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#81737 09/16/02 12:07 AM
Joined: Sep 2002
Posts: 111
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Sean WB Offline OP
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If you are feeding a subpanel(50-125 amp) from a main service panel(200 amp) , do you need to have 4 wires to the sub panel? The grounding and grounded conductors are terminated at same place (theoretically) in the sub panel. therefore you would need to use the supplied "bonding" screw (green).right?
Please clear this up for me, as I have heard /seen many different methods on this. I have installed may subpanels with 3 wires and I REALLY want to know if I am doing this wrong.


I did not get as think so badly as you shocked I did.
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Joined: Nov 2000
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If you are feeding a subpanel(50-125 amp) from a main service panel(200 amp) , do you need to have 4 wires to the sub panel?

Yes

The grounding and grounded conductors are terminated at same place (theoretically) in the sub panel...

No. They are in the disconnect or main load center, whichever is first in line from the meterbase.

therefore you would need to use the supplied "bonding" screw (green).right?

No, not it the sub-panel, but in the first panel in line from the meterbase.

Note: You will need to aquire an equipment ground bus bar for your sub-panel.

Also note: You also must size the sub-feeder conductors according to Table 310.16, for 310.15(B)(6) is for "...conductors that serve as the main power feeder to a dwelling..."

[This message has been edited by sparky66wv (edited 09-16-2002).]


-Virgil
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Sean WB Offline OP
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so in the SP , you would need a ground bar? and it must not be elctrically continuous to the neutral bar?


I did not get as think so badly as you shocked I did.
Joined: Nov 2000
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It definitely is not bonded in any way to the neutral bar (except via the EGC subfeeder back to the main disco or panel, then through the bond to the grounded conductor then back to the sub panel).

No bond screw or bonding jumper in the sub-panel at all. To do otherwise would create a parallel path for the neutral current.


-Virgil
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Sean WB Offline OP
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ok , Thank you for the plain english. So, it is continuous , but at the main panel? ground/neutral bar at sub are seperate, but bonded at main?


I did not get as think so badly as you shocked I did.
Joined: Nov 2000
Posts: 2,236
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Yep, you got it!

[Linked Image]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
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Joined: Sep 2002
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Sean WB Offline OP
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Thank You very much you may be able to help a little situation I have here on this post https://www.electrical-contractor.net/ubb/Forum7/HTML/000185.html


I did not get as think so badly as you shocked I did.
Joined: Aug 2002
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Junior Member
definately a neutral problem, i've seen this scenario many times.

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Sean WB Offline OP
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A neutral from main to sub? or in the building? Im going out there right now.


I did not get as think so badly as you shocked I did.
Joined: Sep 2002
Posts: 111
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Sean WB Offline OP
Member
turns out they kernied the neutral at service drop for the barn.there are three weather heads on the pole and it looks like a birds nest up there.I continued to have same problems today, so I am going to run a new underground service tomorrow for the barn and discontinue the overhead service.
Its either an insulation breakdown in the ungrounded conductors feeding the barn (which are 30+ years old) or I have lost a neutral at the bird nest.
Either way, this was definitely a learning experience.
I need to invest in a megger, whats a good name to get ??


I did not get as think so badly as you shocked I did.
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