sets the limits of the steady current. This value should
NOT be exceeded.
Check the power supply against the nameplate
values; they should agree. Most motors will operate
successfully with the line voltage within 10 percent
(plus or minus) of the nameplate value or within 5
percent of the frequency (hertz). Most 220-volt motors
can be used on 208-volt network systems but with
slightly modified performance. Generally, 230-volt
motors should not be used on 208-volt systems.
To reconnect a dual-voltage motor to a desired
voltage, follow the instructions on the connection
diagram on the nameplate.
Motor-starter-overload-relay heaters of the proper
size must be installed. The motor will not run without
them. Sizing information is found inside the control
enclosure cover. The starting fuses should be checked
in a similar manner. The selection of the correct fuse
size must be according to the NEC® or local
If the motor has not been installed in a clean, well-
ventilated place, clean the area. Good housekeeping,
as well as direct accident and fire-prevention
techniques, must be emphasized.
Check the motor mounts to be sure that they are
secure and on a firm foundation. If necessary, add
grout to secure the mounts.
Rotate the end shields to place grease fittings,
plugs, or any openings in the best, or most accessible,
location. Oil or grease the bearings, if necessary.
In troubleshooting motors, the first step is to shut
down the machine and lock it out for repair or
adjustment. The most valuable troubleshooting asset is
your ability to apply common sense when analyzing a
control operation. Also, experienced Construction
Electricians learn to use sensory functions to diagnose
and locate trouble.
LOOKING may reveal contacts stuck and hung
up, thereby creating open circuits.
LISTENING may indicate loose parts, faulty
bearings, excessive speed, and so forth.
SMELLING may indicate burning insulation or
a coil failure.
TOUCHING may reveal excessive motor shaft
play, vibration, or normal heat.
Using this seemingly oversimplified procedure to
locate a problem may save you many hours of labor.
Consider the length of time it would take to become
thoroughly familiar with a complicated schematic
diagram, compared with locating a few contacts that
are stuck by merely LOOKING.
However, finding a problem in an installation is
not usually this easy. An orderly, step-by-step
approach is required. Circuit operation is separated
into logical parts. Circuits and components are then
divided into smaller parts to determine their
functions, the relationships to one another, and the
effect that they have on each other in the overall
control system operation. Each step leads closer to the
source of the difficulty, finally pinpointing the
problem. This procedure may require the use of a
voltage tester, ammeter, multimeter, jumper wires,
and other tools.
Check the power supply to see if it is on and if it is
correct. Test all protective devices. If a coil does not
energize (fig. 7-27), connect a jumper wire from L1 to
terminal 3 of the control circuit. By jumping across
the contacts of the limit switch and push buttons, you
have separated the circuit operation into logical parts.
If the starter coil is now energized, the problem may
be in the limit switch or STOP or START push
buttons. You now can test smaller circuits and com-
ponents by jumping around them individually. Test
the limit switch, for example, then go to the control
station, if necessary. By an orderly process of
elimination accomplished by testing all possible fault
areas, you can locate the problem accurately and
Figure 7-27.Start-and-hold control circuit.