BS - Electrical (JHO NOTES)

American Wire Gauge System

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

Alternator

AC generator that commercially produces AC current by converting mechanical energy to AC

Typical 240V loads include:

Air conditioning / electric heating systems Electric dryers/ Electric water heaters Large appliances, microwaves and stoves

"Watt Hours", or more commonly kilowatt hours, kWh, are a measure of energy

Energy is the capacity to do work, like create heat, light, or motion

2400 / 4160

Huge commercial buildings and factories

120 / 208 V three phase (three transformers), four wires system

Used in larger buildings because it allows for a variety of electoral loads

The amplitude of the wave represents the

Voltage, and the distance between peaks is one cycle

Primary winding

used for input in a transformer

Secondary winding

used for output and can be divided into segments so that they output voltage depends on which settlements are used.

Wye

used when all the loads in an AC system are connected at a single point and a neutral cable is connected at that center point where the three phases meet. Most low voltage distribution lines are Wye

Delta

used when three phases are connected like a triangle and don't have a neutral cable

Units for Electricity are

watts per square foot

Connection types are the

wye, shaped like the letter Y, and delta, shaped like a triangle

Circuit

a conductor, flow of energy, an electric potential difference (voltage), and some type of medium that creates resistance to flow.

Primaries are usually connected to

a delta

Generator

a machine that converts mechanical energy into electrical energy

Insulation

a material of very low conductivity used to separate electrical conductors and prevent leakage of electrical currents

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

Grounding

a safeguard that allows a current to find an easy path to the earth, eliminating electrical load and protecting people from shock.

Circuits can be interrupted by

a switch

Short Circuit

accidental low-resistance connection between two components of an electrical circuit that are meant to be at different voltages.

Most common form of energy used in buildings is

alternating (AC) current

Transformer

are used to change the voltage (force) of an AC current to a higher or lower value. Separate wires are wound around an iron core.

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

Transducer

device which converts power in one kind of system to power in another form, such as loudspeaker which converts electric power to acoustic power.

Single Phase Electric Power

distribution of AC power using a system in which all the voltages of the sully vary in unison, used when loads are mostly lighting and heating with few large electric motors.

High Voltage

electrical energy at voltages high enough to inflict harm or death upon living things. Used in electrical power distribution, cathode ray tubes, to generate x-rays, and other scientific applications

Direct Current (DC) is used for some types of

elevator motors and low voltage applications like signal systems and controls

Conductor

means by which a current is conducted, typically cable and wire

Current (I)

measured in amps, it's the amount of flow through a circuit

Resistance (R/Ω)

measured in ohms, the amount that slows down the current

Voltage (V)

measured in volts, the amount of force or potential in a circuit

three phase transformers

multiple leads on the secondary windings and different configuration of both the primary and secondary windings can occur

Wye Wye

offers the advantage that one of the transformers can be removed with the reming two transformers can deliver three phase power at 58% of the original bank

Two Wire Secondary

one wire is grounded and becomes neutral

Reactance

part of the electrical resistance in an alternating current circuit cased by inductance and capacitance

Demand factor

ratio of maximum demand or expected power usage to the total connected load

Delta Wye

stable with respect to unbalanced loads

Wye connections are symmetrical so the voltage from each of the three phase wires to the neutral is the same

that means that the voltage from each to phase to the neutral equals the voltage from line to line dived by square root of 3 or 1.73

Ohm's Law

the building block to energy. It states that current is directly proportional to voltage and indirectly proportional to resistance. - If voltage goes up, current goes up. - If voltage goes down, current will go down.

Power Factor (PF)

the phase difference between voltage and current in AC circuits. aka: cosine of the angle between the voltage wave and resultant current wave, ranges from 0.0 to 1.0 and expressed as a percentage

Power is a measure of

the rate at which energy flow

Power (P)

the rate of energy transfer, expressed as energy / time (in hours)

Load Factor

the ratio between the average and maximum power demands of a building

Impedance

the resistance in an alternating current, measured in Ohms.

In parallel circuit, the current at each load depends on

the resistance of each load

Watt

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

Transformers change voltage in a circuit but not

the total power

Volt-Ampere (VA)

the unit used for the apparent power in an electrical circuit, only useful in the context of AC circuits.

Larger Commercial/Industrial require higher voltage and get

three phase services like 277 / 480 volts. Higher voltage allows for a larger number of fixtures to be on a single circuit without an increase in current.

Conduit

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

Parallel Resistances (1/RTotal)

(1/R1 + 1/R2 + 1/R3 +.... 1/Rn) 1 divided by resistance 1 + 1 divided by resistance 2 + 1 divided by resistance 3

Commercial Cost =

(Commercial Cost = Basic Charge + peak kW demand $ + kWh x $/kWh) Commercial Cost = Basic Charge, plus, peak kW demand cost, plus, kWh, times, cost per kWh

Ohm's Law

(I = V / R) Current = Voltage divided by Resistance

Series Resistances (Rtotal)

(R1 +R2 +R3 +....Rn) resistance 1 + resistance 2 + resistance 3

Residential Cost =

(Residential Cost = Basic Charge + kWh x $/kWh) Residential Cost = Basic Charge, plus, kWh, times, cost per kWh

AC 3 Phase Power (watts) W

(W = I x V x PF x √3) Watts = Current times Voltage times Power Factor times square root of 3 or 1.73

AC circuit Power (watts) W

(W = I x V x PF) Watts = Current times Voltage x Power Factor

DC circuit Power (watts) W

(W = I x V) Watts = Current times Voltage

Energy in a system (watt hour)

(W x T) Power times Time

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

120V / 240 V Single Phase (one transformer), Three Wire System

- Most common power for residential and very small buildings. - Single phase systems come from a three wire secondary. - Consists of two hot wires, each carrying 120V and 1 neutral wire. - Appliances that requires 240V use both hot wires. - 120V is used for plugs, lights, and some small equipment.

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.

Busbar

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

Aluminum

- 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

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

- Romex - Flex Metal Clad Cable (BX) - Busbar - Busway

Copper

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

277 / 480 V Three Phase (three transformers), four wires system

- The same as 120 / 208V except for higher voltage. - Smaller feeders, conduit, smaller switchgear because of higher voltages. - Higher voltages result in small currents the equipment needs to carry. - Buildings usually have 277 V fluorescent lighting that requires smaller wiring. - Small step down transformers are used where 120 V service is needed for receptacles and equipment.

Current carrying capacity of a conductor depends on

- size - type of insulation around it - surrounding temperature

When do you go to 240V system?

1. When the current draw is huge 2. When you can save money on wire

Three Phase Transformer Connections

1. Wye Delta 2. Delta Wye 3. Delta Delta 4. Wye Wye

If a neutral is added to a delta, the voltage from two of the phase wires to the neutral is

1/2 of the phase to phase voltage. The voltage from the third phase to the neutral is 0.866 times the phase to phase voltage....no loads are connected between these two points though.

Breakers come in

10A, 15A, 20A, and 30A

Small Buildings usually get

120/240 single phase or 120 / 208 three phase service

The best distribution system for a large, multistory building that principally uses fluorescent or HID lamps is

277 / 480V 3phase, 4 wire

How many BTU is 1 watt?

3.412 BTU

Alternating Current is produced at a frequency of

60 cycles per second or 60 Hz

A lightbulb might consume about

60 watts

Wire Types (No. 8 AGW or smaller)

Aluminum and Copper

Wye Delta

Commonly used in step down transformers, wye connection on the high voltage side reduces insulation cost. The neutral point on the high voltage side can be grounded

Delta Delta

Commonly used in step up transformer for the same reason as Wye Delta

Demand Charge Equation

Demand Charge = maximum power demand times (x) demand tariff

AC Current

Direction of the flow can be reversed rapidly by reversing the voltage resulting in a sine wave when plotted. The standard form of electrical current supplied by the utility grid and by most fuel powered generators.

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 - Use 14 gauge minimum in buildings

120 / 208

Larger buildings with greater variety of loads

277 / 480

Larger buildings, smaller feeders, conduit sizes, switch gears that lower voltage

Busway

Multiple busbars in a metal housing

Where to put a Transformer?

Must be placed outside of a building or within a fireproof vault due to humming noise, toxic fluids, and ventilation requirements

120 / 240

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

The difference between single phase and three phase:

Single phase power is 60 cycles / second, called hertz. Three phase power is 60 cycles / second (again, called hertz) in three phases that are separated in time. Each phase is 1/3 cycles apart. 3 phase system give a wider set of options for use.

208 / 480 V Three Phase (three transformers) System

Three circuits carry three alternating currents which reach their instantaneous peak values at different times. Has an effect of giving constant power transfer over each cycle of the current and makes it possible to produce a rotating magnetic field in an electric motor.

Watts are basically the measurement of an electrical circuit

Watts tell you how fast electrons are moving around the circuit. Represent a unit of energy over time. Imply a rate "per second" value

Low Voltage

circuits that are exempt from the protection of high voltage, most commonly reefs to mains voltage or power transmission lines

A basic electrical circuit consist of a

conductor, current (the flowing electrons), voltage (the potential difference that causes the electrons to move), and some type of resistance to the flow.

Three Wire Secondary

consists of two segments; one lead is at one end of the secondary, a second connected to the midpoint of the secondary and grounded, and the Third is connected to the other end of the secondary

DC Current

current that flows in one direction with constant voltage. - batteries are an example of DC current

Step Down Transformers

decrease the voltage, typical for buildings because voltage coming in is higher than it should be for appliance and lighting

Step Up Transformers

increase the voltage

Extra Low Voltage

is a low risk, and used for things like intercoms, remote lighting, doorbells, HVAC.

3 Phase AC Current

like an AC current but three different circuits each 120 ̊ out of phase with the other and one neutral circuit