Generator transfer switch wiring

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herynkc

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We are planning a generator install. An automatic transfer switch will be added at the service entrance (Generac RXSW200A3)

Current Meter Box and Service Disconnect are conjoined (see first image in the link for existing). The transfer switch will be placed to the right of the existing service disconnect box (see second image for proposed).

I know the point at which the initial service disconnect is made should be the locations where the neutral gets bonded to the ground. So I will have to reconfigure a couple things in the existing service disconnect box. The ground and the neutral conductors coming from the main load center (bottom of first image, main load center is not pictured) will need to be spliced and extended into the transfer switch's box and connected to the bonded ground and neutral bars there.

It shouldnt matter if I leave the ground electrode conductor as is, correct ? (i.e. connected to the Ground/Neutral Bar in the service disconnect panel) or should I move this connection also into the transfer switch's ground bar? I have seen it done both ways.

images:

Generator - Google Drive

drive.google.com drive.google.com
 
With that particular arrangement I would be tempted to leave the existing as my service disconnect and feed my T/S from the load lugs. Your T/S breaker would simply be a secondary) It would simplify the install and the only problem would be that one SP breaker would not be on the generator.
 
augie47 said:
With that particular arrangement I would be tempted to leave the existing as my service disconnect and feed my T/S from the load lugs. Your T/S breaker would simply be a secondary) It would simplify the install and the only problem would be that one SP breaker would not be on the generator.
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I would agree.
(I thought it might help to have another inspector add an opinion)
 
Done like that all the time here. The OP's way is a violation for a number of reasons.

1. Modifying a listed assy.
2. No real way to move the N-G bond to the transfer switch because it is inextricable from the original can
3. No way to unprotected separate service conductors from feeders and also have current flow balance inside the conduit.
4. Unprotected service conductors would be passing through the enclosure for everything else.
 
augie47 said:
With that particular arrangement I would be tempted to leave the existing as my service disconnect and feed my T/S from the load lugs. Your T/S breaker would simply be a secondary) It would simplify the install and the only problem would be that one SP breaker would not be on the generator.
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Exactly what I did at my house.
 
I guess I would put the T/S on the other side of the meter panel and run the feeder out the bottom of the T/S under the meter and into the current panel. You avoid having unfused entrance conductors running through a panel. If that panel ever needed to get swapped out, it would be difficult now with those unfused entrance conductors running through it.

It's going to cost you 2 2" LBs and a couple feet of pipe. It may not look as pretty physically, but it will be nicer electrically.
 
augie47 said:
With that particular arrangement I would be tempted to leave the existing as my service disconnect and feed my T/S from the load lugs. Your T/S breaker would simply be a secondary) It would simplify the install and the only problem would be that one SP breaker would not be on the generator.
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Many thanks for all your replies.

It seems the consensus is to feed the TS from the load lugs of the existing service panel, and then of course NOT bond the neutral to ground in the TS panel. This suggestion was my original plan, however this would involve running new feeders to the inside main/distribution panel which will be pretty costly and time consuming. Also I am used to seeing the TS being made the first point of disconnect (converting the existing service disconnect to a downstream sub panel.) But given the existing setup, I see now (as Birken Vogt points out) that the N to G bond is "inextricable."

I have drawn 2 more examples (#3 and #4 in the link below) that illustrate a revised plan which would involve pulling new feeders. I really wish there was solution without having to do this...

4. panel_after.jpg

drive.google.com drive.google.com

Method #3 would be ideal, however I am not sure I can run that feed for the main load/distribution center back through the service disconnect panel

Method #4 involves turning the existing LB and then running straight up into the TS panel.

Not having that single pole breaker on the generator shouldn't be an issue. Is it necessary tp be separated into its own conduit as pictured in #4?
 
I don't see a #3 but you can bring your TS load back into the service and splice onto the existing feeders
 
augie47 said:
I don't see a #3 but you can bring your TS load back into the service and splice onto the existing feeders
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I accidentally omitted it before, should be visible now above. I think #3 would be equivalent to doing this. obviously the conduit nipple coming back into the service panel would have to be higher to have proper bending clearances, but I drew it lower for the sake of visual clarity.
 
#3 IMO is the way to go. Since they are all load side of the service breaker they can share the same nipple.
 
augie47 said:
#3 IMO is the way to go. Since they are all load side of the service breaker they can share the same nipple.
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As long as I dont exceed 40% of the cross sectional area of that side area in the service panel (312.8) it should work.
 
Since these feeders coming from the TS back into the service panel (which feed the main distribution panel inside) are spliced connections its not necessary to maintain 6x the trade diameter for determining the minimum permissible box width? This is because these are technically not the same conductor? (as per 314.28)

Also was reading this: https://forums.mikeholt.com/threads/nec-314-28-a-2.61842/page-2

It makes no sense to me that there should need to be 14" of width given than these are spliced. The service panels is only about 8" wide.
 
Little Bill said:
You can't enter the TS where you have it drawn unless you use a Meyers hub. It's above the live parts on an outdoor panel.
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Thanks

So use a myers hub on the top conduit OR run the feeders to the TS via the same lower nipple as Augie had suggested above.

I drew 2 conduit nipple to keep the diameter smaller but now that I look at it again using a single larger conduit on the bottom should be feasible.

I’m very doubtful this will ever see weather, as there’s a 6’ eave overhead. But I get it compliance is compliance.
 
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augie47 said:
A 2" nipple can accommodate 6-4/0s, you should be o.k.
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The full-sized neutral does not need to enter and leave the ATS; the load neutral only needs to land on the service breaker's neutral bus. A single neutral sized for the generator is all that is needed between the service neutral and the ATS neutral.
 
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