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Installation Talk Questions/Concerns and help involving the installation of a Guardian Automatic Generator

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Old November 29th, 2008   #1
boltedfaultz
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Default Dual 200 amp services, single generator

Im trying to figure out how to feed 1 building that has been divided into 2 seperate buisnesses, each with its own 200 amp service, with 1 generator. The service consists of a meter main and a main breaker 200 amp panel for each seperate store.

I was thinking of using a 12 circuit prewired ATS for each of the buisnesses, I'm thinking that will be the only way to keep the genset down to a reasonable size to comply with the 2008 NEC Code Change that says we have to size the genset for the load that is automatically being switched.

I was thinking of coming off the genset to a Jbox on the exterior of the building where the feeder from the genset would tie into both feeders going to the 12 circuit ATS.

The thing I am concerned about is when I tie neutrals together in my jbox from the genset, the neutrals from both services will now be tied together. Will this create any hazards "parallel paths" I should be concerned about.

Am I on the right track or is there a better way to accomplish this?

Thanks in advance for any input regarding this install.
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Old November 30th, 2008   #2
NYS SitePower Corp.
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Is it a single meter that feeds both panels, or separate meters? Am I correct in assuming that we're dealing with single phase?

If its under the same single meter, you'll be ok with the two 12-Circuit ATSs.

If there are 2 separate meters (2 services as far as the utility is concerned), you'll technically have to use a pair of 3-pole transfer switches to isolate the neutrals. In this case, the generator is treated as a separately derived source as far as NEC is concerned.

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Old November 30th, 2008   #3
boltedfaultz
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Smile

Thank you for the reply.
Unfortunately it is 2 seperate meters, so I can forget the 12 circuit prewired switches for I have never seen those come in a 3 pole model.

I guess I had better look at a different plan like setting a 100 Amp ATS under each of the 200Amp Load Centers and then add a sub panel next to the Load Centers where I can bring the essential loads in that will need to be powered up during an outage.

So now that I am switching the neutral I guess I will have a few more questions for you.

1)In switching the neutral I believe it means I have seperately derived systems now and should bond the neutral and ground together in the generator?

2)In the transfer switches the neutrals and grounds will be seperate with the ATS bonded via the equpment grounding conductor?

3) With my services having Meter Mains "with disconnecting breakers" that is the first point of disconnect so my neutrals and grounds will be bonded there,
but what about the new added sub panels for the essential loads, those should have the neutrals and grounds seperated?
Again, thanks alot for the reply and any input you might have.
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Old December 1st, 2008   #4
NYS SitePower Corp.
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Quote:
Originally Posted by boltedfaultz View Post
Thank you for the reply.
Unfortunately it is 2 seperate meters, so I can forget the 12 circuit prewired switches for I have never seen those come in a 3 pole model.

I guess I had better look at a different plan like setting a 100 Amp ATS under each of the 200Amp Load Centers and then add a sub panel next to the Load Centers where I can bring the essential loads in that will need to be powered up during an outage.
Yep, you're on the right track. This is how we would do it. (Truth be told, there is a handful of electrical inspectors out there that would probably let the (2) 12-circuit switches fly. This has been a hot topic in our area recently because neighbors want to 'share' generators).

Quote:
Originally Posted by boltedfaultz View Post
So now that I am switching the neutral I guess I will have a few more questions for you.

1)In switching the neutral I believe it means I have seperately derived systems now and should bond the neutral and ground together in the generator?
Correct. You'll also want to consider installing a grounding ring around the generator pad as opposed to just a single rod.

Quote:
Originally Posted by boltedfaultz View Post
2)In the transfer switches the neutrals and grounds will be separate with the ATS bonded via the equpment grounding conductor?
Correct.

Quote:
Originally Posted by boltedfaultz View Post
3) With my services having Meter Mains "with disconnecting breakers" that is the first point of disconnect so my neutrals and grounds will be bonded there,
but what about the new added sub panels for the essential loads, those should have the neutrals and grounds seperated?
Subpanels should be treated as subpanels all the way down the line - correct sepearte grounds & neuts as long as your main disconnect is your bonding point.

Quote:
Originally Posted by boltedfaultz View Post
Again, thanks alot for the reply and any input you might have.
No problem. Remember that if you're bidding against someone else to explain the "right" way vs the "wrong" way to your customer. Your competition may opt for the 12-circuit switches with a lower price; worst case scenario the electrical inspector does not catch it.
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Old December 1st, 2008   #5
E Carr
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I had a post about a month ago with the same scenario.
When I sent a one line diagram to engineering for Nat'l
Grid it was rejected.They said I would have to use manual
transfer switches.The reasoning was in the event of say a
fire there would be too much confusion as to why one of the
residences had power and the other did'nt.By having a manual
switch then there had to be human involvement and as such
a contact person that would know the operation of the system.
That was the explanation given to me and if you're shaking your
heads in wonder don't feel alone.

Ed
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Old December 1st, 2008   #6
boltedfaultz
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Thanks for the replys.

After looking thru many code articles, and with the info here from the site, I am more comfortable going with the 3 pole ATS switches and sub panels.

I believe that as long as I size the generator for the loads in the sub panels and with the proper grounding, bonding, and signage posted at the service and ATS switches that this will pass the plan review and inspections.

I wish I had come across this site last year, there is alot of great info here.

Thanks again
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