Frame Sizes vs. Fuse and Wire Sizes

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Dale Hayes

Senior Member
Fused disconnect frames are sold in 200amp, 400amp, 600amp, 800amp, 1200amp frame sizes, etc.

I have an application that only requires 250 amps.

Can I install three JLLS 250amp fuses into the 400amp frame and size my wire (on the load side of the switch) at 300kcmil for the 250amp load?

Or,

Do I need to size the wire at the line and load side of the switch at 600kcmil for the 400amp frame size?
 
Even though someone could install larger fuses in the future as Crossman said you are only required to match the conductor and fuse sizes. The switch size in this case is irrelevant.
 
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