motor damage and overloading the power system. In
some resistor controllers, the same resistor also helps
The components of the controller are housed within
regulate the speed of the motor after it is started. Other
an enclosure suitable to its location, atmospheric
dc controllers use a rheostat in the motor shunt field
condition, or presence of explosive vapors or liquids.
circuit for speed control.
Enclosures provide mechanical and electrical protection
for both the operator and the motor starter. Controller
enclosures can be classified in the following ways:
Some of the controlled equipment that you will see
Open. Open enclosures provide the least amount
uses logic systems for circuit control. For additional
of protection from dust and moisture. Provides
maximum ventilation to internals.
Electronics Training Series (NEETS), Module 13,
NAVEDTRA B72-13-00-86, Introduction to Number
Dripproof. Dripproff enclosures are the most
Systems and Logic Circuits, is an excellent basic
common type found aboard ship. They are
constructed so that liquid or solid particles can't
enter the enclosure when striking at an angle of
0 to 15 from the downward vertical.
Spraytight. Spraytight enclosures provide more
In this section of the TRAMAN, you will learn how
controllers are constructed.
than usual protection from casual water. They are
constructed to prevent entry of water from spray
at any angle not greater than 100 from the
Controllers are sized numerically according to the
Watertight. Watertight enclosures are
maximum horsepower rating of their connected loads.
constructed so that water sprayed from any angle
Generally, the numbers zero to five (0-5) are used;
will be unable to enter the enclosure.
however, in special circumstances, controllers as large
as 6, 7, or 8 may be used. AC controllers that are
Submersible. Submersible enclosures are
connected to two-speed motors have two numbers
constructed so that water can't enter when the
separated by a slash. The larger number indicates the
unit is submerged underwater. Provides least
rating of the controller at motor fast speed, while the
amount of ventilation to internal components.
smaller number indicates the rating at motor slow speed.
Explosionproof. Explosionproof enclosures are
The controller sizes given in table 6-1 apply to both
constructed so that no gas vapor can penetrate
ac and dc controllers.
except through vents or piping provided for the
Table 6-1.--AC and DC Controller Sizes
A master switch is a device, such as a pressure or a
thermostatic switch, that governs the electrical
operation of a motor controller. The master switch (fig.
6-8) can be manually or automatically actuated. Drum,
selector, and push-button switches are examples of a
manual master switch. The automatic switch is actuated
by a physical force, not an operator. Examples of
automatic master switches include float, limit, or
Depending on where it is mounted, a master switch
is said to be either local or remote. A local switch is
mounted in the controller enclosure, while a remote
switch is mounted near the watchstation or work area
where the motor is to be controlled from.