feeding second service subpanel from ATS that feeds first service

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FREEBALL

Senior Member
Location
york pa usa
OK so Im trying to figure a feeder tap from a generator to feed another panel from a manual ats that is fed from different meter, same service drop keep in mind. This is all single phase for all intensive purposes. The generator is feeding an ATS that is fed by a 200 amp I line breaker from a 600 amp 24ov/ 3ph delta. Im using load shed contactors for the 200 amp panel. That is not the issue. The issue Im having is Im not sure if I should use a 3 pole double throw transfer switch in order to switch the neutral ,to attatch the smaller load to the generator feed to prevent back flow on the neutral since one main service is 600 amp and the second is 200 amp, plus the various other issues like stray currents and such. Im pretty sure this is the way to go. But now grounding both services are in the same room and over the years have shared grounding by multiple conduit runs from each service to refeed and or back feed equipment. I would like to tap off the feed to the panel that is to be generator protected to a 60 amp 3 pole transfer switch. so that all conditions of overload and cycle alerts are still intact through the generac ATS, rather than directly from the generator feed.

However if I do come directly off of the generator feed prior to the ATS I will still have the neutral issue, however My loads will need to be figured less than the rating of the genset since Im now sharing the load. Is there anybody that can give an idea on this because either way I do it the neutral will still be common between the two services in normal power situations.
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
You have to decide whether the generator will be wired as a Seperately Derived System (SDS) or not.
The difference will be whether you make a ground/neutral bond at the generator (SDS) or not (non-SDS.)
If you wire the generator as an SDS, then you must switch the neutral in any MTS or ATS.

As far as "stray" current in the neutral, as long as you do not make a ground/neutral bond at the generator, the neutral can only carry the imbalance between the two generator line outputs. It cannot be part of the current path related to the other (service) power source.
 

FREEBALL

Senior Member
Location
york pa usa
OK I understand the sds and nsds. My concern is the 2 neutrals looped together through the two transfer switches. Im going to have a 600 amp paralled set of neutral neutral conductors being tied to a 200 amp neutral conductor from the same service drop on the other transfer switch, now be it its the same service drop only separate meters should I be concerned with that. As far as losing a neutral on the larger service and the current being transferred through the 200 amp. That is my concern. It would be hard to fatham that since the services are tied at the same point and only sepatated by 10 feet where they enter the building but caused concern in my mind. Any more thoughts I sure would appreciate.

Jeff

PS and thanx for the quick reasponse
 

FREEBALL

Senior Member
Location
york pa usa
well i guess it will work the grounding will find its way back to neutral, since its common. but I believe switching the neutral also is the way to go so in the event of a bad neutral on either side one isnt carrying more than its load., Thanx all for listening. but generators can be confusing. to some i guess.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
OK I understand the sds and nsds. My concern is the 2 neutrals looped together through the two transfer switches. Im going to have a 600 amp paralled set of neutral neutral conductors being tied to a 200 amp neutral conductor from the same service drop on the other transfer switch, now be it its the same service drop only separate meters should I be concerned with that. As far as losing a neutral on the larger service and the current being transferred through the 200 amp. That is my concern. It would be hard to fatham that since the services are tied at the same point and only sepatated by 10 feet where they enter the building but caused concern in my mind. Any more thoughts I sure would appreciate.

Jeff

PS and thanx for the quick reasponse
It is not anything to worry about. If you loose the service neutral you don't get any utility current flowing on the generator neutral.
 
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