Generator bonding

[Jcabrera415]

I have a 3phase generator located outside a building. I am suppling loads inside the building and the building has equiptment supplied by its own in house system. How do I bond the generator and the building? Im looking @ article 250.30 but im a little confused. My generator has a buss where the Egc and the grounded conductor meet.* Does it matter if I use my egc or my grounded conductor? Also The generator is a vehicle monted generator "grounded to the chassis of the generator.

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[ActionDave]

Welcome to the forum.

I have a 3phase generator located outside a building. I am suppling loads inside the building and the building has equiptment supplied by its own in house system.

What do you mean by "in house system"? Is there utility power?

How do I bond the generator and the building? Im looking @ article 250.30 but im a little confused. My generator has a buss where the Egc and the grounded conductor meet.* Does it matter if I use my egc or my grounded conductor? Also The generator is a vehicle monted generator "grounded to the chassis of the generator.

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You need a neutral conductor and an EGC. There are some rare instances where they are combined.

 

[GoldDigger]

I have a 3phase generator located outside a building. I am suppling loads inside the building and the building has equiptment supplied by its own in house system. How do I bond the generator and the building? Im looking @ article 250.30 but im a little confused. My generator has a buss where the Egc and the grounded conductor meet.* Does it matter if I use my egc or my grounded conductor? Also The generator is a vehicle monted generator "grounded to the chassis of the generator.

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If you do not switch the neutral at the transfer switch, then there must be a ground to neutral bond on the main supply system and you will need to disconnect the bond at the generator. Even if the neutral from the generator is not used you should run separate neutral and EGC wires from the generator to the ATS. If you do not choose to do so, and the installation is otherwise code compliant, then the only interconnecting wire you should run would be the EGC and you must then keep the bond at the generator.

 

[Jcabrera415]

I dont have a transfer switch, its two seperate systems for different continus loads im suppling power with the generator not for backup reasons. They just happen to be under the same building and want to bond them together so there is no potential between the buildings system & the generator....

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[Jcabrera415]

Welcome to the forum.

What do you mean by "in house system"? Is there utility power?


You need a neutral conductor and an EGC. There are some rare instances where they are combined.

Thanks. They have a service latteral feeding the building and since I am running the generator And the building power @ the same time I want to bond the generator and the building in order to eliminate voltage from lets say a metal enclosure conected to the building and not the generator.

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[GoldDigger]

Thanks. They have a service latteral feeding the building and since I am running the generator And the building power @ the same time I want to bond the generator and the building in order to eliminate voltage from lets say a metal enclosure conected to the building and not the generator.

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That clarifies things considerably.
The service neutral needs to be connected to the building Ground Electrode System (GES). That is typically done at the service disconnect, the meter or the weatherhead if it is an overhead service.
The generator protective ground must also be connected to the same GES.
I think that you have the option of bonding the generator neutral to its protective ground at the generator or at the building disconnect for the generator, but not at both. You should then run both a neutral and an EGC between generator and building.
There is a special case which allows the service grounded conductor to also serve as the EGC back to the POCO equipment, but there is, AFAIK, no corresponding exception for a non-POCO generator.

If the bond is at the generator and you are not using the neutral you do not have to bring the neutral separately to the disconnect for the generator at the building.

 

[Jcabrera415]

That clarifies things considerably.
The service neutral needs to be connected to the building Ground Electrode System (GES). That is typically done at the service disconnect, the meter or the weatherhead if it is an overhead service.
The generator protective ground must also be connected to the same GES.
I think that you have the option of bonding the generator neutral to its protective ground at the generator or at the building disconnect for the generator, but not at both. You should then run both a neutral and an EGC between generator and building.
There is a special case which allows the service grounded conductor to also serve as the EGC back to the POCO equipment, but there is, AFAIK, no corresponding exception for a non-POCO generator.

If the bond is at the generator and you are not using the neutral you do not have to bring the neutral separately to the disconnect for the generator at the building.

Thanks for the help man. Cheers

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[david]

That clarifies things considerably.
The service neutral needs to be connected to the building Ground Electrode System (GES). That is typically done at the service disconnect, the meter or the weatherhead if it is an overhead service.
The generator protective ground must also be connected to the same GES.
I think that you have the option of bonding the generator neutral to its protective ground at the generator or at the building disconnect for the generator, but not at both. You should then run both a neutral and an EGC between generator and building.
There is a special case which allows the service grounded conductor to also serve as the EGC back to the POCO equipment, but there is, AFAIK, no corresponding exception for a non-POCO generator.

If the bond is at the generator and you are not using the neutral you do not have to bring the neutral separately to the disconnect for the generator at the building.

I work out of the 2008 NEC so correct me if I am wrong

250.30 (A) (1) 2014 NEC
Last sentence if the source is located outside the building

Exception # 2 For transformers in 2014 NEC than they must have realized what they did by limiting the source of the separately derived system to transformers

Exception # 2 In 2017 NEC is applicable all outside sources for separately derived systems

So in essence the neutral is required to be bonded at all outside sources of a separately derived system
You can use a single conductor for the grounded (neutral ) and bond to the equipment ground in the building if no other metallic paths

Edit: Feeder from a separately derived system

 

[jumper]

I have decided that I hate all 2 1/2 pages of 250.30.

 

[ActionDave]

I have decided that I hate all 2 1/2 pages of 250.30.

So it's my first year as an electrician and we are wiring up a gravel pit. All of it is temporary so they are running off of generators. They want to run the whole pit off a 480V three phase during the day then they want to switch to a small single phase 240V generator at night to keep power to the office trailers and save on diesel. Interesting set up, cool job, lots to learn.

The boss and my journeyman are tossing around all this stuff about SDS, non SDS, grounding, XO, bond here, no don't bond there,,,,on and on. I go home and start reading 250.30 and it might as well be a secret code, all the words look like English but I can't tell what they mean, but those guys do and I'm thinking I'm going to learn something. Get back to work the next day and the final plan of action is to, "Bond everything together and see what the inspector says."

Everybody hates 250.30.

 

[jumper]

So it's my first year as an electrician and we are wiring up a gravel pit. All of it is temporary so they are running off of generators. They want to run the whole pit off a 480V three phase during the day then they want to switch to a small single phase 240V generator at night to keep power to the office trailers and save on diesel. Interesting set up, cool job, lots to learn.

The boss and my journeyman are tossing around all this stuff about SDS, non SDS, grounding, XO, bond here, no don't bond there,,,,on and on. I go home and start reading 250.30 and it might as well be a secret code, all the words look like English but I can't tell what they mean, but those guys do and I'm thinking I'm going to learn something. Get back to work the next day and the final plan of action is to, "Bond everything together and see what the inspector says."

Everybody hates 250.30.

No joke, I got tears laughing right now.:thumbsup:

 

[electrofelon]

.....Get back to work the next day and the final plan of action is to, "Bond everything together and see what the inspector says."

Everybody hates 250.30.

Funny, but truth is that is likely the safest. I mean of course not bonding N-G is safest as long as its done right...just opens up a chance for the dirt worshippers to makes it dangerous.