When working with motors, a thorough knowledge of safety procedures may save you from serious injury and prevent damage to equipment.
No one ever said safety was simple, but its benefits far outweigh the extra time and effort involved in efficient motor operation. Safe operation of motors requires careful observance of all safety rules from initial selection to installation, including proper handling, operation, and maintenance. However, if you don't follow recommended safety procedures and adhere to a stringent safety plan, personal injury and loss of the motor and associated controls become much more likely.
Before starting up a newly installed motor, review and implement all safety rules. When working with or operating motors, or any other type of electrical equipment, safety must come first.
After completing proper motor selection and initial visual inspection checks, you can start the motor and conduct a test run (see "Selecting And Installing Motors, Part 1," November 1997 issue, page 56).
Lockout rules are essential You must perform these rules correctly to assure safety of all concerned. Before starting inspection, tests, or checks on the motor, lock open the motor branch circuit switch or circuit breaker. The locking arrangement should accommodate padlocks for several electricians, so each can apply his or her padlock. Remember, you cannot start the motor until you remove all locks. In addition, mark the switch with an easily visible lockout tag, which incorporates a clear warning label instructing users not to touch the switch.
When power is applied, the motor should start up quickly and run smoothly. If it doesn't, visually check the mechanical assembly. If the motor vibrates excessively, turn off power to the motor using proper lockout procedures. Then check for loose mounting bolts, an overly flexible motor-support assembly, or transmitted vibrations from adjacent machinery. You may need vibration analysis instruments for these tests.
At this time, also check the motor voltage supply to be sure it is within 510% of the nameplate value. Also, check electrical connections at the motor starter, termination box, branch overcurrent devices, and switches.
Only qualified personnel should carry out the inspection, maintenance, and repair procedures. A qualified person is one who is familiar with the installation, operation of the motor, repair methods as well as all pertinent safety rules.
In addition, a qualified person should be trained and authorized to energize, deenergize, clear, ground, tag, and lockout circuits and equipment in accordance with established safety practices. This person, who should also be well trained in first aid, knows how to use and care for protective equipment such as rubber gloves, hard hat, safety glasses, face shields, flash clothing, etc.
Why conduct start-up tests? While the motor is still locked-out, make continuity tests, insulation-resistance tests, and other required acceptance tests to check proper motor-circuit connections and motor-winding integrity, and to ensure elimination of moisture.
Next, thoroughly inspect the motor, coupling, and driven load for solid, firm mounting. Make a complete mechanical check. Look for any loose parts, poor grouting, and adequate base components. Complete all alignment tests. Give proper attention to rotating members. For example, before starting, securely fasten pulleys, belts, couplings, gears, etc. and install proper guards. Check all line connections, grounding, overloads, and branch-circuit overcurrent to be sure you size them correctly.
Be sure to observe rotational arrows marked on the end bell. Check for proper direction of rotation with a rotation tester. In some instances, if the motor is supposed to operate in a reverse direction, make sure the motor cooling fan blades are set to rotate so they will provide cooling.
Test running the motor After you detect and eliminate any problems, run the motor unloaded for a short period of time. Then run it under load briefly and check actual running current against the nameplate value.
Be careful when working with rotating machines equipped with thermal protectors, which are required to be labeled "Thermally Protected." If severe overloading, jamming, or other abnormal operating conditions occur, such heat-sensitive protectors operate to open the electric power supply circuit. Such equipment can start automatically when the protector has cooled. Be sure power has been locked-out from such machines before you attempt to service them. You should use manual reset protectors or suitable electric supply disconnect devices and procedures where such potential hazards exist. (Fig. 1, above.)Design E MotorsBecause of the recent passage of th e EPACT law (Energy Policy Act of 1992), you may come across a Design E motor. Developed to meet efficiency requirements of that law, the Design E motor is an efficient motor; but it may have characteristics not correct for the application. Some of these factors can lead to unsafe conditions.
For example, a Design E motor may have lower starting torque than the motor it may be replacing. As such, it may not be able to start the existing load, which results in overheating, possible motor burnout, or worse. More importantly, a Design E motor usually has a much higher starting current than a comparable Design B motor. Starting currents can be as much as 55% higher, resulting in motor tripouts or worse.
Motors or gearmotors that employ capacitors in their start circuits can develop a higher voltage than indicated on the nameplate, across the capacitor and/or capacitor winding (depending upon design). Make sure you take suitable precautions when applying such motors.
Abnormal conditions, such as cutout switch failure, or partial winding failure due to overheating, etc., can occasionally cause certain types of AC motors and gearmotors to start in a direction reverse from normal. The chances are highest when the motor's rotor "sees" a relatively light load.
One-way clutches or similar devices are advisable if such remote risk is not tolerable in the intended application. (See Fig. 2).
Make the most of your motor controls Consider some additional factors when applying motor controls: * Properly guard or enclose control circuits to prevent possible human contact with live circuitry. * The control temperature specifications of each device should be checked. In general, the ambient temperature for remote controls should not exceed 40 DegrC (104 DegrF). In the case of motors/gearmotors, controls must be properly grounded to prevent serious injury to personnel. (See Fig. 3)
Maintenance Important: Before servicing or working on equipment, be sure to disconnect the power source and use a lockout procedure similar to one described earlier. This applies especially to equipment using automatic restart devices instead of manual restart devices, and when examining or replacing brushes on brush-type motors/gearmotors.
Equipment with capacitors Before servicing rotating machines employing capacitors, make sure you always discharge the capacitor or capacitor bank by placing a conductor across its terminals before touching its terminals with any part of your body. This will discharge any dangerous voltage stored in the capacitor.
After completing all motor start-up tests and checks, you are ready to place the motor into service. However, it is wise to double-check the running motor periodically at the outset, making fundamental look, feel, and smell checks.