HI Dan, Thanks for being here! 240.6 on Standard Ampere Ratings for fuses and fixed-trip cb's is pretty well self-explanatory. But, why a fuse with a standard ampere rating of 601 Amps? Is this a special application of some type? Thanks in advance!
That is probably one of the most asked questions when it comes to fuses. In fact I had the same question last week.
The reason there is a 601 fuse is to give flexibility. Class R and J fuses only go up to 600A. Above 600A, a Class L fuse must be used. Class L fuses range from 601A-6000A. The first case size of a listed Class L fuse is 800A with fuses sizes typically of 601, 650, 700, 750 and 800A.
Thus, if you have a circuit that could be sized at 600A, but may have to be increased in the future due to future expansion or motor inrush issues, Class L is the obvious choice. By going with a 601A Class L fuse, in an 800A disconnect, the fuses could be increased in the future up to 800A, provided conductors with an appropriate ampacity are used.
Re: Standard Fuses#8922 04/12/0211:22 PM04/12/0211:22 PM