutral, rather than switched live, the effect can be much worse, as now the total capacitance to earth adds to rather than reduces the leakage current.)

If this makes no sense, come back to me

This is all well & good but if there is no voltage on the cables in the first place, this capacitive 'fix' would not be needed. So, how how did voltage get to be on the cables? Eliminate the voltage & eliminate the problem.

2. Induced voltages in cables can only occur if some cables are parallel to others & these parallel cables MUST have current flowing through them to induce a voltage in the 'secondary' cable. Is this the case? BTW, for this to occur, the cables must be in close proximity to each other for quite a distance & the 'primary' current must be ample (not milliamps). Otherwise, there are many cables (20 or more) bunched together.

3. A floating neutral may have a voltage upon it if it's not earthed & this voltage can be quite high...perhaps tending towards 100 volts. Is the neutral earthed at any point?

[chownah]

So, am I safe, since its in parallel and not series?

Also, why would someone make a C-L series circuit in house wiring?...is this only a theoretic thing?....or should people worry about this.

Also, the fix is perfect...it solved the problem completely with little cost or effort and there is no danger in the circuits involved due to its configuration...at least that I can see......can you see some danger with this configuration? Please remember that the real problem was the flickering of the light that kept me awake...it has stopped completely....the real problem has been fixed.

Yes, you are safe (perhaps. See below).

Someone could make a series L-C circuit by accident or the wrong size cap could be used in a 'capacitor start-run' motor.

I've thought about this situation a lot & here are my thoughts;

1. The capacitor in this instance, was used because an assumed induced voltage was apparent. It was also suggested that the capacitance created by the cables was a part of the problem (must have been a long cable run!). By adding more capacitance in parallel to this already (assumed) capacitive circuit, would simply add to the total circuit capacitance. The only possible way (that I can see) how adding a capacitor to the circuit would fix the problem, is to absorb more current & thereby not allow the otherwise extra current to go to the lamp &/or electronics. The only other possibility is that the extra capacitance changed the phase angle between the cable voltage & the line current & somehow this played a part with the electronic ballast.

2. Induced voltages in cables can only occur if some cables are parallel to others & these parallel cables MUST have current flowing through them to induce a voltage in the 'secondary' cable. Is this the case? BTW, for this to occur, the cables must be in close proximity to each other for quite a distance & the 'primary' current must be ample (not milliamps). Otherwise, there are many cables (20 or more) bunched together.

3. A floating neutral may have a voltage upon it if it's not earthed & this voltage can be quite high...perhaps tending towards 100 volts. Is the neutral earthed at any point?

4. I think that this possibility has been eliminated but is the neutral definitely NOT switched?

5. A fluorescent tube takes about 400 RMS volts to 'strike' to normal operation. Does an electronic ballast need to initially produce this voltage to perform this function? If so, the capacitor will need to be able to handle this 'peak-to-peak' voltage, which is about 440 volts. Is this capacitor rated as such if the tube still needs this voltage to 'strike'?

I'm sorry but I don't completely buy the 'capacitor fix' theory...yet.

I overtaxed myself yesterday so I'm a bit on the slow side this morning so I'll make some quick remarks and perhaps read this post more carefully later and see if I can post some better information later.

Using the wrong size capacitor in a capacitor start motor: The windings of the motor have considerable ohmic resistance and so you could not make an LC circuit that way....you would be making an LRC circuit. Similarly the capacitor which I installed had (among other things) a tube in its circuit....the tube would represent an ohmic load so this circuit would be modeled as an LRC in preference to using an LC model...if this can be done at all since there is an electronic ballast in the loop too which contains I think at least some diodes and at least one other capacitor...so it seems highly unlikely (read this "impossible") that even if the tube was taken out of the circuit that the ballast would be "clean" enough of an inductor to justify modeling the circuit as an LC circuit....seems like the ballast wouldn't act as an inductor at all.

Making an LC circuit by accident...I suppose you could do anything by accident...I think you are showing your propensity for unwarrented concern here. I'm no electrical engineer but I think it would be rather difficult to create a problematic LC circuit for a 50Hz source...for example how about if you go calculate the specs for a capacitor and and inductor which would cause a problem and then we can discuss the likelihood that someone would create an LC circuit with these two components. I think you will see that your concern is unwarranted....but maybe I'm wrong about this.

Item #2: I described the installation in an earlier post....go back and I'm sure you'll find it. I believe you are mistaken and any current in a conductor will create an electrical effect in an adjacent conductor. You used the word "induce" which can be misleading....are you meaning electrically "induced" meaning magnetically coupled or are you using the general sense of the word which would also include effects caused by an electric field as in capacitive coupling.

Item #5: I think if you go read up on electronic ballasts you will find the answer to your questions in this item.

And finally, the "capacitor fix" is not a theory...it is a fact....it has absolutely and positively fixed the problem here which was flickering in a fluorescent tube which was keeping me awake at night.....I don't understand why you keep questioning whether the problem has been fixed....I have clearly stated previously that the problem is fixed....I'm trying to figure out how I can convince you that the flickering has stopped....couldn't you just take my word for it?

Chownah