Generac generator with transfer switch

[Robert Huffman]

Looked at a Generac generator today with an automatic transfer switch box mounted outside that also had a 200 amp power disconnect in it. Would this be considered the first main disconnect which would then mean there should be no jumper between the ground and neutral bars in the main panel inside or would it just disconnect the generator (which is what I suspect but not sure) so the jumper is appropriate?

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[david shapiro]

Robert, I'm having trouble visualizing the setup.
If the ATS is service-rated, and has one input from the generator and the other directly from the electric meter, it is indeed the service disconnect and the panel it feeds may be the main distribution panel but is not the service panel. This means the grounding electrode conductors have to terminate at the ATS or upstream of it, and downstream grounded and grounding conductors must be kept separate, unless the 2023 NEC has been adopted and the setup qualifies for the new electric dryer/cooking equipment exception.
If, OTOH, the ATS has one input from the generator and another from a feeder circuit breaker, and the output goes to another panelboard, then the panelboard containing the feeder breaker may be the service panel, though the second panelboard is not.
The only caveat here is that if the ATS has an manual all-off position, it might qualify to serve for an emergency-responder disconnect under the 230.85 rule.

[Jerry Peck]

If, OTOH, the ATS has one input from the generator and another from a feeder circuit breaker, and the output goes to another panelboard, then the panelboard containing the feeder breaker may be the service panel, though the second panelboard is not.

David, from the above "ATS has one input from the generator and another from a feeder circuit breaker, and the output goes to another panelboard", am I correct in clarifying this with the underlined text as "ATS has one input from the generator and another from a feeder circuit breaker, and the output from the generator goes to another panelboard"?

To clarify that the ATS "output" being referred to feeds a separate 'emergency panel'.

This panel is a "downstream" panel sub-fed from the utility powered panel (which is likely the "service equipment" panel with a main service disconnect) when the ATS is switched to the utility service power.

However, the 'emergency panel' becomes the only energized panel when the ATS loses utility power and switches to generator power.

Many optional standby generators are provided with a panel with a limited number of circuits (8/12/16 circuit 'emergency panels' are common ones I've seen) with the generator sized for the 'emergency panel' and the generator is not sized to be a "whole house" generator.

[david shapiro]

Right you are, Jerry. The output of the ATS is from the generator (or the feeder breaker) to the emergency panel. As we're using the term, "emergency panel" just means the panel that serves loads that the person speccing the job decided should be fed by the generator during outages.

I received an email this evening from another colleague about a building with two distribution panels, one of which was re-fed via a transfer switch that paired a 22 kW generator with the utility feed. I suspect this was not a generac-supplied size emergency panel. I do suspect that here the colleague had tried to double-duty the transfer switch as a first responder's disconnect. I should know more Friday about why he got smacked down.

[Jerry Peck]

David, I'm not sure you answered Robert's question?

Or that my clarification of what you were referring to helped Robert either?

[david shapiro]

Agreed, Jerry.

We were talking hypotheticals. Until Robert clarifies what's actually there, it's guesswork and I can't go yes-no.

The same was true in the case of my other colleague; until I understand what he's got, I'm guessing. Here's what I wrote about that one (my end only):

I'm guessing that power comes into service equipment, with a 400 A bus delivering power to two 200 A service disconnects, each feeding its own distribution panel. Now you want to put a generator and transfer switch between one of those service disconnects and its distribution panel. Sounds okay.

A lot of other configurations would be not okay. The fact that he added a second outside disconnect makes me suspect that it isn't the way I guessed.

Now if what he's talking about is satisfying 230.85, a transfer switch that is service-RATED and has a manual all-OFF position might serve; I think that would be the AHJ's call--is it going to be obvious to a first responder? If it didn't have a manual all-OFF, of course it wouldn't fly. Slightly related, the 2025 edition of NFPA 73--at least in the first draft--is going to require the alternate energy source placards by residential service equipment, whenever it was installed.