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- Trinity County
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My friends, an agricultural couple, and I, trade technical and general help for milk, eggs, and produce. I am promoting safety changes to the following situation:
Their barn and animal area is served by 2 #6 conductors in plastic buried conduit, about 200 ft., hot and neutral, 120VAC, and protected by a 50A breaker. NO equipment grounding conductor. At the barn is a subfeed box with two 20A breakers. In that box, the neutral is bonded to everything - a grounding electrode, the box itself, the green wires and the white wires. Very uncool. Forgive them Lord, for they know not what they do. Then in the subfeed box, are two 20A circuits: 3-wire, with hot, neutral and equipment ground. As stated above, all the neutral, circuit grounding, and grounding electrode wires are connected to the same box-bonded 'neutral' bar, just like in a main panel. Most, if not all, of the outlets are receptacle GFI's.
Please comment on these thoughts of mine: (I had to draw a diagram to even get this far)
1. Shorts of hot to neutral on the 20A circuits will trip the breaker to safety.
2. Ground faults downstream of any GFI will trip it to safety. (like an extension cord to a water trough heater)
3. If a GFI did not trip, that ground fault of hot to equipment case would trip the breaker if >20 amps flow, or if <20A, the 120 volts on the grounding system will be largely drained by the #6 neutral wire back to the service and cause relative safety.
4. If the #6 neutral conductor anywhere between the main and subfeed boxes (a more complex route than I have indicated above) were to open, 120 volts would travel thru a connected load (their fence charger), move on the neutral wire to the error neutral-ground bond, and heat up the grounding system with a fair portion of 120 volts. No GFI would trip because there is no imbalance there plus there is far less than 120 volts potential at the GFI to power its tripping.
This #4 thought was the motivation to post here, I'm not really sure that the GFI's would stay on. What do you think they would do? If they did trip, connected loads would not be able to send 120 volts down the neutral wire to heat up the grounding system, and there would be safety and warning. The warning would be lights going out or being quite dim. I'm aware of the earth's relatively high resistance compared to copper wire.
5. And here's a last result I can think of to expect from my friends dreadful wiring as it presently stands: The sometimes 20+ amps of current (water trough heaters) on this barn feeder circuit, because of the resistance of the #6 neutral conductor, will develop about 2 volts to ground on the neutral at the subfeed box. Because of the error bond, this 2V will be put on the grounding system too, and the cow's water trough will have this 2V present by way of the heater's grounded case. I have read that cattle are extremely sensitive to stray currents that would not affect people. It was stated that 3/4 volt and 3mA is the safety limit, their resistance of mouth-to-4-wet- feet in manure and salty pee being 250 ohms. I'd be interested in advice on how to accurately measure this water trough for such current or voltage.
My friends, being country people, don't take quickly to newly-arrived city slickers like myself, nor to their high-fallutin' book learning, so convincing them to rework the entire feeder to include the equipment grounding conductor using money and time that they don't have is just not happening. Would folks please comment on the 2 following partial fixes I've thought of:
1. Better: An aerial #6 solid grounding conductor to the subfeed box, plus the obvious separation of neutral and ground there. I've become aware of the advisability of running conductors of the same circuit in close proximity, that the magnetic fields cancel and don't cause inductive reactance, which limits current and prevent breaker's tripping. This aerial ground would not honor this, and perhaps limit the current needed to trip the 50A breaker during a hot-to-equipment-ground fault. But I also have the idea that this problem is only a practical problem with metallic conduit, theirs being plastic. Comments?
2. Not As Good: Separate the 20A circuits' grounding systems from the neutral at that subfeeder box, and then have all outlets be GFI protected. It seems that all 3 problems I can think of: 1. hot to neutral shorts, 2. ground faults, 3. opening of the feeder neutral, 4. slight voltage on the far end of the feeder's neutral, -- would all have a safe or safer result --that is if GFI's were protecting all circuits and they always tripped properly. Actually, now that I have written this, and looked at my diagram, I see that a ground fault before the GFI's, like in the subfeed box, would be bad -- a heated up grounding system.
Anyway, I appreciate any insights and advice. And I could print out dire predictions you folks might have from your experiences and show them to my friends, who are actually the most safety-oriented people I know, to a fault, no pun intended, they just don't know electricity.
Best Wishes,
Tom
Their barn and animal area is served by 2 #6 conductors in plastic buried conduit, about 200 ft., hot and neutral, 120VAC, and protected by a 50A breaker. NO equipment grounding conductor. At the barn is a subfeed box with two 20A breakers. In that box, the neutral is bonded to everything - a grounding electrode, the box itself, the green wires and the white wires. Very uncool. Forgive them Lord, for they know not what they do. Then in the subfeed box, are two 20A circuits: 3-wire, with hot, neutral and equipment ground. As stated above, all the neutral, circuit grounding, and grounding electrode wires are connected to the same box-bonded 'neutral' bar, just like in a main panel. Most, if not all, of the outlets are receptacle GFI's.
Please comment on these thoughts of mine: (I had to draw a diagram to even get this far)
1. Shorts of hot to neutral on the 20A circuits will trip the breaker to safety.
2. Ground faults downstream of any GFI will trip it to safety. (like an extension cord to a water trough heater)
3. If a GFI did not trip, that ground fault of hot to equipment case would trip the breaker if >20 amps flow, or if <20A, the 120 volts on the grounding system will be largely drained by the #6 neutral wire back to the service and cause relative safety.
4. If the #6 neutral conductor anywhere between the main and subfeed boxes (a more complex route than I have indicated above) were to open, 120 volts would travel thru a connected load (their fence charger), move on the neutral wire to the error neutral-ground bond, and heat up the grounding system with a fair portion of 120 volts. No GFI would trip because there is no imbalance there plus there is far less than 120 volts potential at the GFI to power its tripping.
This #4 thought was the motivation to post here, I'm not really sure that the GFI's would stay on. What do you think they would do? If they did trip, connected loads would not be able to send 120 volts down the neutral wire to heat up the grounding system, and there would be safety and warning. The warning would be lights going out or being quite dim. I'm aware of the earth's relatively high resistance compared to copper wire.
5. And here's a last result I can think of to expect from my friends dreadful wiring as it presently stands: The sometimes 20+ amps of current (water trough heaters) on this barn feeder circuit, because of the resistance of the #6 neutral conductor, will develop about 2 volts to ground on the neutral at the subfeed box. Because of the error bond, this 2V will be put on the grounding system too, and the cow's water trough will have this 2V present by way of the heater's grounded case. I have read that cattle are extremely sensitive to stray currents that would not affect people. It was stated that 3/4 volt and 3mA is the safety limit, their resistance of mouth-to-4-wet- feet in manure and salty pee being 250 ohms. I'd be interested in advice on how to accurately measure this water trough for such current or voltage.
My friends, being country people, don't take quickly to newly-arrived city slickers like myself, nor to their high-fallutin' book learning, so convincing them to rework the entire feeder to include the equipment grounding conductor using money and time that they don't have is just not happening. Would folks please comment on the 2 following partial fixes I've thought of:
1. Better: An aerial #6 solid grounding conductor to the subfeed box, plus the obvious separation of neutral and ground there. I've become aware of the advisability of running conductors of the same circuit in close proximity, that the magnetic fields cancel and don't cause inductive reactance, which limits current and prevent breaker's tripping. This aerial ground would not honor this, and perhaps limit the current needed to trip the 50A breaker during a hot-to-equipment-ground fault. But I also have the idea that this problem is only a practical problem with metallic conduit, theirs being plastic. Comments?
2. Not As Good: Separate the 20A circuits' grounding systems from the neutral at that subfeeder box, and then have all outlets be GFI protected. It seems that all 3 problems I can think of: 1. hot to neutral shorts, 2. ground faults, 3. opening of the feeder neutral, 4. slight voltage on the far end of the feeder's neutral, -- would all have a safe or safer result --that is if GFI's were protecting all circuits and they always tripped properly. Actually, now that I have written this, and looked at my diagram, I see that a ground fault before the GFI's, like in the subfeed box, would be bad -- a heated up grounding system.
Anyway, I appreciate any insights and advice. And I could print out dire predictions you folks might have from your experiences and show them to my friends, who are actually the most safety-oriented people I know, to a fault, no pun intended, they just don't know electricity.
Best Wishes,
Tom
