Kent Henry
Former EASA Technical Support Specialist
Safety is on everyone’s mind these days. Whether you’re a delivery driver, a salesperson, or a technician, you may need to complete some type of safety training at the customer’s facility just to gain permission to enter their plant. Once in plants, just traveling around you will see all sorts of safety measures, from designated walkways to vehicle speed limits.
Customers look outside their premises as well. Many have begun using a service center’s internal safety program as a measure or qualifier of their worthiness to perform repair or supply services. In meetings with prospective customers or negotiations with current customers, you may need to have documentation of your safety program to hand out with sales or services brochures.
Eye and face protection
If you spend much time in a service center, you may see an occasional eye injury. Speaking from experience, I once had an injury even while wearing safety glasses.
As a young apprentice working in a service center, a bearing exploded about 50 feet (15 m) directly behind me while it was being removed in a hydraulic press. I instinctively closed my eyes when I heard the bearing explode. When I tried to open my eyes, only one eyelid opened; the other was staked to the eye with shards of metal from the bearing. The bearing shrapnel had come from behind me, ricocheting off the inside of my safety glass lens into my eye.
If you’ve ever had an eye injury, it makes you realize how quickly you could permanently lose your eyesight. At the time, side shields were rare; thank goodness, they are the rule these days per safety regulations in most areas.
Eye injuries
Two major reasons workers experience eye injuries on the job are because they were:
- Not wearing eye protection
- Wearing the wrong kind of protection for the job
A 2004 US Bureau of Labor Statistics (BLS) survey of workers who suffered eye injuries revealed that nearly three out of five were not wearing eye protection at the moment of injury. The workers most often reported that they believed protection was not required for the task at hand.
In general, safety regulations require the use of eye and face protection whenever there is a reasonable probability of injury that could be prevented by such equipment. Personal protective eyewear, such as goggles, face shields, safety glasses or full-face respirators must be used when an eye hazard exists. The eye protection chosen for specific work situations depends upon the type of hazard, the circumstances of exposure, other protective equipment used and individual vision needs.
You should educate employees so they recognize the proper level of vision protection for the task being performed. Check your employment regulations and try to obtain a reference chart. Note that these regulations apply to visitors entering your facility as well. Visitors must wear the proper vision protection for the type of hazards they maybe exposed to while traveling through or around your production areas.
An important point to remember is that face shields and welding helmets are secondary protection equipment and they should only be worn over primary eye protection such as glasses or goggles. See Figure 1.
Hand injuries
In the service center, the vast majority of work performed is “handson.” Many decades ago, employees were trained to not wear gloves when possible. The theory was that they were less likely to become entangled in moving equipment.
The vast majority of hand injuries are due to lacerations, puncture, abrasion, and burns. Modern technology has vastly improved the dexterity and comfort of gloves, allowing them to be worn for hours at a time while performing intricate skills. A better understanding of safety contradicts the “old school” training and encourages the use of gloves whenever possible. Studies report a 60% reduction in hand injuries (Liberty Mutual Research Center for Safety and Health – Annual Report 2001) from wearing gloves. Sources for hand protection standards include OSHA Standards - 29 CFR- 1910.138 and ANSI/ISEA 105-2005.
Energy safety
I can recall an instance when I used to work in a service center and a coworker was test running a motor. Another technician asked to use the double hook chain that was hanging loose from the crane hook directly above the energized motor. The coworker was more than happy to let the other use his chain and proceeded to lean against the motor while reaching above it to disconnect the chain from the crane hook.
The instant his hand touched the hook, he violently jumped back as the result of an electrical shock and stumbled to the floor. We quickly pressed the emergency stop and allowed the motor to coast to a stop. The coworker wasn’t injured; just a little shaken from the experience.
After regaining his composure, he wanted to find out what caused the shock. When the leads were disconnected, he measured the resistance to ground of the motor and obtained a reading exceeding 2000 megohms. Not satisfied, he performed a hipot test which the motor passed. He was at a complete loss as to what caused this electrical shock. When the motor was reconnected and energized, we used a voltmeter to probe from the motor frame to the crane hook and read voltage exceeding 60 VAC.
Finally, we examined the ground cable, which to our dismay was still coiled up on the storage hook at the side of motor test center. When we connected the ground cable to the motor, the voltage potential between the motor frame and the crane hook was zero. The ground cable is the single most important connection to a motor being test run, yet can be very easy to overlook as in this example. From that day on, we made the ground cable connection first.
Examples of hazards
Have you ever seen people walk over energized test leads? Our common sense tells us they are insulated. But if someone were to stumble or trip, they could kick them loose or fall on the test leads, causing injury or death.
Another example: When running a DC machine, what happens if we accidentally disconnect the field supply lead? The field loss results in rapid acceleration of the armature to an over-speed and catastrophic failure. In this situation, a technician would have no chance of being able to react quickly enough to hit the emergency stop and save the motor. These examples demonstrate the need to rope off the test area surrounding the test panel and motor to prevent entry and better assure the safety of people and equipment (see Figure 2).
When test running a medium-voltage motor, the danger increases substantially. The best practice is to bolt the test leads directly to the motor leads. Make sure that a ground cable from the test panel is bolted to the frame and making solid contact (i.e., no paint or varnish under the ground lug). It is important that all connections be insulated and separated to provide proper electrical protection. Finally, block off the area where cables run between the test panel and the motor, as well as around the motor, so that no one can enter.
While performing testing with instruments such as megohmmeters, hipot, surge, and other testers, there are potential hazards. We have all probably observed instances where technicians were leaning against or touching a motor when performing tests. If the ground circuit is interrupted or an energized lead terminal contacts the motor frame while under test, the human body may provide an auxiliary path for current flow.
While the current of most test instruments is low — in the milliamp range — the unexpected shock may cause an injury when the person jerks or possibly falls into machinery. While not necessarily lethal, the consequences can cause injury.
Other hazards
A similar shock hazard can occur due to the capacitance of the winding if the motor leads are not properly discharged to the frame or shaft after the completion of testing. When a winding is energized, it behaves as a capacitor and will hold a charge for hours. Always connect the motor leads to ground for at least 10-15 minutes after performing a hipot test!
If a test panel trips during a test run, don’t assume the voltage potential is zero. The test panel may have a contactor with one of its contacts fused or melted, leaving one or more phases still energized. I remember one instance where this occurred; the technician experienced an instantaneous trip upon energizing the motor. The warning light had turned off, indicating the panel was de-energized, and the technician began disconnecting the leads. The technician was asked to stop until we could verify energy conditions were safe.
We were surprised to find that one phase of the test panel was still energized. The contacts of one phase were welded together, leaving that phase energized. This was obviously a condition where injury or death could have occurred if the technician proceeded. The best practice in these instances is to perform a lockout/tagout per safety regulations such as OSHA 29 CFR 1910.147, then check each lead for voltage before proceeding. Never rely on warning lights to indicate a power condition; bulbs do burn out. You could be lured into a false sense of safety.
Use of strapping tape
When measuring vibration while test running a motor, we use a half key with NEMA frame motors or a full key with IEC frame motors. In years past, the most common method to retain the key in the shaft during test runs was applying layers of strapping tape. I don’t believe anyone developed a formula to calculate the layers of tape required, but you knew when you thought there was enough tape applied that you had better add a few more layers just for safety.
Strapping tape was never intended for this application but it seemed to work most of the time. When the tape failed, you quickly learned how much energy you were dealing with as the keys left significant damage in their wake. The next time you strapped a key in a shaft you counted how many rolls of tape you needed instead of layers. Obviously, playing “Russian Roulette” with shaft keys was very poor judgment as they have great potential to injure or even kill people if they come loose. The best method is to use commercially available steel collars. See Figure 3.
These are available in nominal sizes that produce a slip fit over the shaft with a half key inserted in the keyway. These collars provide a reusable safety device to secure keys during run tests and they can be put to good use at the balancing stand as well. The best practice for IEC frame motors is to install the attachment.
A simple guard can be fabricated from some heavy wall mechanical tubing and designed to adjust for shaft height. See Figure 4. Keeping the guard simple, easy to set up, and light enough to move by hand or with a two-wheel cart increases the likelihood it will be used.
ANSI/EASA AR100
More information on this topic can be found in ANSI/EASA AR100
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