generator...sizing ats for exisitng building

[meleconn]

a customer (gas station / conv store) has a 600 a 3 ph 208V system w/ a demand load of 317 A, 1- 600 A 3 ph main disconnect w/5 - 200 a disconnects for interior panels, 1 - 200 A 3 ph disconnect for 1 -3 ph panel tapped off from main disconnect... he bought a 100 kw gen w/ a 400 ats. wants to run everything (recvd info from another electrical co. on purchasing this equip.) I think he needs either a 600A ats to connect to main disconnect (to connect to all) , but if that is the case then he should have a gen capable of 600 A output. if he goes w/ a 400 A ats then the 400 A ats should be w/ load center. cannot find 400 ats w/ load center capable of having 2- 200A breakers to connect to 2 disconnects.. he really wants all of the disconnects to be connected but I do not see where the 400A is capable / code wise. i believe that connecting the 400 ats to the disconnect will be wrong as the overcurrent fuses will be too big, & connecting all the 200 A disconnects to it will be cause fro overload. any suggestions /help is appreciated. thanks mikep

 

[George Stolz]

I am having a hard time reading your post, it helps if you hit the return key now and then, it reduces the "headache factor."

Does this look like what you're dealing with?

View attachment 564

If so, I don't see a problem. If the customer wants a 600A disconnect for future use, that doesn't mean they have to go hog wild with the other components of the system, IMO.

 

[George Stolz]

As I was slipping off to sleep, I realized the ATS is rated for 400A, and should be protected according to that. The 600A breaker wouldn't do that.

There, I said it, now I can go back to bed.

 

[iwire]

As I was slipping off to sleep, I realized the ATS is rated for 400A, and should be protected according to that.

A 100 KVA generator at 208 volt 3 phase should have a breaker on it around 300 amps. That will protect the ATS on the emergency side.

On the 'normal' side over current protection must be added that is 400 amps or less.

If George's diagram is accurate then installing 400 amp fuses in the 600 amp disconnect (use fuse reducers) would get the job done and be code legal.

This is an article 702 standby generator as such the capacity of the generator is up to the owner.