GFCIs and EGCs

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Curious nerd said:
Here's why you're right. The current flow between hot and neutral in the immersed appliance will take all possible paths. Every drop of chlorinated tap water in the pool is part of a (poorly) conductive path. So is any human in the pool. Even though most of the current will flow inside the appliance not all of it will.
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I agree, while most of it will be on the inside, it takes very little current in water to case harm.
 
mbrooke said:
Ok I will sacrifice myself for this one :p I am in the pool, its a small inflatable rubber insulated pool and a 2 wire hair dryer gets dropped in. GFCI outlet.


My theory is I will still get a shock or be killed without taking the hair dryer apart. Why? Water is conductive to a degree. The water will conduct power line to neutral forming a voltage gradient across the water. I could be in that path.
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And I still believe your theory is mistaken.

But let's say you are correct, how will adding a an EGC to the appliance and removing the GFCI help. Let's keep in mind that was your stated goal in this thread.








It proves a point electricity can travel across water.
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That was never in question. But the scenario has a hot object in one location with grounded locations all around it putting a person in between that hot object and those grounded surfaces will put them in the current path.

On the other hand when the current path is just between two points an inch apart it will be tough to get a person close enough to those to points to be in the current path. The gradients would be too low.






It is required to be part of the grid yes, but I am talking about cases where it was no. And FWIW an equal potential grid not only helps a GFCI operate but may reduce the voltage gradient.
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What the heck is your position?

You started out in this thread asking about adding EGCs and reducing GFCIs.

So now we need to add EGCs for scenarios where things that are already required to be grounded but aren't and that will help operate the GFCI that you want to eliminate. :?


By all means please put in a proposal and save us all. :p
 
Curious nerd said:
Here's why you're right. The current flow between hot and neutral in the immersed appliance will take all possible paths. Every drop of chlorinated tap water in the pool is part of a (poorly) conductive path. So is any human in the pool. Even though most of the current will flow inside the appliance not all of it will.
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The influence of those paths will drop very rapidly as the distance increases.
 
iwire said:
That was never in question. But the scenario has a hot object in one location with grounded locations all around it putting a person in between that hot object and those grounded surfaces will put them in the current path.

On the other hand when the current path is just between two points an inch apart it will be tough to get a person close enough to those to points to be in the current path. The gradients would be too low.
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So why both with the equipotential planes in art 547 (agriculture) , and 680 (pools) if the entire jist of a ground is proximity Iwire?

~RJ~
 
romex jockey said:
So why both with the equipotential planes in art 547 (agriculture) , and 680 (pools) if the entire jist of a ground is proximity Iwire?

~RJ~
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In the totally theoretical experiment everyone is using, the water in the kiddie pool is effectively isolated from ground by the rubber membrane surrounding it. In real life both the wet, mucky floor of an agricultural building and the walls/apron of a pool are very much in contact with earth. Add to that the fact that utilities drop ground rods bonded to their neutral every so many poles and there's the possibility that someone else's neutral current will take a short cut through the pool or barn floor to get back to the POCO causing an electrocution hazard.

Back to the theoretical kiddie pool example. Once you're in the pool with the submerged hair dryer, there is very little danger of shock to you. It's when you step in or out and make contact with the moist, grounded grass with the hair dryer on in the water that things get dangerous as at that point you are crossing between two different equipotential planes and most likely death will ensue. Bonding the pool water to the earth around it would greatly lessen that danger.
 
PetrosA said:
Back to the theoretical kiddie pool example. Once you're in the pool with the submerged hair dryer, there is very little danger of shock to you. It's when you step in or out and make contact with the moist, grounded grass with the hair dryer on in the water that things get dangerous as at that point you are crossing between two different equipotential planes and most likely death will ensue. Bonding the pool water to the earth around it would greatly lessen that danger.
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:thumbsup:
How utterly rational and "real world". :D Voltage "gradient" is the red herring. The pool water is energized.
 
al hildenbrand said:
:thumbsup:
How utterly rational and "real world". :D Voltage "gradient" is the red herring. The pool water is energized.
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It is energized by both poles of the supply that has been introduced into the water though so there is also a gradient between those two points. So to energize the entire pool one conductor would need to have more influence in some way then the other.

If the appliance is dropped on one end of the pool and you are standing outside on opposite end on a grounded surface and touch the water are you exposed to more of the ungrounded conductor or more of the grounded conductor? Seems to me it could vary depending on other conditions.

I'd have to guess the ungrounded conductor maybe still energizes the entire pool to some extent because of capacitive effects between the water, the pool shell, and the earth it is sitting on, and that there will be some though very low level current flowing through this capacitor, this also will mean that when you touch the water you do not get hit with full 120 volts but some lesser level because of voltage drop across that "capacitor".
 
kwired said:
If the appliance is dropped on one end of the pool and you are standing outside on opposite end on a grounded surface and touch the water are you exposed to more of the ungrounded conductor or more of the grounded conductor? Seems to me it could vary depending on other conditions.
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What PetrosA's post crystalized in my mind was that the person entering the Kiddie Pool (in his example) is straddling the solid connection to earth and the water. In that state, the person's water immersed foot and calf is the Grounding Electrode that now establishes a clear parallel path through some amount of resistance. The pool water resistance is going to vary wildly, and, no doubt, in situations will be lethally low. The current path in the person is leg to leg through the torso. . . not a leg to arm, but really bad, none the less.

It is my opinion that the bare foot on the damp earth at the edge of a Kiddie Pool is a dominant effect over shadowing the more subtle static, theoretical, prior to Earth-Foot-Legs-Foot-Water connection Voltage Gradient IN the pool water.

Now, whether the pool that is not grounded as part of its construction, is a Kiddie Pool or is something much larger (and ungrounded), the real world says that people first enter the pool, prior to being in the water. The entry point is more likely, in the real world, to bridge grounded surfaces to the "theoretically ungrounded" body of water inside the pool. A person can't easily be immersed in the water without first entering the water. Any ungrounded pool small enough to not be "dive-able" is stepped into - a real world hazard. And a hazard that a Class A GFCI is designed to address, EGC or no.
 
al hildenbrand said:
What PetrosA's post crystalized in my mind was that the person entering the Kiddie Pool (in his example) is straddling the solid connection to earth and the water. In that state, the person's water immersed foot and calf is the Grounding Electrode that now establishes a clear parallel path through some amount of resistance. The pool water resistance is going to vary wildly, and, no doubt, in situations will be lethally low. The current path in the person is leg to leg through the torso. . . not a leg to arm, but really bad, none the less.

It is my opinion that the bare foot on the damp earth at the edge of a Kiddie Pool is a dominant effect over shadowing the more subtle static, theoretical, prior to Earth-Foot-Legs-Foot-Water connection Voltage Gradient IN the pool water.

Now, whether the pool that is not grounded as part of its construction, is a Kiddie Pool or is something much larger (and ungrounded), the real world says that people first enter the pool, prior to being in the water. The entry point is more likely, in the real world, to bridge grounded surfaces to the "theoretically ungrounded" body of water inside the pool. A person can't easily be immersed in the water without first entering the water. Any ungrounded pool small enough to not be "dive-able" is stepped into - a real world hazard. And a hazard that a Class A GFCI is designed to address, EGC or no.
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No disagreement here. As I said other conditions make a difference to what happens. If you are bare footed and step in as you described you are likely subjected to a higher voltage then if you are standing outside with reasonably non conductive shoes and touch the water with a bare hand, and definitely any current that flows passes through different body parts in each situation.
 
mbrooke said:
I disagree. A GFCI is hit or miss when the appliance is 2 prong. If I drop a 2 prong appliance plugged into a GFCI into a non grounded tub or pool the GFCI would not trip. It would produce voltage gradients, often enough to harm, but the GFCI would sense no imbalance. So in terms if providing safety around water, GFCI are somewhat misleading.
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mbrooke said:
GFCI without an EGC has limitations where no ground path exists such as an insulated tub, pool or sink.
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mbrooke said:
However, inflatable pools are another story. Who bonds those?
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mbrooke said:
I still am having trouble understanding if absent EGC are what really got GFCIs into the code.
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Given that the first introduction of the GFI requirement was in the 1971 NEC for pools and exterior outlets, just a scant 9 years after 1962 NEC required EGCs through out the Premises Wiring (System), ungrounded branch circuits abounded. . . I think, that is, in my opinion, the Personnel Safety of the GFCI with respect to the "real world" is "what really got GFCIs into the Code."
 
al hildenbrand said:
Given that the first introduction of the GFI requirement was in the 1971 NEC for pools and exterior outlets, just a scant 9 years after 1962 NEC required EGCs through out the Premises Wiring (System), ungrounded branch circuits abounded. . . I think, that is, in my opinion, the Personnel Safety of the GFCI with respect to the "real world" is "what really got GFCIs into the Code."
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I have to agree.

Adding equipment grounding conductor requirements helps prevent energizing equipment enclosures as it gives us a low impedance path for fault current to flow. Class A GFCI is intended to protect people and senses fault current even if it is flowing into a high enough impedance that a standard overcurrent device wouldn't respond. Other ground fault protection devices do the same thing but at higher levels and have different reasons for their application.
 
romex jockey said:
I could be wrong , but i'm thinking the average Brit cardiac muscle structure isn't 45ma more resistive than American counterparts Mbrooke.

Then again i'm clueless as to the attributes of marmite , spotted dick and jellied eel....

~RJ~
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I just think our values are more conservative. I will have to do more research on this, intriguing none the less.
 
iwire said:
And I still believe your theory is mistaken.

But let's say you are correct, how will adding a an EGC to the appliance and removing the GFCI help. Let's keep in mind that was your stated goal in this thread.
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In areas where complete immersion is not possible the only thing a GFCI guards against is a missing EGC. Therefore if EGC were present on all appliances GFCI would not be needed.

If your claim is correct that an appliance immersed in water is not hazard producing negligible voltage gradient than that would mean an EGC in these places can safely take over a GFCI.


While not a citation, Basically my theory in a few sentences:


http://www.diychatroom.com/f18/common-gfci-malfunction-204528/index3/#post1384716




That was never in question. But the scenario has a hot object in one location with grounded locations all around it putting a person in between that hot object and those grounded surfaces will put them in the current path.
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You made the claim that an appliance dropped in water will not be dangerous unless a person got in between hot and neutral.



On the other hand when the current path is just between two points an inch apart it will be tough to get a person close enough to those to points to be in the current path. The gradients would be too low.
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Current flow is the strongest between the 2 object at opposite potentials, but current will also travel around them.






What the heck is your position?

You started out in this thread asking about adding EGCs and reducing GFCIs.
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Because I am trying to figure out if it was the lack of EGCs and the dangers from that which put GFCIs into the code. Somehow I have a feeling the only role water played was lower the skin resistance increasing the danger of an live frame.






So now we need to add EGCs for scenarios where things that are already required to be grounded but aren't and that will help operate the GFCI that you want to eliminate. :?
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Well I will ask you this, why is it that in 2015 I can still buy 2 prong toaster oven, waffle makers ect that are not double insulated?






By all means please put in a proposal and save us all. :p
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I am working on it :angel:
 
al hildenbrand said:
Given that the first introduction of the GFI requirement was in the 1971 NEC for pools and exterior outlets, just a scant 9 years after 1962 NEC required EGCs through out the Premises Wiring (System), ungrounded branch circuits abounded. . . I think, that is, in my opinion, the Personnel Safety of the GFCI with respect to the "real world" is "what really got GFCIs into the Code."
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But there is one flaw. This requirement did not control what was plugged into outlets. In the 70s and 80s the market was riddled with 2 prong metal case tools and appliances. Even to this day I can purchase 2 prong none double insulated appliances.
 
al hildenbrand said:
Given that the first introduction of the GFI requirement was in the 1971 NEC for pools and exterior outlets, just a scant 9 years after 1962 NEC required EGCs through out the Premises Wiring (System), ungrounded branch circuits abounded. . . I think, that is, in my opinion, the Personnel Safety of the GFCI with respect to the "real world" is "what really got GFCIs into the Code."
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mbrooke said:
But there is one flaw. This requirement did not control what was plugged into outlets. In the 70s and 80s the market was riddled with 2 prong metal case tools and appliances. Even to this day I can purchase 2 prong none double insulated appliaces.
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Try to explain that "flaw" to the countless people who've had a GFCI shut off the power to the two wire, or two wire plus EGC, apparatus that has faulted to their body, and get them to believe their experience (that likely saved their life) was a result of flawed policy and was bad.
 
mbrooke said:
In areas where complete immersion is not possible the only thing a GFCI guards against is a missing EGC. Therefore if EGC were present on all appliances GFCI would not be needed.
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I can think of an exception, a memorable one. I picked up the middle of an outdoor extension cord and got shocked. No visible problem with the insulation. Since I was able to let go, it must have been a fairly high resistance. Whatever was wrong wasn't leaking enough current to trip an OCPD. Oh, wait, I see your point. If that high-resistance fault had been to the metal skin of an appliance, and if there had been an EGC, the appliance case would have been close to the same potential as the dirt I was standing in.
 
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