240.6 question

[Chris Mcc]

Section 240.6 says that among the additional standard ratings for fuses is 601 amperes. Can anyone explain what a 601-amp fuse would be used for?

 

[iwire]

The 601 fits in larger disconnects then the 600.

 

[infinity]

Typically a 601 will fit in an 800 amp frame as Bob said. This allows you to get very close to 600 amps of protection in an 800 amp frame.

 

[Chris Mcc]

I have to ask, why then isn't there a 101-amp fuse or 201, or 401 etc...?

 

[Pierre C Belarge]

The smaller NEMA rated fuses will suffice for the smaller frame sizes you mentioned. There is less of a size gap between the different size breakers/fuses in the smaller sizes.

 

[iwire]

Another member posted this info about a year ago, he works for a major fuse manufacturer.

laughing from reading the responses. A 601 fuse is designed to fit a Class L Switch/Disconnect, with a bolt-in pattern. These are usually installed in the "Mains". Every-once-in-awhile, I get a call out for a 401, 501, 601 amp fuse. As per UL 248, fuses are designed to hold 110% of their rating continuously. Some fuses are also rated to carry 500% for 10-20 seconds to ignore the motor inrush, however clear within 1/2 cycle (.008 seconds).

just my $.02

 

[Chris Mcc]

Thanks very much....learn something new every day!

 

[jim dungar]

600A and smaller fuses are either blade or ferrule mounting. These blade and ferrules sizes are dictated by the ampacity of the fuse. There are fuse reducers available to allow a smaller 400A fuse to be mounted into a 600A "clip".

Above 600A reducers are not available. Historically a 601A fuse was used because per the standards a 600A fuse could not be a bolt-in style.

In just the past few years I have notice that the Class L fuse is now available with ampacities 600A and smaller, so the 601A is no longer needed.