Power Control 421
Motor-controller Enclosures
The purpose of a motor-controller enclosure is obvious. The operator
is protected against accidental contact with high voltages that could cause
death or shock. In some cases, however, the enclosures are used to protect
the control equipment from its operating environment, which may con-
tain water, heavy dust, or combustible materials. The categories of motor-
controller enclosures have been standardized by NEMA. The following
list, courtesy of Furnas Electric Company, summarizes various classifica-
tions.NEMA 1 General-Purpose enclosures protect personnel from accidental electrical
contact with the enclosed apparatus. These enclosures satisfy indoor appli-
cations in normal atmospheres that are free of excessive moisture, dust, and
explosive materials.
NEMA 3 (3R) Weatherproof enclosures protect the control from weather hazards.
These enclosures are suitable for applications on ship docks, canal locks, and
construction work, and for application in subways and tunnels. The door
seals with a rubber gasket. They are furnished with conduit hub and pole
mounting bracket.
NEMA 4 Weathertight enclosures are suitable for application outdoors on ship
docks and in dairies, breweries, et cetera. This type meets standard hose
test requirements. They are sealed with a rubber gasket in the door. NEMA
4X Corrosion Resistant fiberglass enclosures are virtually maintenance free.
These U.L.-listed units are adaptable to any conduit system by means of
readily available metal, fiberglass, or PVC conduit hubs, and are suitable
for NEMA 3, 3R, 3S, 4, and 12 applications because they are dust-tight, rain-
tight, water-tight, and oil-tight.
NEMA 12 Industrial-Use enclosures also satisfy dust-tight applications. These en-
closures exclude dust, lint, fibers, and oil or coolant seepage. The hinged
cover seals with a rubber gasket.
NEMA 13 Oil-tight pushbutton enclosures protect against dust, seepage, external
condensation, oil, water, and coolant spray.
NEMA 7. For atmospheres containing hazardous gas, NEMA 7 enclosures satisfy
Class 1, Group C or D applications, as outlined in Section 500 of the National
Electrical Code Standard of the National Board of Fire Underwriters for Electrical
Wiring and Apparatus. These cast aluminum enclosures are designed for use
in atmospheres containing ethylether vapors, ethylene, cyclopropane, gaso-
line, hexane, naptha, benzine, butane, propane, alcohol, acetone, benzol, lac-
quer solvent vapors, or natural gas. Machined surfaces between the cover
and the base provide the seal.
NEMA 9, For atmospheres containing explosive dust, NEMA 9 enclosures satisfy
Class II, Group E, F, and G applications, as outlined by the National Electri-