Week 18 Chapter 9 Part 1 - Pages 9-1 to 9-35

Question 1

The ampacity of a conductor is related to the conductor size, _____, and type of insulation.

a. Temperature
b. Length
c. Resistance
d. Impedance

Answer 1

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.

Question 2

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

Answer 2

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.

Question 3

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

Answer 3

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.

Question 4

___ is the measure of the total opposition to current flow in an alternating current (ac) circuit.

a. Inductance
b. Impedance
c. Reactance
d. Resistance

Answer 4

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.

Question 5

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

Answer 5

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.

Question 6

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

Answer 6

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.

Question 7

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

Answer 7

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.

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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.

Question 11

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

Answer 11

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.

Question 12

In delta and wye phase configurations, voltages are _____ degrees out of phase.

a. 60
b. 90
c. 120
d. 180

Answer 12

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).

Question 13

The sizing of electrical distribution equipment such as transformers and panelboards is based on _____ power.

a. Expected
b. Apparent
c. Average
d. Real

Answer 13

b. Apparent

p 9-11

The sizing of electrical distribution equipment (e.g., transformers, panelboards) is based on apparent power. This may be somewhat unexpected since it is common to see power consumption listed in real power—watts or kilowatts

Question 14

In a typical electrical power system at a customer site, _____ are used to connect the main electrical service panel to various distribution subpanels within the building.

a. Service wires
b. Transformers
c. Branch circuits
d. Feeders

Answer 14

d. Feeders

p 9-6

See Figures 9.6 and 9.7 illustrate typical electrical power systems.

Question 15

Redundancy is typically expressed through the use of the symbol N where N is equivalent to the need. With N+1 redundancy, the failure or maintenance of any ___ unit(s), module(s), or path(s) will not disrupt operations.

a. Two single
b. Single

Answer 15

b. Single

p 9-31

The failure or maintenance of any single unit, module, or path will not disrupt operations.

Question 16

By definition, the duration of a transient or surge is less than _____ of the normal voltage waveform.

a. One cycle
b. A half cycle
c. 30 seconds
d. A half second
e. One millisecond

Answer 16

b. A half cycle

p 9-18

The duration is less than a half cycle (8.3 milliseconds) of the normal voltage waveform.

Question 17

The authority having jurisdiction (AHJ) _____ generally cover installations of communications equipment that are controlled exclusively by communications utilities.

a. Does not
b. Does

Answer 17

a. Does not

p 9-1

The AHJ does not generally cover installations of communications equipment that are controlled exclusively by communications utilities.

Question 18

When calculating the voltage drop, a value of K = _____ is used to represent the specific resistance of a copper conductor circuit loaded to less than 50 percent of allowable carrying capacity.

a. 18
b. 12
c. 11
d. 10

Answer 18

c. 11

p 9-13

• K = 11 for circuits loaded less than 50 percent of allowable carrying capacity (copper conductor)
• K = 12 for circuits loaded to more than 50 percent of allowable carrying capacity (copper conductor)
• K = 18 for aluminum conductors 30 ºC (86 ºF)

Question 19

A power distribution unit (PDU) allows _____ to be bought into the unit.

a. Multiple smaller feeders
b. A single higher voltage feeder

Answer 19

b. A single higher voltage feeder

p 9-26

A PDU is useful because it:
• Allows a single higher voltage feeder to be brought into the unit instead of multiple smaller feeders. This is less costly than running many small branch circuits. It also handles the voltage drop associated with running the conductors at a lower voltage.

Question 20

When describing power system redundancy, in a ___ electrical system topology, although there are multiple distribution paths, only one path is typically active at any given time.

a. Class 3 or Class 4
b. Class 4
c. Class 3
d. Class 2

Answer 20

c. Class 3

p 9-33

Class 3 is an electrical system that has redundant capacity components and multiple distribution paths (see Figure 9.16). Only one path is typically active at any given time.

Class 4 is an electrical system that is fault tolerant with redundant capacity components and multiple electrical paths that are BOTH active (see Figure 9.17).

Question 21

If the power factor (PF) of a load is not known, the common practice is to use a value of _____ for typical loads.

a. 0.9
b. 0.8
c. 0.7
d. 0.6

Answer 21

b. 0.8

p 9-11

If the PF of a load is unknown, common practice is to use 0.8 for typical loads.

Question 22

You have been asked to provide a N+1 level of power redundancy in the new equipment room (ER) being designed with a Class-II power supply. What should you do?

a. Provide a UPS that serves all of the equipment in the facility.
b. Provide two separate UPS units with an automatic power failure transfer to serve entire facility.
c. Provide two separate UPS units with each one serving half the equipment in the facility.
d. Provide two separate UPS systems with one serving the entire facility and the second on automatic power failure transfer to serve critical circuits only.

Answer 22

b. Provide two separate UPS units with an automatic power failure transfer to serve entire facility.

Question 23

All of the following are used to control static discharge EXCEPT:

a. Ion generator
b. Discharge plates and bracelets
c. Maintenance of humidity of between 30 and 55 percent
d. Installation of isolated grounds

Answer 23

d. Installation of isolated grounds

p 9-19

Static electricity discharges to a conducting surface and causes equipment malfunctions
because of induced noise impulses.
Preventive measures include:
• Using antistatic sprays and floor covering with a low propensity to static.
• Using an ion generator in the area served.
• Using static discharge plates and/or jacks and wrist straps for personnel.
• Maintaining the relative humidity between 30 and 55 percent in the TR and ER.
• Avoiding the wearing of clothing that generates static (e.g., synthetic materials).

Question 24

An isolated ground is used to:

a. Reduce transients
b. Prevent interruptions
c. Reduce EMI/RFI
d. Reduce swells and sags

Answer 24

c. Reduce EMI/RFI

p 8-10

IG is an equipment grounding (earthing) topology that presumably reduces the effects of EMI and RFI on the equipment grounding (earthing) system.

Question 25

The average power consumption in a telecommunications room (TR) is 2260 watts per hour. What is the heat dissipation in BTUs?

a. 7096 BTU
b. 7711 BTU
c. 8104 BTU
d. 8511 BTU

Answer 25

b. 7711 BTU

p 9-11

1. watts × 3.412 = heat dissipated in Btu
2. 2260 x 3.412 = 7711

Question 26

You have been asked what the estimated power cost will be per month (30 days) for the new equipment room you are designing. The power load you have calculated to be an average of 1850 watts per hour. What is the monthly cost assuming the cost of electricity is 7.5 cents (U.S.) per kilowatt hour?

a. $44.40
b. $55.50
c. $99.90
d. $122.80

Answer 26

c. $99.90

p 9-11 see Watt-Hours calculation

Question 27

You have discovered a common mode current on the metallic cable sheaths of your building riser cables. What is the MOST likely cause for you to investigate?

a. Lack of cable protection
b. Two separate and distinct ground references
c. Improper secondary protection
d. Improper physical protection of cable

Answer 27

b. Two separate and distinct ground references

Question 28

A common mode (CM) signal can be converted to a differential mode (DM) signal as a result of a(n):

a. Unbalanced circuit
b. Grounded circuit
c. Poorly timed signal
d. Improper dielectric material

Answer 28

a. Unbalanced circuit