Overcurrent Protection

Question 0

What are the problems created by overload.

Answer 0

Annealing
Rapid oxidation
Burning insulation
Cracking insulation

Question 1

What is overload?

Answer 1

Overload is a moderate increase in current beyond the normal rated current value.

Question 2

What are typical causes for overload?

Answer 2

Too much equipment
Use of improper size equipment
A worn out or seized motor

Question 3

What is overcurrent?

Answer 3

Ranges from six times to several hundred times the normal rated current.

Question 4

What are some causes for overcurrent??

Answer 4

Motor start

Short circuit

Question 5

What are two causes of a short circuit?

Answer 5

Failure of the conductors insulation.

A foreign object makes accidental contact causing line to line short.

Question 6

What is a short circuit?

Answer 6

A larger than normal current that flows outside the normal current path.

Question 7

What is a ground fault?

Answer 7

Another form of short circuit. Short circuit to ground.

Question 8

What are the effects of short circuit current??

Answer 8

Mechanical forces

Thermal energy

Question 9

Voltage rating refers to the ability of the protective device to

Answer 9

Quickly extinguish the arc

Prevent the open circuit voltage from restriking across the open fuse element

Question 10

Current rating

Answer 10

The current the device can carry continuously without opening, deteriorating, or exceeding temp limits

Question 11

Interrupting rating

Answer 11

The maximum short circuit current an overcurrent device can safely interrupt without damaging itself.

Question 12

A fuse may occasionally open when

Answer 12

The ambient temp is high, or excessive vibration.

When the connection is loose or dirty.

Question 13

When replacing a fuse observe the correct:

Answer 13

Voltage rating
Current rating
Interrupting capacity rating
Time current characteristic

Question 14

Standard voltage ratings of low voltage fuses

Answer 14

600V
300V
250V
125V

Question 15

What is the interrupting rating on a HRC fuse.

Answer 15

200 000 A

Question 16

What types of fuses are there

Answer 16

Plug fuses

Cartridge fuses

Question 17

Type W plug fuse

Answer 17

Standard non time delay

Question 18

Type D plug fuse

Answer 18

Time delay

Question 19

What is the maximum rating for plug fuses

Answer 19

30A

125V

Question 20

HRC1 fuse

Answer 20

Provides protection from overload and overcurrent

Question 21

HRC11 fuse

Answer 21

Short circuit protection only

Question 22

What are the four main types of moulded case circuit breakers

Answer 22

Thermal
Thermal-magnetic
Magnetic
Solid state

Question 23

What kind of protection does a magnetic only circuit breaker provide?

Answer 23

Short circuit only

Question 24

Five major components of a circuit breaker.

Answer 24

``` Frame Operating mechanism Trip elements Contacts Terminal connection ```

Question 25

What is trip free

Answer 25

It trips even when it's handle is held in the on position.