Deck 17: Overcurrent Protection: Fuses and Circuit Breakers

Question 1

Describe the class of fuses that is used for control circuit protection.

Answer 1

Class CC fuses are primarily used for control-circuit protection, for the protection of motor control circuits, ballasts, small transformers, and so on.They are UL listed as branch-circuit fuses.Class CC fuses are rated at 600 volts or less and have a 200,000-ampere interrupting rating in sizes from
1/10 ampere through 30 amperes.These fuses measure 1-1/2 in.x 13/32 in.(38.1 mm x 10.3 mm) and can be recognized by a button on one end of the fuse.This button is unique to Class CC fuses.When a fuseblock or fuseholder that has the matching Class CC rejection feature is installed, it is impossible to insert any other 1-1/2 in.x 13/32 in.(38.1 mm x 10.3 mm) fuse.Only a Class CC
fuse will fit intothese special fuseblocks and fuseholders.A Class CC fuse can be installed in a standard fuseholder.

Question 2

Low-voltage power circuit breakers are listed under UL Standard .

A)844
B)1066
C)1215
D)1362

Answer 2

B

Question 3

In the case of a delta, 3­phase, corner­grounded "B" phase system, a device called a can be installed in the "B" phase.

A)service entrance
B)switchboard
C)cube fuse
D)solid neutral

Answer 3

D

Question 4

circuit breakers are the most common type in use today.

A)Power
B)Molded-case
C)Air-frame
D)Insulated-case

Question 5

Fused switches are available in ratings of up to amperes in both 250 and 600 volts.

A)400
B)600
C)4000
D)6000

Question 6

What are peak let-through charts used for?

Question 7

A dual-element, time-delay fuse has one or more fusible elements (links) connected .

A)in parallel
B)in series
C)during overload conditions
D)every 10 seconds

Question 8

When you remove a fuse from a switch, and then take a resistance reading across the fuse using a(n) , a good fuse will show zero or a very minimal resistance.

A)ohmmeter
B)wattmeter
C)voltmeter
D)delimiter

Question 9

Series-rated equipment is also referred to as .

A)series-connected
B)parallel-rated
C)inverse-parallel
D)series-broken

Question 10

For motor branch circuits, the maximum setting of a conventional inverse-time circuit breaker must not exceed percent of the full-load current of the motor.

A)100
B)125
C)200
D)250

Question 11

The Class fuse is a nonrenewable cartridge type and has a minimum interrupting rating of 200,000 RMS symmetrical amperes.

A)H
B)K
C)R
D)T

Question 12

An interrupting rating is a(n) rating, which is a measure of the fuse's or circuit breaker's ability to safely open an electrical circuit under fault conditions, such as an overload, short circuit, or ground fault.

A)recommended
B)maximum
C)minimum
D)average

Question 13

Conventional plug fuses have a base referred to as a(n) base.This base is of the same shape as the base on a light bulb.

A)Edison
B)Tesla
C)filamentous
D)threaded

Question 14

When compared to other types of fuses, the fuse has the lowest energy let-through values.

A)dual-element, time-delay
B)straight current-limiting
C)dual-element, nontime-delay
D)low-overload

Question 15

What is the mechanism through which thermal-magnetic circuit breakers work?

Question 16

and the National Electrical Manufacturers Association establish standards for the ratings, types, classifications, and testing procedures for fuses and circuit breakers.

A)Applied Research Laboratories, Inc.
B)Entela, Inc.
C)The Underwriters Laboratories, Inc.
D)TUV Rheinland of North America, Inc.

Question 17

The terms interrupting rating and are used interchangeably in the electrical industry, but there is a subtle difference.

A)short-circuit rating
B)interrupting minimum
C)interrupting capacity
D)short-circuit capacity

Question 18

Class fuses formerly were called NEC or Code fuses.

A)H
B)J
C)K
D)R

Question 19

What are the factors influencing speed of response of an overcurrent device?

Question 20

What are some prohibitions on the location of overcurrent devices?