SYSTEMS - ELECTRICAL Flashcards
Ampere
electrical current
ampere = I
flow of electrons in a conductor
Impedance
Impedance - Z - resistance in alternating current AC circuit measured in ohms
Ohm
unit of resistance in electrical circuit
Watt
W- electrical power = P
• Watt: the standard measurement of power,
equivalent to 1 joule per second
Energy CALC
E = P*T
Energy = Power * time
measured in watt hours or kilo watt hours
Series circuit
Rtotal = R1 + R2 + R3
Parallel circuit
1/ Rtotal = 1/R1 + 1/R2 + 1/R3
Two-way
SPST - Single pole, single throw
A simple on-off switch: The two terminals are either connected together or disconnected from each other. An example is a light switch.
Three-way
SPDT - Single pole, double throw
A simple break-before-make changeover switch: C (COM, Common) is connected either to L1 or to L2.
needed to control 1 light from 2 locations
Four-way switch
Double pole
DPST -Double pole, single throw
Equivalent to two SPST switches controlled by a single mechanism.
Four-way switch
DPCO - Double pole changeover
or Double pole, centre off
Schematically equivalent to DPDT. Some suppliers use DPCO for switches with a stable center position and DPDTfor those without. A DPDT/DPCO switch with a center position can be “off” in the center, not connected to either L1 or L2, or “on”, connected to both L1 and L2 at the same time. The positions of such switches are commonly referenced as “on-off-on” and “on-on-on” respectively.
Delta connected transformers
have their windings arranged in a triangular shape, which connects all three hot wires together and does not include a neutral wire. This type of source is almost exclusively used by power companies and you will not be able to run most equipment directly off this arrangement.
Wye connected transformers
have their windings arranged in a Y shape, which connects each of the three hot wires to a neutral wire. Wye connected sources give users a choice of voltages and can be used to run most equipment in buildings.
Ground rod
connects electrical system’s ground and neutral to the earth.
Monocrystalline photovoltaics
are more efficient than Amorphous or Polycrystalline photovoltaics.
The number of poles in a switch
The number of poles in a switch refers to the number of separate circuits that the switch controls.
throw count of a switch
The throw count of a switch refers to how many positions (other than off) each switch has.
Underfloor raceWays
Underfloor raceWays
underfloor ducts - proprietary steel raceways cast into concrete floor
Cellular metal floors - part of structural floor, same concept. Cells are closer together
Under carpet cable/wiring - thin, flat, protected wire that can be laid on the carpet without protruding through the carpet.
punch through recepticals
Q. Transformers are used for which of the following purposes?
Provide load control
Distribute power
Change alternating currents
Serve as a switchgear
Transformers are used to change alternating currents.
They are not used for load control or to distribute power.
They are part of switchgear.
Horsepower
• Horsepower: A measure of power equal to 746 watts
• Load Factor
• Load Factor: the ratio between the average and maximum power demands of a building
Motor vs Generator
- Motor: a machine that converts electrical energy into mechanical energy
- Generator: a machine that converts mechanical energy into electrical energy
Transformer, kva
• Transformer: device that transfers energy from one circuit to another by magnetic coupling with no moving parts. It changes the voltage (or force) of an AC circuit to a higher or lower value
Transformers change voltage in a circuit but not the total power
Separate wires are wound around an iron core. The wire with a greater number of winds has a higher voltage, The wire with less winds has a lower voltage
• KVA: is simply 1,000 volt-amps
• Demand factor:
• Demand factor: ratio of maximum demand or expected power usage to the total connected load
watt examples
• Examples:
- • A lightbulb
- • A medium size car
- • A small gas generator
- Examples:
- A lightbulb might consume about 60 watts
- A medium size car might consume about 100,000 watts
• A small gas generator puts out about 2,000 watt
Voltage 120/240
120/240
1 Phase
3 Wires
3 wire Connection
• Residential, small buildings, or where actual load is less than 80A
or
3 Phase
4 Wires
Delta Connection
• High Leg Delta typically only found in older buildings
240
240
1 Phase
3 Wires
Delta Connection
• Commercial
480
480
3 Phase
3 Wires
Delta or Wye Connection
• Commercial
120/208
120/208
3 Phase
3 Wires
Wye Connection
• Larger buildings with greater variety of loads
277/480
277/480
3 Phase
4 Wires
Wye Connection
- Larger buildings, smaller feeders, conduit sizes, switch gears that lower voltage
- large, multistory building that principally uses fluorescent or HID lamp
2400/4160
2400/4160
3 Phase
4 Wires
Wye Connection
• Huge commercial buildings and factories
• A circuit of plugs in your home has two floor lamps (300 watts each), a home entertainment center (750 watts), a computer work station (900 watts), and the occasional vacuum (600 watts).
What is the current expected from this circuit?
What size should the breaker be?
Figure out the load:
• 2 (300 watts) + 750 watts + 900 watts + 600 watts = 2,850 watts
Convert to amps to find the current:
• 2,850 watts / 120 volts = 23.76 amps
Size the breaker:
• Breakers come in 10A, 15A, 20A, and 30A so you’ll need a 30A for the circuit
Conductor
• Conductor: means by which a current is conducted, typically cable and wire
Basic material of electrical system
Sizes are based on American wire gauge (AWG) and thousand circular mil (MCM) designations
Conduit
• Conduit: tubes that house, protect, support, and provide grounding for wiring.
American Wire Gauge System:
A standardized wire gauge system for the diameter of round, solid, nonferrous, electricity conducting wire
Cross-Sectional Area of each gauge is an important factor for determining its current-carrying capacity
Increasing gauge numbers give decreasing wire diameters
No. 36 AWG = 0.005 inches
No. 0000 AWG = 0.46 inches
Larger than 4/0 is MCM cable sizes of 250, 400, and 500.
Circular Mil
Circular Mil: the area of a wire having a diameter of one mil or 0.001 of an inch, used
in specifying wire size
Current carrying capacity of a conductor depends on the size, type of insulation around it, and surrounding temperature
Use 14 gauge minimum in buildings
Aluminum Wire (No. 8 AGW or smaller)
- Requires a special installer
- Oxide can form when joints loosen and/or overheats
- Must be larger than copper to carry amperage
- Limited to primary circuits because of overheating
Commercial
Copper Wire (No. 8 AGW or smaller)
• Same carrying capacity as aluminum but smaller and cheaper
• Most cost effective for small and medium sized wire and cable
Residential/ Small Construction
Romex
Nonmetallic sheathed cables
2+ plastic insulated conductors and ground surrounded
by a moisture resistant sleeve
No conduit required, it’s an alternative
Must be protected from damage within walls, etc.
Residential, Wood Framed less than 3 stories
Flex Metal Clad Cable (BX)
Flexible metal clad cable
2+ plastic insulation conductors encased in spiral wound
strip of steel tape
No conduit is required
Can be easily pulled
Remodel/ Residential
Busbar
Busbar
- Rectangular bars of copper that carry high voltage
- Used in place of very large cables and high currents
• Conduit Types:
Supports and protects wiring and serves as ground and protects surrounding construction from fire in case of overheating
Used for large residential and commercial projects
Rigid Steel
- The safest type
- After pipe is installed (indoor/outdoor) wires are pulled through • Connections are rigid and threaded like pluming pipes
- Connect to J-boxes and devices
Intermediate Metallic
- Steel conduit with thinner walls but same outside diameter as Rigid • More economical
- Use with threaded fittings
Flex (Flexible Metal)
- Used everywhere except underground
- Reduces vibration transmission from equipment where not possible
to install rigid
Electric Metallic Tubing
- Thinnest metal conduit
- Too thin to thread, connections are made with clamps • Easy/fast install
- Not allowed in hazardous areas
Raceways
Channels for holing electrical wires
Under Carpet Wiring:
Under Carpet Wiring: thin, flat wiring that can be laid under carpet without protruding
• Must be used with carpet tile
Cellular Metal Floors:
Cellular Metal Floors: part of the structural floor, essentially metal decking used for cable raceways
- Cells are closer than underfloor ducts
- Preset inserts are placed for tapping
Underfloor Ducts
Underfloor Ducts: proprietary steel raceways cast into concrete floor at regular spacing (4’, 5’, or 6’)
• Feeder ducts run perpendicular to distribution ducts carrying power and wiring from the electrical closet
• Preset inserts are placed along distribution for tapping
Options for protecting a building from lightning
• Lightning Rods and conductors
• A conductive rod is attached to upper points of a roof structure and electrically bonded by bonding conductors called downleads.
• Downleads are connected by the most direct route to one or more grounding or gathering terminals
- *• Overhead grid of wire conductors** extended to the ground
- *• Lighting rods** connected to the building’s steel frame and then to the ground
• Steel framed structures can bond the structural members to earth to provide lightning protection.
• A metal flagpole with its foundation in the earth is its own extremely simple lightning protection system. However, the flag(s) flying from the pole during a lightning strike may be completely incinerated.
• Load Factor vs • Load Control
• Load Factor: the ratio of average power used to the maximum power demand
• Load Control: a building’s electrical system is designed to avoid peak electricity use.
Feeder
• Feeder: set of electrical conductors which extend from the source of energy to a distribution center
Switchgear
• Switchgear: central electrical distribution center that consist of an assembly of switches, circuit breakers and cables or bus-ducts that distribute power to the building
• Panelboard (Breaker Box):
• Panelboard (Breaker Box): a component of an electrical supply system that divides an electrical power feed into subsidiary circuits while providing a protective fuse or circuit breaker for each circuit, in a common enclosure
Branch Circuit:
Branch Circuit: the insulated wires that run between the outlet and the panel board
• Uninterruptible Power Supply (UPS):
• Uninterruptible Power Supply (UPS): an electrical apparatus that provides emergency power to a load when the input source fails. Typically used to protect computers, data centers, telecom equipment, or wherever power outage can disrupt business
• Primary Distribution:
A central electrical distribution center that consists of an assembly of switches, circuits breakers and cables that distribute power to the building is called switchgear
A load center pad-mounted unit substation would typically have a primary voltage range of 2.5-15 kV
The most popular form of exterior transformer installation for individual buildings is mounted on a concrete pad
In a typical building electrical power system wiring closet, dry-type transformers are typically placed between plug-in busways and 120V panelboards
A meter and transformer are included with it to split power into separate circuits, each with a master switch and circuit breaker for protection
Switchgear also distributes power to substations for further transforming and distribution as part of a secondary distribution system
• Secondary Distribution System:
Power is distributed from the main switchgear to panelboards
Panelboards (or breaker box) divides the electrical feed into subsidiary circuits while providing a protective fuse or circuit breaker for each circuit
Typical power voltages of 120V, 240V, and 277V
Distribution is made with wires in conduit, underfloor raceways, or flex cables
Protected by circuit breakers typically 15A and 20A, also come in 10A and 30A…with 100A for main disconnects
One Switch Location: switch type?
One Switch Location: (1) two way (on/off) switch is used
Two Switch Locations:: switch type?
Two Switch Locations: (2) three-way switches (on/off, on/off) are used
Three Switch Locations: switch type?
Three or More Switch Locations: (2) three-way switches, and (1 +) four-way switches
Low voltage Switching:
Low voltage Switching: operated on 24V circuit and controls relays that provide the
120V switching.
Same light can be controlled from several remote positions
Central control station can be set up for monitoring and override
Less expensive than line-voltage wiring and devices for large installations that
need to be flexible.
Outlets hight ada, spacing
height min 15”
Spacing should be 12’-0” max, or so that no point is further than 6’ from an outlet
Floor receptacles must be within 18” of an exterior wall to count as a required
power receptacle in a dwelling
Circuits are usually 15” and at least 20A for the kitchen, pantry, and dining
Joules
Joules are a unit of energy.
Newtons
Newtons are a unit of force.
Pascals
Pascals are a unit of pressure.
• Breakers sizes?
• Breakers come in 10A, 15A, 20A, and 30A
Busway
Busway
• Multiple busbars in a metal housing
kVA
The kVA unit represents kilovolt-amperes, or 1,000 volt-amperes. A transformer with a 1.0 kVA rating is the same as a transformer with a 1,000 VA rating and can handle 100 volts at 10 amps of current.
multiply the required input voltage (V) by the required current load in amperes (l) and then divide that number by 1,000:
kVA= V * l / 1,000
ohms law mnemonic
Woman Are Virgins
Watt = Amps x Volts
Virgins Are Rare
Volt = Amps x Resistance (ohm)
