Power Control 419
Classes of Motor Starters
The types of motor starters that are commercially available are di-
vided into five classes. These classes, which were established by NEMA,
are:- Class A—Alternating current (AC), manual or magnetic, air-break or
oil-immersed starters that operate on 600 volts or less. - Class B—Direct current (DC), manual or magnetic, air-break starters
that operate on 600 volts or less. - Class C—AC, intermediate voltage starters.
- Class D—DC, intermediate voltage starters.
- Class E—AC, magnetic starters that operate on 2200 volts to 4600
volts. Class E1 uses contacts, and Class E2 uses fuses.
Sizes of Manual Starters
A uniform method has also been established for sizing manual mo-
tor starters. Some examples of the sizes of full-voltage manual starters
are:- Size M-O—For single-phase 115-volt motors up to 1 horsepower.
- Size M-1—For single-phase 115-volt motors up to 2 horsepower.
- Size M-1P—For single-phase 115-volt motors up to 3 horsepower.
These sizes are summarized in Table 15-4.Table 15-4. Sizes of Manual Starters
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Maximum Horsepower Rating of Load
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Starter Single-Phase Three-Phase Ampere
Size 115 V 230 V 200-230 V 460-575 V Rating
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M-O 1 2 3 5 20
M-1 2 3 7.5 20 30
M-1P 3 5 — — 30
————————————————————————————————Combination Starters
A popular type of motor starter used in control applications is the
combination starter. These starters incorporate protective devices such as
fused-disconnect switches, air-type circuit breakers, or a system of fuses