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