Fuse / Wire Size Coordination

[Mike01]

At a project site today, there was a 30A disconnect switch with 25A fuses with #12 wire...looking in the code the #12 wire is protected by the 25A fuses but is this acceptable if the switch is rated 30A? Usually I would expect #10AWG wire but the fuses are 25A?

 

[Smart $]

Use of fuses rated less than disconnect rating is commonplace, acceptable, and compliant... but the last two are dependent on other factors of the circuit. For example, you can only protect #12 copper wire with 20A fuses, max [240.4(D)(5)], unless the equipment supplied specifically permits higher [240.3].

 

[topgone]

At a project site today, there was a 30A disconnect switch with 25A fuses with #12 wire...looking in the code the #12 wire is protected by the 25A fuses but is this acceptable if the switch is rated 30A? Usually I would expect #10AWG wire but the fuses are 25A?

Just keep in mind that it will be desirable to have a busted fuse than a busted switch. That means your fuse melts off before your switch does--> a good thing, IMO.