Chapter 2 - Fuses, Disconnect Switches, and Circuit Breakers

TRUE/FALSE

	1.	The 120 VAC circuit is normally protected by a single fuse or circuit breaker.

ANS:	T	PTS:	1	REF:	Protective Factors	

	2.	Switching voltage surges are usually limited to three times normal voltage.

ANS:	T	PTS:	1	REF:	Voltage and Frequency Surges

	3.	By programming a motor-protective relay unit with the motor’s electrical characteristics, the unit’s algorithm will automatically tailor the optimal protection curve to the motor being monitored.

ANS:	T	PTS:	1	REF:	Programmable Motor Protection

MULTIPLE CHOICE

	1.	The typical fuse consists of an element surrounded by a filler and enclosed by the fuse body. The element is a calibrated ____.
a.	insulator	c.	conductor	
b.	transistor	d.	capacitor	

ANS:	C	PTS:	1	REF:	Fuse Construction and Operation

	2.	Peak let-thru current (Ip) and ampere squared seconds (I2t) are two measures for the degree of ____ provided by a fuse.
a.	current limitation	c.	circuit isolation	
b.	time delay	d.	rectification	

ANS:	A	PTS:	1	
REF:	Peak Let-Thru Current (Ip) and Ampere Squared Seconds (I2t)	

	3.	____ is the current-limiting characteristic of a transformer and is expressed as a percent.
a.	Capacitance	c.	Ampacity	
b.	Impedance	d.	Rectification	

ANS:	B	PTS:	1	REF:	Selecting Protective Devices

	4.	The main purpose of a ground fault circuit interrupter (GFCI) is to ____.
a.	determine the interrupting capacity	c.	protect a person from electrical shock	
b.	calculate the available current	d.	gauge the ambient temperature	

ANS:	C	PTS:	1	REF:	Ground Fault Circuit Interrupter

COMPLETION

	1.	All protective devices have a published ____________________, which is defined as the highest current at rated voltage that a device can safely interrupt.

ANS:	interrupting capacity

PTS:	1	REF:	Fuse Types

	2.	____________________ fuses are used today in almost all fuse applications.

ANS:	
Current-limiting time-delay
Current limiting time delay

PTS:	1	REF:	Fuse Types

	3.	Adding a(n) ____________________ to the nonautomatic circuit breaker, by using a bimetallic element in each pole of the breaker, provides automatic tripping.

ANS:	thermal trip unit

PTS:	1	REF:	Circuit Breaker Types