CORRO DUTY Specification
CORRO-DUTY® NEMA Motor Specification for Hostile Environments

This specification covers the requirements of the electrical and mechanical design, electrical insulation, performance, and electrical testing of the U.S. MOTORS® brand line of Severe Duty Premium Efficient Motors, which have been designed to meet or exceed the requirements for 1997 federally legislated efficiency levels and to be suitable for operation in chemical and processing applications.

Motors are available in 143T through 449TS frames at speeds of 1200, 1800, and 3600 RPM, and are 3 phase, 60 hertz, 230/460, 460 or 575 volts, with full voltage across-the-line starting. Some ratings have part winding start capability.

Motors comply with the frame size assignments of NEMA MG 13-1984.

All motors have a 1.15 service factor.

Motors are TEFC and have a degree of protection of IP54 via the use of a rotating shaft slinger. A higher degree of protection via the use of bearing isolator(s) is also available.

Service Conditions
Motors are suitable for continuous duty operation without derating in the wet, corrosive and extremely hostile environments normally encountered in mills, chemical plants, and other applications and under the following service conditions:

Exposure to ambient temperatures from -25 ° C to 40 ° C
Exposure to altitudes up to 1000 m (3300 ft)

Suitable for use in indoor or outdoor applications involving severe duty conditions such as high humidity or chemical laden, corrosive, or salty atmospheres.

Motors are capable of successfully accelerating inertia loads equal to what is specified in section 12.54 of NEMA MG 1-1993.

Electrical Design
Motors are NEMA Design B as defined in section of NEMA MG 1-1993 except where noted as Design A per section

Motors operate successfully at rated load under the various combinations of voltage and frequency variations specified in section 12.44 of NEMA MG 1-1993.

Motors operate successfully under running conditions at rated load and frequency when the voltage unbalance at the motor terminals does not exceed 1%.

Motors are of premium efficiency design and meet or exceed the efficiency for a given rating listed in Table 12-10 of NEMA MG-1 1993. Efficiency testing is done in accordance with IEEE Std 112-1991, subclause 6.4, Method B.

Stator windings are random wound.

The insulation system of the motors is Class F, includes some Class H components, is non-hygroscopic, and is chemical and humidity resistant.

Stators are dipped in varnish and baked. Stators and rotors are protected by a resin and hardener treatment.

Leads are non-braided and non-wicking.

Our Technical Services Group should be consulted for applications utilizing variable speed drives, to determine if motor will operate successfully over the required speed range.

Mechanical Design
Motors are equipped with ball bearings or roller bearings to meet bearing life requirements. Ball bearings have AFBMA C/3 clearances.

Bearings are regreasable without disassembling the fan or fan cover and provide for the elimination of purged grease through fittings extending beyond the fan cover. Polyurea thickened grease is supplied.

Inner bearing caps are provided for bearing retention and to prevent harmful amounts of lubricant from entering the motor interior.

For direct coupled motors run at rated load, bearings will have a maximum temperature rise of 50° C for 4 and 6 pole motors and a maximum temperature rise of 55° C for 2 pole motors.

Bearings provide for an L-10 life of 30,000 hours per ANSI/AFBMA 9 - 1990 based on NEMA belting application limits per NEMA MG 1 - 1993, sec. 14.41

Horizontal motors are modifiable to accommodate oil mist lubrication. The insulation system and motor leads are compatible with mineral oil.

Enclosures have a degree of protection IP 54 (per NEMA MG 1 - 1993, part 5). Rotating slingers are provided to minimize entrance of moisture and contaminants into the bearing chamber.

Condensation drain holes are provided at the low points in the end brackets and are supplied with corrosion resistant, breather drain plugs.

For 182T Frame and above, frame, brackets, fan cover and conduit box are a minimum of grade 25 cast iron.

Ventilating fans are of a non-sparking bronze alloy or non-conductive plastic material. Most ratings use bi-directional fans. On ratings where unidirectional fans are used, the rotation direction of the fan is indicated by a permanent label on the outside of the motor.

The conduit box shall be cast iron and threaded for rigid conduit connection. Conduit box volumes exceed NEMA and boxes are rotatable in 90 degree increments. A ground lug is provided in the box. Lead positioning gaskets are provided between the conduit box and frame and gaskets are provided between conduit box base and cover.

Lifting eyebolts are provided for motor lifting. Eyebolt holes are blind threaded holes.

All fastening hardware is grade 5, zinc or cadmium plated.

Motor cast iron components are oxide primed and painted with vinyl-phenolic paint. This coating is chemical solvent, salt water and acid resistant and shall surpass 96 hour salt spray test per ASTM B117-90.

Motor nameplate is stainless steel and secured with 4 stainless steel drive pins. Nameplates are capable of meeting 720 hour salt spray test per ASTM B117-90.

Airborne Sound
Motor sound power level at no load falls below the levels shown in section 12.53.3 of NEMA MG 1 - 1993 when determined in accordance with IEEE Std 85-1973. (reference = 10-12 watts)

Motor balance and vibration shall meet NEMA standards MG 1- 12.06 & 12.07.

Production Tests
The following tests are performed on all motors:

  1. No load readings of current, power, and speed at rated voltage and frequency.
  2. Mechanical vibration check as described in 8.1.
  3. High-potential test in accordance with section 12.03 of NEMA MG 1-1993

ANSI/AFBMA 9-1990, Load Ratings and Fatigue Life for Ball Bearings.
ASTM B117-90, Test Method of Salt Spray (Fog) Testing.
IEEE Std 85-1973, IEEE Standard Test Procedure for Airborne Sound Measurements on Rotating Electric Machinery.
IEEE Std 112-1991, IEEE Standard Test Procedure for Polyphase Induction Motors and Generators.
IEEE Std 841-1994, IEEE Standard for Petroleum and Chemical Industry - Severe Duty.
NEMA MG 13-1984, Frame Assignments for Alternating-Current Integral-Horsepower Induction Motors.
NEMA MG 1-1993, Motors and Generators.

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