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Old 10-04-2010, 10:56 PM   #1
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Another Generator question


I have a stationary 15kw generator located in a detached building that I want to connect to the house as emergency power.

I've done a search but haven't found what I'm looking for.

What I'm thinking is generator connected to 60A breakers in a sub panel in the outbuilding, 3 -#4 & 1-#6 buried in conduit back to the house, connected to 60A breakers in the main panel with an interlock. neutral and ground not bonded. 2 ground rods at outbuilding connected to ground in generator sub panel with #6. Total distance from generator to main panel is about 80 feet.

There is a seperate 60A sub panel in the outbuilding fed from the main panel in the house. I intend to leave this as is.

Am I way off base or is this acceptable? (NEC 2005)

Can I use the same ground rods at the outbuilding for both the generator and the existing sub panel?

Since this generator is not a portable type is an inlet box necessary?

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Old 10-05-2010, 06:39 AM   #2
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Another Generator question


I would not have a "subpanel" for the generator at the outbuilding, although it is still necessary to have a breaker for the generator output, maybe that is built into the generator.

Ground and neutral not bonded at the generator, first bonding of ground and neutral occurs at the main panel in the main house, which happens automatically no matter how you connect the new 4-4-4-6 wiring into the main panel.

Usage of generator power at the outbuilding is via the older existing subpanel and feed from the main house.

Provided that the older feed between house and outbuilding has separate neutral and ground (4 conductors for 120/240 volt feed), it is okay to interconnect all the ground rods.

With no ground in the older feed, you are really not supposed to have any other metallic path between house and outbuilding besides the older feed wires (not even a water pipe) although homeowners have connected up the generator anyway but not bonding anything in the garage other than the generator itself to the new generator feed.

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Last edited by AllanJ; 10-05-2010 at 06:53 AM.
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Old 10-05-2010, 09:00 AM   #3
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Another Generator question


Quote:
Originally Posted by AllanJ View Post
I would not have a "subpanel" for the generator at the outbuilding, although it is still necessary to have a breaker for the generator output, maybe that is built into the generator.

Ground and neutral not bonded at the generator, first bonding of ground and neutral occurs at the main panel in the main house, which happens automatically no matter how you connect the new 4-4-4-6 wiring into the main panel.

Usage of generator power at the outbuilding is via the older existing subpanel and feed from the main house.

Provided that the older feed between house and outbuilding has separate neutral and ground (4 conductors for 120/240 volt feed), it is okay to interconnect all the ground rods.

With no ground in the older feed, you are really not supposed to have any other metallic path between house and outbuilding besides the older feed wires (not even a water pipe) although homeowners have connected up the generator anyway but not bonding anything in the garage other than the generator itself to the new generator feed.
Thanks for the reply.

The subpanel at the generator is because there are no breakers in/on the generator itself.

The existing feeder to the outbuilding has seperate neutral & ground.

If I understand correctly: I only need 2 ground rods at the outbuilding and they can be connected to both the generator panel and the existing subpanel?
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Old 10-05-2010, 10:03 AM   #4
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Another Generator question


If its not connected at the detached structure, why not move it to the primary structure and use an automatic transfer switch?

Your idea is theoretically possible. However, I am not sure what the NEC has to say about this. Secondly you will need two (2) interlocks and I am not sure how you could arrange that. Back feeding the service panel (main panel) with a listed interlock kit is compliant. If it were me. I would have this large generator moved to a location more suitable for connecting to the main service panel.
You could run a new feeder to the main service/ATS from the generator. The exceptions in Article 225.30 look like they were authored just for you.

(A) Special Conditions. Additional feeders or branch circuits
shall be permitted to supply the following:
(1) Fire pumps
(2) Emergency systems
(3) Legally required standby systems
(4) Optional standby systems
(5) Parallel power production systems
(6) Systems designed for connection to multiple sources of
supply for the purpose of enhanced reliability
(B) Special Occupancies. By special permission, additional
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Old 10-05-2010, 10:21 AM   #5
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Another Generator question


Quote:
Originally Posted by J. V. View Post
If its not connected at the detached structure, why not move it to the primary structure and use an automatic transfer switch?

Your idea is theoretically possible. However, I am not sure what the NEC has to say about this. Secondly you will need two (2) interlocks and I am not sure how you could arrange that. Back feeding the service panel (main panel) with a listed interlock kit is compliant. If it were me. I would have this large generator moved to a location more suitable for connecting to the main service panel.
You could run a new feeder to the main service/ATS from the generator. The exceptions in Article 225.30 look like they were authored just for you.
I am running a feeder from the generator to the main service panel so see no advantage to moving a large noisy generator and it's fuel tank closer to the house.

The ATS is an added expense I have no need for as I need to manually start the generator anyway.

I fail to see where I need the second interlock. The generator is on a seperate feeder and panel connected to the main panel that has the interlock. What am I missing?
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