Code for using a breaker as a disconnect

E

Ericseale

Member
Location
Mississippi
Occupation
Electrician
Im replacing a 400amp interior panel which is currently fed with a 400amp breaker from an 800amp switch gear. Customers load has reduced to the point where a 400a panel isnt needed, so im replacing with a 200a. Why can i not feed the 200a with 200a feeders fed off the 400a main breaker? I get the feeders are undersized for the 400amp but they are then fused at the sub panel, so it would be the same as using a 400a disconnect with 200a feeders going to the sub panel (which the inspector said would be acceptable). I dont see the difference between using the breaker and the disconnect? Any help would be appreciated.
 
As long as the wire is protected per 240.4 (or 240.21) and the panel is protected per 408.36, then it is okay.

Ericseale said:
Why can i not feed the 200a with 200a feeders fed off the 400a main breaker?
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400A breakers do not protect 200A of wire or a panel rated 200A. You can design it to be like a tap or replace the 400A breaker with a 200A breaker. A tap would require the 200A of wire to land in a 200A overcurrent protective device (240.21(B)).

Ericseale said:
I get the feeders are undersized for the 400amp but they are then fused at the sub panel, so it would be the same as using a 400a disconnect with 200a feeders going to the sub panel (which the inspector said would be acceptable). I dont see the difference between using the breaker and the disconnect? Any help would be appreciated.
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Breakers are OCPDs and disconnects. A 400A fused disconnect switch can have the fuses swapped for 200A to make that compliant. Or just be used as a disconnect. Except for taps, overcurrent protection must be at the point of supply.
 
You can only feed the panel with 200A conductors with a 400A breaker protecting the 200A conductors if it can be considered a Tap which has a maximum length of 25'. And the tap must terminate at a 200A breaker for a 200A fused disconnect.
 
Eddie702 said:
You can only feed the panel with 200A conductors with a 400A breaker protecting the 200A conductors if it can be considered a Tap which has a maximum length of 25'. And the tap must terminate at a 200A breaker for a 200A fused disconnect.
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Its on the other side of the same wall, 15’ total length of run. And the panel i would be feeding would have a 200amp main.
 
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