Chuck Yung
EASA Senior Technical Support Specialist

As anyone who is familiar with insurance inspectors, the U.S. Occupational Safety and Health Administration (OSHA) and other regulatory bodies knows, there are rather unique dangers in the electromechanical repair industry. Balancing machines and test panels are high on the list.

Both require easy access – and both pose significant risk to personnel. In most circumstances, unguarded rotating machinery and temporary electrical connections are cause for great concern.

Potential hazards and risks

Because of our daily exposure to some of this equipment, there is a risk of becoming complacent. There are specific ways to address many of these risks, but they start with a frank recognition of the hazards inherent to our industry. Safety comes from the top down. If we expect personnel to take safety seriously, we must set the example. Consider this short list of equipment, and then think about how many stories you’ve heard of near misses when working with them:

• Balancing machines
• Test panels using alligator clips to run 4 kV motors
• Temporary shaft keys held in with tape
• Overhead cranes
• Electrical testing

Balancing machines are used to spin a wide range of rotor / armature sizes at several hundred rpm, presenting an obvious risk to personnel. The operator needs convenient access to the part in order to install balance correction weights. Depending on the part, and the amount of unbalance, achieving an acceptable balance may require several corrections. Should the balance machine and rotating part be guarded against the possibility of accidental contact that might injure or kill personnel?

The solution in some service centers has been to construct chain link fencing around the balancing machine itself, with a gate. The gate should be interlocked to prevent energizing the balancing machine when the gate is open. The operator and balancing instrument are positioned outside the gate. This allows access to the rotor for weight corrections while protecting the operator from accidental contact with potentially deadly results. Some manufacturers of balance stands now also sell safety enclosures for their machines. Whether commercial or shop-made, the door should include an interlock to prevent the balancing machine from being energized unless the door is latched.

Test panels present a hazard only when operating, while the raised test bed tends to be co-opted for use as a work table at other times. Depending on the layout, the gap between the test panel itself and the test bed upon which the motor is placed is treated as a walkway, a shortcut to someplace else in the facility. It’s a hard habit to break, and when a motor is being run, that shortcut might take personnel dangerously close to energized leads. Depending on how the motor is positioned on the test bed, the rotating shaft is yet another hazard.

The first step to minimize risk is to place posts to segregate the test area. Four posts, strung with “caution” tape to isolate the area can be used to temporarily or permanently cordon off the immediate area around the test panel and test bed. See Figure 1. Yellow paint should be used to delineate walkways. Solid yellow, or diagonally striped yellow lines, can designate no-traffic zones.

Our industry has long embraced the convenience of spring-loaded clamps (essentially just large alligator clips) to make temporary electrical connections from the test panel to the motor leads. See Figure 2. How many of us have witnessed someone tripping over a test lead? Not only should the area be cordoned off to prevent personnel from walking across the leads, but those convenient alligator clips should be removed in favor of securely bolted terminal lugs. At the least, consider making this change for motors rated over 600 volts.

Rather than laying test panel leads across the floor, either underground conduit or an overhead conduit can be used to minimize risk of damaging lead insulation. Newer test panels have a flashing / rotating indicator light to alert personnel that the test panel is energized. For those with older test panels, that is an easy addition to any test panel.

While on the subject of testing, most members record vibration levels of the completed electric motor as part of the test run. It is common practice in our industry to use fiberglass reinforced packing tape (see Figure 3) to secure the half keys in the keyway during the test run. Ask a group of your fellow repairers how many of them have seen or heard of a key flying out of a motor under test. Why are we still using that tape for a purpose for which it is obviously not designed.

 

Packing tape is designed for sealing boxes, not for withstanding hundreds of pound-feet of force.

There is an alternative. Use 4” (100 mm) lengths of ¼” (0.25 mm) wall mechanical tubing in assorted shaft diameters. Drill and tap two holes for set screws. Install the half key, then slide the mechanical tubing over the shaft and tighten the set screws against the half key to secure it in place. It’s not necessary to buy every possible size; build an inventory of these guards as motors with different shaft sizes come in for repair. Measure the coupling fit of incoming work, and order the material to fabricate the sleeve so as to have it available when the motor is run.

Or conduct an Internet search for “shaft collars” and take your pick from numerous vendors who supply split or one-piece set-screw collars. See Figure 4. Here are just a few of the many options:

• www.ruland.com
• Climax Metal Products
• McMaster-Carr

Electrical testing

Members use voltmeters and ammeters regularly, so it is easy to forget that the voltmeter in your hand is at the same voltage as anything to which you touch the leads. All should know that handheld voltmeters should never be used to measure voltage greater than the instrument is rated for. It can be a deadly mistake to assume the voltage is what you expect it to be. When measuring voltage, your hands are very close to exposed conductors. Practice “test before touch.” There are non-contact voltage detectors readily available from your local suppliers. Caution: Some of these testers are only suitable for AC circuits. Make certain they are suitable for the AC or DC voltage you are trying to detect. Follow the rules for personal protective equipment; they exist for your safety. (Note that there is an early Simpson meter with a 5000 volt scale using the same thinly insulated probes as modern volt meters.)

Most have been fortunate, but in today’s litigious society and for the sake of employees and coworkers, it is essential to recognize safety hazards and take steps to address them before an accident occurs.

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Categories: Technical topics, Safety, Service center equipment

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