5mA vs. 30mA sensitivity GFCI breaker

[synchro]

Is this equipment portable such that it can be moved off site and check whether it trips a GFCI located somewhere else? That could help verify whether the equipment itself is the problem. ...

Thank you! Yes, I think they tested that the food equipment worked correctly on other GFCI.

...
Was the GFCI breaker that didn't trip on a different circuit in the same panel, at a different panel in the same building, or at a different building?
Is the food warming equipment on a dedicated circuit, or is there another load on the circuit that could be contributing to the total leakage current?

 

[jim dungar]

The GFI circuit breakers or GFI receptacles would not sense that their output and return had a leakage since they would be monitoring the difference in the potential of the phases or phase to neutral conductors associated with what was connected to them.

GFCI devices do not monitor any potential difference. They simply look for a difference between the current on the 'hot' and neutral wires.

 

[romex jockey]

This brings up an interesting point.

If there was a ground fault leakage on a non GFI protected circuit in a commercial kitchen with stainless steel tables, sinks, etc..., and, that leakage energized all the metal objects in the kitchen, what would protect the person standing on the wet floor in contact with the energized metal objects?

The GFI circuit breakers or GFI receptacles would not sense that their output and return had a leakage since they would be monitoring the difference in the potential of the phases or phase to neutral conductors associated with what was connected to them.

Not the culprit that caused the leakage.

JAP>

my mind immediately went to equopotential plane.....~RJ~

 

[curious101]

...
Was the GFCI breaker that didn't trip on a different circuit in the same panel, at a different panel in the same building, or at a different building?
Is the food warming equipment on a dedicated circuit, or is there another load on the circuit that could be contributing to the total leakage current?

Good question. I would have to find out. It would be in the same building, but I'm not sure if the same panel or not. The food warming equipment is on dedicated circuit. Thanks!

 

[romex jockey]

4-6 ma was a choice made consulting the medical community in the late 60's, early 70's.

It was predicated on electrodes placed much like a dfib across the heart, the study producing findings vfib starts around 5 millionths of an amp

the truth is, static charges can produce more ma, and most shock events are not directly across the heart

~RJ~

 

[winnie]

4-6 ma was a choice made consulting the medical community in the late 60's, early 70's.

It was predicated on electrodes placed much like a dfib across the heart, the study producing findings vfib starts around 5 millionths of an amp

the truth is, static charges can produce more ma, and most shock events are not directly across the heart

~RJ~

A normal static discharge (such as walking across a rug and touching a doorknob) might have more mA, but for a much shorter time. The UL standard for GFCI permits 5mA current for something like 7 seconds before tripping.

-Jon

 

[winnie]

Thank you! Yes, I think they tested that the food equipment worked correctly on other GFCI. They need somebody on the site to analyze the situation. Who is usually responsible for this? The manufacturer of the food equipment, the manufacturer of the breaker/panel or the engineer of record or all?

synchro's question was much better than mine about measuring leakage current.

If you have a device which works on one GFCI circuit but not another, then it is _possible_ that the device has real leakage that is just on the threshold of the requirement, and so trips some units but not others.

However it is much more likely that there is something wrong with the first GFCI circuit.

A very common circuit failure that might look like a nuisance trip is if there is a neutral to ground fault in the circuit.

-Jon

 

[jap]

Exactly.

Which is more or less similar to a difference of potential.

So if a leakage current is not coming from the circuit the gfi is monitoring the gfi will not trip and all the conductive surfaces in the kitchen will remain energized unless it's a great enough fault to trip a standard circuit breaker.

Jap>

 

[romex jockey]

The UL standard for GFCI permits 5mA current for something like 7 seconds before tripping.

why not 30ma then?

~RJ~

 

[romex jockey]

A very common circuit failure that might look like a nuisance trip is if there is a neutral to ground fault in the circuit.

Which is going to be a lot more of an issue, as the NEC assumes toroidal protective status for everything.

So we are following suit ,a generation behind all those RCD countries , who's focus eventually turned to earth fault loop status , because the impedance of any given circuit IS the most protective element of it

~RJ~

 

[mbrooke]

The tool you need is a peak reading clamp meter or an oscilloscope with a current probe that can reliably read in the milliamp range. My experience is more in the lab, not in the field, so I don't know who near you would do this sort of work, or what equipment to recommend.

-Jon

The thing is, even if steady state leakage is under 5ma, a peak, ripple or fast rising edge in the sine wave can produce current higher than 5ma.

Steady state or transient, 5ma is an unrealistic value for large appliances.

What protects the user is the EGC.

 

[mbrooke]

This brings up an interesting point.

If there was a ground fault leakage on a non GFI protected circuit in a commercial kitchen with stainless steel tables, sinks, etc..., and, that leakage energized all the metal objects in the kitchen, what would protect the person standing on the wet floor in contact with the energized metal objects?

The GFI circuit breakers or GFI receptacles would not sense that their output and return had a leakage since they would be monitoring the difference in the potential of the phases or phase to neutral conductors associated with what was connected to them.

Not the culprit that caused the leakage.

JAP>

I was simply posing this as a question to see if any more knowledgeable folks on this forum could chime in on their thoughts about this.

Your situation got me to wondering if a fault on a non gfi protected circuit could still be a hazard even on GFI protected piece of equipment.

I think there's a chance it could be.

JAP>

Did someone call me?


Assuming 10ma at 120 volts, that would be a 12,000 ohm equivalent resistor line to ground.


Using a resistive divider with a total of 0.5 ohms on the EGC back to the transformer we obtain 0.005 volts to remote earth.

Equal potential bonding is not needed.

 

[jap]

Did someone call me?


Assuming 10ma at 120 volts, that would be a 12,000 ohm equivalent resistor line to ground.


Using a resistive divider with a total of 0.5 ohms on the EGC back to the transformer we obtain 0.005 volts to remote earth.

Equal potential bonding is not needed.

In other words, keep that EGC in tact and corrosion free regardless of what ground fault protection you have in place.

Correct?

Jap>

 

[curious101]

Thank you so much for all your responses! My situation is still not solved. I guess it's a complex one. Non-motor-rated GFCI or motor rated 5mA sensitivity GFCI is tripping on a food warming equipment, but we don't really know what the cause of this is. 30mA sensitivity GFCI is being considered, but not decided if it's okay to be used and if it would solve the situation. I really think somebody should do a thorough analysis of the situation. It's actually multiple sites where this is occurring. Does anybody know whose responsibility it is to investigate situations like this: food warming equipment manufacturer, GFCI breaker manufacturer, panel manufacturer or engineer of record or all of the mentioned? How can this be done in practical life? Thank you so much, and have a great day!

 

[winnie]

If the NEC requires a GFCI for this location, then only a 5 mA GFCI is acceptable. 30mA GFPE (ground fault protection of equipment) is not acceptable where the NEC mandates GFCI for protection of people.

If this issue is happening with multiple copies of the same equipment from the same manufacturer in different locations, that is a rather different story from one piece of equipment not working on one GFCI circuit but correctly working on a different circuit. Maybe you can describe the entire story; what is(are) the location(s), what is the equipment, what are the circuit ratings, what code calls for the GFCI and why does this code apply. What tests have been done and what situations lead to the system(s) working or tripping the GFCI. Dribbling out details like morsels for a cat won't get you good answers.

Who's responsibility this is depends on the details of the contracts involved. For example it might be a warranty issue on the equipment, or it might in an installing electrician error. If the equipment is performing to spec and has leakage that trips a GFCI, and code requires the GFCI, then it might be the customer responsibility to change the circumstances to avoid this conflict. While I can speculate I cannot begin to provide a definitive answer for 'who has to deal with this'.

-Jon

 

[GeorgeB]

the study producing findings vfib starts around 5 millionths of an amp

I think you mean thousandths; mA, not microAmp

 

[petersonra]

The 30 mA thing is a red herring if the code requires a GFCI, and that had yet to be determined, than a 5 mA device is what is needed.

 

[winnie]

Here is an article from 2014. Since this is an actively developing part of code, I am sure things have changed in the last 7 years. But it provides some useful history.

Now that industrial GFCIs are here, inspectors have a proactive option for shock protection

UL Class A ground-fault circuit interrupters (GFCI) began to be required in kitchens, bathrooms and outdoor outlets in the early ’70s, and have saved many lives over the years: According to...

iaeimagazine.org

-Jon

 

[curious101]

If the NEC requires a GFCI for this location, then only a 5 mA GFCI is acceptable. 30mA GFPE (ground fault protection of equipment) is not acceptable where the NEC mandates GFCI for protection of people.

If this issue is happening with multiple copies of the same equipment from the same manufacturer in different locations, that is a rather different story from one piece of equipment not working on one GFCI circuit but correctly working on a different circuit. Maybe you can describe the entire story; what is(are) the location(s), what is the equipment, what are the circuit ratings, what code calls for the GFCI and why does this code apply. What tests have been done and what situations lead to the system(s) working or tripping the GFCI. Dribbling out details like morsels for a cat won't get you good answers.

Who's responsibility this is depends on the details of the contracts involved. For example it might be a warranty issue on the equipment, or it might in an installing electrician error. If the equipment is performing to spec and has leakage that trips a GFCI, and code requires the GFCI, then it might be the customer responsibility to change the circumstances to avoid this conflict. While I can speculate I cannot begin to provide a definitive answer for 'who has to deal with this'.

-Jon

Thank you!

 

[curious101]

Here is an article from 2014. Since this is an actively developing part of code, I am sure things have changed in the last 7 years. But it provides some useful history.

Now that industrial GFCIs are here, inspectors have a proactive option for shock protection

UL Class A ground-fault circuit interrupters (GFCI) began to be required in kitchens, bathrooms and outdoor outlets in the early ’70s, and have saved many lives over the years: According to...

iaeimagazine.org

-Jon

Thank you!