Download ELECTRICAL TEST ANSWERS April 14, 2004 1. Chapters 1

ELECTRICAL TEST ANSWERS
April 14, 2004
1. Chapters 1 through 4 of the NEC® apply __________.
þ A. generally to all electrical installations
National Electrical Code Section 90-3
B. to special installations and conditions
C. to special equipment and material
D. all of these
2. The demand factors of Table 220-20 apply to space heating, ventilating, and air-conditioning
equipment.
A. True
þ B. False
National Electrical Code Section 220-20
3. A ________ is a circuit that contains some resistors in series and some resistors in parallel to each
other.
A. parallel circuit
B. series circuit
þ C. series-parallel circuit
D. none of these
4. Type FCC cable shall be clearly and durably marked ___________.
A. on the top side at intervals not exceeding 30 inches
B. on both sides at intervals not exceeding 24 inches
C. with conductor material, maximum temperature, and ampacity
þ D. B and C National Electrical Code Section 328-31
5. “Effect ive” is the alternating current voltage or current value that produces the same amount of
heat in a resistor that would be produced by the same amount of direct current voltage or current,
___________ is the same as effective.
A. Peak
þ B. Root-mean-square (RMS)
C. Instantaneous
D. None of these
Effective values of alternating current and voltage are the ones ordinarily referred to when
speaking of alternating quantities. Alternating voltages and currents are constantly changing
in value, within a certain range, from instant to instant even if the load is constant. It is not
practicable to deal with or indicate with instruments these constantly changing values. The
effective value of an alternating current or voltage is the value of a direct current or voltage
that will have the same heating effect. A sinusoidal alternating current which has a maximum
value of 14.14 amp will have the same heating effect as a 10-amp direct current. The effective
value of the alternating current is therefore 10 amp. The practical man deals almost
Name: ______________________________________
exclusively with effective values. Alternating-current measuring instruments indicate effective
values. The relation between effective and maximum values for sinusoidal quantities is given
below and illustrated in Fig A. Effective value is also referred to as rms value (root mean
square).
Effective value = 0.707 x maximum value
Maximum value = effective value/0.707
Example.
Solution.
What is the effective voltage of a circuit that has a maximum voltage of 156?
Substitute in the formula:
Effective value =.0707 X maximum value = 0.707 X 156 = 110 volts
Example.
Solution.
If a voltmeter of an a-c circuit reads 2,200, what is the maximum instantaneous
voltage?
Substitute in the formula:
Maximum value = effective value/0.707 = 2,200/0.707 = 3,110 volts
Fig A