Electrical 3 Test 5
A device that is designed to withstand numerous trip and reset cycles without replacement and can be thermal, magnetic, or solid-state is an
Overload relays
The recommended method of determining short circuit currents is the
Point to point method
All of the following are classifications of medium-voltage fuses except
Proportion fuses
One characteristic of a dual element time delay fuse is that it
Provides back up if protective devices fail to operate
The minimum interrupting rating of branch circuit listed fuses is
10,000 A
The maximum fuse size for a single element non-time delay fuse serving a 10 hp three phase motor is
100 A
500A circuit breaker has a frame size of
1000A
The minimum voltage rating of branch circuit fuses is
125V
A plug fuse with a hexagonal cap has a maximum amperage rating of
15A
If a continuous load on a branch circuit is measured at 12A, the overcurrent protection should be sized at _____.
15A
A feeder circuit with no motor load has a continuous load of 10A and a noncontinuous load of 5A. The feeder overcurrent protective device should be sized at
17.5A
UL Class R fuses have a short circuit interrupting rating of up to ____.
200,000A
A feeder circuit with no motor load has a continuous load of 15Aand a noncontinuous load of 10A. The feeder overcurrent protective device should be sized at
28.75A
A feeder circuit with no motor load has a continuous load of 16A and a noncontinuous load of 10A. The feeder overcurrent protective device should be sized at
30A
The full load current rating of a 300kVa, three phase transformer operating at 480v is
361A
The full load current rating of a 150kVA, three-phase transformer operating at 240V is
362A
A high level short circuit current may exceed
50,000A
If a 120V feeder for nonmotor loads feeds a continuous load rated at 20A and a noncontinuous load at 25A, what size overcurrent protective device should be selected?
50A
For 480V circuits, the arc current seldom exceeds _____.
60% of the available bolted fault current
UL classifies low-voltage fuses at those operating at
600V or less
For proper coordination the total clearing time of any downstream protective device must be below a curve representing which percentage of the minimum melting curve of the fuse being applied
75%
Under normal operation and at currents near its ampere rating, a fuse operates as a
Conductor
One of the first signs of worn motor bearings is most likely to be a(n)
Continuous overloads
Worn motor bearings are most likely to result in a
Continuous overloads
The type of fuse used to prevent nuisance tripping from temporary motor overloads and surge currents is a
Dual element time delay fuse
A conductor with failed insulation contacts the metal edge of a grounded metal wire way. This is known as a
Ground fault
Accidental contact between an electrical conductor and a grounded enclosure is called a
Ground fault
If a circuit breaker has tripped and stays on for a limited time before tripping again after being reset, the problem is least likely to be a
Ground fault
Most arcing faults begin as
Ground fault
A type of fuse with a grooved ring in one ferrule is a Type _____.
R
Which of the following is true with regard to circuit breaker interrupting capacity ratings
UL tests now include NEMA ratings
Which of the following is true with regard to circuit breakers
Under normal conditions, the current flow bypasses the spring and latching mechanism.
An expulsion fuse is best described as a
Vented fuse in which the expulsion effect of the gases produced by the arc and lining of the fuse holder either alone or aided by a spring extinguishes the arc
The interrupting capacity of a circuit breaker is based on its rated
Voltage
A 600V fuse can be used in _____.
a 240V circuit
The voltage rating of a fuse
can be higher than the circuit voltage but never lower
Equipment intended to interrupt current at fault levels must have an interrupting rating at nominal circuit voltage that is ____
equal to the current available at the line terminals of the equipment
When tripped, the circuit breaker handle moves _____.
halfway between the on and off positions
The thermal portion of a standard circuit breaker
protects the circuit from heat damage generated by lower level currents
A 60A circuit breaker has a frame size of _____.
100A
A standard circuit breaker frame size is
100A
What is the frame size of a 30A circuit breaker
100A
The full-load current rating of a 225kVA three-phase transformer operating at 240V
542A
The let-through short circuit current of a 500kVA, 120/208V three-phase transformer is _____.
69,444A
A circuit breaker that trips instantly or fails to reset is most likely the result of
A short circuit
Which of the following best describes the maximum short circuit current that a fuse or circuit breaker will safely interrupt
AIC
When circuit breakers are classified as 100A through 2000A frames, these numbers are normally referred to as the
Frame size
Which of the following is true with regard to fuses
Fuse holder clips that have lost their spring cannot be repaired with pliers, they must be replaced
Overcurrent protection is covered in
NEC Article 240
Types of fault current include overloads, short circuits, ground faults, and
arc faults
A plug fuse is typically used in a
branch circuit
Each of the following is a basic, factor to a consider when applying any fuse except
manufacturer's brand name
When a common circuit breaker trips, the handle is in the _____.
middle position
A single-element fuse
provides an instantaneous trip for high levels of current
The magnetic portion of a standard circuit breaker
provides an instantaneous trip for high levels of current
Which of the following is within the basic scope of Underwriters Laboratories
safety
Which of the following is commonly referred to as motor branch circuit protection
short circuit protection
Circuit breakers are classified by
the largest ampere rating of its range