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#8919 04/09/02 10:17 PM
Joined: Apr 2002
Posts: 4
R
Junior Member
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!

#8920 04/10/02 08:37 AM
Joined: Nov 2000
Posts: 2,236
Member
Great Q!

I always thought that was a typo... and how could they possibly tell the difference between a 600 and a 601? (Put >601A on it and the 601 will open first?)


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
#8921 04/12/02 11:34 AM
Joined: Mar 2002
Posts: 29
D
Member
Randy,

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.

Thanks,
Dan

#8922 04/12/02 10:22 PM
Joined: Nov 2000
Posts: 2,236
Member
Dan,

Thanks, as usual, when one finally understands the "why's", it's easier to remember...

Now it makes sense...

[Linked Image]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

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