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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 |
 120 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 |
 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 |
 Weatherproof
lever switch on outdoor lightsSafely 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 Buy 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 |
 Larger image of gridSingle 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 imageThe 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 |
 See
LargerPower 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 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.  Primary 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 |
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 Large image of Fuse Full image  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 imageDistribution 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 |
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 Larger imageDistribution 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.  -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 voltAlternating 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. |
 Example
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.  -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 |
 Attaching service to a poleLocal 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. |
 Larger imageMeter 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 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 |
 Pulling 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 |
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 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. |
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 Larger imageBasic 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 |
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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. |
 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 |
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| 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. |
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 For
safety, always put cover over Breaker box <> circuit
breakers can overheat from aged breakers or loose wires and cause
sparks that ignite a fireBlank plates must be left in place if no breaker is inserted into box. |
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