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inside main breaker box
This page covers electricity from power pole to residential circuit breaker box
Other pages: Electricity inside home
Electricity from power plant to power pole: What is 3-phase electricity
Electricity from power pole to commercial business: Identify transformer configurations
For commercial electricity: How to wire 3-phase
Neutral connects to transformer. Ground wire connects to Neutral wire.
Ground wire is smaller diameter than Neutral. Ground and Neutral work together for household safety, stability of grid, and to help absorb overvoltages and shorts caused by lightning, equipment failure, surges from inductive loads etc.
poles carry high-volt, low-amp electricity
-High-volt low-amp lets power company transmit electricity long-distance without heat loss caused by high amperage.
-Before entering house, electricity is converted to lower volts and higher amps at transformer. Different transformers are used for different voltages. -Residential transformers receive 7200 volts from 1 high voltage line and a neutral. The transformer reduces voltage to 120Volts and splits the voltage into two 'out-of-phase' 120Volt Hot wires that enter home. The two out of phase hot wires offer 240Volt potential used to power water heaters, air conditioner etc. While 120 volts is used for outlets and lights.
-Note: 3 wires enter home <> 2 hot wires and 1 neutral wire <> the neutral also connects to ground wire at pole. Neutral wire to home and inside home is same gauge as hot wires so it can carry voltage equal to the hot. Ground wire is smaller gauge than neutral wire. The ground wire is buried under the soil and is used for safety and to stabilize the grid.
Where power comes from: What is 3 phase
Read about transformers
Read details about 3-phase
residential electric service
-It's easier to photograph above-ground electric service, but many homes and businesses have underground utilities.
-All 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 wires arrive in underground conduit pipe instead of dropping down from a pole.
-Transformers for underground service are inside ground-level boxes or underground vaults, and perform exactly same function as above ground.
|Fuse cutout located on power pole
-High voltage distrubtion wires carry 4500-7200 volt that must pass through a fuse before connecting to transformer.
-Fuse will trip when heat exceeds fuse rating, protecting transformer from surge caused by lightning, overload, malfunctions etc.
-Electric company resets fuse using long fiberglass pole.
-Far left image shows high voltage line terminating on a strain insulator located on last pole at end of street.
Names of parts on electric pole
|Lineman resets fuse at night|
|Parts on residential electric service|
-After 7200 volt distribution Hot wire travels through the fuse, it drops down to the lightning or surge arrestor, and then connects to top of the transformer. Not shown is the Neutral wire which connects separately to top of transformer, and also connects to ground wire.
-The ground wire is bonded to the shell of the transformer before traveling 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. Disadvantage is light flicker when heavy amp loads turn on, such as air conditioner.
-Electricity leaves the transformer and travels through 3-wire bundles called triplex that contains 2 Hots and 1 Neutral.
why you need ground wire
Large heavy-load transformers contain oil for coolant. Household transformers shown above are air-cooled.
-7200 volt hot connects to fuse and then drops down to the arrester and then into the transformer. The Neutral wire also connects to the top of the transformer, and the Neutral connects to ground wire which is bonded to the transformer shell before going down side of pole into soil.
-Triplex wire (not shown) connects to the 3 secondary outputs, before dropping down to home.
-Each home and business has a transformer or transformer bank depending on the electric service.
-Residential distribution transformers are generally standard, as pictured to the left. Sometimes the hot wire is located at the top of pole, and in areas more prone to lightning, the Neutral, or static wire, is at top of pole to protect the service by giving lightning a direct path to ground through the Ground wire. The purpose of the transformer is to change 7200 high-volt low-amp distribution into usable 120-240 low-volt high-amp electricity.
-High-volt low-amperage is used on overhead conductors to increase transmission distance by reducing heat loss from high amperage. Voltage is lowered at each home to increase safety and make household appliances affordable since high-voltage requires heavy, expensive switchgear. The grid is engineered to balance function and cost objectives.
-The grid is defined by three parts: transmission and distribution and end user.
-Transmission lines carry very high voltage and wires are located highest from the ground on tall poles or towers, using the air as insulation from ground. Transmission lines travel long distance from power generator to local substations. Transformers and switchgear for transmission lines are found inside a fenced-off substation and not at local home or business.
-Distribution lines leave the local substation and travel shorter distances to each business and home in the community. Distribution lines carry 4500-7200 volts and are lower on the poles than transmission lines.
Read: Transformer theory .pdf
Read: Distribution transformers .pdf
Read more about electricity generation: What is 3-phase electricity
Read about commercial electric service
See another image of household single phase and split phase
Read about source of electric power
household distribution transformer
Inside each transformer are 2 coils of insulated wire, called the primary coil and secondary coil. High voltage (4500-7200 volts) enters the primary coil on two wires from service side and household voltage leaves the secondary coil on three wires called triplex.
-When current flows through 7200 volt coil, it causes current to flow through secondary coil, even though the coils do not touch or have any shared wires. This is a principle of electromagnetic theory.
-Different Voltage and amperage is achieved by varying the number of wraps on each coil etc.
-Electric power can travel both directions through a transformer. If home has solar panels, and the panels generate voltage that exceeds household usage, the reverse happens and the secondary coil energizes the primary coil. Read about solar
service drop wire
-2 Hot wires and 1 neutral wire leave transformer and drop to weatherhead located on side of home or local pole.
-Triplex is commonly used for drop wires and contains 1 non-insulated aluminum wire for Neutral, and 2 insulated aluminum wires to carry Hot1 and Hot2 from transformer to meter box.
-Normally 1 Hot wire is solid black and other Hot wire is solid black with yellow stripe.
-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 requirements.
-After leaving the transformer, the Neutral wire is same gauge as Hot wires, so in emergency the Neutral can carry voltage equal to incoming Hot.
-Neutral is always connected to Ground wire. Ground wires are smaller and used for safety. The entire grid is bonded together by the Neutral-Ground system and serves to stabilize the grid. The ground also assists circuit breakers by absorbing shorts and overheating events that trip and can damage breakers.
-Taking additional step of bonding all ground rods and wires together at home helps protect service from surge caused by nearby lightning. Bonding means the TV and phone lines etc are all grounded together in an array.
Why you need ground wire
Ground wire is smaller gauge than neutral
to get electric service
-Call local electric company: Ask for specifications and permit for connecting electric service.
-Electric company may required licensed electrician before approving installation, or in rural areas they may allow homeowner to install the meter box and weatherhead.
-Specifications must be followed:
-Install meter box and weatherhead on side of any stationary building. -Unskirted Mobile homes and RV and temporary buildings and dilapidated structures usually require separate pole for meter and weatherhead.
RVs will plug into outlet that is attached to conduit below the meter box. -Power cut off required at connection point.
-Breaker box can be installed on pole. Or conduit can be run underground into any structure where it terminates in a breaker box. Breaker box must have a main breaker.
-Height of weatherhead, height of meter box, size of conduit, size of wire, size and type of pole, location of ground rod, ownership of property, billing address, setback distances, proximity of power pole and transformer, trees, other buildings, etc must be considered.
-Generally there must be 8' ground rod installed at the pole with proper grounding ... local codes for ground vary by type of soil, moisture and temperature.
-Meter box, conduit, wire, ground rod and weatherhead available at local store. Install meter box and conduit and ground rod.
-Run wire from meter to weatherhead, and leave specified amount of wire hanging out of weatherhead. Power company will inspect meter and wires, and then attach drop-wire from pole, install meter into meter box, then re-engage fuse at power pole to energize the service.
Electric company will not connect power unless conduit terminates into a shut off box or is continuous to a main breaker shut off inside breaker box.
Example service installation manual
box and weatherhead
-2 hot wires and 1 neutral wire drop down from transformer and enter weatherhead.
-Older neighborhoods and rural homes often have above ground service with weatherhead. When home or business has underground service, there is no weatherhead, and instead the transformer can be inside underground vault or at ground level and electricity is delivered to meter box in underground conduit.
-Purpose of weatherhead is to keep water out of mast, meter box etc.
Water must be kept out of mast and underground conduit, or short can occur.
-Moisture can cause rusted box and deterioration of electrical connections.
-All electricity must be routed through the meter box so power company can measure the number of kilowatt hours consumed.
-Three wires enter meter box. Same 3 wires arrive for underground or above ground service connections.
-Hot wires from power company connect to lugs on one side. Hot wires going to breaker box connect to lugs on other side. Neutral wires connect to same 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.
-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 the meter box have live electricity. Never assume power is OFF.
How to wire service disconnect
and meter box
-Pulling a meter requires a stout pull downward and then upward <> typically you 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 whole house including breaker box <> 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, and thwart efforts to get free electricity.
-Buy used and reconditioned meters and install around house to track electric usage of each appliance.
How to install your own electric meter
|Aluminum vs Copper|
-Aluminum is used for overhead wires and for triplex because of it's high conductivity, strength, durability, low weight, and cost. Copper is too heavy and too expensive for long spans of wire.
-Aluminum will expand when it gets hot and is not suitable for insude the home.
Wires entering the meter box can be aluminum, but the wires leaving the meter box and going to main breaker box should be copper.
All wiring inside home should be copper.
|-2 Hot wires / 1 Neutral wire/ enter main
-Ordinary household wiring is called 'single-phase' or 'split phase.'
-120 volt is generally called single-phase and 240 volt is split-phase.
-The available voltage is determined by how the electric company sets up the transformer.
-2 Hot wires and 1 neutral wire arrive from meter box.
-Blue color added to 1 hot wire for illustration <> in real breaker box, the 2 hot wires are black
-The 2 hot wires connect to the Main Breaker <> a lug is tightened very tight to hold wire in place. Neutral is connect to neutral busbar.
-Each hot wire connects to different busbar through the main breaker > here the busbars are named A and B > the 'blue' hot wire provides power to blue busbar <> remember, blue color added for illustration only
-Hot busbars are 120 Volts each > they never touch each other > they are suspended away from the main box by insulators
-240 Volt potential exists between busbar A and busbar B
-On some apartment and condo services, 208 Volt potential exists between busbar A and busbar B, and 120 Volt between each hot busbar and either busbar A or B
See basic 120V and 240V water heater circuits
between 120Volt and 240Volt
-Inside main breaker box are Three busbars.
-One busbar is Neutral busbar.
-Two busbars are Hot busbars.
-Each Hot busbar is 'out of phase' with the other.
-Bare ground wires are bonded to Neutral busbar as redundant safety.
All residential single-phase circuits require Two wires to complete circuit.
**120Volt circuit requires 1 Neutral wire and 1 Hot wire.
-Hot wire can come from either Hot busbar.
-By Code, these wires are Black-Hot and White-Neutral.
-If either wire is interrupted, the circuit turns OFF. By code the Black Hot wire is switched ON-and-OFF.
**240Volt circuit also requires 2 wires to complete circuit.
-In the case of 240V, the circuit requires 2 Hot wires.
-One Hot wire from each 'out of phase' busbar is required to complete 240Volt circuit.
-These wires 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.
If either wire in 240V circuit is interrupted, the circuit turns OFF.
See 30 amp switch turning off water heater
|Main breaker warning
-Screws on main breaker are HOT at all times.
-Even when main breaker is OFF, both screws are HOT.
-Only if meter is PULLED are these screws safe to touch.
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.
|120Volt and 240Volt
-Image shows 120Volt line and 240volt line.
-Both circuits have ground wire.
-Each 120 and 240 require two wires to complete circuit.
-120V requires 1 hot and 1 neutral
-240V requires 2 hots
-Ground wires are for safety.
Read more about 240 volt
-Neutral not necessary to complete 240Volt circuit. However some 240Volt lines have additional neutral wire. However,
-240Volt lines can be white and black or red and black
-Modern breaker boxes have separate Neutral and Ground busbars that are bonded together electrically. Older boxes often have one busbar for both Neutral and Ground.
-Illustration shows Neutral and Ground busbars on same side of box so it is easier to illustrate wires. In actual box, the Neutral and Ground busbars are on opposite sides.
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
meter on subpanel
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
How to install electric meter on water heater
Figure volts amps watts
Formulas for ohm's law
What is electricity
How a generator works
to replace circuit breaker
Breakers are held in place at both ends <> one end locks into a cleat -or- snaps onto a bar <> other end of breaker rotates to busbar and then 'stabs' onto the busbar
Push firmly to make sure breaker is stabbed all the way down
When replacing a breaker, check busbar for damage or burning from previous breaker <> busbars are frequently damaged by aging breakers that arc and burn <> arcing will damage busbar so new breaker will no longer work in the same slot. Read steps 32-37:
When lights flicker, check breaker immediately before sparking causes damage in breaker box. Check breaker and listen for fizzing or crackling sound. Check if the breaker screw is tight against wire. Flickering lights are usually a loose wire at a plug, but it pays to check breaker first to avoid busbar damage.
Always put cover back on breaker box to prevent sparks from leaving breaker panel.
Read how to replace circuit breaker
Water heater is tripping breaker
How to replace circuit breaker
How to wire gfci
Can AC breaker be used for DC breaker
How to reset circuit breaker
Not enough space for circuit breakers/ use tandem
How to install subpanel
Why you need ground wire
See inside breaker box
How to wire safety switch
How to wire whole house surge protector
Figure volts amps and watts
Figure correct wire and breaker
Types of surge protection
Transformers sitting at electric yard
Each transformer is multi-tap
Multi-tap means the transformer can be configured for different voltages and applications
Household electric service
Why you need ground
Pulling electric wire/ photos
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
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.
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.
phase electricity is more efficient than
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.
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.
can convert electricity many different ways.
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.
|AC/ DC||DC (direct current)
is power from a battery. This
type electricity can be stored and used later.
AC electricity cannot be stored without using inverters to store power in DC (direct current) battery. And then it must be inverted back from DC to AC, and each conversion causes power loss due to heat.
Edison, the inverter of the light bulb, originally promoted DC current, and his first large-scale model was to light a city block with DC power using his light bulbs. But it was quickly apparent that DC current could not be transmitted long distance, so AC power is standard service worldwide today.
The problem with AC power is that is cannot be stored, so power generation must anticipate demand, and have enough generators operating to meet demand.
Solar and wind generated electric power has disadvantage since generation occurs at specific times, but not always when electricity is demanded. With wind power, the location of the generator is not often close to where people live, meaning that long-distance transmission loss cuts into overall efficiency.
|Three phase motors
require connecting all three
Similar to 240volt that requires two hot wires
Different 3-phase motors require different voltages.
electric prices result because electricity cannot be stored
Once the grid is electrified, any unused capacity is wasted. Power plants want to produce just enough to meet the demand so additional fuel is not consumed at the power plant.
Generally, coal power plants are slower to come on-line. Natural gas power plants can be turned on-and-off more rapidly. Power companies have to anticipate demand so that power is available at peak demand times.
The capacity issue, among other problems, is why power companies have 'peak' electric prices.
Read about off-peak water heater options
|Basic household wiring
Basic water heater circuit
Figure volts amps watts for electric water heater
How to wire tankless electric
How to change water heater temperature using timer
Change water heater from 240Volt to 120Volt
How to wire thermostats
How to wire water heater for off peak operation
How to twist wire
How to wire Cooper 277 pilot light switch
How to wire combo switch-outlet
How to replace 3-speed fan switch
How to wire dimmer
How to wire 3-way dimmer
How to wire occupancy switch
How to wire motion detector
How to wire TM811 and TM8111 switches
How to wire wall timers
How to wire box timers
How to wire off-delay timer
Wire off-delay timer
How to wire pin timers
How to wire and troubleshoot photo eyes
Reverse photoeye so it turns on in day
24 Volt photoeye
24 volt programmable timer
How to wire switches
How to add switch
How to add 3-way switch
Timer for 3-way switch
Timer for 4-way switch
How to add outlet
How to wire 3-way switches
How to wire 4-way switches
Troubleshoot Malibu outdoor lights
Select and install wire connectors
Select wire size
How to wire arc fault breaker
How to wire GFCI
How to wire GFCI combo
Basic water heater circuit
How to wire water heater for 120Volt
Install old work box
How to drop wire from attic
How to wire 240volt outlets
How to install 3-phase timer
How to wire 3-phase outlets
How to wire 3-phase surge protector
What is 3-phase
How to wire whole house surge protector
How to wire under-counter water heater
See inside main breaker box
How to solder wires
Whole house surge protector
3-phase surge protection
Difference between 120 volt and 240 Volt
Difference between 50Hz and 60Hz
How to install electric meter on water heater
How to wire water heater thermostat
How to wire water heater with switches and timers
Intermatic timer enclosures
Read how to convert AC water heater to DC/ high voltage
Convert AC water heater to DC/ low voltage
How to wire DC solar water heater
DC relays for solar water heater
How to add another thermostat to water heater
How many Kwh to heat water
Chart for figuring heating time for electric heater
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