400a ATS for 2 200a panels

TJon40's

Member
Location
Texas
Occupation
Electrician
I have looked around and only found a couple 400a split 200a srevice entrance rated transfer switches, the Briggs and Stratton and Milbank. The Briggs and Stratton says it must be used with their generators, and the Milbank looks too busy inside from the factory. I am limited on space so installing 2 200a switches is out. The generator will be a used 50kw diesel Kholer. Kholer makes 400a ser ats with double lugs on the load side, would that be the way to go, or am I getting into 240.21?
 

kwired

Electron manager
Location
NE Nebraska
I have looked around and only found a couple 400a split 200a srevice entrance rated transfer switches, the Briggs and Stratton and Milbank. The Briggs and Stratton says it must be used with their generators, and the Milbank looks too busy inside from the factory. I am limited on space so installing 2 200a switches is out. The generator will be a used 50kw diesel Kholer. Kholer makes 400a ser ats with double lugs on the load side, would that be the way to go, or am I getting into 240.21?
If it has overcurrent protection then likely yes 240.21 will be applied. Might not really be that big of an issue for you depending on arrangement of items. You basically have a 10 foot rule a 25 foot rule and outside taps of unlimited length to contend with.
 

bzzt

Member
Location
mn
Occupation
wirer
Do ATS's need to have load shedding to prevent overloading the gen or is that just for critical wiring?
 

kwired

Electron manager
Location
NE Nebraska
Do ATS's need to have load shedding to prevent overloading the gen or is that just for critical wiring?
some do some don't. Often it is just relay contacts to control the load being shed and additional wiring is necessary to get things done.
 

TJon40's

Member
Location
Texas
Occupation
Electrician
If it has overcurrent protection then likely yes 240.21 will be applied. Might not really be that big of an issue for you depending on arrangement of items. You basically have a 10 foot rule a 25 foot rule and outside taps of unlimited length to contend with.
The transfer switch would be right next to the meter base with a nipple and then a gutter underneath the two to feed the 200's. The 400a breaker on the ATS would be the overcurrent protection for the 2 200a panels and the grounds and neutrals will be separated in the 200's.
 

kwired

Electron manager
Location
NE Nebraska
The transfer switch would be right next to the meter base with a nipple and then a gutter underneath the two to feed the 200's. The 400a breaker on the ATS would be the overcurrent protection for the 2 200a panels and the grounds and neutrals will be separated in the 200's.
Feeder tap rules would apply, but shouldn't really make you change what you would otherwise do in your situation.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Do ATS's need to have load shedding to prevent overloading the gen or is that just for critical wiring?
They do if the transfer switch is automatic and the total load exceeds the output of the generator. 702.4(B)(2).
 

bzzt

Member
Location
mn
Occupation
wirer
They do if the transfer switch is automatic and the total load exceeds the output of the generator. 702.4(B)(2).
That’s what I was getting at. The generator is rated for 208amps and feeds two-200a panels with an automatic transfer switch


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kwired

Electron manager
Location
NE Nebraska
That’s what I was getting at. The generator is rated for 208amps and feeds two-200a panels with an automatic transfer switch


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But is your total load calculation over 208 amps? Just because you have 400 amps worth of mains doesn't necessarily mean you are anywhere close to 400 amps of load being all that possible.
 
Either way wouldn't he have to split it back to 2 separate 200amp breakers after his 400 ATS? Because the feeders (SER, etc.) are longer than tap rules (I assume) and are probably only 3/0 copper or equivalent. I'm just curious how you could put OCPD at 400amps on 3/0 copper.
 

rnatalie

Senior Member
Location
Catawba, NC
Occupation
Retired Electrical Engineer
My own personal house has essentially the METER feeding a 400 disconnect and then a Generac HTS (400A ATS). My "main" panel is a 400A subpanel. This feeds a couple of branch circuits and four other subpanels. My house is over 10,000 sf and has 8 panels.
 

kwired

Electron manager
Location
NE Nebraska
Either way wouldn't he have to split it back to 2 separate 200amp breakers after his 400 ATS? Because the feeders (SER, etc.) are longer than tap rules (I assume) and are probably only 3/0 copper or equivalent. I'm just curious how you could put OCPD at 400amps on 3/0 copper.
I thought he was supplying two 200 amp breakers, but if not then yes.

There is no length limitation for outside feeder taps either - but there is rules in 225 about multiple feeders to a separate building/structure to consider, easy way around that though is to parallel them, then it is a 400 amp conductor, and make the taps at the second building/structure.
 

kwired

Electron manager
Location
NE Nebraska
I was thinking similar, why a 400 amp transfer switch then? Why not just do one of the 200A sets?
Cause they potentially need to run "anything" when in standby?

I'd likely suggest similar though - put the more desired loads to have during utility outage on one panel and the rest of the loads in the other panel.
 

kwired

Electron manager
Location
NE Nebraska
But it's not compliant to have a 200A Genny connected to a transfer switch with more than 200 A of load.
right, that why I questioned what is the load earlier? 400 amp breaker doesn't mean there is 400 amp of load, might only be 50 amps for all we know. Chances are it is closer to 200 since OP said it is a 208 amp generator, or there is at least closer to 200 amp of load they do desire to be able to run, but that would require separation or load shedding if on ATS.
 

TJon40's

Member
Location
Texas
Occupation
Electrician
With the load calculation for the house, a 30kw would work, but they have a shop they want thrown into the mix as well. So currently it's a 320a meter base with triple barrel lugs feeding everything.

The 2 200a panels have main breakers. That being said with 3/0 ran parallel it's good for 400a, but the issue is that it's 3/0 split between 2 separate 200a breakers? What I had initially thought was to feed the 400a service entrance rated ats with 600mcm, then on the load side feed the 2 200a mains with 3/0.

I've only done single 200a services, or when I wired the house one panel was just the circuits the customer wanted to be backed up. Not many people in Texas want to spend money on a backup generator till now.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Are the 200a feeds 3-wire service conductors or 4-wire feeders? If the former how hard would it be to make them the latter?
 

kwired

Electron manager
Location
NE Nebraska
With the load calculation for the house, a 30kw would work, but they have a shop they want thrown into the mix as well. So currently it's a 320a meter base with triple barrel lugs feeding everything.

The 2 200a panels have main breakers. That being said with 3/0 ran parallel it's good for 400a, but the issue is that it's 3/0 split between 2 separate 200a breakers? What I had initially thought was to feed the 400a service entrance rated ats with 600mcm, then on the load side feed the 2 200a mains with 3/0.

I've only done single 200a services, or when I wired the house one panel was just the circuits the customer wanted to be backed up. Not many people in Texas want to spend money on a backup generator till now.
That makes them feeder taps, still works just need to comply with 240.21(B). 3/0 on 400 amp is able to use 10 or 25 foot rule. Outdoors has no length limitation.
 
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