Page 129 - Pipeline Rules of Thumb Handbook

116 Pipeline Rules of Thumb Handbook

(b) Breakdown torque is the maximum-torque at rated voltage (c) NEMA Type II—A weather protected machine which has
and frequency without abrupt speed drop. in addition to the enclosure defined for a Type I weather-
protected machine, its ventilating passages at both intake and
(c) Full-load-torque is the torque necessary to produce rated discharge so arranged that high velocity air and airborne par-
horsepower at full-load speed. ticles blown into the machine by storms or high winds can be
discharged without entering the internal ventilating passages
(d) Locked-rotor current is the steady-state current of the leading directly to the electric parts of the machine itself. The
motor with the rotor locked at rated voltage and frequency. normal path of the ventilating air which enters the electric
parts of the machine shall be so arranged by baffling or sepa-
rate housings as to provide at least three abrupt changes in
direction, none of which shall be less than 90deg. In addition,
Locked Rotor an area of low velocity, not exceeding 600ft/min., shall be pro-
Code Ltr kVa/hP vided in the intake air path to minimize the possibility of
moisture or dirt being carried into the electric parts of the
A 0–3.14
machine.
B 3.15–3.54
C 3.55–3.99
(b) Totally Enclosed Non-Vent means that a motor is not
D 4.0–4.49
equipped for cooling by external means.
E 4.5–4.99
F 5–5.59
(c) Totally Enclosed Fan-Cooled means the motor has a fan
integral with the motor but not external to the enclosed parts.

7. Selection of enclosure—The two general classifica- (d) Explosion-Proof means the enclosure is designed to with-
tions are open, which permits passage of air over and around stand an explosion of a specified gas which may occur within
the windings; and totally enclosed, which prevents exchange the motor and to prevent the ignition of gas around the motor.
of air between inside and outside of frame (but is not strictly
airtight). 8. End shield mountings—Three types of end shields
with rabbets and bolt holes for mounting are standard in the
(a) Open Drip-Proof—means that liquid or solid particles industry:
falling on the motor at an angle not greater than 15 degrees
from vertical cannot enter the motor. (a) Type C Face provides a male rabbet and tapped holes.

(b) NEMA Type 1—A weather protected machine with its (b) Type D Flange has a male rabbet with holes for through
ventilating passages constructed to minimize the entrance of bolts in the flange.
rain, snow and airborne particles to the electric parts and
having its ventilating openings so constructed to prevent the (c) Type P base has a female rabbet and through bolts for
passage of a cylindrical rod 3/4in. in diameter. mounting in the flange (used for mounting vertical motors).

Hazardous locations

Definition of Class Locations

Reprinted with permission from NFPA 70-1990, the 500-5. Class I Locations. Class I locations are those in
National Electrical Code®, Copyright© 1989, National Fire which flammable gases or vapors are or may be present in the
Protection Association, Quincy, MA 02269. This reprinted air in quantities sufficient to produce explosive or ignitible
material is not the complete and official position of the mixtures. Class I locations shall include those specified in (a)
National Fire Protection Association, on the referenced and (b) below.
subject which is represented only by the standard in its
entirety. (a) Class I, Division 1. A Class I, Division 1 location is a loca-
The National Electrical Code and NEC are registered tion: (1) in which ignitible concentrations of flammable gases
trademarks of the NFPA. or vapors can exist under normal operating conditions; or (2)