Manual Motor Control and Overload Protection

Question 1

All electric motor use control devices. The five function served by these devices include:

Answer 1

1. Start/Stop Control
2. Motor and Circuit Protection
3. Speed Control
4. Jogging
5. Reversing

Question 2

The four common requirement of a motor installation are:

Answer 2

1. Disconnect
2. Short Circuit Protection
3. Controller
4. Overload Protection

Question 3

Can you use overloads as short circuit protection?

Answer 3

No, because overload is specifically designed to protect the motor. If the motor draw excessive current over time, fuses will not initiate due to its current not great enough.

Question 4

What is the difference between motor controller and motor starter?

Answer 4

Motor controller open and closes the power wires to start and stop a motor. Motor starter is a motor controller that includes overload protection for the motor.

Question 5

A common example of jogging control of an electric motor is the positioning of a table on a _________

Answer 5

CNC mill

Question 6

Motor starters fall into two basic categories, based on the method used to close their contacts. The two basic categories of motor starters are:

Answer 6

Manual Starters and Magnetic Starters

Question 7

What is the difference between manual starter magnetic starter?

Answer 7

Manual starters have contacts that open and close when an operator manually actuates a pushbutton or lever. Since they are starters, they also include overload protection for the motor.

Magnetic starters open and close their contacts using a magnetic coil

Question 8

The two basic type of manual motor starters are based on the type of AC motor they start and the horsepower rating of the motor. The two types are:

Answer 8

1.Fraction Horsepower Manual Starter
2. Integral Horsepower Manual Starters

Question 9

How can fractional horsepower manual starter be use?

Answer 9

It can only be used on single phase motors rated for one HP or less. They are usually available for toggle switch style, which can be either single pole or two-pole.

Question 10

what is low -voltage protection-?

Answer 10

A device that has low voltage protection will prevent the automatic restart of the motor when recover from power outage.

Question 11

The three most common types of overloads are:

Answer 11

Thermal, Magnetic and solid state overloads

Question 12

The two common types of thermal overloads:

Answer 12

Melting alloy and Bimetallic

Question 13

Bimetal strip: For hot conditions, the adjustment knob permits the overload relay to be adjusted between _____ to_____ of motor full-load current.

Answer 13

100% to 115%

Question 14

Bimetal strip: For cold conditions, the adjustment knob permits the overload relay to be adjusted between ____ to ____ of motor full-load current.

Answer 14

85% to 100%

Question 15

Thermal overload relay trips faster due to _________.

Answer 15

High ambient temperatures

Question 16

The two basic methods of constructing a relay or contactor.

Answer 16

1. clapper type
2. bridge type

Question 17

Clapper type Relays: when the coil is energized, the ________ is attracted to the _________ inside the coil

Answer 17

armature, iron core

Question 18

what does shading coil do?

Answer 18

Shading coil provide a time delay for the magnetic field to prevent chatter.