Main Breaker

[wirenut46]

I have a service 480/277 volt three phase. I am setting a 400/amp 3 pole main circuit breaker in a nema 3 r enclosure outside under the gutter with a ct cabinet. My wire size going into the building is 500 kc mil. I want to set a 400 amp panel 277/480 inside 80 foot away. My question is do i need a main breaker on the 400 amp panel inside it will be used for the warehouse lights that are 277 volt. I will also be feeding a transformer 480/277 to 120/240 to feed a panel up front for the office area it will be 120/240 200 amp. Do i need a disconnect at the transformer feeding the 120/240 volt panel and does it need to be a main breaker.

 

[petersonra]

I have a service 480/277 volt three phase. I am setting a 400/amp 3 pole main circuit breaker in a nema 3 r enclosure outside under the gutter with a ct cabinet. My wire size going into the building is 500 kc mil. I want to set a 400 amp panel 277/480 inside 80 foot away. My question is do i need a main breaker on the 400 amp panel inside it will be used for the warehouse lights that are 277 volt.

Is the outside breaker located on the same building as the new panel?

I will also be feeding a transformer 480/277 to 120/240 to feed a panel up front for the office area it will be 120/240 200 amp. Do i need a disconnect at the transformer feeding the 120/240 volt panel and does it need to be a main breaker.

The CB at the new 400A panel that feeds the 480-240/120 xfmr can serve as the disconnecting means if it has a padlock attachment on the breaker.

The 120/240 PB does not have to be a main breaker style. You do have to provide for both transformer secondary and transformer secondary conductor protection. The easiest way might end up being with an appropriately sized main in the 120/240 PB.

 

[augie47]

If your 400 amp breaker is mounted on the structure it may serve as the "main" for an interior panel so long as your conductors are properly sized and your interior panel is rated not less than the exterior main (buss rating)./
Your transformer would need to comply with 240.21(C) and would require a disconnecting means on the secondary in accordance with the secondary rules in 240.21(C), normally no greater than 25 ft.

sorry, Bob. stepped on you but basically the same answer, I think.

 

[wirenut46]

outside breaker

outside breaker

It is not mounted on the building sitting 10 foot away at a remote location right behind the building looks like they built a 4 foot wall with a door but no roof where all the service equipment is.

 

[augie47]

Quite possibly a AHJ call, but if the 400 amp breaker is mounted on/in a separate structure, your inspector might well enforce Part II of 225.30 and 250.32 requiring you to have an additional disconnect nearest the point of entry to the second structure.
There are a boatload of Code requirements if you need to go that route.... way too many to
detail here. If you AHJ approaches it as "one structure supplying another" you need to review all the pertinent sections of 225 Part II and 250.32. It's very involved.

Note there are exceptions to 225.32 which might apply.
I would suggest you read that Section 1st and see if there are more specific questions you might need to ask.