drilman
speaking to the motor running protection only here are a few general thoughts
The motor running protection is established in section 430.32 A, motors more than 1 Hp. Your installation (1.15 SF) allows the MRP set at 125% of Name Plate current 9 A. I agree with your calculation of 11.25A
430.32 (A) (1), States; “Separate Overload Device A separate overload device that is responsive to motor current. This device shall be selected to trip or shall be rated at no more than the following percent of the motor nameplate full-load current rating:
Note: "not more than" (125%)
I would not apply the 12A fuse. The Buss Electrical Protection Handbook suggests a 10 Amp dual element fuse for this motors overload protection.
This web site
http://www.bussmann.com/products/electrical/Group2.asp, and
http://www.bussmann.com/products/electrical/Group3.asp indicates that the RK 1, and 5 fuses will hold for a minimum of ten seconds at 500% of its rated current. That indicates to me that on hard start or actual overload the 10A fuse will hold to 50A for 10 seconds(or longer). The 12 Amp fuse will hold 60A for ten seconds (or longer).
Generally thermal devices are rated as class 10, 20, and 30 with these numbers indicating the approximate time in seconds they will endure there rated current (generally selected at 125% of motors name plate current).
I would not exceed the 10 Amp device if you intend to connect the motor in the manner you describe.
If you get a motor controller usually the overload devices are selected off the manufactures lable, but the Code will still limit the size to 11.25A.
[This message has been edited by cpal (edited 08-17-2004).]
