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Old 10-24-2011, 12:08 AM   #16
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if it was code i am sure it would work. more curious about what are the potential hazards. why did they change it back? an example would help me understand more clearly.

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Old 10-24-2011, 12:20 AM   #17
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if it was code i am sure it would work. more curious about what are the potential hazards. why did they change it back? an example would help me understand more clearly.
That I couldn't tell you. Only thing i can think is trying to keep only one path for your neutrals current to go. Mainly for electrolysis. I could be completely off base though.
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Old 10-24-2011, 12:38 AM   #18
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Thanks for your patience, help and input. I am just trying to wrap my head around this so i don't sound like a knuckel-head when I call the clown who flubbed this. Also just general curiosity how electricity works. I appreciate the knowledge.
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Old 10-24-2011, 12:49 AM   #19
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if it was code i am sure it would work. more curious about what are the potential hazards. why did they change it back? an example would help me understand more clearly.
The 4th wire or "ground" wire is there for the same reason you have a 3rd prong or "ground" prong on an outlet, and that has a separate ground wire. Same exact thing!

The problem is that it is fairly common for main electrical wires to "come loose" and no longer make a connection...

It also happens that ground wires outside get run over by the lawn mower and cut. In one case I saw, a car scraped against the side of a building and broke the ground wire. Whatever, ground wires get broken. These tend to not get fixed and may be that way for years.

So if you have the neutral connected to the ground in a subpanel, and the neutral connection comes loose, and the ground is broken...

Then feeding off that panel are 3 prong outlets.... An appliance with a grounded metal case is connected to the 3rd ground prong... There is no neutral, there is no ground, the ground connection in the panel now becomes a "HOT", and so does the metal case on that appliance (via the ground connection)!

Basically turned on appliances connect the hot to the "floating" neutral, then that goes to the "floating" ground via the bonding screw in the panel or shared neutral/ground bar, then back out to all ground connections at outlets.

Everything grounded would then become hot. This includes metal cases on refrigerator, range, washing machine, and other appliances. Possibly metal water pipes in house. Maybe air conditioning ducts.

BETTER is to have a separate ground all the way back to the main panel. It is isolated from the neutral at the subpanel. Safer.
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Old 10-24-2011, 01:00 AM   #20
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P.S. Different states have different [year] NEC rules. Some states ammend the rules. So see which NEC you are on the following map, then say what state here and what year NEC that is. Then maybe someone will know what rules there were if older or for your particular state...
http://www.nema.org/stds/fieldreps/N.../implement.cfm
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Old 10-24-2011, 01:03 AM   #21
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Wow! Great explanation. So what is the purpose of ground wire that is connected to the grounding rod outside of a sub panel that only has 3 feed wires.
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Old 10-24-2011, 01:24 AM   #22
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Originally Posted by Billy_Bob View Post
The 4th wire or "ground" wire is there for the same reason you have a 3rd prong or "ground" prong on an outlet, and that has a separate ground wire. Same exact thing!

The problem is that it is fairly common for main electrical wires to "come loose" and no longer make a connection...

It also happens that ground wires outside get run over by the lawn mower and cut. In one case I saw, a car scraped against the side of a building and broke the ground wire. Whatever, ground wires get broken. These tend to not get fixed and may be that way for years.

So if you have the neutral connected to the ground in a subpanel, and the neutral connection comes loose, and the ground is broken...

Then feeding off that panel are 3 prong outlets.... An appliance with a grounded metal case is connected to the 3rd ground prong... There is no neutral, there is no ground, the ground connection in the panel now becomes a "HOT", and so does the metal case on that appliance (via the ground connection)!

Basically turned on appliances connect the hot to the "floating" neutral, then that goes to the "floating" ground via the bonding screw in the panel or shared neutral/ground bar, then back out to all ground connections at outlets.

Everything grounded would then become hot. This includes metal cases on refrigerator, range, washing machine, and other appliances. Possibly metal water pipes in house. Maybe air conditioning ducts.

BETTER is to have a separate ground all the way back to the main panel. It is isolated from the neutral at the subpanel. Safer.
I could be wrong but I think your logic is a little off. The ground and neutral are bonded at the services diconnect either way. I could be wrong because like I said, I'm not positive. I really think it has to do with only having one path for the neutral. For example if you had a 3 wire sub panel and you had a metal water pipe bonded at each side, your neutrals current could go through the water pipe instead of the feeders neutral conductor. This wouldn't pose much threat to personnel but it may rot out the water pipe

That's my theory anyway. Maybe speedy petey knows for sure



Ground rods are for lightning protection
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Old 10-24-2011, 08:11 AM   #23
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The purpose of keeping ground and neutral separated after the main disconnect is to eliminate objectionable currents on the grounding/bonding system. Grounding/bonding conductors are not to have current flowing on them under normal circumstances, only under fault conditions. Fault currents are not considered objectionable currents. As we know, a neutral is a current carrying conductor.

In lay-mans terms, it keeps metallic things from being energized…duct work, plumbing, siding, gutters, etc. Since metallic items are bonded to the grounding system, they should not be carrying current under normal conditions. Any connection of the grounding/bonding system to a neutral conductor after the main disconnect will cause the grounding system to be current carrying, and thus a potential shock hazard.

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