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PDD > SYSTEMS - ELECTRICAL > Flashcards

SYSTEMS - ELECTRICAL Flashcards

1
Q

Ampere

A

electrical current

flow of electrons in a conductor

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2
Q

Energy

A

product of power and time also called work

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3
Q

Impedance

A

Impedance - Z - resistance in alternating current AC circuit measured in ohms

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4
Q

Ohm

A

unit of resistance in electrical circuit

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5
Q

Watt

A

W- electrical power = P

• Watt: the standard measurement of power, equivalent to 1 joule per second

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6
Q

DC Currents

A

used for some types of elevator motors, or low-voltage applications just signal systems controls and similar equipment.

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7
Q

AC currents

A

rotating coil in magnetic field creates alternating current. represented with sine wave. Most common form used in buildings.

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8
Q

ohms law for DC CIRCUITS

A

I = v / r

current = force / resistance

ampere = volts / ohms

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9
Q

Power calc DC circuits

A

P = v * I

Watt = VOLT X Ampere

Power = Force x Current

the rate, per unit time, at which electrical energy is transferred by an electric circuit.

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10
Q

How to Calculate Watts

A

W = V * A

Watt = volts * ampere

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11
Q

Energy CALC

A

E = P*T

Energy = Power * time

measured in watt hours or kilo watt hours

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12
Q

Series circuit

A

Rtotal = R1 + R2 + R3

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13
Q

Parallel circuit

A

1/ Rtotal = 1/R1 + 1/R2 + 1/R3

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14
Q
A

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.

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15
Q
A

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.

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16
Q
A

Four-way switch

Double pole

DPST -Double pole, single throw

Equivalent to two SPST switches controlled by a single mechanism.

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17
Q
A

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.

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18
Q

Wire Colors

AC - 120-240

A
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19
Q

Wire Colors

DC

A
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20
Q

120 volt, single phase, two wire

A

one hot and one neutral, for sheds.

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21
Q

120/240 volt, single phase, three wire

A

two hots and one neutral, for houses

(A/C and other large appliances runs on 240 volt with both hot 120s supplying power in-phase).

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22
Q

120/208 volt, three phase, four wire:

A

three hots and one neutral, for schools and other medium sized buildings

(elevator runs on 208 volt with all three hot 120s supplying power out-of-phase).

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23
Q

277/480 volt, three phase, four wire:

A

three hots and one neutral, for large office buildings

(lights run on 277 volt, elevators and A/C run on 480 volt, and plug loads are still supplied with 120 volt service).

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24
Q

Delta connected transformers

A

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.

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25
Q

Wye connected transformers

A

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.

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26
Q

Ground rod

A

connects electrical system’s ground and neutral to the earth.

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27
Q

Monocrystalline photovoltaics

A

are more efficient than Amorphous or Polycrystalline photovoltaics.

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28
Q

The number of poles in a switch

A

The number of poles in a switch refers to the number of separate circuits that the switch controls.

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29
Q

throw count of a switch

A

The throw count of a switch refers to how many positions (other than off) each switch has.

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30
Q

Underfloor raceWays

A

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

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31
Q

Q. Transformers are used for which of the following purposes?

Provide load control

Distribute power

Change alternating currents

Serve as a switchgear

A

Transformers are used to change alternating currents. They are not used for load control or to distribute power. They are part of a switchgear.

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32
Q

Horsepower

A

• Horsepower: A measure of power equal to 746 watts

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33
Q

• Load Factor

A

• Load Factor: the ratio between the average and maximum power demands of a building

34
Q

Motor vs Generator

A
  • Motor: a machine that converts electrical energy into mechanical energy
  • Generator: a machine that converts mechanical energy into electrical energy
35
Q

Transformer, kva

A

• 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: a rating for transformers equal to the product of volts and amperes divided by 1000. The product of the KVA and the power factor gives the power in kilowatts

36
Q

• Demand factor:

A

• Demand factor: ratio of maximum demand or expected power usage to the total connected load

37
Q

watt examples

  • Examples:
  • A lightbulb
  • A medium size car

• A small gas generator puts out

A
  • 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
38
Q

Voltage 120/240

A

120/240

1 Phase

3 Wires

3 wire Connection

• Residential, small buildings, or where actual load is less than 80A

3 Phase

4 Wires

Delta Connection

• High Leg Delta typically only found in older buildings

39
Q

240

A

240

1 Phase

3 Wires

Delta Connection

• Commercial

40
Q

480

A

480

3 Phase

3 Wires

Delta or Wye Connection

• Commercial

41
Q

120/208

A

120/208

3 Phase

3 Wires

Wye Connection

• Larger buildings with greater variety of loads

42
Q

277/480

A

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
43
Q

2400/4160

A

2400/4160

3 Phase

4 Wires

Wye Connection

• Huge commercial buildings and factories

44
Q

• 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?

A
  • 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
45
Q

• Electricity Service

A

For every energy unit consumed (usually a kWH) the electrical utility charges a little bit.

Typical rates are:
• 5.5 cents / kWh for residential
• 1.75 cents / kWh for large industrial

Tiered rates are often implemented
• You pay so much for the first batch of kWh, then a little more for the next batch…

Your demand is measured every 15 minutes by the utility company and you pay the

largest demand they measured that month

Residential Cost = Basic Charge + (kWh) x ($/kWh)

Commercial Cost = Basic Charge + peak kW demand $ + (kWh) x ($/kWh)

46
Q

Conductor

A

• 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

47
Q

Conduit

A

• Conduit: tubes that house, protect, support, and provide grounding for wiring.

48
Q
A
49
Q

American Wire Gauge System:

A

A standardized wire gauge system used since 1857 for the diameter of round, solid, nonferrous, electricity conducting wire

Cross Sectional area of each gauge in 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 (aka 4/0 pronounce “four aught”) = 0.46 inches

Larger than 4/0 is MCM cable sizes of 250, 400, and 500.

50
Q

Circular Mil

A

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

51
Q

Aluminum Wire (No. 8 AGW or smaller)

A
  • 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

52
Q

Copper Wire (No. 8 AGW or smaller)

A
  • Same carrying capacity as aluminum but smaller and cheaper
  • Most cost effective for small and medium sized wire and cable

Residential/ Small Construction

53
Q

Cable Types (No. 6 AGW or larger, or several conductors assembled into a single unit )

Romex

A

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

54
Q

Cable Types (No. 6 AGW or larger, or several conductors assembled into a single unit )

Flex Metal Clad Cable (BX)

A

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

55
Q

Busbar vs Busway

A

Busbar

  • Rectangular bars of copper that carry high voltage
  • Used in place of very large cables and high currents

Busway

• Multiple busbars in a metal housing

56
Q

• Conduit Types:

A

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
57
Q

Raceways

A

Channels for holing electrical wires

58
Q

Under Carpet Wiring:

A

Under Carpet Wiring: thin, flat wiring that can be laid under carpet without protruding

• Must be used with carpet tile

59
Q

Cellular Metal Floors:

A

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
60
Q

Underfloor Ducts

A

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

61
Q

Options for protecting a building from lightning

A

• 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.

62
Q

• Load Factor vs • Load Control

A
  • 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.
63
Q

Feeder

A

• Feeder: set of electrical conductors which extend from the source of energy to a distribution center

64
Q

Switchgear

A

• 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

65
Q

• Panelboard (Breaker Box):

A

• Panelboard (Breaker Box): a component of an electrical supply system which divides and electrical power feed into subsidiary circuits while providing a protective fuse or circuit breaker for each circuit, in a common enclosure

66
Q

Branch Circuit:

A

Branch Circuit: the insulated wires that run between the outlet and the panel board

67
Q

• Uninterruptible Power Supply (UPS):

A

• 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

68
Q

• Primary Distribution:

A

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 in 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

69
Q

• Secondary Distribution System:

A

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

Breakers should be oversized when a motor in involved

When designing a system, plan ahead. Where will it come in from, where is the main panel, and how much will it grow?
• Typically you should oversize systems by about 25% for future expansion • 25% of the breaker box should be empty holes for new circuits

In commercial spaces, an electrical closet might be preferable to a stand-alone panelboard for a building of 6 or more stories.

70
Q

• Branch Circuits

A

• Branch Circuits

Every circuit has a hot, neutral, and ground wire

Ground and neutral have two unique functions in an appliance connection

Hot wire is the start of the lead, neutral is the other side of the lead together these

power the appliance (e.g.: power goes in the hot, to the appliance, and out the neutral

back to the panel)

Third prong on a plug is the ground, which protects life safety

If the neutral leg breaks, the ground still is there to keep it safe

71
Q

One Switch Location: switch type?

A

One Switch Location: (1) two way (on/off) switch is used

72
Q

Two Switch Locations:: switch type?

A

Two Switch Locations: (2) three-way switches (on/off, on/off) are used

73
Q

Three or More Switch Locations: switch type?

A

Three or More Switch Locations: (2) three-way switches, and (1 +) four-way switches

74
Q

Low voltage Switching:

A

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.

75
Q

Outlets hight ada, spacing

A

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

Kitchen counters need at least two circuits, with no more than 4 outlets per 20A

No point on a wall above a counter can be greater than 24” from an outlet

76
Q

Feeder cables

A

Feeder cables bring power from the main distribution panel to subpanels in large buildings.

77
Q

Branch circuits

A

Branch circuits distribute the power from the subpanels throughout the building.

78
Q

switchgear

A

The switchgear measures, controls, and distributes the power at the main electrical panel.

79
Q

Joules

A

Joules are a unit of energy.

80
Q

Newtons

A

Newtons are a unit of force.

81
Q

Pascals

A

Pascals are a unit of pressure.

PDD (20 decks)

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