Deck 13: System Protection

Question 1

Low-voltage power circuit breakers commonly have ____ set(s) of contacts.

A) one
B) two
C) three
D) four

Answer 1

B

Question 2

____ means that when an overload or fault condition occurs, only the part of the electrical system that is in jeopardy is disconnected.

A) Dependent coordination
B) Ground-fault protection
C) Selective coordination
D) System protection

Answer 2

C

Question 3

____ air circuit breakers are used in low-voltage (600 volts or less), low-current circuits.

A) Low-voltage
B) Molded-case
C) Medium-voltage
D) High-voltage

Answer 3

B

Question 4

Classify low oil (also called oil poor) circuit breakers.

Question 5

Circuit breakers actually have two different current ratings. One is the trip rating, and the other is the ____ rating.

A) fuse
B) ground
C) selective
D) interrupt

Question 6

What is an auxiliary switch?

Question 7

The ____ is the point at which a breaker responds to a short-circuit current through a magnetically actuated trip arrangement.

A) long-time delay
B) frame size
C) instantaneous pickup current
D) instantaneous opening

Question 8

What are some required and recommended uses for ground-fault protection devices?

Question 9

The amount of current that will flow during a short-circuit condition is determined by two factors: the voltage and the ____.

A) impedance
B) power
C) coil strength
D) fuse strength

Question 10

A ground-fault protective device consists of a ground-fault sensor and a ____.

A) relay
B) circuit breaker
C) transformer
D) fuse

Question 11

There are two basic types of oil circuit breakers, the full tank or dead tank type and the low oil or ____ type.

A) half tank
B) oil poor
C) low tank
D) oil-free

Question 12

What is indicated by the long-time delay portion of the time-current curve?

Question 13

In magnetic-type circuit breakers , there is ____ time delay in the opening of the contacts when an overload occurs.

A) zero
B) very little
C) medium
D) very high

Question 14

What is the mechanism behind the operation of a thermal circuit breaker?

Question 15

One method used by circuit breakers to sense circuit current is to connect a(n) ____ in series with the load.

A) battery
B) ammeter
C) coil
D) resistor

Question 16

When an electric arc occurs in air, gas molecules in the air ____.

A) become polarized
B) become ionized
C) form dimers
D) start a chain reaction

Question 17

The three major types of circuit breakers are air, oil, and ____.

A) water
B) vacuum
C) alcohol
D) mercury

Question 18

A system containing only ____ is the easiest situation to coordinate.

A) main circuit breakers
B) branch-circuit breakers
C) ground-fault protectors
D) fuses

Question 19

____ trips are used to open the circuit breaker contacts by energizing the solenoid from an external source.

A) Shunt
B) Fuse
C) Interrupt
D) Coil

Question 20

Coordination among multiple ground-fault protectors is achieved by using a lower ____ setting and progressively shorter time settings on each of the downstream devices.

A) trip
B) interrupt
C) fuse
D) arc