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What’s Watt?

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What’s Watt

Wye Line-to-Neutral Voltage 120 120 277 374

Wye or Delta Line-to-Line Voltage 208 240 480 600

Electrical Service Voltages

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What’s Watt

Single Phase

Single-Phase electrical service wires usually have a three wire configuration. This type of single phase wiring is most commonly found in the United States. It provides 120 Volts for lighting and conventional plug loads and 240 volts for single phase appliances.

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What’s Watt

Common Electrical Services

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Single Phase Three Wire

What’s Watt

Three-Phase

Three-phase electric power is the most common method of alternating-current electric power generation, transmission, and distribution. It is also used to power large motors and other heavy loads. A three-phase system is generally more economical than others because it uses less conductor material to transmit electric power than equivalent single-phase systems at the same voltage. There are two types: three phase, four-wire wye and three phase three-wire delta.

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What’s Watt

Common Electrical Services

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Three Phase, Four Wire Wye

What’s Watt

Common Electrical Services

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Three Phase, Three Wire Delta

What’s Watt

So, What’s a Watt?

A Watt is a unit of power, named after Scottish Engineer James Watt, defined as one joule per second What’s a Watt mean to us? As a unit of power it remains constant as other variables change. Therefore, a watt is a watt is a watt.

Example- A 10kw electric heater is an electric heater rated 10kw whether the voltage available to is 120V, 208V, or 480V, and regardless of whether single or three phase are available.

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What’s Watt

Basic Formulas

• Single PhaseWatts=Volts x Amps, KW=Volts x Amps /1000

• Three PhaseWatts=Volts x Amps x 1.73KW=Volts x Amps x 1.73/1000

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What’s Watt

Determining Amperage

• Amperage is the amount of electricity flowing • Example: What is the amperage of a 12kw unit electric unit

heater @ 120v, single phase?• 12kw=12,000w = volts x amps• 12,000w = 120 x amps • amps = 100a• Using NEC, this heater would require a 125a/1p breaker &

#1 AWG wire• Huge wire and breaker for a relatively small piece of

equipment• What can we do? Raise the voltage! Make it 3 phase!

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What’s Watt

Determining Amperage – 3 phase

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Example: What is the amperage of a 12kw unit electric unit heater @ 208v, three phase?12kw=12,000w = volts x amps x 1.7312,000w = 208 x amps x 1.73 amps = 33aUsing NEC, this heater would require a 40a/3p breaker & #8 AWG wireMuch smaller wire and breaker for a relatively small piece of equipmentAlways spec higher voltages and three phase on large pieces of equipment

What’s Watt

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What’s Watt

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