API Std 547 (R2022)

This standard covers the requirements for form-wound induction motors for use in general purpose petroleum, chemical and other industrial severe duty applications and with the following characteristics:

a) rated 185 kW [250 horsepower (hp)] through 2240 kW (3000 hp) for four-, six-, and eight-pole speeds;
b) rated less than 600 kW (800 hp) for two-pole (3000 or 3600 RPM) motors of totally enclosed construction;
c) rated less than 930 kW (1250 hp) for two-pole motors of WP-II type enclosures;
d) rated less than 375 kW (500 hp) for vertical motors;
e) drive centrifugal loads;
f) drive loads having inertia values not exceeding those listed in NEMA MG 1 Part 20; and
g) operated as motors, not induction generators.

Unless otherwise specified, motors conforming to this standard shall be suitable for operation within their rating under the following service conditions:

a) exposure to an ambient temperature in the range of -18 °C to 40 °C (0 °F to 104 °F);
b) exposure to a maximum altitude of 1000 m (3300 ft) above sea level;
c) indoor or outdoor severe duty applications, such as humid, chemical (corrosive), or salty atmospheres;
d) horizontal foot mounted;
e) installation in a Class I, Zone 2 or Division 2 hazardous (classified) location;
f) constant frequency sinusoidal input power;
g) not subject to frequent transient overvoltages (e.g. switching surges, lightning surges); and
h) direct coupled without a gear, fluid coupling, or other speed modification device.


Unusual service conditions shall be brought to the attention of those responsible for the design, manufacture, application, and operation of the motor. Among such unusual conditions are:
a) exposure to:

1. combustible, explosive, abrasive, or conductive dust;
2. dirty operating conditions where the accumulation of dirt will interfere with normal ventilation;
3. nuclear radiation;
4. abnormal shock, vibrations, or mechanical loading from external sources;
5. abnormal axial or side thrust imposed on the motor shaft;
6. altitude or ambient temperature outside the range covered in 1.2;
7. reciprocating or positive displacement loads; and
8. offshore applications;

b) conditions under which the variation from rated voltage or frequency, or both, exceeds the limits given in NEMA MG 1 (or IEC 60034-1);
c) conditions under which the AC supply voltage is unbalanced by more than the limits given in NEMA MG 1 (or IEC 60034-1);
d) operation at speeds other than rated speed;
e) operation on an adjustable speed drive;
f) load inertia greater than and/or starting conditions more severe than given in NEMA MG 1;
g) orientation of a foot-mounted motor in any position other than horizontal;
h) vertical flange-mounted motors;
i) coupled through a belt, gear, fluid coupling or other speed modification device; and
j) requirements for enclosure purging or pre-start ventilation.