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Ground/neutral bonding (again)


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I have been seeing this quite a bit lately and want to know if there is any type of exception that I am not aware of.

There is a main panel box (service disconnect) at the power pole outside of the home. Ground wire from a driven ground rod runs into the panel and the grounds and neutrals are bonded.

4 wires (2 hots, ground and neutral) run in conduit underground from the panel at the pole, into the home and feed the distribution panel box in the garage. Here, the ground and neutrals are again bonded. This I know is incorrect. However, is it allowed if there is another main disconnect switch installed in the garage panel box or is the first disconnect switch at the pole the only one that counts.

I just can't understand why if it is incorrect, why I am seeing it so often; especially in the municipalities.

BTW: I have searched numerous threads on this and I suppose I just haven't quite found an answer for my question

Thanks

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Hi Jesse,

The grounded conductors (neutrals) and equipment grounding conductors (grounds) are not supposed to be bonded after the service disconnect. When the main disconnect is outside, the service grounding conductor connects to the service grounding electrode there and the neutrals must be isolated from the enclosure on their own bar in the sub[/b] panel that's inside. The only bonding screw or strap you should see is the one connecting the ground bus, where all of the EGC's are, to the enclosure. But then again, you already knew that - you were just seeking confirmation.

I see it all the time too; believe it or not, there are "licensed" electricians out there that have never learned these rules and when it's explained to them they look just like a deer caught in the beam of one's headlights.

ONE TEAM - ONE FIGHT!!!

Mike

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Jesse,

If it makes you feel better, I second guess myself on this all the time.

Just 3 days ago, I found a panel wired in the 80's that was originally the service equipment. An addition was added, so a meter main was installed on the exterior. Did they re- wire the panel inside the home----nope. (electrician did the work I am told-- it's on the same home as my post regarding all of the roof issues).

Nothing like going with the lowest bidders out there.

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I have been seeing this quite a bit lately and want to know if there is any type of exception that I am not aware of.

There is a main panel box (service disconnect) at the power pole outside of the home. Ground wire from a driven ground rod runs into the panel and the grounds and neutrals are bonded.

4 wires (2 hots, ground and neutral) run in conduit underground from the panel at the pole, into the home and feed the distribution panel box in the garage. Here, the ground and neutrals are again bonded. This I know is incorrect. However, is it allowed if there is another main disconnect switch installed in the garage panel box or is the first disconnect switch at the pole the only one that counts.

I just can't understand why if it is incorrect, why I am seeing it so often; especially in the municipalities.

BTW: I have searched numerous threads on this and I suppose I just haven't quite found an answer for my question

Thanks

Before the 2008 NEC, there was an option in 250.32(B) that allowed you to omit the equipment grounding conductor when feeding one structure from another. This option was only allowed if there were no continuous metallic paths connecting the bonding systems in each structure (as Richard described above). In this case, the second structure's grounding and neutral wires would all be bonded at its disconnect where there would also be a grounding electrode conductor connected to the earth.

However, even then, if the feeder contained four wires, then you had to keep the grounding and bonding wires separate all the way back to the first structure's disconnect.

In the 2008 NEC, the option is gone. All new feeders are supposed to include an equipment grounding conductor. There's still an exception for existing buildings though. So if the building pre-dates the 2008 NEC and you want to upgrade a panel, you can still use the old feeder without an equipment grounding conductor.

I know it's confusing.

- Jim Katen, Oregon

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Bonding the neutrals and grounds in both panels causes the equipment grounding conductor to become a parallel conductor for the neutral. Normal every-day current will flow between the two panels on both wires. Depending on what else is connected to the grounding system it can also cause current to flow other places where it should not (such as water pipes, CATV wires, gas pipes etc). Attached picture shows over 2 amps flowing through the CATV system when the grounding system was re-bonded improperly.

Click to Enlarge
200927121110_2%20Amps%20On%20CATV%20Ground.jpg

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