GFCI protected circuits

[DLB]

"For the GFI/ GFCI to be fully compatible without the risk of unnecessary triggering, it must have a leak current threshold rating of 30mA (0.003A)."

That is two different ratings, 30 mA and 3 mA, neither of which is GFCI Class A. Class A is the only version most of us would encounter, 5 mA, +/- 1mA leak current. Class A is the classification for human safety. That is a poor answer, at best. Dangerous, in fact, and an invitation for litigation if anyone is injured or killed in an accident where GFCI would have protected them. The NEC is constantly increasing the locations and applications requiring Class A protection. Users have reported success with higher quality Class A devices.

- David

[RFGuy]

"For the GFI/ GFCI to be fully compatible without the risk of unnecessary triggering, it must have a leak current threshold rating of 30mA (0.003A)."

That is two different ratings, 30 mA and 3 mA, neither of which is GFCI Class A. Class A is the only version most of us would encounter, 5 mA, +/- 1mA leak current. Class A is the classification for human safety. That is a poor answer, at best. Dangerous, in fact, and an invitation for litigation if anyone is injured or killed in an accident where GFCI would have protected them. The NEC is constantly increasing the locations and applications requiring Class A protection. Users have reported success with higher quality Class A devices.

- David

David,

Yeah, they made a mistake in trying to calculate the amp rating. I would assume the 30mA is accurate and the 0.003A is inaccurate. I would focus more on the content of their message. They are clearly telling owners of their equipment that a higher threshold rating GFCI is needed for cases where you have nuisance tripping. That is the takeaway here in my opinion. Makes sense based on past discussions where I have pointed out the non-sinusoidal & asymmetrical switching currents involved for a switched reluctance motor and driving circuitry. Many PowerPro owners, I believe, have no problems on a GFCI receptacle and often in those cases I do believe the brand and/or quality of the GFCI receptacle IS the difference. However, for those who continue to have issues with GFCI nuisance tripping when used with a PowerPro they could try to use it on a non-GFCI receptacle when all other methods of remedy have failed IMHO. OF course local building codes might disagree with this and it is up the individual whether they choose to do so or not. I have stated before on this forum the why behind my belief in that GFCI's are not needed for properly grounded, correctly wired and properly shielded modern tools like a PowerPro. IF I was running an old Skil saw with 2 prong cord over a concrete garage floor in my bare feet then of course I would want a GFCI on it. How many of us do that though?

Excerpt #2 from Teknatool on GFCI use:
If the GFI/ GFCI installed on the outlet does not have enough have a high enough leak current threshold, the DVR
motors should be plugged into an unprotected outlet as the DVR motor controller circuit is integrated with a surge
protector.

[RFGuy]

David,

So, I guess the 30mA rating is actually for GFPE (Ground-Fault Protection of Equipment) devices. This makes sense for why only ground fault breakers have the 30mA rating, i.e. because they are only protecting equipment and not personnel so no need to protect at a lower setting. GFCI devices have to protect at the 5mA (+/- 1mA) level as discussed previously on this forum...otherwise tripping at a higher level could result in a human's muscle's latching and not being able to let go of the device during a ground fault event. Clearly more protection is better than no protection, so ideally one would have a working GFCI receptacle protecting against ground faults while operating the PowerPro. It would just be nice to know which brands and models of GFCI receptacles work best for the PowerPro. Also, I suspect that more line filtering would only benefit the situation and likely cut down on false triggering of the GFCI. I was thinking in the worst case, i.e. if the PowerPro owner has done everything that they can to eliminate the nuisance trips that if they continue to have them, that the Teknatool advice would be useful. I agree that it does put any manufacturer in a difficult position, i.e. their product doesn't work as advertised so how will they remedy it when it doesn't comply with government mandated GFCI devices? Erring on the side of caution as you suggest is probably the right thing to do for everyone, so apologies if my last post was too cavalier. I just know that many of these GFCI devices are garbage. I have had several go out (malfunction) on me so I question will they even work when I need it? I know the circuitry inside and the theory behind their use as well as the intent of the NEC code. I had hoped to demystify it a bit in our discussions on this forum, but might have been better to just leave it alone. Anyway, thanks for the discussion as always.

[DLB]

For clarity, I'm not disagreeing with using the tools on unprotected outlets. I mostly use mine on an unprotected 230VAC outlet. Where I feel these recommendations cross the line is that they advocate, or may be interpreted that way, defeating required protection on an entire branch circuit which may contain one or many outlets that may be used for numerous applications.

Shopsmith's recommendations, IIRC, are much more in line with my thinking. 1) Use the equipment on unprotected outlets if available. 2) Change the protection to a GFCI circuit breaker for the branch circuit in question. Works, as far as I know, and does so without code violations or defeating safety devices. (I'm not sure where I read this, and can't locate it now.)

- David

[RFGuy]

David,

Thanks. Well, I changed my mind after thinking about the potential internal circuitry inside of the PowerPro. As I understand it, there is an inverter driver that excites each stator sequentially. There are different topologies for these, but a common one for SRM motors is the asymmetrical bridge inverter topology (https://en.wikipedia.org/wiki/Switched_ ... verter.svg). Not knowing which one or being able to review the PowerPro schematics, it is difficult for me to identify potential leakage paths for the PowerPro design. When I wrote my previous response I had been thinking more along the lines of a simple induction motor load and/or simple consumer electronics type application...so I kind of dismissed the potential risk for ground fault. Having a HV driving circuit like this presents the opportunity for many more potential leakage paths to ground. Every FET has leakage, but the actual schematic and topology choices can either mitigate that leakage or exacerbate it. Passive components (R's, L', C's) have leakage too. Even with a good schematic design and topology selection, there can be damage in the way of EOS (electrical over stress) or ESD (electrostatic discharge) in the worst case, which could cause one or more of the components to start leaking. Another concern is how they did the substrate connections on those FET's, e.g. is unbalanced (120V operation) more or less dangerous for leakage paths than a balanced (240V operation) connection (due to where those substrate ties connect)? I can't say without seeing the schematics. Not trying to scare PowerPro owners here, but just pointing out that it gets complicated to determine all the potential failure modes where a user might accidentally end up in the path of an undesired leakage current. All of these potential leakage paths could stay internal to the PowerPro and never complete a circuit through the operator, but anytime you have a leakage path in a circuit you need to identify possible paths it can take and the impedances involved. When the impedance to ground, through a human, is lower than through the internal circuit it is always a bad outcome...

Yeah, I wouldn't want to compromise other taps from the same branch circuit either. One should try to get the GFCI to work on the PowerPro, but if not should probably have at least a GFPE (breaker) on it. I would be curious to learn of what Shopsmith recommends on this if you find it. Thanks again.

[RFGuy]

David,

I went back and looked at this again and I pulled up the document from Teknatool, rather than the webpage description. The GFCI guidance is clear in this document that I am including below. Of note is that the 30mA or 0.03A is correct here so my assumption was correct, i.e. it was just a typo on the amperage conversion on the webpage. Also, of note is they basically say that there could be a current imbalance of at least 5mA due to DVR motor operation which obviously is enough to trip a GFCI receptacle. I find this easy to believe given the difficulty in creating perfect switching transients with FET's in the driver circuitry as well as the creation of non-sinusoidal & asymmetric waveforms involved. Of course, they don't acknowledge that around 5mA is also around about the same current level that can cause muscles to latch during a ground fault shock event preventing the user from letting go. I am not sure, but I believe this 5mA rating in the NEC came from what is the level for this in a child; I believe the level in an adult is much higher though (see 2nd excerpt below).

Their legal department likely has no idea they are recommending this and the ramifications for it.

Excerpt from Teknatool GFCI document:
What is a GFI/ GFCI?
Ground Fault Interrupter (GFI) or Ground Fault Circuit Interrupter (GFCI) is a common protection device found in
your outlets (often around kitchens, workshop etc) where electrical appliances may draw a large amount of
electrical current during operation. GFI’s main purpose is to protect the human body from electrical shock when
someone touches a Hot/ Live wire or a short circuit. It is also used to protect the connected electrical circuits from
electrical current surges to prevent damage to the circuits. The GFI will shut off and isolate power source when it
detects an imbalance in current coming out from its outlet, the threshold of this imbalance is denoted as the
“Leak Current Threshold”.

GFI/ GFCI compatible with DVR products
The GFI/ GFCI compatibility between the GFI and DVR products is mainly dependent on the value of the leak
current threshold. Due to the electrical characteristic of the DVR motor, there might be a large imbalance in
current during its operation which may be enough to trigger the GFI/ GFCI in a typical household. Typical GFI
found in households will be rated with a leak current threshold of 5mA (0.005A) which may trigger during the
operation of the DVR motor.

A GFI/ GFCI with a leak current threshold rating of 30mA (0.03A) is recommended to be compatible with the DVR
motors without the worry of triggering during operation.

Note:
Frequent triggering of GFI will not cause any harm to the electronics of the DVR motor as it has an integrated
protection against it.
If the GFI/ GFCI installed on the outlet does not have enough have a high enough leak current threshold, the DVR
motors should be plugged into an unprotected outlet as the DVR motor controller circuit is integrated with a surge
protector.

Excerpt from online article on "let go" range for GFCI's:
OSHA documents spell out the general relationship between the amount of current received and the reaction when current flows from the hand to the foot for just one second.

• At 1 mA you feel a slight tingle.

• At 5 mA you feel a slight shock, not painful but disturbing. The average individual can let go, but involuntary reactions can lead to injuries.

• At 6–25 mA there is painful shock, and muscular control is lost.

• The 9–30 mA level is called the freezing current or “letgo” range. At this level many humans cannot get their muscles to work, and they can’t open their hand to let go of a live conductor.

• At 50–150 mA there will be extreme pain, respiratory arrest, and severe muscular contractions. The individual cannot let go, and death is possible.

• At 1,000–4,300 mA there is ventricular fibrillation (the pumping action to the heart ceases). Muscular contraction and nerve damage occur. Death is most likely.

• At 10,000+ mA there will be cardiac arrest with severe burns and probable death.

https://issuu.com/wtwhmedia/docs/power_ ... s/10260419

[DLB]

In a changing world where the NEC has historically never failed to expand the household GFCI requirement on their 3 year cycle, 'plug it in an unprotected outlet' doesn't seem like a good solution. But 'defeat the (required) GFCI' seems worse. If I bought a piece of equipment today that would not work on a Class A GFCI circuit and the manufacturer gave this answer I would not find it an acceptable response. And I don't think there is any foundation offered for the implication/assertion that DVR and GFCI are inherently incompatible (if that is the interpretation I'm meant to reach). The way I see it, they are saying that their implementation cannot be expected to work with GFCI.

- David

[RFGuy]

In a changing world where the NEC has historically never failed to expand the household GFCI requirement on their 3 year cycle, 'plug it in an unprotected outlet' doesn't seem like a good solution. But 'defeat the (required) GFCI' seems worse. If I bought a piece of equipment today that would not work on a Class A GFCI circuit and the manufacturer gave this answer I would not find it an acceptable response. And I don't think there is any foundation offered for the implication/assertion that DVR and GFCI are inherently incompatible (if that is the interpretation I'm meant to reach). The way I see it, they are saying that their implementation cannot be expected to work with GFCI.

- David

David,

Yeah, I agree with you. They definitely seem to be in a Catch-22 situation here. As I understand the circuitry and motor design, I can see why this might be more of a problem with this type of design, but that doesn't excuse it. There are circuit and system techniques that could be used to mitigate any effect from this being seen by the GFCI powering it IMHO. Kind of why I am curious about the schematics for any of the StriaTech motors, but I doubt I will ever find one to review. I do wonder if the balanced (240V operation) is less prone to this, but then there aren't any 240V GFCI receptacles are there? You would need to have a 5mA triggering ground fault circuit breaker instead, right?

[DLB]

Yeah, I agree with you. They definitely seem to be in a Catch-22 situation here. As I understand the circuitry and motor design, I can see why this might be more of a problem with this type of design, but that doesn't excuse it. There are circuit and system techniques that could be used to mitigate any effect from this being seen by the GFCI powering it IMHO. Kind of why I am curious about the schematics for any of the StriaTech motors, but I doubt I will ever find one to review. I do wonder if the balanced (240V operation) is less prone to this, but then there aren't any 240V GFCI receptacles are there? You would need to have a 5mA triggering ground fault circuit breaker instead, right?

When I looked, I didn't find any 240V GFCI receptacles. The only exceptions to CBs (yes, 5mA) for 240V I saw was a disconnector for a hard wired installation. I'm not sure what advantage this offers, it wasn't cost. Best guess: HVAC techs might be allowed to de-energize the circuit and replace the disconnect but not allowed to open the main panel and install a GFCI breaker.(?) Saving cost by not needing an electrician for the job.

- David

[JPG]

"let it go' blurb left off the cooking of internal organs scenario.(gross but real)