Type of Current

Motors can be purchased to operate on either single phase or three phase, direct or alternating current, at several voltages. The voltage and the type of current used depend on the size of the motor and the electrical service available. The phase refers to the number of cycles of alternating current, Figure 28.2.

~ 90 180 270 360 450 540 630 720 Electrical degrees

~ 90 180 270 360 450 540 630 720 Electrical degrees

FIGURE 28.2. Two complete cycles of single phase alternating current.

FIGURE 28.2. Two complete cycles of single phase alternating current.

FIGURE 28.3. Two complete cycles of three phase alternating current.

Electrical degrees

FIGURE 28.3. Two complete cycles of three phase alternating current.

In three phase alternating current service, three single-phase, 60 cycle currents are combined so the peak voltages are an equal distance apart, see Figure 28.3. Three phase current is recommended over single phase for larger loads, and is required by most electrical service companies for motors over 5-10 horsepower.

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