fuse size in uglys book

[S'mise]

I sized a control panel to a 15hp motor to the flc (table says 21A) and multiplied that by 175% for a dual element time del fuse and get 36.75, next size up rule put me at 40amps. Why does my Uglys book say the max is 30? :?

 

[kwired]

I sized a control panel to a 15hp motor to the flc (table says 21A) and multiplied that by 175% for a dual element time del fuse and get 36.75, next size up rule put me at 40amps. Why does my Uglys book say the max is 30? :?

NEC table 430.52 is max. Does Ugly's say max or is it just a recommended size? My Square D slide chart motor calculator also says 30 amp time delay for your application - but is just a suggestion for most applications and not a maximum size.

 

[augie47]

Uglys is a good reference but I think you will find it tends to undersize allowed OCP and oversize conduit.
For field installs it might be more practical. Considering the costs, most electricians would probably go for the 30 amp fuse and disconnect as long as it was sufficient.

 

[S'mise]

thanks

thanks

Ahhh, your right. Thanks for clarifying. Is there a rule of thumb for figuring a minimum size? Say, start with 140% flc for a (time del fuse)?