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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

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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 single phase1

Generating Single Phase

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 phase1

Generating Three Phase

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.

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