split-phase motor

[skittleslove]

Where in the 2002 code book can i find information on this question:
The load on a split-phase motor is sufficent to prevent the motor from getting up to speed. which is likely to happen?

A. the fuse is blown
B. starting winding burn out
C. the running winding burns out
D. none of these

 

[tom baker]

Re: split-phase motor

Why does this look like a test question? You won't find an answer (directly) to this question in the NEC. this question requires you to have knowledge of how a motor operates.
Hint: what is a split phase motor? how does it start?

 

[gramps]

Re: split-phase motor

you probably need to go to the EASA website and check out their troubleshooting guide. i dont think you'll find the answer to your question in the NEC.


gramps

 

[harryg]

Re: split-phase motor

Split-phase
The split-phase motor, also called an induction-start/induction-run motor, is perhaps the simplest kind of single-phase motor you'll find in the plant. It has two windings: a start and a main winding. The start winding is made with smaller gauge wire than the main winding and has much higher resistance. This results in different currents and magnetic fields in the two windings. These two magnetic fields, displaced from each other, form a rotating field that causes the rotor to turn.
Split-phase motors use a switching mechanism that disconnects the start winding when the motor comes up to approximately 75 percent of rated speed. Thereafter, the main winding operates independently. A centrifugal switch on, the motor shaft is most common.
The split-phase motor's simple design is typically less expensive than other single-phase motor types made for industrial use. However, the simplicity limits performance. Starting torque is low; 100 to 175 percent of rated load. In addition, the split-phase motor develops high starting current relative to motor horsepower, also called locked rotor current. In addition, because of the small wire used in the start winding, prolonged starting times can cause the motor to overheat and the start winding to fail. Therefore, don't use this motor if high starting torque is required.
Other split-phase motor limitations include relatively low breakdown torque (200 to 300 percent of rated load), and unreliable thermal protection due to the high locked rotor current relative to running current. Also, these motors usually are designed for single voltage, limiting application flexibility.
Good applications for split-phase motors include small grinders, small fans and blowers, and other low starting torque applications with horsepower requirements ranging from 1/20 to 1/3 hp. Avoid any applications requiring high cycle rates or high torque.