Chapter 9 - Power Distribution Flashcards
The ampacity of a conductor is related to the conductor size, _____, and type of insulation.
a. Temperature
b. Length
c. Resistance
d. Impedance
a. Temperature
p 9-17
The ampacity of a conductor is related to the conductor size, temperature, and means of insulation. NEC Article 310, Conductors for General Wiring, provides detailed information on the ampacity of conductors.
Article _____ of NFPA 70 [the National Electrical Code (NEC)] allows information technology equipment (ITE) rooms to make exceptions to other mandatory NEC chapters.
a. 345
b. 443
c. 75
d. 645
d. 645
p 9-23
Article 645 essentially allows ITE rooms to make exceptions to other mandatory NEC chapters if all of the specific requirements of Article 645 are followed. It is not permissible to select which requirements of Article 645 can be utilized.
In a _____ direct current (dc) distribution topology, power is directed from the switchboard to a secondary distribution bay before going to the load(s).
a. Centralized
b. Distributed
c. Decentralized
d. Structured
c. Decentralized
9-53
Under Switchboard Section: The two types of power board distribution are:
• Centralized (distribution goes to the loads directly from the power board)
• Decentralized (dc power is distributed to a secondary distribution bay and is distributed from the secondary bay to the loads)
To fully recharge a lead-acid battery, because of chemical losses within the battery, ___ percent more energy (power) must be returned to the battery than has been removed during discharge.
a. 10
b. 20
c. 30
d. 40
a. 10
p 9-55
To fully recharge a lead-acid battery, because of chemical losses within the battery, 10 percent more energy (power) must be returned to the battery than has been removed during discharge. NiCd batteries require 40 percent more energy return.
Gelled electrolyte cells are classified as ___
a. Alkaline
b. Flooded lead-acid
c. Valve-regulated lead-acid
d. Wet
c. Valve-regulated lead-acid
p 9-63
Battery cells used for telecommunications applications include:
• Alkaline
• Vented lead-acid (VLA), which is also known as flooded lead-acid (FLA)
• Valve regulated lead-acid (VRLA). Gelled electrolyte cells are part of this classification
The use of more than _____ parallel cells in a battery plant is not recommended because of the possibility of unequal charging.
a. 3
b. 4
c. 5
d. 6
c. 5
p 9-69
The use of more than five parallel cells in a battery plant is not recommended. Imbalance problems that lead to unequal charging of the individual strings may be caused by:
• Differences in the resistance of the paralleling connectors.
• Different resistances of each string of cells (i.e., differing cell internal resistance and intercell connector resistance).
When providing 120/240 V single-phase three-conductor residential electrical service, the transformer coil is center-tapped and the connections are _____ degrees out of phase.
a. 45
b. 90
c. 120
d. 180
d. 180
p 9-5
Figure 9.5 shows a single-phase system in a three- conductor configuration. In this configuration, the transformer coil has been center-tapped. This is the typical configuration of 120/240 V residential electrical service. Because the connections are 180 degrees out of phase, the voltage from end to end is double the voltage from either end to the center tap.
The transfer time associated with a static transfer switch (STS) is typically one:
a. Millisecond
b. One cycle
c. Quarter cycle
d. Half of a cycle
c. Quarter cycle
p 9-50
STSs are devices that can transfer electrical loads between two synchronized power sources in a break before making (open transition) transfer in a fraction of a second, typically one quarter of a cycle.
___ is the measure of the total opposition to current flow in an alternating current (ac) circuit.
a. Inductance
b. Impedance
c. Reactance
d. Resistance
b. Impedance
p 9-8
The net reactance is equal to the difference between capacitive and inductive reactance. This reactance can be combined with the resistance to calculate the impedance (Z), which is the total opposition to ac current flow and is measured in ohms.
When describing power system redundancy, a _____ electrical system topology has a single path serving the communications equipment.
a. Class 1
b. Class 2
c. Class 1 or Class 2
d. Class 1, Class 2, or Class 3
c. Class 1 or Class 2
p 9-32 & 33
Note, “single path serving the COMMUNICATIONS equipment” is the key phrase. Both Class 1 & 2 have a single path serving the communications equipment, but NOT a redundant path to serve components and multiple distribution paths (see Figure 9.16). That is Class 3.
The load capacity of a given power system is the amperage that is available to the user at the _____ system voltage.
a. Minimum
b. Phase-balanced
c. Maximum
d. Nominal
d. Nominal
p 9-3
The available power of a given system is the amperage that is available to the user at the nominal system voltage. This also can be stated in volt amperes or watts. In larger systems, these are expressed as kilovolt-amperes or kilowatts.
For telecommunications, the nominal (dc) operating voltage in the United States is negative ___ V. It is referred to as negative because the positive side of the system is intentionally grounded.
a. 2
b. 12
c. 24
d. 48
d. 48
p 9-52
It is referred to as negative because the positive side of the system is intentionally grounded. There are also numerous pieces of ICT equipment that operate at positive 12 VDC.
For cellular radio, the nominal operating voltage is positive 24 V. It is referred to as positive because the negative side is intentionally grounded.
Battery protection devices should be capable of interrupting short circuit current, which is approximately _____ times the rated ampere-hour (AH) capacity of the battery.
a. 2
b. 7
c. 10
d. 11
c. 10
p 9-71
Protection devices should be capable of interrupting the battery’s short circuit current, which is approximately 10 times the rated AH capacity.
If a standard transformer is used to feed a large number of harmonic producing loads, consider derating the transformer by as much as _____ percent.
a. 20
b. 50
c. 70
d. 80
c. 70
p 9-21
If a standard transformer is used, consider derating the transformer by as much as 70 percent when a large number of harmonic producing loads are being fed. This method of design typically has additional costs and lower efficiencies.
___ are used to reduce voltage waveform distortion that affects sensitive electronic equipment.
a. Voltage regulators
b. Harmonic filters
c. Isolation transformers
d. Power line conditioners
e. Harmonic mitigating transformer
b. Harmonic filters
p 9-38
Harmonic filters are used to reduce voltage waveform distortion that affects sensitive electronic equipment. These filters screen out harmonics and high-frequency noise. Some of the better surge protecting devices, voltage regulators, and power line conditioners include harmonic filters.
A ___ may be appropriate where harmonics are found to be a concern within the electrical system based on load make up or actual field measurements in an existing system.
a. Voltage regulators
b. Harmonic filters
c. Isolation transformers
d. Power line conditioners
e. Harmonic mitigating transformer
e. Harmonic mitigating transformer
p 9-37
Harmonic mitigating transformers come in a variety of configurations and are usually tailored to the application. They utilize winding connection and phase shifting techniques internal to the transformer to reduce harmonic content and their effects on the electrical system.
These transformers eliminate the need for 200 percent neutrals, K-rated transformers, and other costly oversizing design techniques built into the electrical system.
The online double-conversion UPS is the most frequent type of UPS system used in ITS design and construction.
a. True
b. False
a. True
p 9-41
Online double-conversion UPS units exist in different designs, and each has its own unique advantages and disadvantages. The online double-conversion UPS is the most frequent type of UPS system used in ICT design and construction.
___ or passive standby UPS units are devices that power the load directly from the utility and only provide backup power when the utility power goes below preset tolerances.
a. Off-line
b. Line-interactive
c. Online double-conversion
a. Off-line
p 9-40
Off-line or passive standby UPS units provide limited line conditioning. It is not recommended that standby power systems be used to support critical communications loads
___ UPS units are basically off-line UPS units with line conditioning included. Electronic or magnetic energy storage is used to sustain the load during transfer to inverter.
a. Off-line
b. Line-interactive
c. Online double-conversion
b. Line-interactive
p 9-41
These units work well in most circumstances, but they have the following limitations:
• There is no frequency regulation.
• Battery reserve time and recharge time may be limited.
• Some may not be suitable for use with generators.
• The isolation of power source to load in a line- interactive UPS unit is not as good as in an online double conversion UPS unit.
Which one of the following is not a device used to filter and/or regulate utility supplied power?
a. Surge protective device (SPD)
b. Harmonic filter
c. Shielded isolation transformer
d. Standby UPS
d. Standby UPS
p 9-35
Devices that filter and/or regulate the utility supplied power: –Isolation transformers –Shielded isolation transformers –Harmonic mitigating transformers –SPDs –Voltage regulators –Power line conditioners –Harmonic filters
All lead-acid battery cells require the addition of water to the electrolyte at regular intervals in order to maintain a minimum level.
a. True
b. False
b. False
p 9-64
VRLA cells have vent or pressure-relief (regulator) valves, and addition of water to the electrolyte is not required.
The NEC states that “A sealed cell or battery is one that has no provision for the addition of water or electrolyte or for external measurement of electrolyte specific gravity.
When describing power system redundancy, a Class 1 electrical system topology typically:
a. Does not include a generator or a UPS system
b. Includes both a generator and a UPS system
c. Includes a UPS system
d. Includes a generator
b. Includes both a generator and a UPS system
p 9-31
This system typically has a generator and UPS system, both sized at N capacity (need). See Figure 9.14
A remote power panel (RPP) has ___ at the desired voltage to a grouping of ___.
a. Multiple feeders; transformers
b. Multiple feeders; panelboards
c. A single feeder; transformers
d. A single feeder; panelboards
d. A single feeder; panelboards
p 9-27
RPPs are basically PDUs without transformers. An RPP has a single feeder at the desired voltage to a grouping of panelboards and also typically has the surge suppression to protect the equipment.
Additional cost and space requirements are two disadvantages of a(n) _____ redundant multi-module UPS topology since the backup UPS is not normally used to power the critical load.
a. Isolated
b. Parallel
c. Distributed
d. Series
a. Isolated
p 9-45
Multiple isolated redundant UPS systems can be deployed together if necessary. One drawback of an isolated redundant system is that the backup UPS is not normally used to drive the critical load, so it is a costly and space-consuming system (see Figure 9.21).
When calculating information technology equipment (ITE) loads served by a UPS system, the power factors of the UPS systems typically range from:
a. 0.90 to 1.00
b. 0.85 to 0.95
c. 0.80 to 0.90
d. 0.75 to 0.85
c. 0.80 to 0.90
p 9-27
UPS ratings are given in kilowatts and kilovolt-amperes with power factors typically ranging from 0.80 to 0.90. At the same time, most modern pieces of ITE have power factors approaching 1.00.
In delta and wye phase configurations, voltages are _____ degrees out of phase.
a. 60
b. 90
c. 120
d. 180
c. 120
p 9-5
In the delta and wye configurations, where the voltages are 120 degrees out of phase, the phase-to-neutral voltage equals the phase-to-phase voltage divided by (1.732).
