NCCER Electrical Level 3 Mod 9 Practice Questions and Correct Answers

3 basic types of 3ø motors Synchronous motor Wound rotor induction Squirrel cage induction 3 factors that cause the magnetic field to rotate The voltages of a 3ø electrical system are 120° out of phase with one another The three voltages change polarity at regular intervals The stator windings around the inside of the motor are arranged in a specific manner to induced rotation They sync speed of 3 phase motor is based on 2 factors Number of stator poles Frequency of the ac line in hertz The formula for sync speed is 120F divided by P F= Frequency P= Number of poles When a motor is operated at 240 volts the current draw of the motor is ___ the current draw of a 480 volt connection Double I= E/R Multiply the full load current of the largest motor ___ then add the sum of the remaining motors to the result. The combined total will give the minimum feeder ampacity 1.25 The motor horse power is shown in the far left column of Table 430.250 Short circuit/ground fault protection non time delay fuses can be sized at ___ of the full load current 300% Motor wound or DC motors may be sized at ___ of the motor full load current 150% dual-element, time-delay fuses may be sized up to ___ of the motors full load current for all standard motors 175%