Protection Devices

Question 1

Do general distribution circuits require protection against short circuit and overloads?

Answer 1

yes

Question 2

Do short circuits normally have lower or higher values than overloads?

Answer 2

higher

Question 3

Does a short circuit path have higher impedance than normal?

Answer 3

no

lower

Question 4

What do overcurrent devices protect against?

Answer 4

protect circuits and equipment from excessive temperatures by currents than are higher than normal

Question 5

What are two protective devices?

Answer 5

overcurrent and overload

Question 6

What are the two main types of fuses?

Answer 6

time delay, non-time delay

Question 7

The instantaneous trip mechanism in a circuit breaker, which provides for short circuit protection, is provided by a _____ _____ element

Answer 7

electromagnetic responsive

Question 8

What are the two current ratings on an overcurrent device?

Answer 8

continuous, interrupting

Question 9

What are the two main types of circuit breakers?

Answer 9

instantaneous and time limit

Question 10

On what type of circuit would you find an overload device?

Answer 10

motor

Question 11

What are the two types of protection offered by fuses?

Answer 11

non-time delay, time delay

Question 12

What are the two ampere ratings that overcurrent devices have?

Answer 12

continuous rating, interrupting rating

Question 13

What are the two mechanisms of a thermal magnetic circuit breaker?

Answer 13

a bimetal strip, short circuit sensing element or solenoid

Question 14

Which mechanism of thermal magnetic circuit beakers causes the breaker to trip during a prolonged overload condition?

Answer 14

half, quarter

Question 15

A non-time delay fuse can clear a short circuit condition in less than ____ of a cycle and higher short circuit current in less than _____ of a cycle

Answer 15

the bimetal strip

Question 16

Describe the sequence of events that occur to a time delay fuse responding to a short circuit condition

Answer 16

the fuse link vaporizes and the surrounding arc quenching filler extinguishes the arcing current

Question 17

What is the best fuse selection for sensitive equipment

Answer 17

an ultra acting fuse

Question 18

Why is it important to know the interrupting rating of a fuse or breaker?

Answer 18

it must be able to turn off the circuit without blowing up

Question 19

List the four factors that affect the maximum available short circuit current

Answer 19

kVA of transformer

Percent IZ

Circuit Voltage

Impedance of short circuit path

Question 20

Is a circuit breaker a means of disconnecting in a motor circuit?

Answer 20

yes

Question 21

What must a disconnect in a motor circuit be able to disconnect?

Answer 21

all ungrounded conductors

Question 22

Is a magnetic motor starter a motor disconnect?

Answer 22

no

Question 23

List the two basic control requirements for a motor branch circuit

Answer 23

disconnecting means, motor control

Question 24

Can a non-time delay fuse provide both short circuit and overload protection?

Answer 24

no

Question 25

A motor attempts to drive _____ load that is connected to it

Answer 25

any

Question 26

Motor starting current is usually _____ than its full load current

Answer 26

several times higher

Question 27

True or False?

Most motors are not damaged by a brief overload

Answer 27

true

Question 28

Do breakers and non-time delay fuses protect against overcurrent protection?

Answer 28

yes

Question 29

True or False?

A factory installed bimetal disk in a thermally protected motor protects the motor against short-circuit currents

Answer 29

false

Question 30

The heater of an overload device is connected directly into the motor control circuit.

True or false?

Answer 30

true

Question 31

Can a motor controller have a lower horsepower rating than the motor it controls?

Answer 31

no