OCP for feeders

[Npstewart]

Is it possible to have a 400A enclosed breaker (main) in a electric room feeding a 200A MCB panel with #3/0? Wouldn't the #3/0 conductors be over-fused from the electric room to the panel.

Im having a constructive argument with a co-worker, thanks guys.

PS> Im looking for the code section. thanks

 

[raider1]

240.4 requires conductors to be protected against overcurrent in accordance with their ampacities specified in 310.15, unless permitted or required in 240.4(A) through(G).

So the general rule is that feeder conductors must be protected from overcurrent at their rated ampacity in accordance with 310.15.

Chris

 

[jumper]

How about this?

240.4 Protection of Conductors. Conductors, other than
flexible cords, flexible cables, and fixture wires, shall be
protected against overcurrent in accordance with their ampacities
specified in 310.15, unless otherwise permitted or
required in 240.4(A) through (G).

 

[Robert Hutcherson]

I believe it should be handled similar to feeder tap and the limitations under that code article.

 

[raider1]

I believe it should be handled similar to feeder tap and the limitations under that code article.

I agree that the feeder tap rules could be used in this case.

Chris

 

[Npstewart]

Thats funny because I said the same thing. These conductors are basically un-protected so I would think it would be a feeder tap.

We ended up changing the 400A to a 200A breaker so everything matches now.
I appreciate the help.

 

[LarryFine]

Is it possible to have a 400A enclosed breaker (main) in a electric room feeding a 200A MCB panel with #3/0? Wouldn't the #3/0 conductors be over-fused from the electric room to the panel.

I was goint to ask about the feeder length, but you guys already got there.