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See inside main breaker box
This page covers electricity from power pole to residential circuit breaker box
This is called single-phase residential electric service


Related pages: Basic wiring inside home
Electricity from power plant to power pole: What is 3-phase electricity
Electricity from power pole to commercial business: What is 208 volt    Identify transformer configurations
For commercial electricity: How to wire 3-phase
Difference single-phase and 3-phase

Multimeter
Test for breaks in wire/ Test for voltage
Most appliance require 80% rated voltage to function correctly
Buy
Analog multimeter
Multimeters at Amazon
Klein multimeter
Electric testers at Amazon
Clampmeter for testing amp flow on line
Resource:
How to test and replace element
How to test thermocouple
Element tests for 120 volts
How to test wire

Safety when testing wires:
Never touch wet or previously flooded appliance.
Never stand on wet surface when working on electric.
Never stand on bare soil, put down dry boards.
Tape tester leads to wood sticks to keep hands away from power.
Use non-contact voltage tester before touching wires.
Never touch or lean into any made of metal.
Remove metal objects from pockets.
Do not use oxygen or fuel accelerants in same room as electrical repairs

Resource:
Basic house wiring
GFCI receptacle120 volt 15 amp devices including GFCI, timers, switches, plugs, wifi controls etc can be installed on 15 or 20 amp breaker.

120 volt GFCI, outlet, receptacle that is rated 20 amp can be installed on 20 amp breaker only, but NOT on 15 amp breaker.  
Buy
15 amp GFCI
20 amp GFCI

Use outlet tester to check for correct wiring on any 120 volt straight-blade outlet.
Buy:
Klein testers
Outlet tester
Circuit breaker finder
Electric usage monitor
Southwire armored cable cutter
Electrical tools must be insulated.
Always best to disconnect power, but insulation failure, lack of proper grounding, grounded neutral, lack of GFCI, out-of-code wiring, generator operating without transfer switch, and other problems still pose a risk to anyone working on electric power ... even when breaker is off.

Buy:
Electrician tools kits
KLEIN TOOLS
Tools kits
IRWIN tools
KNIPEX
Lever switchWeatherproof lever switch on outdoor lights
Safely operate outdoor toggle switch
Replaces outdoor cover
Install over top of ordinary switch
Works with single-pole, double-pole, 3PST, 3-way, 4-way switches etc
Use weatherproof box for outdoor
Can be used indoor or outdoor

Buy:
Cantex lever switch
Leviton lever switch
Outdoor lever switches at Amazon

Resource
Cantex-toggle-switch-covers.pdf
Cantex-PVC-junction-boxes.pdf

Use nipper instead of pliers or screwdriver for removing staples (and nails). Do not damage cable or wires inside cable.

Code
-Cable SHALL BE secured without damage to the outer covering. NEC sec. 336-15
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End cutting nippers at Amazon

 
When removing insulation from wire, do NOT score or put cuts on surface of copper wire. Doing so increases resistances on wire and creates weak point.
Buy tools:
Wire strippers at Amazon
Linesman pliers
Pro linesman plier
Needle nose pliers
End cutting nippers at Amazon

power plant to house electricityLarger image of grid
Single phase household electricity comes from the 3-phase electricity produced at power plant.

Illustration shows 3 phase from power plant to household single-phase.
Three phase transmission and distribution consists of 3 Hot wires and a Neutral wire.
Each Hot wire is called a phase.
In conventional power plants (coal, gas, nuclear, hydroelectric etc) the Neutral wire originates at the generator, same as the Hot wires come from the generator, but unlike Hot wires, the Neutral is grounded at the generator and bonded to the ground rod at each tower, pole and installation along the way, protecting the grid against lightning and malfunction with a giant array of grounding.

Single phase is achieved by taking one Hot wire and a Neutral off the 3-phase line. The Hot and Neutral are then connected to residential transformer, also called a distribution transformer.

Transformers are used throughout the grid to raise and lower voltages as needed.
High voltage can jump or arc over long distance. The risk of high voltage is managed by using the insulating properties of air ... and suspending high voltage lines high off the ground ... and using transformers to reduce voltage as power lines get closer to people.

Starting at the the large power transformer at local, or secondary, substation. See image

The substation transformer lowers 69,000 volt subtransmission lines into safer 12,400 volt or 12.4 kV. distribution lines that are suspended closer to the ground, and travel along local streets where they supply electricity to each neighborhood, home and commercial service along the way.

Distribution lines have 3 Hot wires and a Neutral.

Since volts and amps are inversely proportional, then when volts are lowered, amperage is raised.

The residential distribution transformer reduces 7,200 volt distribution to safer 120-240 household voltage, at same time raising amperage by pulling just 8 amp off the power line to supply a 250 amp residential service.

More detail
Voltages are standard, such as 125,000, 69,000, 7,200 etc. Volts are the force that pushes amperage, or electrons, across the wire. While amperage rises and falls as loads turn on-off, voltage generally remains unchanged. A major goal of the grid is to maintain steady voltage, and to mitigate voltage drops and spikes.

Voltage is measured across Hot lines on the power pole. For example, 12,400+ (12.4 kV) volt is measured from Hot wire to Hot wire, and this is called LINE voltage ... while 7,200 volts (7.2 kV) is measured from Hot wire to Neutral, and called phase voltage, which is Line voltage divided by square root 3 or 1.732.  Read more  Read more

When 3-phase distribution lines reach a neighborhood, 1 Hot wire and 1 Neutral wire are taken off the 3-phase line, and this connection is where distribution becomes the 7,200 volt single phase line that travels through a neighborhood and supplies electricity to distribution transformers located at each home.
Resources:
Difference single-phase and 3-phase
Color code for wire
Electricity arrives from the poleSee Larger
Power poles carry high-volt, low-amp electricity
-High-volt and low-amperage lets power company transmit electricity long-distance from the power plant without heat loss caused by high amperage.

Before entering a house, a distribution transformer is used to convert electricity into safer lower volts and higher amps.
Different transformers are used for different voltages.
-Residential transformers receive 4500-7200 volts from 1 high voltage line and a neutral.
-The transformer reduces voltage into safer 120-240 Volt service that drops down from pole via two 'out-of-phase' Hot wires and a Neutral that enter home.

-Unlike the high volt distribution line that requires wide space between wires and heavy switchgear etc, the 120-240 volt household power works nicely since the voltage can be safely contained inside small plastic and metal boxes, switched with small switches, home automation, cell phone chargers etc, and the higher amperage managed by using correct size wire and circuit breaker.
Is it 220 or 240 volt?

-Note: 3 service wires drop down from pole and enter the weatherhead, and then down to meter box before entering main breaker box located inside home. This is called the Line side of the service panel (breaker box), or service entrance, or transformer secondary. <> The three service wires include 2 hot wires and 1 neutral wire <> the neutral also connects to ground wire at pole (see photo1 see photo2), and to ground wire that is bonded to the Neutral busbar in main breaker box.

On every pole and tower and installation on the grid, the Neutral wire is bonded to a ground wire that connects to a ground rod that is driven into the soil, creating a giant array of grounding across the grid that is used for safety and to stabilize the grid against overvoltage events such as lightning, equipment failure, short circuit etc.
Resources:
Where power comes from: What is 3 phase
Difference between household and commercial electricity
Read about electric power from power plant
Why you need ground wire
Underground residential electric serviceUnderground residential electric service is same as above-ground service
-It's easier to photograph above-ground electric service.
-All residential electric services, above and below ground, follow same pattern from power line => to transformer => to meter box => through the meter => to main breaker box.

-Meter and meter box for underground service is the same as above ground, except service wires arrive in underground conduit pipe instead of dropping down from a pole.
-Transformers for underground service are located inside ground-level boxes or underground vaults, and perform exactly same function as above ground transformers located on poles.
-Underground lines last longer and experience less resistance and heat loss than above ground lines, but above ground can be installed, repaired and upgraded to carry higher voltage with less cost.

Larger image
Parts for residential electric service
Fig S1 shows detail labeling for residential electric service.

Distribution transformers are steel cans that contain two coils (or windings) of wire that share an iron core, but share no wires. Since the two coils are separate and share no wires, then this is an isolation transformer. All transformers on grid are isolation type (vs autotransformers commonly used in commercial applications).

The two coils are called 1) the Primary coil or primary side and 2) the Secondary coil or secondary side.

parts on electric polePrimary side:
Transformers have 2 bushings located on top that connect to each end of the primary coil. The high voltage Hot wire from pole drops down and connects to one bushing, and the Neutral connects to the other bushing. This energizes the primary coil and magnetizes the iron core, which induces lower voltage on the secondary coil. (using principle of magnetic induction)

Secondary side:
The transformer also has three taps located on side of can, near the top, that connect to the secondary coil. The Triplex is a 3-wire bundle that connects to the three taps, X1 X2 X3, with Nuteral connecting to X3 center tap, and Hots connecting to X1 X2 taps on each side. Then the Triplex drops down to home and delivers 120-240 volt.

Grounding:
Note the Neutral wire is at top of pole and drops down and connects to the Neutral bushing on transformer. When Neutral is at the top, as shown, it serves a secondary purpose of shielding the installation from lightning strike.
The Neutral wire connects to a copper ground wire at top of pole, where lightning is re-directed into earth. The ground wire travels down the side of pole and connects to each metal part plus the steel transformer can before arriving at bottom where it connects to a ground rod. See image

Unlike the Neutral that connects to ground wire that touches each metal part ... the Hot wire is highly insulated from touching other parts on the service installation ... except where it connects to the strain insulator, the Hot clamp, top of Fuse, trough the fuse and then down to Arrester bushing before connecting to the Hot bushing on top of transformer. This prevents the Hot from energizing metal parts and causing short circuit that would trip the fuse.

Guy wires
The two 'down guys' that angle down from left side of pole help support pole against wind, ice and environmental stresses. The guy has 2 sections at the top, called guy strain insulators, that are made of fiberglass to insulate from lightning or surge events that could energize the 6-strand galvanized steel guy wire that is anchored into ground. See image

Fuse on power pole
Large image of Fuse
Full image
Tripped fuse
Open or tripped fuse
Larger image
Dropout fuse or Fuse cutout

High voltage distribution lines carry 4500-7200 volt that must pass through a fuse cut-out before connecting to Hot bushing on top of transformer.

Image shows high voltage Hot wire terminating on a strain insulator located on last pole at end of street.

A 'hot clamp' clips on the Hot wire and brings power down to top of fuse.
Power passes through the fuse before dropping down to arrester bushing and then to the Hot bushing located on top of transformer.

Fuse will trip when heat exceeds fuse rating, protecting transformer and service from lightning, overload, malfunctions etc.

-Electric company resets fuse using long fiberglass pole. See image
Open fuse will shut off power to transformer, but has no effect on distribution line.

Resources:
Names of parts on electric pole
Larger image
Distribution transformer

-After 7200 volt distribution Hot wire travels through the fuse, it drops down to the lightning or surge arrestor, and then connects to Hot bushing on top of the transformer.
-The Neutral wire connects to Neutral bushing on top of transformer.
-The ground wire is bonded to the shell of the transformer and travels down length of pole into soil at base. All poles, transformers, and electrical services are grounded.
-The transformer shown supplies electric service to two homes instead of more typical single home.
-Power leaves the transformer from 3 secondary bushings located on side of transformer and travels to each home via 3-wire bundles of triplex.
Resources:
why you need ground wire
distribution transformerLarger image
Distribution transformer image from JEA
-7200 volt Hot wire drops down to an insulator, then passes through the fuse, then to the arrester, and then connects to primary input or bushing at H1.
-The Neutral wire connects to the top of the transformer on primary input or bushing at H2, and the Neutral also connects to ground wire which is bonded to the steel transformer can before going down side of pole into soil.
-3-wire bundle of Triplex wire (not shown) connects to the 3 secondary outputs or taps at X1 X2 X3, before dropping down to home and delivering 120-240 volt.

-Residential electric services are generally standard. Sometimes the incoming Hot wire is located at the top of pole, and Neutral wire is located below the transformer. But in areas more prone to lightning, the Neutral is located at top of pole to 'shield' or protect the service by giving lightning a direct path to ground via the Neutral-ground connection.

The purpose of the transformer is to 1) convert 7200 high-volt low-amp distribution into usable 120-240 low-volt high-amp electricity for home, and to 2) isolate the 7200 volt distribution voltages from the 120-240 volt household voltages.

Isolating the higher and lower voltages using an isolation transformer as shown, guarantees that high voltage wires can never come into contact with household wires, and so extremely dangerous 4,500-7,200 volt power will never occur inside household wiring. Read more

Resources:
Read: Transformer theory .pdf
Read: Distribution transformers .pdf
Read more about electricity generation: What is 3-phase electricity
Read about commercial electric service
Larger image
Another image
Inside household distribution transformer
Inside each transformer are 2 coils (or windings) of insulated wire, called the primary coil and secondary coil.
The 2 coils are each wrapped around a shared iron core, but otherwise share no Hot wire. Although the Neutral wires are connected to same grounding, the Neutral comes off the center tap, and therefore carries no power.

-Note that the secondary side to home has 3 wires ..,  a Neutral wire from center tap, or center point of secondary coil ... and Hot1 and Hot2 that arise from opposite ends of the secondary coil.

120-240Volt transformer-Utilizing magnetic induction, when the primary coil is energized with 4500-7200 volts, it magnetizes the shared iron core, causing the secondary coil to be energized with lower voltage. The voltage is lower because there are more turns of wire on the primary than the secondary.

-Lower and higher voltage and amperage is achieved by varying the number of wraps or turns of wire on each coil. This is called the turns ratio: Voltage per turn x number of turns. See formula
For example, if the primary coil has 30 times more wraps or turns of wire than secondary coil, then 7200 volt primary is converted to 120-240 volt secondary service.

-Note that electric power can travel both directions through a transformer. If home has solar panels feeding back into grid, the primary and secondary coils are reversed, so home can supply .3 amp @ 7,200 volt to the distribution line.  Read more
Same applies to a home generator. This illustrates the importance of turning off main breaker during power outage if you have generator or solar panels.
Connecting Hot1 and Hot2 to a load gives you 240 volt

Alternating currect
-Connecting the 7200 volt Hot and Neutral across the transformer's primary coil 'completes the circuit' causing electrons to oscillate back and forth 60 times per second, matching the rotation of power plant generator.
This is called alternating current.

-The back-n-forth motion of electrons on the primary coil causes electrons on the secondary coil to oscillate back-n-forth at the same 60 Hz frequency, which means household electricity has same 60 Hz back and forth motion of electrons.

The back-n-forth movement of electrons through the load is what energizes the load
-To get 240 volt in a home, you pull a Hot wire from each end of the secondary coil: We call these wires Hot1 and Hot2.
-Hot1 and Hot2 are 'out of phase' from each other, so Hot1 carries electrons that are going opposite direction from Hot2.

-When Hot1 and Hot2 are connected to a 240 volt load, the electrons race through the load going one direction, and then reverse and race back through the load again going other direction.
-The back-n-forth movement of electrons through the load energizes the load because that's how AC electricity works.

-If you connect two Hot1 wires to a load, nothing happens because both wires come from same end of secondary coil. Each Hot wire must come from oposite end of secondary coil for it to work.

120 Volt
-By pulling a Neutral off the center of the coil, you get 1/2 voltage or 120 volt potential.
As a result, 120 volt is achieved using 1 Neutral wire and 1 Hot wire (either Hot1 or Hot2).
-The same thing happens with 120 volt. The electrons change direction and move back-n-forth 60 times per second, except at 1/2 power.
Math: 120 volt x 30 amp load = 3600 watts. Watts is power.
240 volt x 30 amp load = 7200 watts, or exactly double the power. So 120 volt delivers 1/2 power compared with 240 volt.

Residential drop wireExample service drop wire
-2 out-of-phase Hot wires and 1 neutral wire leave transformer and drop down to weatherhead located on side of home or nearby pole.
-Triplex is commonly used for drop wires and contains 1 bare, stranded aluminum wire for Neutral ... and 2 insulated stranded aluminum wires to carry Hot1 and Hot2.

-Typical Triples has a solid black vwire for one Hot and black wire with yellow stripe for other Hot.
-Triplex means 3 wires twisted together to form 1 cable. Quadraplex is 4 wires twisted together to form 1 cable. Different types of bundled cables are available to meet various needs.

Triple drop wire-Neutral is always connected to the Ground wire for safety and stability. This is true inside the house, same as on the grid. During a short circuit or insulation failure inside home, the ground wire assists household circuit breakers and wires by instantly redirecting as many electrons as possible into the ground rod and eath until breaker can trip.
Resource:
Why you need ground wire
Electricity at meter poleAttaching service to a pole

Local codes vary, but generally, if building is getting started, or temporary, or delapidated, or is un-skirted mobile home with wheels, or RV, then power must be attached to a pole, and not to the structure.

A permanent home or mobile home that is skirted with wheels removed can attach power to side of building.
All electrical must be attached to firm structure like wall 2x4 and not to unsupported siding.
Meter box and weatherheadLarger image
Meter box and weatherhead

-The 2 hot wires and 1 neutral drop down from transformer and enter weatherhead.
-Older neighborhoods and rural homes typically have above ground service with weatherhead, and enough room to play baseball ... and neighbors don't live within talking distance.
When home has underground service, there is no weatherhead (or space to play baseball without clunking a car), and instead the transformer is located inside underground vault and electricity is delivered to meter box via underground conduit.

-Purpose of weatherhead is to keep water out of mast, meter box etc.
-Moisture will cause deterioration of electric service, and deterioration is major factor for fire risk.

-All electricity must be routed through the meter so power company can bill for the number of kilowatt hours.
Meter and meter box
Meter Box
-Three wires enter meter box. Same 3 wires arrive for both underground and above ground service connections.

-2 out-of-phase Hot wires from power company connect to top lugs. Hot wires going to breaker box connect to bottom lugs. Neutral wires connect to middle lug. Ground wire may be connected to Neutral lug or to separate terminal. Use large allen wrench or hex wrench to tighten lugs very tight against wire. If wire is aluminum, then apply anti-oxidant to prevent oxidation before installing.

-The meter 'stabs' into meter box using 4 prongs, comparable to extension cord plugging into wall socket.

-The meter completes the circuit, letting electricity flow to Main Breaker Box. If the meter is missing, then the lugs inside meter box have live electricity, unless fuse on service pole is in open position. Never assume power is OFF.

Resource:
How to wire service disconnect
Meter and meter boxPulling a meter
-Pulling a meter requires a stout pull downward and then push upward <> typically you use two hands clapsed over meter and pull downward on the top of meter and then push up, going up & down to loosen and remove meter > removing meter will turn off electricity to breaker box, and to whole house <> however meter box will still contain live electricity <> stand on dry boards when pulling meter <> turn off all circuit breakers in main breaker box before pulling or re-installing meter to eliminate arc of electricity just as meter prongs makes contact with lugs.

-Modern electric company practices have a locking band around each meter to prevent tampering, but it can stop DIY folks from doing some electrical repairs, like replacing main breaker panel. Rural areas, where codes permit, the homeowner can request the band removed temporarily while repairs are made.

-Buy used and reconditioned meters and install around house to track electric usage of each appliance.
Resources:
How to install your own electric meter
Inside Main Breaker Box
Larger image-2 Hot wires / 1 Neutral wire/  enter main breaker box
-Each out-of-phase Hot wire connects to different busbar
-The Neutral connects to Neutral busbar, which is bonded to the Ground busbar.
-The 2 Hot busbars are blue and black (color added for illustration) > the 'blue' Hot wire provides power to blue busbar> and black Hot wire to black busbar.

-Hot busbars never touch each other or touch the box > they are suspended away from the main box by insulators

-240 Volt potential exists between blue busbar A and black busbar B.
-120 Volt potential exists between either Hot busbar and the Neutral busbar.
Larger image
Basic 240V water heater circuit

All residential single-phase circuits require Two wires plus ground

**120Volt circuit requires 1 Neutral wire and 1 Hot wire, plus ground.
-For 120 volt, the Black Hot can come from either Hot busbar. White Neurtal comes from Neutral busbar.
-When switching 120 volt, the Hot wire is turned off. Never switch a Neutral wire off.

**240 volt requires 2 out-of-phase Hot wires plus ground.
Note: a double breaker pulls a Hot  wire from each Hot busbar, while a single breaker can pull off either Hot busbar, depending which slot it is installed.
-With 240 volt, the wire color can be Black and White or Black and Red, and with heavier gauge wires, like 6 gauge and 4 gauge, the wires are Black and Black.
-When switching 240 volt, both wires can be switched off - or - one wire can be switched off.
-If either wire in 240V circuit is switched off, the circuit turns OFF.
Resources:
See 30 amp switch turning off water heater
Main breaker warning Main breaker warning
-Screws are Hot on main breaker all times.
-Even when main breaker is OFF, both screws are HOT.
-Only if meter is PULLED are these screws safe to touch.
main breaker box
Larger image
-Illustration shows Neutral and Ground busbars on same side of box so it is easier to illustrate wires, but in actual box, the Neutral and Ground busbars are on opposite sides.

120Volt and 240Volt breakers
-Image shows 120 volt line and 240 volt lines.
-All circuits have ground wire.
-Each 120 and 240 require two wires to complete circuit.
-120V requires 1 Neutral from Neutal busbar and 1 Hot from a single breaker.
-240V requires 2 Hots from a double breaker
-Ground wires are needed for safety. FYI .... a GFCI does not respond immediately without a ground. Even double-insulated appliances and tools are not fully protected since they have no ground.
Resources:
Read more about 240 volt

-Neutral is not used for 240Volt circuit. However some 240Volt lines have a Neutral wire, shown above as 10-3 wire..
-Modern breaker boxes have separate Neutral and Ground busbars that are bonded together electrically.
Neturals and ground are supposed to be connected to correct busbar, but modern wiring often has Ground on Neutral bar etc.
Older boxes can have one busbar for both Neutral and Ground.

Resources:
Color code and wire sizes
Basic 120 volt and 240 volt water heater circuits
How to wire 240 volt outlets
How to wire 3-phase outlets and timers
How to convert 240Volt  water heater to 120volts
Question: Are both sides of 240 volt breaker 30 amp or 15 amp ?

Answer: both side of 240 volt breaker are 30 amp. You can make a 240 breaker by combining 2 single-pole breakers, but that code requires you to install a 'common bar' between the breaker so if one trips, then the other breaker also trips.
For safety, always put cover over Breaker box <> circuit breakers can overheat from aged breakers or loose wires and cause sparks that ignite a fire

Blank plates must be left in place if no breaker is inserted into box.

Larger image
Install meter on subpanel

Resources:
How to install subpanel
New and used electric meters
How to install electric meter on water heater or subpanel
How to wire tankless electric water heater

Color code for wire and wire sizes
Resources:
How to install electric meter on water heater

Resources:
Figure volts amps watts
Formulas for ohm's law
What is electricity
How a generator works

transformers
Larger image
Transformers sitting at electric yard
Each transformer is multi-tap
Multi-tap means the transformer can be configured for different voltages and applications

Resources:
3-phase electric
Household electric service
Why you need ground
Formulas-for-Ohms-law
Pulling electric wire/ photos
Transformers
Transformers

Transformer
Symbol for transformer
Transformers can convert electricity many different ways.
Resource:
Transformer manuals
Transforming electricity is limited only by mathematics governing the natural world.
For example using a transformer, high voltage and low amperage can be converted to lower voltage and higher amperage used inside each home. There is inverse relationship between volts and amps shown in following formula: Volts x amps = watts.
See electrical formulas

 High voltage 3-phase from the power plant can be converted into many different 3-phase voltages depending on which transformer is used. Resources:
Read about Delta and Wye
The reverse is also possible: Using a transformer, single phase residential power can be converted into certain types of 3-phase.
Since solar generated power is DC (direct current) instead of AC (alternating current) a transformer called an inverter will convert DC solar power into more useful AC power. Different inverter voltages are available by wiring the transformer differently.

Small transformers are used inside each home to convert 120V single phase electricity into low-voltage AC or DC electricity used to recharge cell phones or computer battery or power the 12 volt AC doorbell or 24 volt AC HVAC systems or low voltage outdoor lights.

Electricity is a wave that oscillates.
In the US the wave oscillates at 60 cycles per second. This is called 60 Hz.which appears on appliance labels. Each TV, refrigerator, computer, microwave, etc will have a label that shows Hz or hertz.
Countries such as Australia and India use 50 Hz.
Appliances made for 60 Hz will not work with 50 Hz electricity, and vice versa.
Some timers made by Intermatic and Tork are rated 50-60 Hz and will work globally.
Resources:
How electric power arrives at each home

In household electricity, both Hot busbars are identical except out of phase with each other.
With 120 volts a single wave oscillates up and down.
Using 240Volts doubles the wave, and since each wave is out of phase with the other, it is like adding an extra cylinder to the engine, and gives added power.
Phasing and voltage is determined by the transformer.
 

3 phase service
3 phase service back of store
Larger image
Larger image 2
Three phase electricity is more efficient than single-phase
Many businesses and schools use 3 phase electricity.
Electricity is generated at the plant by spinning 3 coils through a magnetic field.
Each coil is separated by 120 degrees.
Each coil produces a wave or pulse of electricity, and since each coil is slightly behind the other during rotation, the result is a 3-phase wave. This type of electricity is AC or alternating current.
Power is sent out on 3 separate wires, one wire from each of the 3 generator coils. Each wire is Hot.
Transmission lines are high voltage and low amperage to reduce heat loss. This allows long-distance transmission. Power from the generator is re-transmitted in several directions at local transformer stations. Eventually, there is a limit to distance electricity can be transmitted.
The field of super-conductivity works to solve problems of transmission loss.

Generally, if a business has 3-phase service, then power is pulled from each of the 3 Hot wires and routed through transformers that determine exact voltage of the service. There are a range of different 3-phase voltages, each determined by the transformer. Most 3-phase buildings also have transformer that convert power to 120 volt single-phase available for ordinary outlets.
Resources:
How to install 3-phase timer     Read about Delta and Wye     What is 3-phase

Unlike 3-phase, Residential power does not require all 3 Hot wires.
For residential neighborhood, only 1 high voltage Hot wire enters the neighborhood. The single hot wire arrives at each home at a transformer where voltage is reduced and amperage increased. The transformer coil splits the single hot wire so that power entering home has both 120 volt single phase and 240 volt split-phase available as shown in illustrations above.

So each neighborhood is powered by 1 of the 3 Hot wires coming from power plant. Generally, when one area draws power from 1 of the 3 Hot wires, then next area will draw power from 2nd Hot wire. Then the following area draws power from 3rd Hot. This keeps power draw balanced across all 3 Hot wires.

Electricity leaves power plant What is 3-phase electric: power plant to end user





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