Chapter 9 Flashcards
AHJ
Authority Having Jurisdiction
The building official, electrical
inspector, fire marshal, or other
individuals or entities
responsible for interpretation
and enforcement of local
building and electrical codes.
TDMM.* Page G-14
Alternating Current
(ac)
A current flow that alternates
periodically (usually sinusoidal)
in magnitude and direction.
TDMM.* Page G-7
Apparent Power
The product of the measured
voltage and measured
amperage. Expressed in
volt amperes.
TDMM.* Page 9-10
Arc Flash
A short circuit through the air.
When insulation or isolation
between electrified conductors
is breached or can no longer
withstand the applied voltage, an
arc flash occurs.
TDMM.* Page 9-28
AWG
American Wire Gauge
A system used to specify wire
size. The greater the wire
diameter, the smaller
the AWG value.
TDMM.* Page G-8
Capacitance
1 . The ability of an electronic
component to store electrical
energy.
2. The opposition to a change in
voltage.
TDMM.* Page G-30
Delta
The difference between two
values, symbolized with a
triangle (△).
TDMM: Page G-54
Direct Current (dc)
Current flow that has a constant
direction. The letters dc are also
used generically to refer to any
constant waveform or signal
(e.g., a battery voltage of 3 volts
direct current [Vdc]).
TDMM: Page G-58
Frequency
The number of cycles that a
periodic signal completes in a
given time. If the unit of time is
one second, the frequency is
stated in hertz (Hz). One Hz is
equal to one cycle per second.
TDMM.* Page G-83
Harmonics
Multiples of the basic frequency
of a sine wave (e.g., the third
harmonic of 60 Hz power
frequency is 180 Hz).
TDMM.* Page 9-79
Impedance
The total opposition to ac
current flow. Measured in ohms.
TDMM.* Page 9-8
Inductance
1 . The property of an electrical
force field built around a
conductor when current flows
through it.
2. The resistance to change in
current.
TDMM: Page G-95
ITE Power
Information Technology
Equipment Power
The power consumed by ICT to
manage, monitor, control,
process, store, and route data
within the data center, excluding
all infrastructure technology
equipment.
TDMM.* Page G-96
LOTO
Lockout/ Tagout
A means to protect personnel
from the unexpected start-up or
reenergization of equipment by
ensuring that equipment
remains completely shut off
during routine maintenance
and repairs.
TDMM.* Page 9-29
LVD
Low Voltage Disconnect
A device that is used to
disconnect the battery at a
preset voltage during battery
discharge and allow
reconnection only when utility
power has been restored. Called
a “no volt release” in the
United Kingdom.
TDMM.* Page 9-54
Noise
Unwanted electrical signals that
are induced onto, or superimposed
upon, the power line.
TDMM.* Page 9-79
PDU
A device that has a transformer,
surge suppression, single-point
ground, panelboards, and
monitoring under a single
enclosure.
TDMM.* Page 9-26
Phase Difference
The relationship in time
between two waveforms
of the same frequency.
TDMM.* Page 9-3
Phase Configuration
The number of phases and the
type of connection between the
utility and the user.
TDMM.* Phase 9-4
Power
1 . The rate of transfer or
absorption of energy per unit time
in a system.
2. The energy required to operate
an electrical device (e.g., motor,
amplifier, telephone transmitter).
TDMM.* Page G-146
Reactance
The opposition to the flow of ac
current caused by inductance
and capacitance. Expressed
in ohms.
TDMM.* Page 9-8
Redundancy
Providing secondary
components that either become
instantly operational or are
continuously operational so that
the failure of a primary
component will not result in
mission failure.
TDMM.* G-761
Resistance
A measure of opposition a
material offers to the flow of
direct current. Measured
in ohms.
TDMM.* Page G-765
RPP
Remote Power Panel
A power distribution cabinet
downstream from a power
distribution unit (PDU) or
uninterruptible power supply
(UPS), typically containing
circuits and breakers, without a
transformer, located
near the load.
TDMM.* Page G-763
SDS
Safety Data Sheet
A document prepared by the
manufacturer describing all
known chemical, radiological,
and other hazards of a specific
product. Formerly called
material safety data sheet
(MSDS).
TDMM.* Page G-168
Short Circuit
A faulty or accidental connection
between two points of different
potential in an electric circuit,
bypassing the load and
establishing a path of low
resistance through which an
excessive current can flow.
TDMM.* Page 9-13
Sine Wave
The mathematical representation
of an alternating voltage
or current waveform.
TDMM.* Page 9-2
SPD
Surge Protection Device
A protective device for limiting
transient voltages by diverting or
limiting surge current. It has a
nonlinear voltage-current
characteristic that reduces voltages
exceeding the normal safe system
levels by a rapid increase in conducted
current. Also called a voltage limiter,
overvoltage protector, (surge) arrestor,
or transient voltage surge suppressor
(TVSS).
TDMM.* Page G-189
STS
Static Transfer Switch
A device 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.
TDMM.* Page 9-50
UPS
Uninterruptible Power Supply
A system that provides a continuous
supply of power to a load using stored
energy when the normal source of
energy is not available or is of
unacceptable quality. A UPS will
provide power until the stored energy
of the system has been depleted, or
when the acceptable quality of either
an alternative source of power (e.g.,
generator) or the normal source of
power returns to acceptable quality.
TDMM.* Page G-202
Wye
A power system in which only
one point (usually the midpoint
of a supply transformer bank) is
grounded. If the neutral is
present, it is not grounded
along the line.
TDMM.* Page G-211
What is an ac circuit?
An electrical current that
periodically reverses (alternates)
its direction of flow because the
polarity of the voltage source
constantly changes
TDMM.* Page 9-2
What term is used to
describe the mathematical
representation of an
alternating voltage or
current waveform?
Sine wave
TDMM: Page 9-2
What is a sine wave cycle?
One variation of the sine wave
from zero to maximum
(positive), back through zero,
to minimum (negative),
and back to zero
TDMM.* Page 9-2
What term is used to
describe the number of
times a sine wave cycle
occurs in one second?
Frequency
TDMM.* Page 9-2
What unit of measure is
used to express the
frequency of a sine
wave cycle?
Hertz (Hz)
TDMM.* Page 9-2
How is the rms value of a
sine wave calculated?
By multiplying the zero-to-peak
value of the sine wave by 0.7071
TDMM.* Page 9-2
Name 4 defined
characteristics of ac power
provided by commercial
utility sources.
1 .Frequency (in Hz)
2.Voltage (in V)
3.Power (in kVA or kW)
4.Phase (single or three-phase)
TDMM.* Page 9-2
Name 2 typical frequencies
provided by commercial
utility sources.
1.50 Hz
2.60 Hz
TDMM.* Page 9-3
What is the most common
single-phase service
voltage value?
120/240 v
TDMM.* Page 9-3
What are the most
common three-phase
service voltage values?
*208 Y/120 V
*240 v
480 Y/277 V
TDMM. Page 9-3
What is the available power
of a given system?
The amperage that is available
to the user at the nominal
system voltage
TDMM.* Page 9-3
What units of measure are
used to express the
available power for
a large system?
*Kilovolt-ampere (kVA)
*Kilowatt (kW)
TDMM: Page 9-3
What does phase
difference describe?
The relationship in time
between two waveforms
of the same frequency
TDMM.* Page 9-3
What does it mean if two
waveforms are described
as being “in phase”?
That the two waveforms match
each other in electrical degrees
TDMM.* Page 9-4
How many waveforms are
produced when electrical
power is generated?
3 waveforms, each 120 degrees
out of phase with the others
TDMM.* Page 9-4
What is phase
configuration?
The number of phases and the
type of connection between the
utility and the user
TDMM.* Page 9-4
What term is used to
describe the electrical
system between the
serving utility and the
customer’s site?
Distribution system
TDMM.* Page 9-6
What is the
electrical wiring system?
The cabling between the
connection to the distribution
system at the customer’s site
and various equipment (loads)
to be powered
TDMM.* Page 9-6
Name 3 characteristics of
various loads that affect
the amount of power
required for those loads.
1 .Resistance
2.Inductance
3.Capacitance
TDMM.* Page 9-7
Which characteristics are
responsible for creating the
difference between the real
power (in watts) and the
apparent power (in volt-
amperes) for the required
load of an ac circuit?
Inductance and capacitance
TDMM.* Page 9-7
True or False
The formula for Ohm’s law
always applies to
dc circuits.
True. The formula for Ohm’s law
always applies to dc circuits, but
it only applies to ac circuits that
are purely resistive (e.g.,
incandescent lamps, resistive
heating elements).
TDMM.* Page 9-8
What is reactance?
The opposition to the flow of ac
current caused by inductance
and capacitance
TDMM.* Page 9-8
What term is used to describe
the total opposition to ac
current flow?
Impedance
TDMM.* Page 9-8
What is inductive
reactance?
The portion of impedance that
opposes a change in current
flow because of magnetic
field coupling
TDMM.* Page 9-8
What is capacitive
reactance?
The portion of impedance that
opposes a change in voltage
because of electric
field coupling
TDMM.* Page 9-8
What formula is used to
calculate the power for a
purely resistive ac circuit?
P=V x I
TDMM.* Page 9-9
What determines the lag
time in an ac circuit with
inductive reactance?
The amount of inductance
TDMM.* Page 9-9
What is apparent power?
The product of the measured
voltage and measured
amperage
TDMM.* Page 9-70
How is apparent power
expressed?
In volt-amperes (VA)
TDMM.* Page 9-10
Where are measurements
for apparent power
performed?
On the line side of the system
TDMM.* Page 9-10
Where are measurements
for real power performed?
On the load side of the system
TDMM.* Page 9-70
How is real power
expressed?
In watts (W)
TDMM.* Page 9-10
What is used to show the
relationship between watts
and volt-amperes?
Power factor (PF)
TDMM.* Page 9-10
What measurement is
commonly used for typical
loads if the PF is unknown?
0.8
TDMM.* Page 9-71
What type of power is used
to size electrical
distribution equipment?
Apparent power
TDMM.* Page 9-11
What unit of measure is
used to indicate the
amount of power that is
consumed by a circuit at
any given time?
Watts
TDMM.* Page 9-11
How are watt-hours
determined?
By multiplying the number of
watts consumed by the number
of hours that the watts are
being consumed
TDMM.* Page 9-11
What unit of measure is
used for heat?
British thermal unit (Btu)
TDMM.* Page 9-11
What is the efficiency of a
circuit or load?
The amount of input power
required to provide a
predetermined output power,
expressed as a percentage
TDMM.* Page 9-12
What does horsepower (HP)
measure?
Mechanical power
TDMM.* Page 9-72
What factors must be
known in order to calculate
voltage drop?
*R = Resistance per foot of the
conductor (ohms/ft) (amperes)
*l = Current in the conductor
*L = One-way length of circuit
(footage)
*A = Cross-sectional area of
conductor (circular mils)
K = Specific resistance
TDMM. Page 9-12
What is a short circuit?
A faulty or accidental connection
between two points of different
potential in an electric circuit,
bypassing the load and
establishing a path of low
resistance through which an
excessive current can flow
TDMM.* Page 9-73
Why is a short circuit study
performed?
To determine the required
ratings for the power distribution
system equipment
TDMM.* Page 9-13
What is the purpose of the
AWG system?
To provide a standard reference
for comparing various conductor
materials
TDMM.* Page 9-15
What has an AWG system
number represented
historically?
Roughly the number of steps
involved in the process
of wire drawing
TDMM.* Page 9-75
What is the relationship
between the AWG number
and the size of the wire
it represents?
It is an inverse relationship. The
smaller the number, the larger
the wire.
TDMM.* Page 9-75
What is a circular mil?
A unit of area equal to the area
of a circle one mil in diameter
TDMM.* Page 9-15
What formula is used to
convert circular mils to
square mils?
Square mils = Circular mils x 0.7854
TDMM.* Page 9-76
Name 3 characteristics
related to the ampacity
of a conductor.
1 .Conductor size
2.Temperature
3.Means of insulation
TDMM.* Page 9-17
Name 4 forms of distortion
that may be present in the
power created by the utility.
1 .Voltage fluctuations
2.Current fluctuations
3.Frequency variations
4.Noise
TDMM.* Page 9-18
Define surge as it relates to
voltage and current
fluctuation.
Short duration (usually subcycle)
rapid increase in voltage or
current that can often be up to
thousands of volts in amplitude.
The duration is less than a half
cycle (8.3 milliseconds) of the
normal voltage waveform.
TDMM.* Page 9-18, Table 9.3
Define swell as it relates to
voltage and current
fluctuation.
An increase in the nominal
voltage or current lasting from
0.5 cycles to one minute.
TDMM.* Page 9-18, Table 9.3
Define sag as it relates to
voltage and current
fluctuation.
A decrease in nominal voltage
or current lasting 0.5 cycles
up to one minute.
TDMM: Page 9-18, Table 9.3
What is overvoltage?
An increase in the nominal
voltage for more than
3600 cycles (one minute)
TDMM.* Page 9-18, Table 9.3
What is undervoltage?
A decrease in the nominal
voltage for more than
3600 cycles (one minute)
TDMM.* Page 9-18, Table 9.3
What term is used to refer
to a total absence of
voltage on one or more
phase conductors for a
period of time?
Interruption
TDMM.* Page 9-18, Table 9.3
True or False
Frequency variation is a
common occurrence.
False. Frequency variation is not
a common occurrence.
TDMM.* Page 9-19
Name 3 sources of
frequency variation.
1 .lnadequately regulated source
2.Utility company correction
3.Switching
TDMM.* Page 9-19
What are the harmonics of
a sine wave?
Multiples of the basic frequency
(e.g., the third harmonic of a 60
Hz power frequency is 180 Hz)
TDMM.* Page 9-79
What is the maximum
allowable total harmonic
distortion of the voltage
waveform per IEEE 519?
5 percent
TDMM.* Page 9-79
What term is used to
describe unwanted
electrical signals that are
induced onto, or
superimposed upon, the
power line?
Noise
TDMM.* Page 9-19
Name 2 categories of
noise related to
power distribution.
1 .Common-mode noise
2.Differential-mode noise
TDMM.* Page 9-19
What type of noise is
present between phase and
ground or between neutral
and ground, but not
between each line?
Common-mode noise
TDMM.* Page 9-79
What is differential-mode
noise?
Noise that is present between
phases or phase and neutral.
Also known as normal
mode noise.
TDMM.* Page 9-19
What is an isolated ground
(IG)?
An equipment grounding
(earthing) topology that was
theorized to reduce the effects
of electromagnetic interference
and radio frequency interference
on the equipment grounding
(earthing) system
TDMM.* Page 9-79
Name 2 methods for
identifying IG receptacles.
1 .Continuous orange receptacle
coloring
2.Beige receptacle marked with
an orange triangle upon its face
TDMM.* Page 9-19
Are IG systems recommended
for use with voice and
data equipment?
No. IG systems are not
recommended for use with voice
and data equipment. Though such
an equipment grounding (earthing)
system is permitted (provided it
meets stringent wiring techniques),
it defeats the purpose of an
equipotential plane that is desired
for all EFs, ERs, and TRs.
TDMM.* Page 9-19
How does electrostatic
discharge cause equipment
to malfunction?
By inducing noise impulses
TDMM.* Page 9-20
What level of humidity
should be maintained in an
ER or TR to prevent
electrostatic discharge?
30 to 55 percent
TDMM.* Page 9-20
What is a potential result of
a current imbalance?
High-magnitude neutral currents
TDMM.* Page 9-20
What is the NEC guideline
for sizing feeder and
branch circuit conductors?
Feeder and branch circuits
should be sized for the
noncontinuous load plus
125 percent of the
continuous load.
TDMM.* Page 9-20
What is the guideline for
sizing the neutral
conductor?
It is advised to size the neutral
conductor to carry 200 percent
of the rated load, which must be
continuous from the outlet all
the way back to where the
source is derived.
TDMM.* Page 9-21
What is a drawback
associated with installing
oversized neutrals?
Increased construction costs
TDMM.* Page 9-21
What is the purpose of a
three-phase K-rated
transformer?
To dissipate the heating effects
caused by harmonics on the
neutral conductor
TDMM.* Page 9-21
What does the K rating of a
transformer denote?
The transformer’s ability to
safely dissipate the heating
effects caused by harmonics on
the neutral conductor
TDMM.* Page 9-21
What type of receptacle is
generally recommended for
any critical equipment
loads?
Locking type
TDMM: Page 9-22
What is galvanic corrosion?
A breakdown in the electrical
connection between the two
dissimilar metals
TDMM.* Page 9-23
What is the maximum
distance a listed ITE power
cord can extend?
4.5 m (15 ft)
TDMM.* Page 9-24
What is the purpose of
the EPO switch in
an ITE space?
To provide a safe electrical
shutdown of all electrical
equipment in the ITE space,
especially in case of fire
TDMM.* Page 9-24
What is a possible negative
impact of an EPO switch
in an ITE space?
It could act as a single point of
failure for critical ITE.
TDMM.* Page 9-24
Name 3 ways that power is
distributed to equipment.
1 .Panelboards
2.Power distribution units (PDUs)
3.Remote power panels (RPPs)
TDMM.* Page 9-25
Name 2 main types of
OCPDs.
1 .Circuit breakers
2. Fuses
TDMM.* Page 9-25
What type of device has a
transformer, surge
suppression, single-point
ground, panelboards and
monitoring under a single
enclosure?
Power distribution unit (PDU)
TDMM.* Page 9-26
What device can be
described as a PDU without
a transformer?
Remote power panel (RPP)
TDMM.* Page 9-27
What term is used to
describe a short circuit
through the air?
Arc flash
TDMM.* Page 9-28
What is the maximum
temperature of
an arc flash?
-19,427ºC (35,000ºF)
TDMM.* Page 9-28
What is the purpose of
having a qualified engineer
perform an arc flash
hazard analysis?
TO have the engineer provide
recommendations for mitigating
hazards as well as labels to be
installed on equipment
TDMM.* Page 9-29
What is the purpose of
LOTO procedures?
To protect personnel from the
unexpected start-up or
reenergization of equipment by
ensuring equipment remains
completely shut off during
routine maintenance and repairs
TDMM.* Page 9-29
What type of device
provides a physical means
to render an energy
source inoperable?
Lockout (LO) device
TDMM.* Page 9-29
What information is
included on a tagout
(TO) device?
*Who locked out the equipment
*When the equipment was
locked out
The reason and duration of the
lockout
TDMM. Page 9-29
Name 4 benefits of
incorporating LOTO
procedures into a
facility’s operation and
maintenance plan.
1 .Preventing injuries or fatalities
2.Avoiding unnecessary
penalties, fines, or litigation
3.Avoiding shutdowns to critical
operations
4.Maximizing uptime,
productivity, and profitability
TDMM.* Page 9-29
Name the 4 basic steps of
a LOTO procedure.
1.ldentify the energy source.
2.Isolate the energy source.
3.Lock and tagout the energy
source.
4.Prove that the energy source is
effectively isolated.
TDMM.* Page 9-30
What does N represent
when defining redundancy
requirements?
N = Need
TDMM.* Page 9-31
What are the common
expressions of
redundancy?
*N-Base requirement
*N+1 redundancy
*N+2 redundancy
*2N redundancy
2(N+1) redundancy
TDMM. Page 9-31
What is the purpose of the
Uptime Institute’s tier
system?
To provide a methodology to
evaluate a data center’s site
infrastructure in relation to a
desired operational
availability target
TDMM.* Page 9-31
What is the focus of
ANSI/BICSI 002?
The expected performance of
systems and the overall site,
providing the flexibility to meet a
site’s specific needs
TDMM.* Page 9-31
What is the redundancy
capacity of a Class 1
electrical system?
There is no redundant capacity.
TDMM.* Page 9-32
What class is assigned to
an electrical system with a
single path with redundant
components?
Class 2
TDMM.* Page 9-33
How many paths are
typically active in a Class 3
electrical system?
Only 1
TDMM.* Page 9-33
Why are Class 4 electrical
systems rare?
The number components that
need to be installed to obtain the
level of redundancy results in an
expensive solution.
TDMM.* Page 9-34
Name the 3 major
categories of power
conditioning devices.
1 .Devices that filter and/or
regulate the utility supplied
power
2.Equipment that regenerates
the utility supplied power or
generates its own power
3.Static uninterruptible power
supply (UPS) units
TDMM.* Page 9-36
Name 3 alternatives to
static UPS units.
1 .Rotary UPS units
2.Flywheel UPS units
3.Modular UPS units
TDMM.* Page 9-36
True or False
An isolation transformer
has no electrical
connection between the
primary and the secondary.
True. An isolation transformer
has no electrical connection
between the primary and
the secondary.
TDMM.* Page 9-36
When are shielded isolation
transformers preferred over
standard isolation
transformers?
When the total load is made up
of more than 20 percent of
nonlinear type equipment
TDMM.* Page 9-37
What is the purpose of a
surge protection device
(SPD)?
To limit, clamp, or divert
surges and transients
TDMM.* Page 9-37
Where are SPDs installed
when the stage approach
is used as recommended?
*Service entrance panel as a
service protector
*Distribution panelboard level
Branch circuit panelboard level
TDMM. Page 9-37
What is the purpose of
voltage regulators?
To adjust the line voltage to the
load up or down, as necessary,
providing that the input voltage
remains within the range of the
regulator
TDMM.* Page 9-38
What is a power line
conditioner?
A unit that incorporates two or
more conditioning and
protection methods and
sometimes has a power
distribution means complete
with main and branch
circuit breakers
TDMM.* Page 9-38
What is the purpose of a
harmonic filter?
To reduce voltage waveform
distortion that affects sensitive
electronic equipment
TDMM.* Page 9-38
How do motor generators
provide electrical isolation
from the utility line?
By using the utility to drive a
motor, which in turn drives a
generator, producing an ac
waveform at the desired voltage
TDMM.* Page 9-39
What component in the
motor generator is used to
ride through short outages
of up to a few seconds?
A flywheel
TDMM.* Page 9-39
How are engine generators
typically used?
As a standby power source
when long-term backup
is required
TDMM.* Page 9-39
Name 4 factors that must
be considered when
designing an engine
generator system.
- Size of the load
- Level of redundancy required
- Cost, space, and
environmental constraints - Total cost of ownership of the
generator system
TDMM.* Page 9-39
Name 3 typical
generator topologies.
1 .Single generator (N)
2.Multiple generators (N+l)
3.Paralleled generators
TDMM.* Page 9-39
What is the purpose of a
static UPS unit?
To protect critical loads from
most types of power
fluctuations
TDMM.* Page 9-40
When do off-line UPS units
provide backup power?
When the utility power goes
below preset tolerances
TDMM.* Page 9-40
What is a line-interactive
UPS unit?
An off-line UPS unit with line
conditioning capabilities
included
TDMM.* Page 9-41
How does an online
double conversion UPS
unit charge a battery?
By completely rectifying the ac
line from ac to dc
TDMM.* Page 9-41
What type of UPS is the
most common in ICT
design and construction?
Double conversion
TDMM.* Page 9-41
What is the purpose of a
maintenance bypass?
To provide an isolated path
around the UPS so that the
critical load can continue to be
supplied with utility power
TDMM.* Page 9-41
Name 5 factors that must
be considered when
designing a UPS system.
1.Critical load calculation
2.Critical load support interval
3.Level of redundancy required
4.Cost, space and environmental constraints of the particular
project
5.Total cost of ownership for the UPS and battery system
TDMM.* Page 9-42
What is the most common
multimodule UPS
configuration?
Parallel redundant UPS system
TDMM.* Page 9-43
What is a possible
drawback of a parallel
redundant UPS system?
The common output bus or
common static switch can be
seen as a single point of failure.
TDMM.* Page 9-44
What is a possible
drawback of an isolated
redundant UPS system?
It is a costly and space-
consuming system.
TDMM.* Page 9-45
What is an advantage of a
distributed redundant
UPS system?
One distribution path can be
taken down, and the critical load
will not be affected.
TDMM.* Page 9-46
Name 2 disadvantages
associated with using a
ring bus topology for
a UPS system.
- High cost
- Complexity
TDMM.* Page 9-47
Name 5 advantages
associated with using
rotary UPS units.
- Efficiency
- Tolerance for short circuit currents
- Tolerance for input voltage and
frequency departures - Tolerance for large step load
changes - Tolerance for high inrush currents
TDMM.* Page 9-48
Name 3 advantages of
using a flywheel UPS unit
instead of a static UPS unit.
1 .Lower life cycle cost
2.Less space required
3.Less taxing on engine generators
TDMM.* Page 9-49
What drawback is
associated with modular
UPS units?
It contains more components
than other topologies, which
increases the likelihood of
component failure.
TDMM.* Page 9-49
What type of device can
transfer loads between two
synchronized power
sources in a break before
making transfer in a
fraction of a second?
Static transfer switch (STS)
TDMM.* Page 9-50
What is an advantage
associated with a
point-of-use STS?
There are two power switches
all the way up to the critical load,
minimizing single points
of failure
TDMM.* Page 9-57
Name 3 factors that
determine the amount of
protection that an electrical
system needs.
1 .Site power distribution design
2.Known existing power problems
3.Potential power problems
TDMM.* Page 9-51
What is the nominal
operating voltage for
telecommunications in the
United States?
Negative 48 V
TDMM.* Page 9-52
What is the nominal
operating voltage for
cellular radio in the
United States?
Positive 24 V
TDMM.* Page 9-52
Where is the voltage
usually set for a
rectifier/charger?
To the float charge voltage
required by the battery
TDMM.* Page 9-53
What is the central point of
the dc power system?
Switchboard
TDMM.* Page 9-53
Name the 2 types of power
board distribution.
- Centralized
- Decentralized
TDMM.* Page 9-53
What piece of equipment is
used to change dc power
to ac power?
Inverter
TDMM.* Page 9-53
What is a low voltage
disconnect (LVD)?
A device that is used to
disconnect the battery at a
preset voltage during battery
discharge and allow
reconnection only when utility
power has been restored
TDMM.* Page 9-54
What is a disadvantage of
using an LVD?
A failure of the LVD contactor or
its control circuit can cause the
load to be accidently
disconnected.
TDMM.* Page 9-54
What is the advantage of
placing the LVD on
the load side?
All loads will be disconnected
and reconnected at the
same time.
TDMM.* Page 9-54
What is the worst-case value
for output current (I out)?
Maximum output current at
current limit of charger
(usually 110 percent)
TDMM.* Page 9-58, Table 9.5
How is the worst-case value
for output voltage (Vout)
calculated?
By multiplying the manufacturer’s
equalize or boost level per cell by
the number of cells per
battery string
TDMM.* Page 9-58, Table 9.5
What is the worst-case value
for input voltage (Iin)?
The lowest nominal voltage that
is normally on the utility line
TDMM.* Page 9-58, Table 9.5
In dc cable, how much voltage drop is allowed over the total system, battery to load?
1 V (standard practice)
TDMM.* Page 9-59
Name the 2 most important
aspects of planning the
installation of a dc system.
1 .Power flow
2.Clearances
TDMM.* Page 9-61
The bending radius must
not be less than _ times
the overall diameter for
unshielded cables.
The bending radius must not be
less than 8 times the overall
diameter for unshielded cables.
TDMM.* Page 9-62
True or False
Batteries store electricity *
False. Batteries do not store
electricity. They do, however,
store energy in chemical form,
which is converted into an
electrical form during the
discharge chemical reaction.
TDMM.* Page 9-63
What is the nominal voltage
of a lead-acid battery cell?
2V
TDMM.* 9-63
What is the nominal voltage
of an alkaline battery cell?
1.2 v
TDMM.* Page 9-63
What 2 factors determine
the capacity of a
battery cell?
1 .Size of cell plates
2.Quantity of cell plates
TDMM.* Page 9-63
How does connecting cells
in parallel affect battery
capacity?
Connecting the cells in parallel
will increase battery capacity.
TDMM.* Page 9-63
Name the 3 main types of
battery cells used in
telecommunications
applications.
1 .Alkaline
2.Vented lead-acid (VLA) (also
known as FLA)
3.Valve regulated lead-acid (VRLA)
TDMM.* Page 9-63
Name 3 characteristics
of the NiCd cell.
1 .Performs well in applications that
involve temperature extremes
2.Can tolerate more abuse in terms
of charging and discharging
3.Has a long life expectancy
TDMM.* Page 9-63
What is the typical design
life of a VLA cell?
10 to 20 years
TDMM.* Page 9-64
Why is a vent included in
the top cover of a
VLA battery cell?
Because gases are generated
during the charging process
TDMM.* Page 9-64
Name the 2 gases
produced by a VLA cell.
1 .Oxygen
2.Hydrogen
TDMM.* Page 9-64
A minimum of — changes
of room air volume per
hour is recommended.
A minimum of 4 changes of
room air volume per hour
is recommended.
TDMM.* Page 9-64
Why must water in a VLA
battery cell be replenished?
To maintain a minimum level
and ensure that all the cell
plates are totally immersed
TDMM.* Page 9-64
Do VRLA battery cells
require the addition
of water?
No. The NEC states: “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.”
TDMM.* Page 9-64
When does cell venting
normally occur?
When the battery is subjected to
overcharging or over-
temperature operation
TDMM.* Page 9-64
True or False
VRLA batteries do not
require any ventilation.
False. VRLA batteries do require
ventilation because they release
a small amount of hydrogen gas
under normal operating
conditions.
TDMM.* Page 9-65
What is the typical life
range of a VRLA cell?
3 to 20 years with capacities
up to about 3000 AH
TDMM.* Page 9-65
How should the typical
lifespan of a VRLA battery
be estimated?
By dividing the expected
battery life in half
TDMM.* Page 9-65
How can you determine
the required number of
battery cells?
By dividing the load
nominal voltage by 2
TDMM.* Page 9-66
Normally, what is the
manufacturer’s specified
input voltage “window”?
The range between the cell
cutoff voltage and the cell
equalized (boost) charge voltage
TDMM.* Page 9-66
Name 4 pieces of
information that is needed
for battery cell sizing.
- Direct current required in amperes at minimum voltage or load in volt-amperes or watts
- Direct current input window of the load
- Operating temperature of the
battery - Battery backup time required
TDMM.* Page 9-66
How is battery sizing in
watts typically used?
For reserve times of less than an
hour since the manufacturer
typically presents data for short
reserve times in that format
TDMM.* Page 9-67
When is battery sizing in
amperes typically used?
When reserve times of one hour
and above are involved
TDMM.* Page 9-68
What is the recommended
maximum number of
parallel cells in a
battery plant?
5
TDMM.* Page 9-69
Name 2 causes of
imbalance problems in
parallel cells.
1 .Differences in the resistance
of the paralleling connectors
2.Different resistances of each
string of cells
TDMM.* Page 9-69
What is typically the
optimum temperature at
which a battery should be
maintained?
25 ºC (77 ºF)
What happens to a battery
if it operates below its
optimum temperature?
The battery has less capacity,
but the life expectancy is
extended.
TDMM.* Page 9-69
What happens to a battery
if it operates above its
optimum temperature?
The battery has greater capacity,
but the life expectancy is
decreased.
TDMM.* Page 9-69
Name 3 steps the ICT
designer should take if it is
not possible to design a
battery room with a
nominal temperature that
approximates 25 oc (77 OF).
1 .Factor temperature
compensation into the sizing
calculations.
2.Employ rectifiers that will
compensate the charging voltage
to allow for the operating
temperature of the battery.
3.Seek the manufacturer’s
assistance or other expert help.
TDMM.* Page 9-69
What happens if the battery
has too low a float
charge voltage?
The battery will become
undercharged and chemically
damaged, and recharge time
will be prolonged.
TDMM.* Page 9-69
What are the effects of a
too high float charge
voltage?
Excessive cell gassing and plate
expansion, which ultimately
cause cell failure
TDMM.* Page 9-69
True or False
Wet cells may be
configured on racks or
housed in cabinets.
False. Wet cells should only be
placed on open racks.
TDMM.* Page 9-70
What is the minimum depth
requirement for battery
racks and cabinets?
1 m (3.3 ft) deep
TDMM.* Page 9-70
Name 3 safety items that
are required for locations
that contain a flooded
cell battery.
*Acid neutralizer (baking soda)
*Eye-wash facility
Adequate spill containment in
accordance with the IBC
TDMM. Page 9-70
Why are fused switches
and circuit breakers
recommended?
Fused switches and circuit
breakers can be used to
disconnect the battery from the
rest of the power system for
maintenance and repair.
TDMM.* Page 9-71
What is the approximate
value of a battery’s short
circuit current?
Approximately 10 times the
rated AH capacity
TDMM.* Page 9-71
What is the heart of the
backup power system?
The battery
TDMM.* Page 9-71
Define major alarms.
Major alarms are those that
indicate the power system is
either not functioning or is
operating abnormally and is in
need of immediate attention.
TDMM.* Page 9-72
Define minor alarms.
Minor alarms are those that
indicate the power system is
operating in a reduced capacity
or has a minor malfunction and
is in need of attention.
TDMM.* Page 9-72
Name 8 types
of major alarms.
1 .Rectifier fail
2.High voltage
3.Low voltage
4.Fuse/circuit breaker
5.Inverter fail
6. Temperature
7.Monitor/control
8.Battery
TDMM: Page 9-72, Table 9.7
What type of DC minor
alarm is activated when the
total load current increases
above a preset limit?
Overcurrent alarm
TDMM.* Page 9-73, Table 9.8
Name 2 types of
remote alarms.
1 .Cabled remote
2.Dial-up remote
TDMM: Page 9-74
What is the purpose of a
cabled remote alarm?
To transmit power system
alarms to another room or
building within a relatively
short distance
TDMM.* Page 9-74
What is the purpose of a
dial-up remote alarm?
To transmit alarms to a distant
location usually over the
telephone network
TDMM.* Page 9-74
Name 5 features that can
be controlled by a power
system controller.
1 .System operating voltage
2.Prioritized load shedding on
battery discharge
3. Temperature compensation
4.Boost or equalizing charging
5.Local or remote periodic testing
TDMM.* Page 9-76
Name 2 reasons that stand-
alone battery monitors
become popular.
1 .Because of the importance of
battery performance
2.Because the battery can be the
weakest component in the
system
TDMM.* Page 9-76
In the United States, what
type of conductor is color
coded with green or green
with one or more
yellow stripes?
Equipment grounding (earthing)
conductor
TDMM.* Page 9-77, Table 9.70
In the United States, what
colors are typically used to
identify grounded (neutral)
conductors?
White or natural gray
TDMM.* Page 9-77, Table 9.10
In the United States, what
color is typically used to
identify a 208Y/120 Phase A
conductor?
Black
TDMM: Page 9-77, Table 9.10
In the United States, what
color is typically used to
identify a 208Y/120 Phase B
conductor?
Red
TDMM.* Page 9-77, Table 9.70
In the United States, what
color is typically used to
identify a 208Y/120 Phase C
conductor?
Blue
TDMM.* Page 9-77, Table 9.70
Name 2 ways that cable
cores are required to be
identifiable at their
terminations per
BS 7671.
1 .By color
2.By numbering/lettering
TDMM.* Page 9-78
True or False
BS 7671 permits over-
marking in another color at
terminations for multicore
cables with green and
yellow conductors.
True. BS 7671 permits over-
marking in another color at
terminations for multicore
cables with green and yellow
conductors, but it is prohibited
for single core green and
yellow conductors.
TDMM.* Page 9-78
In the United Kingdom and
Ireland, what colors are
used to identify protective
conductors?
Green and yellow
TDMM: Page 9-79, Table 9-79
In the United Kingdom and
Ireland, what color is used
to a functional earthing
conductor?
Cream
TDMM.* Page 9-79, Table 9-79
In the United Kingdom and
Ireland, what color is used
to identify the phase of a
single-phase circuit of a ac
power circuit?
Brown
TDMM.* Page 9-79, Table 9-79
In the United Kingdom and
Ireland, what color is used
to identify neutrals and
mid-wires?
Blue
TDMM: Page 9-79, Table 9-79
