Leviton GFCI nuisance tripping and circuit analysis

[tersh]

hmmm, profile lists 'engineer'? An engineer afraid to hook up a scope to simple 240 V 60 Hz? Untrained and an engineer? a locomotive or 'sanitary' engineer?

All you need to do to get your full data is to hook up a scope with a current probe (you don't even have to touch any 240 V wire with a clamp on probe) and look at the waveform. You will undoubtedly SEE a differential current at transitions.
Gar probably has already taken some waveforms and waiting to see if any others have

Using a small SP motor I see differential currents in the 10o's of mA at switch operations.
Another hint: the inductance of small sp motor is 500 mH, a 1/2 HP motor is only 2.6 mH - what does that tell you?

I was engineer 25 yrs ago but left the field and went to medical and neuroscience after I realized that the most advanced electronic in the universe is a cell and it's nanotech.

But after learning lately our country doesn't have EGC in any appliance. I tried to go back to it once again to try to be familiarize with GFCI to help protect 108million filipinos who don't know the concept of EGC or GFCI.

I'll try your idea after finding someone with oscilloscope, especially since we will be stuck with that only brand of 240v GFCI in the world for the next 30 years. I don't want to buy one just for it because after that, what would I do with an oscilloscope afterwards, I don't want to try it on other items as I don't want to take any risks with electricity. One wrong Zap and you don't wake up forever.

That said. I'd like to focus on something now.

The typical time/current for class A GFCI in USA products are controlled by UL. But with the 240v GFCI OEM made by an unknown manufacturer in china using cloned chip and distributed worldwide as OEM, I want to make sure the time the relay opens is as good as the USA GFCI products.

This is the relays and sense coil of the 240v china GFCI (or the Meiji GFCI outlets we have).

Notice there are two solenoids compared to the USA GFCI with only one like:

The Leviton one has only one solenoid

I takes time to build magnetic field. I just wondered why there were two electromagnetics in the china GFCI. Anyone has theory why two? The contacts just goes up and up. The top solenoid probably attracts the contacts upward, but why is there another one on the right? A seasoned electrician I asked doesn't know why either.

Remember the circuit diagram (for both which is identical) only has one solenoid:

Also with an oscilloscope, how can you measure how fast the relay open when there is current imbalance. When I find someone with oscilloscope, I'll try to figure it out too.

 

[tersh]

I was engineer 25 yrs ago but left the field and went to medical and neuroscience after I realized that the most advanced electronic in the universe is a cell and it's nanotech.

But after learning lately our country doesn't have EGC in any appliance. I tried to go back to it once again to try to be familiarize with GFCI to help protect 108million filipinos who don't know the concept of EGC or GFCI.

I'll try your idea after finding someone with oscilloscope, especially since we will be stuck with that only brand of 240v GFCI in the world for the next 30 years. I don't want to buy one just for it because after that, what would I do with an oscilloscope afterwards, I don't want to try it on other items as I don't want to take any risks with electricity. One wrong Zap and you don't wake up forever.

That said. I'd like to focus on something now.

The typical time/current for class A GFCI in USA products are controlled by UL. But with the 240v GFCI OEM made by an unknown manufacturer in china using cloned chip and distributed worldwide as OEM, I want to make sure the time the relay opens is as good as the USA GFCI products.

This is the relays and sense coil of the 240v china GFCI (or the Meiji GFCI outlets we have).

Notice there are two solenoids compared to the USA GFCI with only one like:

The Leviton one has only one solenoid

I takes time to build magnetic field. I just wondered why there were two electromagnetics in the china GFCI. Anyone has theory why two? The contacts just goes up and up. The top solenoid probably attracts the contacts upward, but why is there another one on the right? A seasoned electrician I asked doesn't know why either.

Remember the circuit diagram (for both which is identical) only has one solenoid:

Also with an oscilloscope, how can you measure how fast the relay open when there is current imbalance. When I find someone with oscilloscope, I'll try to figure it out too.

In the USA. When the power is removed to the GFCI receptacle, does the relay contacts closed or opened? In the China clone 240v, the contacts have memory. Meaning if power is removed and it's in open position, it will remain open. If it's closed when power is removed, it will remain closed.

The following is a user of the USA GFCI explaining the circuit. I couldn't get from this whether when power is removed, the contacts become closed or has memory? What do you guys think?

I'm asking because I'm wondering if the second solenoid in the china clone is for purpose of memory. Is there circuit setup really designed for dual solenoid and memory?

 

[tersh]

Explain the source is 3A. I would be more concerned with the voltage of the source.

If you do not have any testing labs, such as UL, you are taking the word of the manufacturer that their equipment works as they claim. How they test is up to them. They may test it on 100 __________, and if 95% of them live it's good enough. They may not test at all.

I just realized something. Since the Philippines centertap is the one grounded (at least in the capital), the line to soil is only 120v, not 240v. Since 120v can cause lower current to the human body than 240v. Thank god we used the same US system where the centertapped is grounded instead of one of the two hots. In Europe, it's one of the 2 hots that are grounded.

So advantage of US power system is less chance of electrocution when using GFCI. Is this why there is no 5mA RCD in Europe?

Also this means it is safer to have the centertap grounded rathan than transfer the ground to one of the hots in the Philippines, right?

Whatever, we used the same 120v line to ground so we both get shock similarly so the following questions concern us 120v grounders.

Does the above graph means that if the current passing through the body 500mA. No GFCI can help? Please give instances when the human body is exposed to 500mA. Remember a GFCI doesn't limit the current but only makes it trip faster, so if you were exposed to 500mA. The GFCI won't make it 5mA. It won't be fast enough to trip it. It is said in one of gar's references that:

"It does not​

limit the magnitude of ground fault current. It does limit the length of time that a ground fault will flow. In other words, you will still receive a severe shock during the time it takes the GFCI device to trip “off.”fault will flow. In other words, you will still receive a severe shock during the time it takes the GFCI device to trip “off.”". ​

 

[tersh]

I am pondering the following:

The GFCI chip is powered by connection to the AC line through a resistor, a diode, and the 'trip solenoid' (which I presume is supposed to do double duty as a filter choke). The capacitor from pin 6 is a decoupling capacitor to filter the rectified AC.

The circuit has a residual current detection circuit that uses an op-amp connected to a sense coil, using standard op-amp feedback through Rset. The output of this amplifier connects to a pair of comparitors so that when the output of the RCD is high enough the system is triggered.

Also connected to the _output_ of the op-amp is the 'grounded neutral detection' circuit. The way this works is that if the neutral is grounded upstream of the GFCI, the combination of the ground-neutral loop, the various capacitors and the second toroid creates a feedback path that makes the sense op-amp oscillate and drive a detectable current through the ground-neutral loop.

I am wondering if particular inductive loads can interact with the grounded neutral detection, and dump current into pin 1 via the power supply connection, and trip the circuit not by creating an actual residual current, but rather by creating a current spike at pin 1 of the chip.

Tersh, if you want to continue to research this, I think that the next step would be to build a proper spice model of the circuit, and simulate what happens with various inductive loads, _or_ probe the circuit using a good oscilloscope. You might also hire someone to do this research.

Very, very interesting, since you have clearly demonstrated a case where there is no 'residual current', but you are consistently tripping this circuit.

-Jon

Winnie. It took me about an hour 2 weeks ago when I first tried to understand the purpose of the second grounded neutral sense coil. I just need to verify if I even understood it right and some issues I still hadn't understood and need clarifications. This second sense coil would only work if the appliance has ground (or EGC) connected between the output of the GFCI and the input, right? Or is the loop internal to the circuit? I think not. But just verifying.

https://www.powerelectronictips.com/teardown-leviton-ground-fault-circuit-interrupter/

"GFCI makers can use several methods to detect ground to neutral current. The Fairchild chip uses a scheme which makes use of the definition of fault current resistance as spelled out in UL 943, the U.S. standard for ground-fault circuit interrupters. The standard specifies that GFCIs trip with fault currents of 6 mA for specified ground fault resistances and for a specified combination of ground to neutral resistance and wire resistance between load/neutral and earth ground. In UL tests, the resistance of the combination of grounded and grounding conductors of the cable or cord are quite low, 0.4 and 1.6Ω at most."

Any references why the second sense coil would produce difference in current merely by oscillating when there is current passing from the ground of the output to the input? But there is clearly current leaking that the first sense coil should be able to detect even without second grounded neutral sense coil? So why the second required?

I wonder if the Siemens GFCI breaker do this method too. So far, it hasn't trip a single time connecting to the fridge for a week already. I have 2 fridges, both trip on the meiji gfci outlet. And it's been a day already without tripping too when I connected the LC filter strip between the meiji and the second fridge. Usually it trips twice a day. If it won't trip 2 more days, then simply putting LC filter would solve it.

However for the rest of people who experienced nuisance tripping with brand new fridge on their GFCI. I wonder what could be other reasons (beside bad insulation where the fridge actually leaks).

Many thanks for the help!
​

 

[winnie]

I don't fully understand the circuit. It is there to detect a neutral to ground fault in the wiring downstream of the GFCI, so the loop you drew in blue is outside of the circuit, and outside of the GFCI unit entirely.

Consider what happens if you have a neutral to ground fault. Remember that in the US the neutral is tied to ground at the main panel, so there is only a very slight voltage between neutral and ground anywhere in the system. So in the event of a neutral to ground fault, there might not be much residual current. My understanding is that the second toroid is there to create something detectable in the event of a neutral to ground fault.

However in your situation (240V circuits, no neutral conductors) there is no possibility of a neutral to ground fault! All the grounded neutral toroid and sense circuit does is provide a path for nuisance trips. I presume that these GFCIs are designed for use in areas which use 240V hot to neutral.

-Jon

 

[tersh]

I don't fully understand the circuit. It is there to detect a neutral to ground fault in the wiring downstream of the GFCI, so the loop you drew in blue is outside of the circuit, and outside of the GFCI unit entirely.

Consider what happens if you have a neutral to ground fault. Remember that in the US the neutral is tied to ground at the main panel, so there is only a very slight voltage between neutral and ground anywhere in the system. So in the event of a neutral to ground fault, there might not be much residual current. My understanding is that the second toroid is there to create something detectable in the event of a neutral to ground fault.

However in your situation (240V circuits, no neutral conductors) there is no possibility of a neutral to ground fault! All the grounded neutral toroid and sense circuit does is provide a path for nuisance trips. I presume that these GFCIs are designed for use in areas which use 240V hot to neutral.

-Jon

But in our case. The line to ground is 120v. So how do you deal with ac system that is 240v but grounding is 120v. Or just imagine what would happen if you connect your US black and red wire line to line to produce 240v..if there is ground fault. It is 120v fault. Right.i wonder if there is no difference in the china clone 240v gfci whether the fault is 120v or when used in europe where the ground fault is 240v. What do you think?

 

[winnie]

In your system, you have 120V faults to ground, just as might be seen in the US.

What you don't have are 0V faults. There is no way a GFCI installed without a neutral will need to detect a neutral to ground fault.

120V L-N, 240V L-L or 240V L-N the GFCI residual current measurement is the same. But the section of the circuit dedicated to detecting N-G faults is not useful if N is not present.

-Jon

 

[tersh]

In your system, you have 120V faults to ground, just as might be seen in the US.

What you don't have are 0V faults. There is no way a GFCI installed without a neutral will need to detect a neutral to ground fault.

120V L-N, 240V L-L or 240V L-N the GFCI residual current measurement is the same. But the section of the circuit dedicated to detecting N-G faults is not useful if N is not present.

-Jon

I tried to read about 0v faults or ground to neutral fault in the US and in the leviton teardown video. I know one could still be electrocuted by becoming path of a broken neutral.. because the current passes thru a person.. is it talking about this? Or is it talking about intact neutral.. where the current can still pass thru a person and it returns to neutral and can this cause shock? I know it wont trigger the first sense coil but can it really cause shock or electrocution this ground to neutral fault.. without any broken neutral?

 

[tersh]

I tried to read about 0v faults or ground to neutral fault in the US and in the leviton teardown video. I know one could still be electrocuted by becoming path of a broken neutral.. because the current passes thru a person.. is it talking about this? Or is it talking about intact neutral.. where the current can still pass thru a person and it returns to neutral and can this cause shock? I know it wont trigger the first sense coil but can it really cause shock or electrocution this ground to neutral fault.. without any broken neutral?

Winnie. What I meant above was this:

In USA neutral system. It is shown above that touching the neutral wouldn't make the current pass through a human body because it will avoid the path as "it has got another path with zero resistance". So why is there a second grounded neutral sense coil in the GFCI? Is it only to protect broken neutral where the person becomes the path (which can give them shock)? But then even if the person becomes the path of the broken neutral, if he doesn't touch the ground, there would still not be any ground-neutral fault so the 2nd sense coil won't trip either.

If it's the former, how can it cause shock when the current has zero resistance path to travel? Kindly give a scenario when this former case can still cause shock enough to electrocute. I'm aware all this for USA ac system only and don't apply to the Phils where all power is line to line 240v. I'm just curious of US electricity because I go to new york too some months. Thanks.

 

[ptonsparky]

Winnie. What I meant above was this:

In USA neutral system. It is shown above that touching the neutral wouldn't make the current pass through a human body because it will avoid the path as "it has got another path with zero resistance". So why is there a second grounded neutral sense coil in the GFCI? Is it only to protect broken neutral where the person becomes the path (which can give them shock)?

If it's the former, how can it cause shock when the current has zero resistance path to travel? Kindly give a scenario when this former case can still cause shock enough to electrocute. Thanks.

Most of the current takes the path of least resistance. Not all. In your drawing the human becomes one of those paths. Swimming pools and hospitals are two of the locations that require extra attention to detail so there is no human in that path.

The neutral does not have zero resistance.

 

[winnie]

I suspect that a grounded neutral itself can't cause much shock risk, because the voltage of the neutral is very low. The resistance (and thus voltage) of this path is _not_ zero, but it is low.

Rather the grounded neutral can reduce the sensitivity of the GFCI to shock hazard.

Keep in mind that a GFCI _cannot_ detect shocks that are running from hot to neutral. Hot to neutral current is simply load current that the GFCI is not sensitive to.
With a grounded neutral, some unknown portion of a downstream hot to ground fault connect back to the neutral and would pass through the GFCI on the neutral and thus not be detected as residual current.

-Jon

 

[tersh]

Most of the current takes the path of least resistance. Not all. In your drawing the human becomes one of those paths. Swimming pools and hospitals are two of the locations that require extra attention to detail so there is no human in that path.

The neutral does not have zero resistance.

Oh. I got the figure from the 31 replies from someone's question at https://www.quora.com/Will-touching-a-neutral-wire-render-an-electric-shock-Why

 

[mopowr steve]

Oh. I got the figure from the 31 replies from someone's question at https://www.quora.com/Will-touching-a-neutral-wire-render-an-electric-shock-Why

Oh No! more bad information.

 

[ptonsparky]

Oh. I got the figure from the 31 replies from someone's question at https://www.quora.com/Will-touching-a-neutral-wire-render-an-electric-shock-Why

The ‘electricity’ is not trying to get back to earth. It is trying to get back to the transformer. Earth becomes involved if the transformer secondary is grounded either purposely or accidentally.

 

[tersh]

I am pondering the following:

The GFCI chip is powered by connection to the AC line through a resistor, a diode, and the 'trip solenoid' (which I presume is supposed to do double duty as a filter choke). The capacitor from pin 6 is a decoupling capacitor to filter the rectified AC.

The circuit has a residual current detection circuit that uses an op-amp connected to a sense coil, using standard op-amp feedback through Rset. The output of this amplifier connects to a pair of comparitors so that when the output of the RCD is high enough the system is triggered.

Also connected to the _output_ of the op-amp is the 'grounded neutral detection' circuit. The way this works is that if the neutral is grounded upstream of the GFCI, the combination of the ground-neutral loop, the various capacitors and the second toroid creates a feedback path that makes the sense op-amp oscillate and drive a detectable current through the ground-neutral loop.

I am wondering if particular inductive loads can interact with the grounded neutral detection, and dump current into pin 1 via the power supply connection, and trip the circuit not by creating an actual residual current, but rather by creating a current spike at pin 1 of the chip.

I tested your above theory that

particular inductive loads can interact with the grounded neutral detection so I removed the entire winding of the 2nd grounded neutral sense coil. This was the original last December (the top is the 2nd grounded neutral sense coil, the bottom is the main sense coil).

​

Here the top 2nd grounded neutral sense coil was pulled out entirely a while ago.

Here the shaded pole motor was inserted into the GFCI outlet, and just the same. The motor trips 4 out of 5 times (even without the 2nd coil present). Note the test button still works so I'm 100% sure I removed the 2nd grounded neutral sense coil (1:200) and not the first sense coil (1:1000).

(For professionals, engr, ex-engr, electrician only)​

With the 2nd sense coil eliminated. What is your next guess what part of the circuit the inductive load can affect? Putting LC filter strip can eliminate it.

Tersh, if you want to continue to research this, I think that the next step would be to build a proper spice model of the circuit, and simulate what happens with various inductive loads, _or_ probe the circuit using a good oscilloscope. You might also hire someone to do this research.

Very, very interesting, since you have clearly demonstrated a case where there is no 'residual current', but you are consistently tripping this circuit.

-Jon

I couldn't find electrical engineers with oscilloscope. In my country, electrical engineers either got the degree to be familiar with the products and sell electrical items or they work at the power company. So they don't own an oscilloscope.

 

[tersh]

About why there are two solenoids in the china made clone.

In most of the GFCIs in the US, is it not the "reset" function (re-closing the contacts) is purely mechanical, not electronic. The single solenoid is used only to open the contacts. But in the china clone. The reset is not mechanical but by means of switch contacts. Here the top switch contact is for Reset, the bottom switch contract is ror Test. There is 2 rubber with metal inside the enclosure to conduct the contacts.

​

Here are two solenoids in more detail:

When you press the Test button at bottom, the Contacts open.. and even if you remove the power, the contacts remain open:

When the Reset button was pressed at the top, the Contacts closed, and contacts remain closed even when power was removed. I used the red and blue rubber button with gloves to press it.

This is zoom of the inside when the contacts was closed:

I'm asking what kind of mechanism inside where if the contacts were closed or opened by the solenoids. They remain closed and open? There are no springs inside.

And also I'm asking this because I don't want to pull up the solenoids because then the GFCI can no longer be useable. and I don't want to spend another $30 to experiment on the cause of the inductive kicks. So any theory about the 2 solenoid puzzles? Thanks.

 

[gar]

190113-2059 EST

tersh:

Look at your circuit diagram.

For the GFCI to trip the SCR must be triggered. There are basically three ways.

1. A very high rate of rise of voltage to the anode causing triggering. Not too likely.

2. A voltage exceeding the anode breakdown voltage.

3. A signal getting to the gate. This is the path that the GFCI integrated circuit drives. But that circuit has been designed to be somewhat of a low pass filter. Inverse time function.

What I suspect, but may not be correct, is that a high rate of dv/dt capacitively couples to the wire to the SCR gate. In Leviton GFCIs I have looked at there there is a long tracel between the location of C3 and the SCR gate. This is how I am guessing the trigger signal gets in.

Experiments you could run are:

1. Cut the lead from pin 6 to C3. Does tripping still occur?

2. Connect a fractional inch wire, in other words short, between gate and cathode of the SCR with the pin 6 to C3 still open. Does tripping occur?

Depending upon these results other experiments can be performed.



.

 

[tersh]

190113-2059 EST

tersh:

Look at your circuit diagram.

For the GFCI to trip the SCR must be triggered. There are basically three ways.

1. A very high rate of rise of voltage to the anode causing triggering. Not too likely.

2. A voltage exceeding the anode breakdown voltage.

3. A signal getting to the gate. This is the path that the GFCI integrated circuit drives. But that circuit has been designed to be somewhat of a low pass filter. Inverse time function.

What I suspect, but may not be correct, is that a high rate of dv/dt capacitively couples to the wire to the SCR gate. In Leviton GFCIs I have looked at there there is a long tracel between the location of C3 and the SCR gate. This is how I am guessing the trigger signal gets in.

Experiments you could run are:

1. Cut the lead from pin 6 to C3. Does tripping still occur?

2. Connect a fractional inch wire, in other words short, between gate and cathode of the SCR with the pin 6 to C3 still open. Does tripping occur?

Depending upon these results other experiments can be performed.



.

I cut the pin 6 lead or leg (so pin 6 was completely disconnected from the pcb):

It is supposed to be the power to the chip:

Is it possible that even when pin 6 was cut. There is still power to the circuit from other pin(s)?

The shaded pole motor still trips at 4 out of 5 times.

With my 240v GFCI plug in tester with ground connected to soil. Pressing the test doesn't work anymore. The shaded pole motor was used to trip it. Before cutting pin 6, the GFCI tester works all the time.

So it's the SCR problem and not the chip (supposed no power gets inside the chip from other pins? what do you think?)

 

[gar]

190113-2524 EST

tersh:

So it appears you have run part of the experiment. And your results seem to imply that my guess is at least partially correct.

The test button won't work because that introduces a signal into the IC and not directly to the SCR gate. Now do the short distance gate to cathode short of the SCR input.

.

 

[tersh]

190113-2524 EST

tersh:

So it appears you have run part of the experiment. And your results seem to imply that my guess is at least partially correct.

The test button won't work because that introduces a signal into the IC and not directly to the SCR gate. Now do the short distance gate to cathode short of the SCR input.

.

Is the arrow in blue the SCR?

The thing is designated "BT169 1702". Is it the SCR? The left pin is connected to pin 7 of the chip (as shown in circuit diagram).

When I shorted it with alligator click (the red curve), the shaded pole motor no longer trips! (after 20 switches). Usually it trips every 4 out of 5 times. So your theory seems to be correct

If it is the SCR. What does shorting the cathode and gate do to the SCR?