Grounding

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I had a situation where I was inspecting a disconnect switch on a single phase system. The electrician pulled in 4 wires. Two hot a neutral and a ground. He terminated everything correctly but ran the ground to a lug on the enclosure instead of landing it on the Neutral/grounding buss. Is this correct? If it is Why? He said that if you land the ground on the Neutral/ground buss and there is a short in the enclosure then it could back feed through the Neutral. could someone enlighted me please.
 

bdarnell

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Indianapolis, IN
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Retired Engineer
Re: Grounding

Jim Hughes71 said:
Is this correct? If it is Why?

NEC Article 250 gives specific directives on where the grounded conductor can be connected to the grounding electrode system. Basically they are all at or near service entrance only. The grounded conductor can not be connected to an equipment grounding conductor anywhere on the load side of the service disconnecting means.
 

pierre

Senior Member
" The grounded conductor can not be connected to an equipment grounding conductor anywhere on the load side of the service disconnecting means."


Almost true ;), there are some permitted connections for that situation.
 
Grounding

Thanks for the replies. What about the issue of if you land the ground wire to a Neutral/Ground buss and there is a short to the enclosure it could back feed through the Neutral? Is this correct?
 

roger

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Actually the Neutral connection at the source is what ultimately clears the fault, so the "Grounded Conductor" (Neutral) and the "Equipment Grounding Conductors" must be connected at the service point.

Once a down stream device, switch, panel, or what have you comes into the scene things change, the "Grounded Conductors" and the "Equipment Grounding Conductors" must remain separated downstream of the service equipment to prevent current division (paralleling) on these two conductors.

The EGC should never carry current except in a fault event, but when it does it must carry it to the Neutrals source.

Roger
 

Mike03a3

Senior Member
Location
Virginia
roger said:
Actually the Neutral connection at the source is what ultimately clears the fault, so the "Grounded Conductor" (Neutral) and the "Equipment Grounding Conductors" must be connected at the service point.

Once a down stream device, switch, panel, or what have you comes into the scene things change, the "Grounded Conductors" and the "Equipment Grounding Conductors" must remain separated downstream of the service equipment to prevent current division (paralleling) on these two conductors.

The EGC should never carry current except in a fault event, but when it does it must carry it to the Neutrals source.

Roger

That being the case, shouldn't the neutral and grounding busses be separated rather than a "Neutral/grounding buss" as described?
 

roger

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Yes, when we are talking about feeders, (with the exception of a feeder under 250.32(B)(2)) but fault current "back feeding" through a Neutral is not the reason for the seperation.

Roger
 
Correct. Neutral and ground should only be bonded at first means of disconnect. Bonding to the enclosure you described is correct unless there is a egc in the enclosure specifically designed for that purpose.
 
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