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HVACR317 - Refrigeration. Three Phase Power Three Phase Motors. Single Phase Power. Up until now we have been talking about single phase power . Characteristics are: Single sign wave that modulates 60 times per second between positive.

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Hvacr317 refrigeration

HVACR317 - Refrigeration

Three Phase Power

Three Phase Motors

Single phase power
Single Phase Power

  • Up until now we have been talking about single phase power. Characteristics are:

  • Single sign wave that modulates 60 times per second between positive.

  • Motors (other than shaded pole) have a start winding and a run winding.

  • L1 and Neutral or L1 and L2 are standard sources.

Single phase power1
Single Phase Power

  • Single phase power also has a few problems; mainly that the power pulsates and modulates through 0 volts three times each cycle.

Three phase power
Three Phase Power

  • Three phase power contains three sine waves that run 120 degrees out of phase with each other.

Three phase power1
Three Phase Power

  • There are three reasons why three phase power is superior to single phase power:

  • The horsepower rating of three phase motors and the amperage ratings of three phase transformers are about 150% greater than single-phase transformers and motors of similar frame sizes.

Three phase power2
Three Phase Power

  • Three reasons, cont’d:

  • Three phase power is supplied mainly to larger commercial and manufacturing customers.

  • Three phase power requires a third line from the power company as well as three phase breakers.

Generating single phase
Generating Single Phase

  • Remember a single phase generator spins a magnet inside a coil of wires. The magnet has north and south poles, which generate an alternating current in the wires.

  • Example of this on the next slide

Generating three phase
Generating Three Phase

  • To generate three phase power, there are three coils of wire set inside the generator, exactly 120 degrees apart from each other electrically.

  • As the magnet moves through each of the three windings, the current produced is 120 degrees out of phase with the other two windings.

Generating three phase2
Generating Three Phase

  • This out of 120 degree difference produces three sine waves that are 120 degrees out of phase with each other.

Generating three phase3
Generating Three Phase

  • Notice on the sine wave diagram that there is no more than a single sine wave going through zero at any one time.

  • In a single phase system, this same effect can be produced by a capacitor on the start winding of the motor.

Single phase disconnect switches
Single Phase Disconnect Switches

  • Single Phase systems will use a disconnect switch with two fuses.

  • This disconnects Line 1 and Line 2

Three phase disconnect switches
Three Phase Disconnect Switches

  • Three phase disconnect switches will use three fuses or disconnects.

  • Three phase disconnects will use L1, L2, and L3, as there are three live legs required.

Residential single phase breaker panel
Residential/Single Phase Breaker Panel

  • A Residential or a Single Phase breaker panel has two hot legs (L1 and L2) and a neutral bar (N) running through the center.

Three phase breaker panel
Three Phase Breaker Panel

  • A three phase commercial breaker panel has an L1, L2, and L3 running through the panel.

Three phase breaker panel1
Three Phase Breaker Panel

  • It is important to know the phase of the system you are reaching into. Because there is no neutral, all the legs in a commercial breaker panel are live (or hot).

  • Make sure you use your meter to verify the voltage in the panel.

  • HVAC technicians may not do ANY work inside a panel other than verifying voltage.


  • At this time ask any questions you have on three phase power supplies. We are now going to move on to three phase motors.