While I have not seen anything on it, it would not surprise me if inductive loads will trip the GFCI as the current and voltage is out of phase some ammount. This would probably be very large when the motor is first started. I would assume a large capacitor could also cause a probem, but that is seldom seen.
Don't confuse voltage and current. The GFCI only looks at current and Dr Kirchoff says the current entering a circuit will equal the current coming out at any instant (whether that tracks voltage or not). The only issue with a GFCI is that all of the current going in comes out the circuit conductors and not out via a ground fault.
I am not confusing the current and voltage. My thinking is that with a large inductor like a motor there may be enough delay in the current going through the motor to trip the GFCI. That is the current on the output will be differant than the input due to the current lag. As I said, I have not seen this reported anywhere and do not know if it would actually hapen. Just something to think about.
If the current reaches a steady state, the current will be the same, but due to a lag when first switched on, the current will be differant for a fraction of a second. With anything but pure resistance there is always the dv/dt to factor in. That is the voltage or current will have some time delay from zero to the maximum value depending on the ammount of inductance in the circuit.
ne for Amana appears legit, as I searched the text and found it on the Aman a official website at
just about impossible to install a dryer in a location that doesn't require GFCI protection. 6' from a sink edge. Bam! Basement or garage: Bam! Even i f none of those applies, all the conditions that apply for GFCI and make th em a good idea in a kitchen or bathroom or basement, apply at least as much in a laundry.
Those alleged quotes have no link so you can check them. Wherever they came from, they are obviously written by people with little technical knowledge, as there is nothing there that really explains much of anything:
"Thank you for contacting Electrolux Home Products. We do not recommend the use of GFI outlets as they can go bad and cause loss of power to an applia nce."
I wouldn't use one on a fridge/freezer, because GFCIs can sometimes falsely trip. It's rare, but sometimes they do for unknown reasons. But I agree with Gfre, if you plug a fridge in and it trips the GFCI all the time, something is wrong.
"Some appliance components could create enough resistance to trip the GFI o utlet during normal use."
Total nonsense and whoever wrote that is an idiot. In fact, it sounds like all of this was written by some summer intern in response to someone asking a question.
"The spark igniter on a gas range will cause the GFCI to trip."
I'm not familiar with how a spark ignitor actually works, but it sounds very odd to me that line current would be diverted to ground. I would think they would use a transformer to generate the spark high voltage, in which case there should be no line current flowing to ground to trip the GFCI.
One thing that even this crappy advice doesn't say is that using a GFCI will damage the appliance. If you have one on a freezer and it falsely trips and no one notices it for days, then you would have a problem. If I had to speculate, I'd wonder if one reason appliance manufacturers don't want them on anything is that when a GFCI trips, even for a valid reason, then dummies find out that their microwave, whatever, doesn't work and call their help line. No GFCI, less calls.
It's also obvious that their recommendations are inconsistent with using countertop appliances in homes built in the last 30+ years, as those receptacles must be GFCI protected. The fact that people are using microwaves, blenders, food processors, mixers, etc pretty much shows that GFCIs do work with appliances.
What changes with inductance is the relationship between voltage and current, ie they will no longer be in phase with each other. But the current entering an inductor has to be the same as the current leaving it. Otherwise where is the current piling up? The electrons have to go somewhere and the only somewhere is out the other conductor. Since the GFCI is only looking at current differences, it should not see a difference.
And if this effect existed, it would be totally incompatible with NEC and existing equipment. For example, pool pump motors now have to be on a GFCI. I did some work on mine 3 years ago and updated to GFCI. I've had 2 1hp pumps running 3 summers now on a GFCI and no trips.
As I said, I have not
It still doesn't change Kirchoff's law. The electrons can't pile up, what goes in comes right out on the other conductor.
The current does not flow without a time delay. It takes a very short time for the current to make its way through an inductor. Electricity flows close to the speed of light in a streight piece of wire. It takes about a nanosecond for it to travel around 4 inches. If you could put a fast enough meter in line you would see the current go up while a meter on the other end of this piece of wire would still be zero. When the current is cut off, the meter on the input side would go to zero and a nanosecond later the current on the output side would go to zero. Almost no time at all. Put 100 feet of wire into a coil and you make an inductor. Depending on the DC resistance in the circuit, it can take a few mili seconds for the current to reach its maximum value. If you put a piece of wire around the earth about 7 times, there would be a one second delay in the action of the two meters, enough to see. After that one second delay then both meters would show the same ammount of current.
That is why I brought up the idea that it may be possiable for the GFCI to see more current going into a motor than comming out of it for a fraction of a second.
Also the electrons that go into one of the wire are not the same ones comming out the other end. Not exectally like, but similar to a long string of marbles. You push another marble in to the string and one flies out, but it is not the same one.
Again you are confusing current with voltage. The current may lag the voltage but the current is the same going in as it is coming out at any given instant. That is Kirchoff's law. (perhaps, minus the speed of light)
No I am not confusing the voltage/current lag. That is totally differant.
Kirchoff's law only applies to a steady state or pure resistance.
From
There are many violations of the law when reactance and time is added to AC circuits.
Please read and understand this :
KCL and KVL both depend on the lumped element model being applicable to the circuit in question. When the model is not applicable, the laws do not apply.
KCL, in its usual form, is dependent on the assumption that current flows only in conductors, and that whenever current flows into one end of a conductor it immediately flows out the other end. This is not a safe assumption for high-frequency AC circuits, where the lumped element model is no longer applicable.[2] It is often possible to improve the applicability of KCL by considering "parasitic capacitances" distributed along the conductors.[2] Significant violations of KCL can occur[3][4] even at 60Hz, which is not a very high frequency.
In other words, KCL is valid only if the total electric charge, , remains constant in the region being considered. In practical cases this is always so when KCL is applied at a geometric point. When investigating a finite region, however, it is possible that the charge density within the region may change. Since charge is conserved, this can only come about by a flow of charge across the region boundary. This flow represents a net current, and KCL is violated.
KVL is based on the assumption that there is no fluctuating magnetic field linking the closed loop. This is not a safe assumption for high-frequency (short-wavelength) AC circuits.[2] In the presence of a changing magnetic field the electric field is not a conservative vector field. Therefore the electric field cannot be the gradient of any potential. That is to say, the line integral of the electric field around the loop is not zero, directly contradicting KVL.
It is often possible to improve the applicability of KVL by considering "parasitic inductances" (including mutual inductances) distributed along the conductors.[2] These are treated as imaginary circuit elements that produce a voltage drop equal to the rate-of-change of the flux.
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Yes, and whatever comes in one end of a wire connected to a motor comes out the other end at the same rate.
If you could put a fast enough
Yes, for the nanosecond delay due to the length of the wire. What you are claiming is very different, ie that inductance adds a substantial delay to that, sufficient to trip a GFCI. In reality, current in equals current out. All the inductive loads on GFCIs would be tripping if that were not true.
When the current is cut off, the
Yes, but while it's reaching that peak value, the current in is equal to the current out. You can't pile up electrons.
If you put a piece of wire around the earth about 7 times,
Now you're conflating the time delay of electron traveling around the earth with the "alleged" time delay of electrons flowing through a motor due to inductance. The former is real, the latter is false. There is no time delay of the current flowing out of a motor due to inductance. The inductance acts to limit the rate that the current can change, but the current in is always the same as the current out. Otherwise, explain where the electrons are piling up.
It can't. Physics says so. Electrons can't pile up.
Yes, they are not the same electrons, but it has nothing to do with the issue. The rate that they are going in equals the rate that they are coming out. It's like the water going into a 20ft long pipe is not the same water that's coming out, but the rate of water in is the same as the rate of the water out. Aside from the physics, which is irrefutable, I have two 1hp motors here on a single GFCI. In 3 years, it's never tripped.
All that said, if you have a piece of equipment tripping a GFCI, the equipment or the GFCI is bad.
This requirement for GFCIs has been around for years and there are millions of pieces of equipment running perfectly on a GFCI.
If you are so confident it is a false trip, try that test I suggested, float the EGC, ground yourself and hold that EGC. I bet you will want to let go pretty quick. Just hope you can.
Uhm, no.
If there is zero current flowing on the "other end" then that half of the circuit could be open for that instant in time.
But if that half of the circuit was open, there would be no current flow at all.
Where do you propose that the current in the circuit between the GFCI and motor is flowing, if not in the conductors?
and that whenever current flows into one end of a
Now you're really off in the wilderness. No one in physics or EE's consider 60hz, high frequency or short wavelength. And the current in that moror *is* only flowing in the conductors. It's 60hz, not 100Mhz. Good grief.
It is often possible to improve the applicability
Good grief. For proof you're now relying on a youtube video of a helicopter servicing a 1 million volt power line? And another one for a non-contact pencil type voltage detector? Neither of those have anything to do with a motor connected to a GFCI.
Now you're really off in the wilderness. No one in physics or EE's consider 60hz, high frequency or short wavelength. It's most certainly low frequency. And the current there *is* only flowing in the conductors.
If there is indeed this big milisecond delay in current, why aren't all the GFCI's out there tripping all the time on motor loads?
Yes, you would see a delay. Nothing moves faster than the speed of light. Ask the phone company. But this nanosecond delay is not the issue at hand. Ralph is claiming that inductance in a motor leads to milisecond delays, and that is untrue, because electrons can't pile up. The same inductance that is limiting electron flow out of the inductor is also limiting electron flow *in* to the inductor.
No idea what that even means.
No idea what that even means.
Because major appliances have 3-wire grounded cords, they don't pose much of an electric shock, even without a GFCI, and a washer may have to be operated in wet conditions where there will always be some leakage to ground (into the cabinet, harmlessly, if the washer is grounded), and a GFCI tripping with a refrigerator plugged into it could spoil the food inside, which itself could be deadly.
GFCIs are designed to resist nuisance trips, and UL standards allow a time delay that varies with the amount of leakage, from about 6 seconds for the minimum 5mA - 6mA leak, to just
30 milliseconds for a 200mA leak that's likely to kill. Also UL has revised its standards, I think as late as 2006, to require more resistance to nuisance tripping. I tested a much older Leviton GFCI made in the 1980s or 1990s and based on either a General Instruments or National Semiconductor chip by connecting it to a table saw (induction motor, grounded), an handheld circular saw (universal motor, ungrounded), and a tabletop fluorescent lamp (ungrounded) but couldn't make the GFCI trip with any of them. The fluorescent lamp is the old style that requires holding down a button for a few seconds, and it tends to cause the worse interference and will crash or lock up computers that don't have good line filters.
There are three problems with your analysis.
The first is that the length of wire in a motor is nowhere near the length of wire wrapped 7 times around the earth. Electricity travels at near the speed of light, or about 1 ns per foot. If you had 50 ft of wire, it's about 50ns. GFCI's aren't looking for, nor are they capable of responding to anything that fast. The test standard I believe is 25ms.
The second is, you're assuming some asymmetry, that doesn't exist. You're proceeding from the point of view that when I close a switch to a motor, everything starts to happen on just the one wire with the switch and then it propagates through the motor, finally reaching the other wire and back to the GFCI. The motor has two wires going to it. You're just looking at what happens on the wire where the switch gets closed. But in reality the other wire is connected all the time, assuming it's a single pole switch. So, just as the ying is starting on the closed switch, the yang on the other wire that's been connected the whole time, is simulataneously going on. If current is being pushed into one end, it's at the same time being pulled out the other end. How would the two wires and the electrons know the difference between wire A and B? And I don't see any reason why the "pushing" on one end would be unbalanced from the "pulling" on the other end.
The third is that motors are routinely used with GFCIs all the time. I don't know of any GFCI's that are specifically rated or designed to work with motors. Nor do I know of any motors specifically designed or rated to work with GFCIs. If this current delay phenomena causing trips were real, then there should be problems everywhere. Millions of motors and GFCI would be tripping, all the time, because they have similar wire lengths, similar inductance, etc. The fact that they aren't, suggests that the few that do trip are tripping not from something that is inherent in the design of all of these, but from something that is wrong with a small percentage of them and I'd suspect that's leakage to ground.
That's true, but it has nothing to do with the issue.
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