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 requirements.
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 efficiently.
Figure 7-27. - Start-and-hold control circuit.Continue Reading