Main breaker or disconnect?

Status
Not open for further replies.

B W E

Member
Hey guys, i'm sure this is a dumb question but I have been flipping back and forth through the NEC and handbook and can't find a definitive answer.

I am going to be installing a 30 kva 480 -208/120 transformer in a room adjacent to the electrical room. The transformer will then feed a 125 or 150 amp panel in the same room as the new transformer. Do I need OCP on the secondary, such as a fused disco or a main breaker in the new panel? Or can the secondary run straight to a Main Lug loadcenter? Screen shot 2011-04-05 at 4.06.10 PM.jpg The transformer is the small red box in the corner, and the loadcenter is the red box in the middle on the wall.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Your secondary conductors must meet the requirements of 240.21(C).
In addition, your secondary panel must meet the requirements of 408.36.

In summation, you do need a secondary OCP device which can be the panel main as long as your conductors comply with 240.21(C) (length, etc)
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Also note if you are planning a panel with a 125A or 150A mcb (or some other 125A or 150A secondary protection) then the primary of the transformer must be protected as "primary only" per Table 450.3(B).
 
Status
Not open for further replies.
Top