Specifying Electrical Infrastructure Flashcards
All circuits must have these three physical items that are connected:
- Conductive material, such as wires
- A voltage source, such as a battery
- A “load,” such as a light source
The rate of electrons flowing through a circuit per second. Measured in amperes. It is typically represented in math by I for “intensity” or A for “amperes.”
A. Current
B. Voltage
C. Resistance
D. Power
A. Current
The electrical potential to create current flow in a circuit.
A. Current
B. Voltage
C. Resistance
D. Power
B. Voltage
The property opposition of the flow of electrical current. Measured in ohms.
A. Current
B. Voltage
C. Resistance
D. Power
C. Resistance
The energy dissipated or consumed when an electrical device is working. Measured in Watts.
A. Current
B. Voltage
C. Resistance
D. Power
D. Power
A _____ is a passive electrical component that produces equal impedance to current flow. Current passes through in direct proportion to voltage, independent of frequency, as outlined in Ohm’s law.
resistor
There are two types of electrical current:
- Direct Current (DC)
* Alternating Current (AC)
The speed of the current change is its frequency, or cycles per second, measured in _____.
hertz (Hz).
There are two common frequencies used worldwide: __ Hz and __ Hz.
50 Hz and 60 Hz.
The voltage of an AC wall outlet is typically __ V in North America or __ to __ V in most other parts of the world.
120 V / 230 to 240 V
AV equipment uses power from the outlet, but there are other voltages your AV design may employ, such as for loudspeaker and control systems, that are typically less than the voltage from the outlet. Sometimes these types of systems are classified as _____.
low voltage
_____ is the total opposition to current flow in an AC circuit. Measured in ohms and symbolized by the letter Z.
Impedance
_____ is the opposition to the changes in voltage and current associated with the AC waveform.
Reactance
The term _____ is used when you are working with DC, such as currents that are powered by a battery or other DC source.
resistance
The term _____ is used when you are working with AC, electrical power, loudspeaker circuits, and audio interfaces.
impedance
_____ restricts the flow of current and is frequency-independent, which means the resistance value does not change with the frequency of the current passing through it.
A. Resistance
B. Impedance
A. Resistance
_____ restricts the flow of current and is frequency-dependent, which means There will be different values for low and high frequencies.
A. Resistance
B. Impedance
B. Impedance
All current seeks to ____.
A. go to ground
B. return to the source
B. return to the source
In a _____ circuit, all the electrons leave the source of power (such as a battery), travel through each part of the circuit, and return to the source. The current flows through the entire circuit, and voltage is divided across the loads. Wire has resistance; therefore, it’s considered a load in the circuit.
A. series
B. parallel
A. series
In a _____ circuit (Figure 10-4), the voltage remains the same across the loads. Cur- rent divides and takes all available paths to return to the source, while the resistance of each path determines how much current flows through each path.
A. series
B. parallel
B. parallel
A _____ is a circuit component that stores electrical energy.
capacitor
Capacitors _____ high frequencies and _____ low frequencies.
pass / block
As frequency _____ in this circuit, so does current flow.
increases
A(n) _____ has the opposite effect of a capacitor. It opposes any change in current.
inductor
An inductor is also known as a ____.
coil
Inductors ____ high frequencies and ____ low frequencies.
block / pass
A _____ is a passive electromagnetic device usually consisting of at least two coils of wire (inductors) with no electrical connection between them.
transformer
EGC stands for _____
A. electrical grounding connector
B. equipment grounding connector
C. electrical grounding conductor
D. equipment grounding conductor
D. equipment grounding conductor
_____ refers to the overhead service conductors from the last pole, other aerial support, and underground feeds outside the building, connecting to the service-entrance conductors at the building or other structure.
A. Service Drop B. Service Entrance C. Service Panel D. Distribution Panel Board E. Feeders F. Subpanels
A. Service Drop
The _____ is the point at which power enters the building.
A. Service Drop B. Service Entrance C. Service Panel D. Distribution Panel Board E. Feeders F. Subpanels
B. Service Entrance
The _____, receives the incoming power and adds a ground conductor.
A. Service Drop B. Service Entrance C. Service Panel D. Distribution Panel Board E. Feeders F. Subpanels
C. Service Panel (a.k.a. - switchboard)
The _____ distributes the power to subpanels throughout a facility.
A. Service Drop B. Service Entrance C. Service Panel D. Distribution Panel Board E. Feeders F. Subpanels
D. Distribution Panel Board
The _____ are circuits that carry power between the service panel and the distribution panel.
A. Service Drop B. Service Entrance C. Service Panel D. Distribution Panel Board E. Feeders F. Subpanels
E. Feeders
____ have current-limiting devices, such as circuit breakers or fuses. An individual circuit might provide power to all the lights in the room, or several electrical convenience outlets, but the total power consumed on the circuit cannot exceed the current-limiting device’s rating or else the circuit breaker trips or a fuse blows.
A. Service Drop B. Service Entrance C. Service Panel D. Distribution Panel Board E. Feeders F. Subpanels
F. Subpanels
You should plan for a decent buffer between the needed amperage and the circuit’s rating. In the U.S., this buffer is defined by the NEC as __ percent of capacity.
80
UL uses the term _____ for power strips.
relocatable power taps (RPTs)
In the context of electrical power, _____ refers to an earth connection or something that extends an earth connection.
ground
Outside of North America, the term ____ is used instead of ground.
earth
The ____ is an overcurrent protection device and will protect users and electrical equipment from damage due to an overload or short circuit by interrupting current flow.
circuit breaker
Current seeks to return to the source, and the _____ conductor is the path that current normally takes.
A. hot
B. cold
C. neutral
D. ground
C. neutral
_____ is when you use a grounding conductor separate from the neutral conductor. Generally, this wire is green or green-yellow.
Equipment grounding
An accidental connection between the line conductor and the metal enclosure of a device is called a _____.
ground fault
A _____ is a power system designed especially for AV systems and associated computers and utilizes an isolated ground. Such systems are useful in critical-listening environments that require a low noise floor, such as broadcast studios, postproduction facilities, performing arts centers, recording studios, and other critical listening environments.
technical power system
An _____ is a receptacle in which the grounding terminal is purposely insulated from the receptacle mounting.
isolated receptacle
Interference, or ____, is any electrical signal in a circuit that’s not the desired electrical signal. The most common evidence is a hum or buzz.
noise
_____ is defined as an undesirable 50 or 60 Hz noise emanating from an audio system. It can manifest in a video system as a rolling bar on the display.
Hum
_____ is a hum with additional harmonic energy.
Buzz
_____ is the transfer of energy from one circuit to another via an electrical or magnetic field. There is no physical contact between circuits during this energy transfer.
Field theory
The expanding, contracting, and direction-changing signal on the AC conductor—at 60 cycles per second— is transferred to the second conductor. This is called _____.
magnetic-field coupling
A positively charged conductor (lacking electrons) creates an electric field in the surrounding region, attracting electrons. This attraction—the electric field—creates a negative charge in a nearby conductor through what is called _____.
electric-field coupling
_____ is the maximum safe voltage of the insulating material between two conductors before the dielectric breaks down and an arc occurs, equalizing the charge between the two bodies or conductors.
Dielectric strength
A _____ is a metallic partition between two areas. It’s used to control the propagation of electric and magnetic fields from one area to the other.
shield
Shielding works bidirectionally. It prevents signals from getting out or getting in, stopping what are known as _____ and _____.
egress and ingress
There are three basic types of cable shielding: _____, _____, and _____.
foil, braid, and a combination of the two.
_____ employs any magnetically permeable material to absorb and conduct magnetic lines of flux to redirect them away from an unintended victim, such as a circuit.
Magnetic shielding
The purpose of _____ shielding is to lead current to the equipment-grounding conductor and back to the source.
electric-field
A _____ is any electrically conductive continuous loop.
ground loop
The rejection of interference that is induced commonly on two conductors is known as _____.
common-mode rejection (CMR)
The formula for common-mode rejection is as follows:
(S1 + N1) – (–S2 + N2) = ST + NT
where:
• S1 is the signal on the first conductor.
• N1 is the noise on the first conductor.
• – indicates the difference (differential).
• S2 is the signal on the second conductor.
• N2 is the noise on the second conductor.
• ST is the total signal.
• NT is the total noise.
The common-mode rejection ratio is expressed in _____.
decibles (dB)
One of the best defenses against common-mode noise is to specify _____.
transformers
A _____ is a passive electromagnetic device, usually consisting of at least two coils of wire (inductors) with no electrical connection between them. These coils often share an iron-based core that concentrates the magnetic lines of force in one coil, thereby inducing voltage into the other coil.
transformer
Conduit for AV cabling should not contain more than __ 90 degree bends without a pull box.
two
Conduit for AV cabling should have a bend radius of least __ times the internal conduit diameter for conduits of 2 in or less.
six
Conduit for AV cabling should have a bend radius of least __ times the internal conduit diameter for conduits larger than 2 in.
ten
One cable can occupy __ percent of the conduit’s inside area.
53
Two cables can occupy __ percent of the conduit’s inside area.
31
Three or more cables can occupy __ percent of the conduit’s inside area.
40
Conduit capacity formula (one cable)
D > √ (d2 / 0.53)
where:
• D = Inner diameter of the conduit
• d = Outer diameter of the conductor
Conduit capacity formula (two cables)
D > √ [(d2+ d2) / 0.31]
where:
• D = Inner diameter of the conduit
• d = Outer diameter of the conductors
Conduit capacity formula (three cables)
D > √ [(d2+ d2+d2….) / 0.40]
where:
• D = Inner diameter of the conduit
• d = Outer diameter of the conductors
_____ can occur when one cable slips in between the other two as they’re being pulled so that they lay side by side in the conduit.
Jamming
The jam ratio formula is as follows:
Jam = ID / [(OD1+OD2+OD3) / 3]
where:
• ID = Inner diameter of the conduit
• OD = Outer diameter of each conductor
A jam ratio of anything between ___ to ___ should be avoided.
2.8 to 3.2
