Motor calculations
Stator windings can best be described as
A structure of copper or aluminum wire coils
The motor circuit calculations reflected in this module are described in NEC
Article 430
Generally the most effective method of power factor correction is the installation of blank at the cause of the poor power factor
Capacitors
MS CP's are known as what
Motor short-circuit protectors
The main types of devices used to provide motor overload protection include
Overload relays fuses and circuit breakers
The speed at which the magnetic field rotates is known as the
Synchronous speed
These motors must not have fuses size more than 150 percent of the motor's full load current rating where absolutely necessary for proper operation
Wound rotor and direct current motor
The blank is the number by which the horsepower rating is multiplied to determine the maximum safe load that a motor may be expected to carry continuously at its rated voltage and frequency
service factor
The formula for synchronous speed is synchronous speed equals
120 times frequency divided by the number of poles
Some three phase motors designed for operation on voltage is higher than 600 volts may have more than 12 leads motors with blank or blank leaves are comin in hot voltage situations
15 or 18 leads
A circuit breaker suitable for use as a motor disconnecting means must have a current rating of at least blank percent of the motor full load current
175
If necessary for problemo to restoration do element time delay fuses maybe size up to blank of the motors full load current for all standard motors with the exception overwhelmed rover and rec current motors
175 percent
In general NEC table for 30.52 specifies that short circuit ground fall protection no one time delay fuse can be sized at blank of the motor full load current for ordinary motors all those for a while and rotor or direct current motors may be sized at
300% and one hundred and fifty percent
The NEC recognizes the use of instantaneous trip circuit breakers without time delay for short circuit protection of motor branch circuits such breakers are acceptable only if they are blank and are used in combination motor starters
Adjustable
The main purpose of motor overload protection is to protect the motor from what
Damaging overload currents
Doubling the voltage on a dual voltage motor does what
Halves the full load current
When a motor is operated at 240 volts the current draw of the motor is blank the current draw of a 480 volt connection
It is double the current draw
The synchronous speed of a three phase motor is determined by two factors
Number of stator poles and frequency of the AC line in hurts
Motor short circuit protectors for fuse like twice is designed for use only in special type of usable switch combination motor starter the combination lock for short circuit protection blink disconnecting means and motor control all with assured coordination between short circuit interrupter and the overload devices
Overload protection
Generally two levels of overcurrent protection required for motor branch circuits they are
Overload protection and short circuit protection which includes ground fall fault
NEC section 430. 5134 30.58 require the branch circuit protection for motor controls protect the circuit conductors control apparatus and the motor itself against overcurrent due to
Short circuit or ground fault
These are three basic types of 3 phase motors
Squirrel cage induction motor round rotor motor synchronous motor
The principle of operation for all three phase motor is a rotating magnetic field there are three factors that cause the magnetic field to rotate
The voltages of a three phase electrical system or a hundred and twenty degrees out of phase with each other the three voltages change polarity at regular intervals the stator windings around the inside of the motor are arranged in a specific manner to induce rotation
True or false and MSC P is designed for use only in a special type of a fusible switch combination motor starter
True
When absolutely necessary for proper operation the rating of dual element time delay fuses may be increased but must never be more than blank of the motor full load current rating
Two hundred and twenty five percent
The two most common three phase motor configurations are
Y and Delta
The type of three phase motor is determined by
The rotor or rotating member