Residential Service Disonnect location w/ ATS & gen

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Npstewart

Senior Member
I have a residential project that we did a while ago, and now we are adding a generator right before construction. They sent me the specifications for a 80KW generator with a NON service rated auto transfer switch that they want to use.

Right now I have the following setup:

A meter can feeding the ATS, then the ATS feeds the MDP panel UNDERGROUND which is inside, NOT immediately adjacent to the meter.

My question is, the feeder is outside the building the whole time because it is traveling underground. I think I should put a fused disconnect outside prior to the transfer switch correct? I know the easiest way would be for them to buy a service rated ATS, but I am trying to work with what I have already.

I added a quick sketch, see attachment .

Thanks
 

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legato

Member
Location
Mountain View, CA
Occupation
Consulting Electrical Engineer
I would say that would be a good idea.

If you needed to isolate the ATS a disconnect ahead of it on the normal (POCO) line would be a good idea.
 

Npstewart

Senior Member
Thats a good point. Without the disconnect the ATS wouldn't be able to be serviced. But further more, I was thinking if the was some type of fault on the outside, there wouldn't be any over-current protection.

I know it is probably legal not to have a disconnect but I do think it is a good idea.

Any other opinions would be appreciated, thanks.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Without the disconnect, the job would not be Code compliant.
230.82 lists equipment that can be connected ahead of your service disconnect and a non-service rated ATS is not one of the items allowed.
 
I have a residential project that we did a while ago, and now we are adding a generator right before construction. They sent me the specifications for a 80KW generator with a NON service rated auto transfer switch that they want to use.

Right now I have the following setup:

A meter can feeding the ATS, then the ATS feeds the MDP panel UNDERGROUND which is inside, NOT immediately adjacent to the meter.

My question is, the feeder is outside the building the whole time because it is traveling underground. I think I should put a fused disconnect outside prior to the transfer switch correct? I know the easiest way would be for them to buy a service rated ATS, but I am trying to work with what I have already.

I added a quick sketch, see attachment .

Thanks

I don't think you have a 80KW gen on this house if you have a meter base. But if you do have an 80KW on a 400 amp service it's over kill! The generator does not have to be sized to the service only the ATS bus and protection. There is a thing called "Load Management" which allows you to you smaller generators on large loads.
 
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augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I don't think you have a 80KW gen on this house if you have a meter base. But if you do have an 80KW on a 400 amp service it's over kill! The generator does not have to be sized to the service only the ATS bus and protection. There is a thing called "Load Management" which allows you to you smaller generators on large loads.

maybe a 400 amp meter base
 
My point is even with a 400amp service you do not need a 80kw generator, way too big for home use, 27 to 30kw with load management will do the job, maybe even smaller depending on the load.
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
My point is even with a 400amp service you do not need a 80kw generator, way too big for home use, 27 to 30kw with load management will do the job, maybe even smaller depending on the load.

I had one where I only needed a 225 amp service, but the boss bought a 80 kw genset, so I had to change the service to a 400!:roll:
 

kwired

Electron manager
Location
NE Nebraska
My point is even with a 400amp service you do not need a 80kw generator, way too big for home use, 27 to 30kw with load management will do the job, maybe even smaller depending on the load.

You need a generator sized for the load connected to it if it automatic transfer. If there is 80 kw of load then you need 80 kw. You probably mean to state that there likely is not 80 kw of load - especially if there is load management devices or if the transfer switch only powers specific circuits instead of the entire service.

I had one where I only needed a 225 amp service, but the boss bought a 80 kw genset, so I had to change the service to a 400!:roll:

Why? You could have a 10Mw generator supply only a 30 amp feed if you want. It will use a lot of fuel for the work being done but it will work.
 
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