Theoretical GFCI question, Fridge should never be on one?

[kwired]

I ran across a florescent fixture that would occasional trip a GFCI due to what I call Capacitor bleed off. About every fourth or fifth turn off, the GFCI would trip. I could see the same happening in an appliance that had capacitors connected to them.

If it is happening when you turn it off - it is probably inductive kickback. Inductive kickback it a high voltage transient that occurs when the magnetic field of a coil collapses after opening the circuit. This same principle is how ignition systems on internal combustion engines worked before electronic ignition systems came about.

 

[ggunn]

My fridge is not on the single GFCI circuit in my home. I wouldn't want it to be; the GFCI is sometimes tripped for days and I don't know it.

 

[ptonsparky]

My fridge is not on the single GFCI circuit in my home. I wouldn't want it to be; the GFCI is sometimes tripped for days and I don't know it.

Wellllll, plug your fridge into it and you will know. Unless of course you ignore the light in your fridge and it has been burned out for months now.

 

[Curious nerd]

Why would an inductive spike trip a GFCI? What does it look like to the GFCI circuitry? We know it can, of course, from the classic residential troubleshooting situation where there's a nuisance trip when someone turns the bathroom fan off. To keep things simple, let's start by assuming it's a circuit without a surge-protected power strip attached anywhere, so there's no MOV to create a ground fault if voltage gets too high.

 

[mbrooke]

This thread had been about GFCIs in general, not limited to dwelling unit kitchens.

I spend my time in commecial kitchens which require all 15 and 20 amp 125 volt receptacles to be GFCI. That results in many refrigeration units being supplied by a GFCI.

I don't mind new ways of looking at this You bring up a good point.


BTW, is it true that the real reason why GFCI are required in commercial kitchens is because the integrity of the grounding conductor could be jeopardized?

 

[mbrooke]

I ran across a florescent fixture that would occasional trip a GFCI due to what I call Capacitor bleed off. About every fourth or fifth turn off, the GFCI would trip. I could see the same happening in an appliance that had capacitors connected to them.

Believe it or not a lot of older magnetic rapid start ballasts have a capacitor that connects phase to ground in the ballast to help with starting. Ill have to find the schematic.

 

[GoldDigger]

Believe it or not a lot of older magnetic rapid start ballasts have a capacitor that connects phase to ground in the ballast to help with starting. Ill have to find the schematic.

That is probably done so that the shell of the fixture, which runs parallel to and close to the outside of the tube, is referenced to one of the two cathodes to help start the arc.

 

[glene77is]

[/SIZE]

A capacitor to ground can trip a GFCI; a capacitor across line and neutral should not.

Thank you Charlie B.
You and GAR have been the mainstays of engineering on this forum.

glene77is

 

[glene77is]

Even if I did not sure what I would be recording exactly. I have no idea what is really doing it.

mBrooke,

It is good that you are "requiring" an engineering answer to this issue.
All too often, well experienced electricians toss back quotes from NEC as "the" answer to an issue.

The real world is an Electrical Engineer's paradise,
and the NEC code is there to protect our lives and devices. (90.1(a))

The code is full of rules for safety not engineering explainations about reality.
Keep pushing for an engineer's explaination !!!

 

[ptonsparky]

mBrooke,

It is good that you are "requiring" an engineering answer to this issue.
All too often, well experienced electricians toss back quotes from NEC as "the" answer to an issue.

The real world is an Electrical Engineer's paradise,
and the NEC code is there to protect our lives and devices. (90.1(a))

The code is full of rules for safety not engineering explainations about reality.
Keep pushing for an engineer's explaination !!!

The engineer will explain "why" for the prosecution. The electrician will explain "why" for his own defense.

 

[iwire]

mBrooke,

It is good that you are "requiring" an engineering answer to this issue.
All too often, well experienced electricians toss back quotes from NEC as "the" answer to an issue.

The real world is an Electrical Engineer's paradise,
and the NEC code is there to protect our lives and devices. (90.1(a))

The code is full of rules for safety not engineering explainations about reality.
Keep pushing for an engineer's explaination !!!

To each their own type of thing. Many times I just don't care to know the engineering reason. It is not always helpful to me. I consider myself a practical kind of guy, I only want to know what will help me do my job. Also keep in mind this forum is primarily a code site, not an engineering one.


That said, hopefully someone can provide the info mbrooke seeks.

 

[mbrooke]

That is probably done so that the shell of the fixture, which runs parallel to and close to the outside of the tube, is referenced to one of the two cathodes to help start the arc.

I think that is the exact reason!

 

[ggunn]

Wellllll, plug your fridge into it and you will know. Unless of course you ignore the light in your fridge and it has been burned out for months now.

I could be away on vacation when the GFCI trips; sometimes a heavy rain will do it. No, thanks. I'll just leave the fridge plugged into a regular outlet if it's all the same to you.

 

[mbrooke]

mBrooke,

It is good that you are "requiring" an engineering answer to this issue.
All too often, well experienced electricians toss back quotes from NEC as "the" answer to an issue.

The real world is an Electrical Engineer's paradise,
and the NEC code is there to protect our lives and devices. (90.1(a))

The code is full of rules for safety not engineering explainations about reality.
Keep pushing for an engineer's explaination !!!

Thank you!

Once the actual reasoning behind rules are understood as well as the physics behind electricity is mastered only then does the real safety begin.

 

[iwire]

Thank you!

Once the actual reasoning behind rules are understood as well as the physics behind electricity is mastered only then does the real safety begin.

Ok teach me something, how will knowing the exact reason why an old appliance is tripping a GFCI add to safety?

My SOP is if an appliance keeps tripping a GFCI I recommend disposal or professional repair of it. To me that is as safe as it can get.

A recent example, about a year ago a supermarket had a brand new commercial grade vegetable juicer that from the first time it was plugged in would trip the GFCI when switched on. This would be immediate and consistent. If I moved the unit to another location without a GFCI it would run fine. They asked me to remove the GFCI protection, I refused to do so and recommended they return the unit. Later I found out they had someone else remove the GFCI.

Fast forward to another supermarket chain who bought the same brand unit and it also would not run on a GFCI. Here is the difference though, this chain did contact the vendor of the machine and the vendor said 'Yes, we know that is an issue, we will send out a board'. One of our other guys installed the new board and the tripping stopped.

My point is that knowing the precise cause was not important, knowing that the unit was the issue and not the GFCI was what was important to safety.


Now if you want to go more in depth for your own curiosity and education more power to you but please don't try say safety will be greater for it as far as the issue we are discussing.

 

[mbrooke]

Ok teach me something, how will knowing the exact reason why an old appliance is tripping a GFCI add to safety?

My SOP is if an appliance keeps tripping a GFCI I recommend disposal or professional repair of it. To me that is as safe as it can get.

A recent example, about a year ago a supermarket had a brand new commercial grade vegetable juicer that from the first time it was plugged in would trip the GFCI when switched on. This would be immediate and consistent. If I moved the unit to another location without a GFCI it would run fine. They asked me to remove the GFCI protection, I refused to do so and recommended they return the unit. Later I found out they had someone else remove the GFCI.

Fast forward to another supermarket chain who bought the same brand unit and it also would not run on a GFCI. Here is the difference though, this chain did contact the vendor of the machine and the vendor said 'Yes, we know that is an issue, we will send out a board'. One of our other guys installed the new board and the tripping stopped.

My point is that knowing the precise cause was not important, knowing that the unit was the issue and not the GFCI was what was important to safety.


Now if you want to go more in depth for your own curiosity and education more power to you but please don't try say safety will be greater for it as far as the issue we are discussing.

But you did find the precise cause in that one by doing the right thing. Sitting down analyzing while probing for info. The maker of the machine gave the reasoning behind it.

In no way am I implying that the GFCI is 100% at fault. I don't know whos at fault, that's why I am asking to understand. If I know what the root cause is I know how to handle it. Say the root cause is indeed a ground fault in the unit. I can then say "this refrigerator needs to be repaired or replaced" Say the root cause is older GFCIs not responding well to transients. I can then say "this GFCI should be replaced with a newer version"


Ill word it like this. And yes both us know the code doesn't allow the example I will state. Take a ground rod. For years I saw electricians driving them in hopes they would trip a breaker during a fault on light posts, IGs, kiosks, ect. After all electricity seeks the easiest path to ground? Right? However, what they didn't know was ground rod resistance was never 0.2 ohms. Often it wasn't even 25 ohms. And electricity takes all paths back to the source. It is this piece of knowledge that allows us to understand not only why the code doesn't allow for ground rods to be an effective ground fault current path but as to why its dangerous. I take it you imply knowledge of the code is sufficient enough... and that's where those who poorly grasp the physics may hide behind, but ultimately understanding why code says what it does makes for the better electrician. Simply memorizing the code is not enough. Same with taking courses in school like math, you don't just memorize, you know the reasoning behind it.


And ultimately, those who wright the code or at least vote on it need to know the EXACT science behind it. If they don't its a gamble.

 

[kwired]

Ok teach me something, how will knowing the exact reason why an old appliance is tripping a GFCI add to safety?

My SOP is if an appliance keeps tripping a GFCI I recommend disposal or professional repair of it. To me that is as safe as it can get.

A recent example, about a year ago a supermarket had a brand new commercial grade vegetable juicer that from the first time it was plugged in would trip the GFCI when switched on. This would be immediate and consistent. If I moved the unit to another location without a GFCI it would run fine. They asked me to remove the GFCI protection, I refused to do so and recommended they return the unit. Later I found out they had someone else remove the GFCI.

Fast forward to another supermarket chain who bought the same brand unit and it also would not run on a GFCI. Here is the difference though, this chain did contact the vendor of the machine and the vendor said 'Yes, we know that is an issue, we will send out a board'. One of our other guys installed the new board and the tripping stopped.

My point is that knowing the precise cause was not important, knowing that the unit was the issue and not the GFCI was what was important to safety.


Now if you want to go more in depth for your own curiosity and education more power to you but please don't try say safety will be greater for it as far as the issue we are discussing.

One needs to understand to some extent how a GFCI works to solve some of these issues though. For the single appliance that trips the GFCI you can narrow it down to an issue with that appliance and not know much more about GFCI's I guess, but like a recent call I had with GFCI tripping in a dwelling unit garage - they had three freezers as well as outdoor receptacle with a pond pump plugged into it all protected by a single GFCI. You need to know what to look for and narrow down which item is the one causing trouble. Once you narrow it down you can either choose to have someone *more qualified* look at the offending freezer, look into it yourself or tell owner to replace it.

*I use the term more qualified rather loosely here as I have told people there was something wrong with a refrigerator before yet an alleged refrigerator repair man tries to say there is nothing wrong with it an I had to dig into it a little myself and prove to him what was wrong with it. They don't generally know what a GFCI is for or how it works and are likely to recommend removing the GFCI instead of finding out why it is tripping from my experiences.

I guess this is not a direct answer to your first question of how does it add to safety though. Consumers however don't really like calling an electrician because a device is tripping and all he can tell them is they need to replace that $2000 refrigerator, and charge them $100 or more just to tell them that, they want a better deal and will next call the appliance repair guy who will remove the GFCI and then everything appears to work (though safety has been compromised) and they only charge $50 and the consumer gives the electrician a bad name after this incident.