John, you reminded me of something I meant to ask before. Do you have an explanation as to why GFCI seem to trip a lot with electric heaters. Only happens when turning on or off. Could the cheap switches need capacitor to reduce inductive kick maybe? Know the theory of GFCI but don't quite get it. Thanks Dave
I dont think it has to do with any sort of "inductive kick" as heaters (notwithstanding a real small fan on some) are mostly resistive loads. However, even if they were inductive, thats NOT what trips them, its an imbalance of say 5 milliamps between the Line and Neutral that causes the trip. As best I recall (hey I retired in 1991) they have a torroidal coil which encircles the Line and Neutral and if BOTH are carrying the same current theres no voltage induced since as they (N and L) are out of phase they cancel each other out BUTTTTTTTTT if some of the current is returned OTHER THEN via the Neutral cuz its leaking, such as say a short to case, theres net current through the coil inducing voltage which trips the breaker.......
My "best guess" is nuisance trips in "cheap" heaters is because theres just enough leakage current (5 milliamps I think, thats NOT much)thats NOT being returned by the Neutral but instead maybe the equipment grounding conductor or moisture or the surface upon which they sit etc etc etc. Some have those porcelain looking insulators which hold bare wire are mounted to the metal case, perhaps that makes them susceptible to leakage current.
Now as far as reasons why surges or power spikes or some sort of high frequency might cause a trip, you need someone smarter then me to tell you. The only things I'm coming up with are high resistance leaks caused by moisture or cheap desing, someone more current in ELECTRONICS (my experience was more electrical power distribution and design) can enlighten us maybe
John T
My "best guess" is nuisance trips in "cheap" heaters is because theres just enough leakage current (5 milliamps I think, thats NOT much)thats NOT being returned by the Neutral but instead maybe the equipment grounding conductor or moisture or the surface upon which they sit etc etc etc. Some have those porcelain looking insulators which hold bare wire are mounted to the metal case, perhaps that makes them susceptible to leakage current.
Now as far as reasons why surges or power spikes or some sort of high frequency might cause a trip, you need someone smarter then me to tell you. The only things I'm coming up with are high resistance leaks caused by moisture or cheap desing, someone more current in ELECTRONICS (my experience was more electrical power distribution and design) can enlighten us maybe
John T
Anonymous-0
Well-known Member
Dirt in the heater drawn in by the fan can cause leakage to ground. And that will trip the GFCI.
The fan motor is inductive, but that shouldn't bother the GFCI. Like John T. says, the big load is purely resistive and that will absorb any inductive kicks.
Gerald J.
The fan motor is inductive, but that shouldn't bother the GFCI. Like John T. says, the big load is purely resistive and that will absorb any inductive kicks.
Gerald J.
MarkB_MI
Well-known Member
- Location
- Motown USA
Dirt in the heater would explain the GFCI tripping when you turn it on: As soon as it's hot any moisture is driven out of the heater, eliminating the leakage.
I have no idea why the GFCI would trip when you turn the heater off, however.
I have no idea why the GFCI would trip when you turn the heater off, however.
buickanddeere
Well-known Member
GFI's will also trip when using electric drills,skill saws and large quartz or halogen work lights.It's the high inrush current.
A series motor or cold lamp/heating element measures almost a dead short when at startup/cold.
A series motor or cold lamp/heating element measures almost a dead short when at startup/cold.
I think it is the inductive kick that trips the electronics in certain brands of GFCI's. I had a Eagle Brand GFCI in my basement bathroom that would trip the GFCI about 9 times out of 10 when turning the vent fan off - never turning on. I tried several other Eagle Brands and all did the same thing.
I replaced with a Leviton and it has never tripped since. And yes the Leviton does work with an external test.
I replaced with a Leviton and it has never tripped since. And yes the Leviton does work with an external test.
CH(upstate,NY)
Member
I love hereing you, b&d and Geralds responses to these questions. In this case it might be EMF inducing a current to the neutral tripping the breaker. Thoughs old lines of force? It's been a long time out of college.
Gotta thank Nilola Tesla.
Darn if I know, seems like any induced EMF would get into BOTH the Line and Neutral, but it only takes like 5 milliamps DIFFERENCE in the current to trip as I recall. Similar, even if theres higher inrush current (like an inductive kick) its the same in Line and Neutral so I just dont see that. Ima still thinkin more along the lines of dirt or dust or moisture etc.. I been retired since 1991 and just not up on this stuff so much anymore like my friends Gerald or Buick man who still practice...
Fun chat
John T
Fun chat
John T
Pale Rider
Member
A distinct possibility is that the problem is caused by high inrush current and may have nothing to do with a short or dirt which bleeds off a fractional current. The device under discussion need not involve some sort of inductive or capacitive device in the circuit to trip out. A large resistive device has, until it builds up an electrical field and the heated element begins to add some amount of resistance, a large amount of element which is being saturated with electrons and theoretically capacitive for a very brief time period before an equal amount of current begins to flow out of the cirucit via the neuatral. But the GFCI by design, will be out of it's parameters. If I recall correctly 6 milli-amps in a couple of thousandths of a second. It does just what it is designed to do--senses an imbalance and interupts the circuit.
This can perhaps better be understood by a heater or other device sitting on a linoleum floor which doesn't even have a ground. There IS NO current bleeding off through some sort of short circuit...there's NO ground path for it to go. Yet the GFCI trips out. It's because of start up inrush.
The same principal is also sometimes true for motor loads on a GFCI when they are turned off. Sure, there is no more current entering the circuit...but as the electrical field collapses it is still briefly sending out current on the neutral conductor. Once again, the GFCI is sensing more current leaving the circuit than is entering it---a current imbalance, and it does just what a GFCI is designed to do---interupt the circuit. Resistive heater loads usually do NOT trip the GFCI in being turned OFF as does an inductive motor load because the heated element releases the final electrons in a more graduated manner instead of all at once as does a collapsing motor winding field. Enough so, so that the GFCI does not exceed its desine parameters.
A GFCI doesn't know the difference between imbalanced current coming into a circuit and leaving the ciruit by some other current path than the monitored neutral, ie. a short circuit and the difference between a current imbalance, even though very brief caused by current inrush when turning a device on or current outrush by means of a turned off appliance.
Some GFCI's are more senstive than others and this not infrequently results in nuisance tripping. It can be something that you're just going to have to live with if you are going to continue to use the appliance. Assuming it is not indeed a short of some kind, you can try a different appliance, you can live with it or you can try using another brand of GFCI. Sometimes it will do the trick. Those are pretty much your choices. If you are convinced it is not a short circuit issue, I'd try getting a commercial grade GFCI from an electrical supply house. They are definitely better, though of course commeasurately more expensive. But I'll bet it will address your problem.
Good Luck!
This can perhaps better be understood by a heater or other device sitting on a linoleum floor which doesn't even have a ground. There IS NO current bleeding off through some sort of short circuit...there's NO ground path for it to go. Yet the GFCI trips out. It's because of start up inrush.
The same principal is also sometimes true for motor loads on a GFCI when they are turned off. Sure, there is no more current entering the circuit...but as the electrical field collapses it is still briefly sending out current on the neutral conductor. Once again, the GFCI is sensing more current leaving the circuit than is entering it---a current imbalance, and it does just what a GFCI is designed to do---interupt the circuit. Resistive heater loads usually do NOT trip the GFCI in being turned OFF as does an inductive motor load because the heated element releases the final electrons in a more graduated manner instead of all at once as does a collapsing motor winding field. Enough so, so that the GFCI does not exceed its desine parameters.
A GFCI doesn't know the difference between imbalanced current coming into a circuit and leaving the ciruit by some other current path than the monitored neutral, ie. a short circuit and the difference between a current imbalance, even though very brief caused by current inrush when turning a device on or current outrush by means of a turned off appliance.
Some GFCI's are more senstive than others and this not infrequently results in nuisance tripping. It can be something that you're just going to have to live with if you are going to continue to use the appliance. Assuming it is not indeed a short of some kind, you can try a different appliance, you can live with it or you can try using another brand of GFCI. Sometimes it will do the trick. Those are pretty much your choices. If you are convinced it is not a short circuit issue, I'd try getting a commercial grade GFCI from an electrical supply house. They are definitely better, though of course commeasurately more expensive. But I'll bet it will address your problem.
Good Luck!
Fun discussion, I been retired from electrical engineering since 1991 so youre gonna have to help me understand some of this ......hey I enjoy learning here also
You say:
"A large resistive device has, until it builds up an electrical field and the heated element begins to add some amount of resistance, a large amount of element which is being saturated with electrons and theoretically capacitive for a very brief time period before an equal amount of current begins to flow out of the cirucit via the neuatral".
MY QUESTIONS: So where is that "unequal" amount of current going thats NOT flowing out of the heater??????? I kinda thought current INTO a heating element (say nichrome wire) equals current OUT ????????
If you say its theoretically capacitive, a discharged capacitor is INITIALLY a short circuit right when voltage is first applied and current flows easily (depends on Impedance) until that big empty electron bank fills up at which time (to DC at least) it appears as an open circuit and current flow ceases. Of course were dealin with AC here so it charges up and the polarity reverses (1/60 of second) BUTTTTTTTT even if it a capacitor as you claim I STILL THOUGHT CURRENT INTO A CAPACITOR HAS TO EQUAL CURRENT OUT OF IT. Its true that in a capacitor the voltage LAGS the current and in an inductor the current LAGS the voltage butttttttt still why isnt current in equal to current out????????
I GUESS MY QUESTION IS HOW DOES CURRENT OUT HAVE A DELAY VERSUS THE CURRENT FLOWING IN???????
If that big strip of nichrome wire (I consider it almost pure resistive) is a capacitor, I still see current flowing into it has to be the same flowing out buttttttttt if I understand your post, you seem to be saying the current that flows out is somehow delayed (and that window of unequal current trips the GFCI) I UNDERSTAND HOW A GFCI WORKS I just dont understand your theory of current out is somehow delayed????????? I do undestand capacitor action quite well actually and Impedance and Time Constant and RC circuits btu I see the capacitor as an intial (right after time = 0+) short and later an open and the impedance effect but I STILL THINK CURRENT IN EQUALS CURRENT OUT OF THAT NICHROME WIRE EVEN IF IT WERE A CAPACITOR
Thanks, love this electrical chat, PLEASE explain how the current is delayed before it flows out, to me even if the AMOUNT of current is more or less depending on resistive as temp increases or capacitive reactance I DO NOT UNDERSTAND HOW IT COMES OUT THE NEUTRAL SOMEHOW LATER????
God Bless yall
John T Toooooo long retired electrical engineer n rusty on this stuff
You say:
"A large resistive device has, until it builds up an electrical field and the heated element begins to add some amount of resistance, a large amount of element which is being saturated with electrons and theoretically capacitive for a very brief time period before an equal amount of current begins to flow out of the cirucit via the neuatral".
MY QUESTIONS: So where is that "unequal" amount of current going thats NOT flowing out of the heater??????? I kinda thought current INTO a heating element (say nichrome wire) equals current OUT ????????
If you say its theoretically capacitive, a discharged capacitor is INITIALLY a short circuit right when voltage is first applied and current flows easily (depends on Impedance) until that big empty electron bank fills up at which time (to DC at least) it appears as an open circuit and current flow ceases. Of course were dealin with AC here so it charges up and the polarity reverses (1/60 of second) BUTTTTTTTT even if it a capacitor as you claim I STILL THOUGHT CURRENT INTO A CAPACITOR HAS TO EQUAL CURRENT OUT OF IT. Its true that in a capacitor the voltage LAGS the current and in an inductor the current LAGS the voltage butttttttt still why isnt current in equal to current out????????
I GUESS MY QUESTION IS HOW DOES CURRENT OUT HAVE A DELAY VERSUS THE CURRENT FLOWING IN???????
If that big strip of nichrome wire (I consider it almost pure resistive) is a capacitor, I still see current flowing into it has to be the same flowing out buttttttttt if I understand your post, you seem to be saying the current that flows out is somehow delayed (and that window of unequal current trips the GFCI) I UNDERSTAND HOW A GFCI WORKS I just dont understand your theory of current out is somehow delayed????????? I do undestand capacitor action quite well actually and Impedance and Time Constant and RC circuits btu I see the capacitor as an intial (right after time = 0+) short and later an open and the impedance effect but I STILL THINK CURRENT IN EQUALS CURRENT OUT OF THAT NICHROME WIRE EVEN IF IT WERE A CAPACITOR
Thanks, love this electrical chat, PLEASE explain how the current is delayed before it flows out, to me even if the AMOUNT of current is more or less depending on resistive as temp increases or capacitive reactance I DO NOT UNDERSTAND HOW IT COMES OUT THE NEUTRAL SOMEHOW LATER????
God Bless yall
John T Toooooo long retired electrical engineer n rusty on this stuff
Anonymous-0
Well-known Member
That time is rather short. Electrons move about a foot a nanosecond. So if there's 20 feet of nichrome coiled up that's 20 nanoseconds it take the current to get from one end of the heating element to the other. That's with air around it. The line cord has dielectric and probably there the electrons move about 0.8 ft / ns.
The nichrome doesn't change resistance as much as other metals like tungsten. A tungsten lamp resistant goes up 15 or 16 times from cold to hot, so the turn on surge is serious. Nichrome that is 80 NI 20 Cr if 1 ohm at 77F is 1.019 ohm at 1000F then it goes down to 1.003 around 1500F and back up to 1.014 at 2000F. Less than 2% change. Others like Chromel D change by 25% from 77F to 2000F. Most change more than 80/20 but less chan Chromel D according to my handy Electrical Engineer's handbook.
And since the temperature of nichrome wire in air rises slowly (it doesn't glow for an appreciable fraction of a second if that fast) what little the resistance changes isn't rapid.
And the initial current into the coil depends on the transmission line characteristic impedance of the wire and it surroundings, likely quite a bit higher than the resistance of the heater coil. More like 100 ohms than the 9 ohms of a 1.5 KW resistance heater.
More likely the switch closes slowly and bounces a lot and that creates a high frequency current (might be audible in an AM radio as a "scratch") that affects a GFCI that doesn't properly filter out RF effects.
Gerald J.
The nichrome doesn't change resistance as much as other metals like tungsten. A tungsten lamp resistant goes up 15 or 16 times from cold to hot, so the turn on surge is serious. Nichrome that is 80 NI 20 Cr if 1 ohm at 77F is 1.019 ohm at 1000F then it goes down to 1.003 around 1500F and back up to 1.014 at 2000F. Less than 2% change. Others like Chromel D change by 25% from 77F to 2000F. Most change more than 80/20 but less chan Chromel D according to my handy Electrical Engineer's handbook.
And since the temperature of nichrome wire in air rises slowly (it doesn't glow for an appreciable fraction of a second if that fast) what little the resistance changes isn't rapid.
And the initial current into the coil depends on the transmission line characteristic impedance of the wire and it surroundings, likely quite a bit higher than the resistance of the heater coil. More like 100 ohms than the 9 ohms of a 1.5 KW resistance heater.
More likely the switch closes slowly and bounces a lot and that creates a high frequency current (might be audible in an AM radio as a "scratch") that affects a GFCI that doesn't properly filter out RF effects.
Gerald J.
MarkB_MI
Well-known Member
- Location
- Motown USA
I could buy your explanation for a device with a grounded chassis. But not for something that's isolated from ground, such as your heater on a linoleum floor. There might be some capacitance, but the neutral is the only available current path, so current in still equals current out. And you'll have to admit, the capacitance in a typical heater is going to be relatively small and probably completely offset by the inductive reactance of the blower motor.
Pale Rider
Member
Hi John,
MY QUESTIONS: So where is that "unequal" amount of current going thats NOT flowing out of the heater??????? I kinda thought current INTO a heating element (say nichrome wire) equals current OUT ????????
Well, the way it was taught to me during my apprenticeship is: Yes, ultimeatly current flowing in equals current flowing out, but by virtue of the large amount resistance in this case a resistance of the heating element, there is in fact a delay affecting the timing of the current flowing out--a slight capacitive affect as regards current. It is enough to show up in a quick reacting device whose method is to ensure that the current coming in on the hot is equal to the current flowing out on the neutral within this case I believe is two one thousandths of a second. For a brief moment during the initial current rush, the two are not measureably equal. It is not uncommon for this amount to be outside the parameters of an inexpensively manufactured GFCI.
With something like an electric razor, or hair dryer that occasionally also trips out a GFCI upon being turned off it is the final collapse of the electrical field that is feeding the current escaping out on the neutral even though no current is any longer entering the circuit by virtue of the switch having been turned off. Evidently there is just that much stored in the magnetic lines of flux that form around the windings. The collapse isn't instantaneous, though it happens very quickly it can fall outside the parameters that a household GFCI works within.
I recall one time checking a circuit in the vicinity of our electric fence charger. I couldn't get within at least a yard--I seem to remember more like four or five feet of the electric fence with my proximity tester without the tester simply being on all the time. I was surprised to say the least. I was struck at first by the distance involved and also by the fact that the tester which I would have thought would have pulsed along with the charge sent to the fence but it did not. I reasoned that even though a fencer converts the signal to DC it is a PULSED DC and that during the build up and discharge of each cycle there must be a great deal of relative current movement, especially since the signal involved several thousand volts being measured by a tester normally used to measure 120-600 volts. What's more--in turning off the electrical fence charger so I could continue my trouble shooting with regard to some unrelated equipment--I noticed that after unplugging the unit, the lights indicating a signal being sent actually functioned TWO MORE TIMES after the unit was unplugged, though the second and final time was dimmer than a full normal signal. Again I was very surprised but the only thing that made sense to me was that the great length of the fence wire and the attendant build up and collapse of the electrical field of the pulsed DC allowed the circuit to take on a capacitive characteristic to a limited degree even though in strict Ohm's law terms we normally think of a piece of straight conductor as being a conductor with only a slight amount of inherent resistance according to it's composition. This capacitive affect allowed for two more flashes of the "ON" light indicator even after the unit was unplugged. I don't know if they all do that. I just know I saw it and that it surprised me enough to make an impression on me that I remembered very distinctly.
I GUESS MY QUESTION IS HOW DOES CURRENT OUT HAVE A DELAY VERSUS THE CURRENT FLOWING IN???????
To sum it up, the way I understand it, it has to do with the fact that if you get resistance, either by a highly resistive component or a great deal of a low resistive component the amount of resistance becomes large enough that it begins to alter the circuit in a slightly capacitive way--not as much as what we think of in a straight up capacitor but often, enough to trip out a common household GFCI. I've seen the same affect on large breakers with GFCI protection built into them to protect equipment--I'm going from memory here but I beleive the trip threshold in that circumstance is 50 milli-amps--when the circuit involves much larger pieces of equipment or branch circuits of much greater length than those found in standard residential circuits or GFCI's. If what I'm trying to illustrate wasn't true there would be no need to upsize the larger equipment protecting GFCI's. But, the principal holds true, and a much higher GFCI threshold is required. Equipment would be failing all of the time if it were protected by a the common household personal protection which I believe is six milliamps. Current in WILL eventually equal current flowing out be it capacitive in the case of a large amount of resistance or inductive in the case of a building or collapsing electrical field, there is an ever so slight delay and thus a briefly unequal amount of current in the two conductors being monitored by the internals of the GFCI during start up and shut down. I'm really not sure if it has anything to do with the current leading the voltage in the event of capacitance, and the current lagging the voltage in the case of inductance during each individual cycle or if it has more to do with the simple time lag of involved with building up an electrical circuit from a de-energized state. I'm afraid my knowledge on the matter only extends so far and I'm drawing on lessons taught some time ago.
I'm not an electrical engineer, but I do have a Master electricians license. I'm not saying this in some arrogant way, only to seek to give some means of illustrating that I have some basis for what I'm trying to say. I certainly don't know it all by any stretch but that is the way it was taught to us in our apprenticeship and it seems to have been born out in various ways over the course of my career and field experience.
MY QUESTIONS: So where is that "unequal" amount of current going thats NOT flowing out of the heater??????? I kinda thought current INTO a heating element (say nichrome wire) equals current OUT ????????
Well, the way it was taught to me during my apprenticeship is: Yes, ultimeatly current flowing in equals current flowing out, but by virtue of the large amount resistance in this case a resistance of the heating element, there is in fact a delay affecting the timing of the current flowing out--a slight capacitive affect as regards current. It is enough to show up in a quick reacting device whose method is to ensure that the current coming in on the hot is equal to the current flowing out on the neutral within this case I believe is two one thousandths of a second. For a brief moment during the initial current rush, the two are not measureably equal. It is not uncommon for this amount to be outside the parameters of an inexpensively manufactured GFCI.
With something like an electric razor, or hair dryer that occasionally also trips out a GFCI upon being turned off it is the final collapse of the electrical field that is feeding the current escaping out on the neutral even though no current is any longer entering the circuit by virtue of the switch having been turned off. Evidently there is just that much stored in the magnetic lines of flux that form around the windings. The collapse isn't instantaneous, though it happens very quickly it can fall outside the parameters that a household GFCI works within.
I recall one time checking a circuit in the vicinity of our electric fence charger. I couldn't get within at least a yard--I seem to remember more like four or five feet of the electric fence with my proximity tester without the tester simply being on all the time. I was surprised to say the least. I was struck at first by the distance involved and also by the fact that the tester which I would have thought would have pulsed along with the charge sent to the fence but it did not. I reasoned that even though a fencer converts the signal to DC it is a PULSED DC and that during the build up and discharge of each cycle there must be a great deal of relative current movement, especially since the signal involved several thousand volts being measured by a tester normally used to measure 120-600 volts. What's more--in turning off the electrical fence charger so I could continue my trouble shooting with regard to some unrelated equipment--I noticed that after unplugging the unit, the lights indicating a signal being sent actually functioned TWO MORE TIMES after the unit was unplugged, though the second and final time was dimmer than a full normal signal. Again I was very surprised but the only thing that made sense to me was that the great length of the fence wire and the attendant build up and collapse of the electrical field of the pulsed DC allowed the circuit to take on a capacitive characteristic to a limited degree even though in strict Ohm's law terms we normally think of a piece of straight conductor as being a conductor with only a slight amount of inherent resistance according to it's composition. This capacitive affect allowed for two more flashes of the "ON" light indicator even after the unit was unplugged. I don't know if they all do that. I just know I saw it and that it surprised me enough to make an impression on me that I remembered very distinctly.
I GUESS MY QUESTION IS HOW DOES CURRENT OUT HAVE A DELAY VERSUS THE CURRENT FLOWING IN???????
To sum it up, the way I understand it, it has to do with the fact that if you get resistance, either by a highly resistive component or a great deal of a low resistive component the amount of resistance becomes large enough that it begins to alter the circuit in a slightly capacitive way--not as much as what we think of in a straight up capacitor but often, enough to trip out a common household GFCI. I've seen the same affect on large breakers with GFCI protection built into them to protect equipment--I'm going from memory here but I beleive the trip threshold in that circumstance is 50 milli-amps--when the circuit involves much larger pieces of equipment or branch circuits of much greater length than those found in standard residential circuits or GFCI's. If what I'm trying to illustrate wasn't true there would be no need to upsize the larger equipment protecting GFCI's. But, the principal holds true, and a much higher GFCI threshold is required. Equipment would be failing all of the time if it were protected by a the common household personal protection which I believe is six milliamps. Current in WILL eventually equal current flowing out be it capacitive in the case of a large amount of resistance or inductive in the case of a building or collapsing electrical field, there is an ever so slight delay and thus a briefly unequal amount of current in the two conductors being monitored by the internals of the GFCI during start up and shut down. I'm really not sure if it has anything to do with the current leading the voltage in the event of capacitance, and the current lagging the voltage in the case of inductance during each individual cycle or if it has more to do with the simple time lag of involved with building up an electrical circuit from a de-energized state. I'm afraid my knowledge on the matter only extends so far and I'm drawing on lessons taught some time ago.
I'm not an electrical engineer, but I do have a Master electricians license. I'm not saying this in some arrogant way, only to seek to give some means of illustrating that I have some basis for what I'm trying to say. I certainly don't know it all by any stretch but that is the way it was taught to us in our apprenticeship and it seems to have been born out in various ways over the course of my career and field experience.
Pale Rider
Member
Well to my mind it seems to underscore my point. Without a ground the only POSSIBLE path for the current to flow is out the neutral yet in many cases the GFCI trips anyway. Why do you think that is? The current has only one path. It because in the case of a resistive heater it's because of time delay caused by inrush. The current in and out is being measured and found to be unequal. The GFCI does just what it's supposed to do and interupts the circuit. I've seen it occur on more than one heater WITHOUT any blower motor and thus no inductive reactance.
Just to add my two cents which is about all it is worth. My background is that I have been an electronic technician since 1956 when I was in Navy electronics school. I have been retired for some time but I still work on industrial electronics for businesses and airports. I only work on troubles that others have not been able to solve and if I take the job – my promise is no matter how many hours I spend if I do not fix the problem –there will be no charge. I have never had a no charge situation.
My guess is that it is the spike or inductive kick back that pops the GFCI. To my knowledge the GFCI contains a common core transformer with two primaries with one for the hot and one for the neutral. (the transformer just has a turn or two so it is not big) The two primaries are out of phase so as long as the current is equal, the secondary or signal winding will be zero. If there is an imbalance in either coil then the signal winding will have an output that will trigger a switch that opens the GFCI. A dead short should not trip the GFCI as the current will still be equal in each winding. It may burn the GFCI windings open or do other damage but the GFCI is not to protect from a short or high input rush of current from a resistive load. A spike from any source ( I have seen two way radios trip GFCI’s) will be usually a positive spike and if it will either add or subtract from the 60 Hz line depending on the instantaneous phase of the AC at the time. The spike passes through the signal winding and the GFCI trips.
I mention before that I had one brand of GFCI that tripped from a bathroom vent fan but another brand did not. My guess is that some manufactures have designed a slight delay or use a zero crossing detector chip to smooth out the slight spikes to prevent nuisance tripping. I have a friend that made the mistake of plugging in his old refrigerator in his garage with a GFCI to come home after a two week vacation trip to find out his GFCI had tripped and ruined everything in the refrigerator. Just my two cents.
My guess is that it is the spike or inductive kick back that pops the GFCI. To my knowledge the GFCI contains a common core transformer with two primaries with one for the hot and one for the neutral. (the transformer just has a turn or two so it is not big) The two primaries are out of phase so as long as the current is equal, the secondary or signal winding will be zero. If there is an imbalance in either coil then the signal winding will have an output that will trigger a switch that opens the GFCI. A dead short should not trip the GFCI as the current will still be equal in each winding. It may burn the GFCI windings open or do other damage but the GFCI is not to protect from a short or high input rush of current from a resistive load. A spike from any source ( I have seen two way radios trip GFCI’s) will be usually a positive spike and if it will either add or subtract from the 60 Hz line depending on the instantaneous phase of the AC at the time. The spike passes through the signal winding and the GFCI trips.
I mention before that I had one brand of GFCI that tripped from a bathroom vent fan but another brand did not. My guess is that some manufactures have designed a slight delay or use a zero crossing detector chip to smooth out the slight spikes to prevent nuisance tripping. I have a friend that made the mistake of plugging in his old refrigerator in his garage with a GFCI to come home after a two week vacation trip to find out his GFCI had tripped and ruined everything in the refrigerator. Just my two cents.
MarkB_MI
Well-known Member
- Location
- Motown USA
Kirchoff's current law: The sum of the current into a node must equal zero.
This holds true at any instance in time, not just the steady-state. So regardless of why the GFCI trips, it's not due to the current in being different than the current out, unless there is a third path. That's pretty much what John T was saying.
This holds true at any instance in time, not just the steady-state. So regardless of why the GFCI trips, it's not due to the current in being different than the current out, unless there is a third path. That's pretty much what John T was saying.
buickanddeere
Well-known Member
An incandescent lamp does function very similar as the "heater" in a vacuum tube which is the source for electrons.
There are electrons knocked loose and out of the circuit when a filament heats up from stone cold.
I still lean more towards higher current during the first of half of an AC cycle vs. less current during the 2nd half of the cycle as the filament heats up/resistance increases.
There are electrons knocked loose and out of the circuit when a filament heats up from stone cold.
I still lean more towards higher current during the first of half of an AC cycle vs. less current during the 2nd half of the cycle as the filament heats up/resistance increases.
John T
Retired Physics Buff...also. If the nichrome wire in the heater element is straight, the current-in, current-out theory is correct. Most heaters though have coiled nichrome wire elements which do in fact exhibit inductance. This phenominon would be greater on start up and shut down and indeed for a short time would exhibit a distinct power factor current lagging voltage condition. The collapsing field on shut down of an inductive source will generate a small current sometimes strong enough to trip a GFCI device. Actually the coils of an electric heater element if the dimensions are selected to be resonant will vibrate at the 60 Hz rate or some resonant frequency because of the alternating field created. For the same reasons, GFCI devices do not do well in induction motor circuits because of the start up current lag and inductive kick at shutdown.
KM
Retired Physics Buff...also. If the nichrome wire in the heater element is straight, the current-in, current-out theory is correct. Most heaters though have coiled nichrome wire elements which do in fact exhibit inductance. This phenominon would be greater on start up and shut down and indeed for a short time would exhibit a distinct power factor current lagging voltage condition. The collapsing field on shut down of an inductive source will generate a small current sometimes strong enough to trip a GFCI device. Actually the coils of an electric heater element if the dimensions are selected to be resonant will vibrate at the 60 Hz rate or some resonant frequency because of the alternating field created. For the same reasons, GFCI devices do not do well in induction motor circuits because of the start up current lag and inductive kick at shutdown.
KM
Anonymous-0
Well-known Member
Fence chargers will fire one more time after being unplugged.Most of my customers have been shocked because they were too quick to touch the fencers out put terminal after they pulled the ac plug..Most chargers charge a capacitor and switch the charge into the transformer with an SCR.You just learned something new.
Anonymous-0
Well-known Member
GFIs fail often and I wouldnt depend on them.I opened one that had a lightning strike.A small transistor was split in half.Many will fail to test.This discussion proves that you can get to the point where you know too much about a subject.Lightning strikes on the power lines are common and GFIs will be damaged.
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