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What is 277 volt
277 volt is derived from commercial 3-phase transformer configurations.
Use only 600 volt wire.
Lamp cord, extension cords are not rated 600 volt.
Use copper wire only. Aluminum wire is fire risk and should be avoided or installed by professional.

30 amp breaker use 10 gauge /


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10-2 gauge/ 30 amp
10-3/ 30 amp
Southwire electric tools
Yellow 12 gauge 20 amp


Yellow/ #12 gauge wire for 20 amp
with ground
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12-2 gauge/ 20 amp
12-3/ 20 amp

NMB is house wiring
UF is underground
Rolls of stranded wire
White 14 gauge 15 amp


White/ #14 gauge wire for 15 amp
with ground
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14-2 gauge/ 15 amp
14-3/ 15 amp

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armored cable
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Armored cable
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Southwire armored cable cutter
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Rolls of stranded wire

Stranded wire
stranded wire
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Rolls of stranded wire
50-60 amp breaker use 6 gauge /
6-2 wire
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6-2 wire
Southwire electric tools
NMB is house wiring
UF is underground
40-50 amp breaker use 8 gauge /
6-2 wire
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8-2 wire
Southwire electric tools
NMB is house wiring
UF is underground
    
Copper ground wire
Use same size as other wire in circuit

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12 gauge copper ground wire
Ground wire
Green ground wire
Ground pigtails
Ground rods/ ground clamps at Amazon

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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.
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-277 volts is a standard voltage available in the US, found in commercial applications such as business or building.

-There are a variety of standard voltages across the world.
Voltages are a function of power generation, mathematics of electricity, transformer configuration, availability of conductive materials, cost, safety, and need for standardization.
Standardization makes it possible to mass produce electric wire, switches, appliances etc.
Variety of standard voltages:
-Different transformers and different wiring configurations allow selection of voltage choices for business and industry with 3 wire and 4 wire varieties of WYE and Delta including 208-120, 240-120, 480-277V and 600-347V etc, with 480V being the Hot-to-Hot line voltage, and 277 being the Hot-to-Neutral phase voltage calculated using a ratio of √3 or 1.732.
In the US, there are usually no choices for residential homes, and 120-240 is standard. This means you would encounter 277 volts in a building or business, but not at a residential house or apartment.
-It all starts with standardization, and is determined by the transformer(s) installed at each location.

Voltages are not exact:
For example a 240 volt service can provide 250 volt, 236 volts, etc and still be within acceptable range. Typically, anything less or more than 80% rated value can cause failure.
Resources:
Basic household wiring
What is 3-phase
How to wire 3-phase
Neutral currents in 3-phase WYE .pdf
3-phase 277-480 volt service
Full image
3-phase arrives at building
Commercial voltages and 277 volt:
-Typical buildings, businesses and factories have 3 transformers that provide three-phase service.
The 3-phase service is the source for 277 volt, but not every commercial installation has 277 volt, unless specified for the service.

How it happens: If a 480-270 volt service is specified by the architect, builder, end user or electrical engineer, the power company connects three-phase 7200 volt distribution line to the three transformers on the primary side. Correct wiring is selected to produce 480-480-480-270 Volt on the secondary side.

-The resulting service gives 3 wiring options:
3-wire 3-phase 480 volt for motors etc,
2 wire 480 volt single-phase,
2-wire 277 volt single-phase.

With this type of 3-phase service:
480 is the hot-to-hot line voltage,
277 is the hot-to-neutral phase voltage.
Resources:
Difference between single-phase and 3-phase
What is 208 volt
Identify transformer configurations
What is 3 phase
3-phase wye with neutralLarger image
Wye with Neutral and Ground

There are numerous ways that banks of two and three transformers can be wired to deliver 3-phase power to end user. These include WYE, Delta, Open WYE, open Delta etc.

277 volt comes from WYE configuration. This image describes the wiring for 3-phase WYE service shown in illustration above.

Each transformer contains two coils of wire: the primary and secondary coils. So the three transformers would hold 6 coils of wire. However, the focus of the illustration is to show the wiring only for the three transformers on the secondary side, or the customer side of the service. The primary coils are not shown.

There are 3 loops of wire, each loop in the illustration `represents a secondary coil inside a transformer.  All 3 coils are wired together at one end. This is represented by the common point where all three coils come together. The Neutral is connected to the common point. The ground wire is also connected at the common point.
At the other end of each coil is the Hot wire that carries power from the transformer to the end user breaker box.
The resulting 3-phase service has 3 Hot wires, 1 Neutral wire and a ground wire that enter the main breaker box.
3-phase service panel480-277 volt 3-phase service panel/ Ground not shown
3-phase Power leaves the transformer and passes through an electric meter that registers billable wattage.

From the meter, the electric power enters the main panel box, and connects to 3-pole  main breaker.
3-pole means there are 3 places for wires to connect. And each pole is electrically separated from other poles.

Main breaker box is same for WYE or Delta service, with 3 hot wires. But in some cases of Delta, there is no Neutral wire present.
WYE services like 120-208, 277-480, 347-600 etc volt have a Neutral wire.

Main breaker feeds each hot wire to separate hot busbar.
There are 3 Hot busbars, each electrically separated from the other, and each carries power from one Hot wire.

There are 3 ways to wire from the WYE main panel.
a) Install three-pole circuit breaker and draw 480 volt 3-phase power where 3 wires leave breaker and go to motor switch, or other use etc.
b) Install 2-pole breaker and and draw 2 Hot wires for 480 volt single phase.
c) Install single-pole breaker and draw 1 Hot and a Neutral wire for single-phase 277 volt.

Resources
How to wire 3-phase electric
See wiring for 3-phase non-balanced water heater

Larger image
Example single-pole breaker in 3-phase panel
Color added for illustration

Single and double breaker can be added to 3-phase panel
Or single-phase can be drawn from one or 2 poles of a 3-pole breaker.

In the case of 277 volt, 1 Hot wire is drawn from the circuit breaker and 1 Neutral wire is drawn from the Neutral busbar.
Many timers and other devices are rated for 277 volt
Look for rating label
Illustration shows 277 volt timer controlling 3-pole contactor that switches power ON-off to 3-phase load.

1 Hot and 1 Neutral are drawn off the 3-phase line to yield 277 volt.

Resources:
How to wire 3-phase timer
3-phase astronomic timer
Surge protection for 3-phase is installed on the Hot lines, and not the Neutral.
The Neutral wire redirects overvoltage directly to the ground connection.

Resource
How to wire 3-phase surge protection
Amps and watts with 277 volts
Calculations are the same for all electricity around the world: Volts x Amps = Watts. Or watts divided by volts = amps.
Compare 120, 240 and 277 volt. For example if the Load (motor, lights etc) consumes 8000 watts.
8000 divided by 277 volts = 28.88 amps requiring 30 amp breaker and #10 gauge wire.
8000 divided by 240 volts = 33.3 amps requiring 40 amp breaker and #8 gauge wire.
8000 divided by 120 volts = 66.6 amps requiring 70 amp breaker and #4 gauge wire.
Amperage is heat. If wire gets hot, then energy is being wasted. The more heat on the wire, the larger the wire and circuit breaker must be to maintain efficiency. Larger wire and the conduit needed to hold the wire costs more, especially if the load is spread over a large area like commercial lighting. The mathematics shows that using 277 volts is a less expensive way to handle large loads.

"Industrial and commercial 3-phase electric systems differ from residential single-phase: 3-phase power is more complex, but more efficient in motor applications, and large area uses. Higher voltages of 277/480v and 347/600v distribution systems are more efficient, but considerably more dangerous, and should only be maintained and modified by trained and qualified electricians."
Resource:
Difference between single-phase and 3-phase
120-277 volt troffer120-277 volt troffer
Troffers or ceiling lights used for commercial buildings and residential homes are available at local box store.
These lights are rated for 120-277.

Electronic ballasts available at local box store are also rated 120-277 volt.

Most switches sold at local box stores are rated 120-277 volt. Switches have rating embossed on each device. It's important to consider amp rating of switch and not just the voltage.

Ordinary 2-prong straight-blade-with-ground outlets are rated 125 volt but not for 277 volt. Of course you cannot plug a computer or desk lamp into 277 volt or it will burn up.

To differentiate outlets, there is a standard Nema code and Nema configuration based on voltage and amp rating of outlet as illustrated below with the locking receptacles.
277 volt locking receptacle 277 volt locking receptacle
277 volt is derived from 3-phase 480-277 service.
One Hot leg and a Neutral wire are pulled from the breaker box to create 277 volt potential
Extreme danger from high voltage 480-277, wiring should be done by licensed electrician
Buy:
Connectors
L7-15R 277 volt 15 amp
L7-20R 277 volt 20 amp    
L7-30R 277 volt 30 amp
Outlets
Leviton 4760  15A
Leviton 2330  20A
Leviton 2630  30A
Resources:
What is 277 volt
How to wire 3-phase
Difference single-phase and 3-phase
How to wire 277 volt outlet and plug277 volt twist lock
The center wire is the Neutral. The top wire is Hot, and bottom wire is ground.
Note also that Neutral is connected to ground.
The ground is not a Neutral and must serve as unobstructed pathway directly to earth.

Resource:
How to wire twist lock plugs
Why you need ground wire
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