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Unformatted text preview: get the equipment service manual, the service representative opened the panel cover of the voltage regulator's control cabinet in preparation to trace the low-voltage wiring in question (the wiring was not color-coded). The service representative climbed onto a nearby cabinet in order to view the wires. The technician returned and began working inside the control cabinet, near exposed, energized electrical conductors. The technician tugged at the low-voltage wires while the service representative tried to identify them from above. Suddenly, the representative heard the victim making a gurgling sound and looked down to see the victim shaking as though he were being shocked. Cardiopulmonary resuscitation (CPR) was administered to the victim about 10 minutes later. He was pronounced dead almost 2 hours later as a result of his contact with an energized electrical conductor. To prevent an incident like this, employers should take the following steps: Establish proper rules and procedures on how to access electrical control cabinets without getting hurt. Make sure all employees know the importance of de-energizing (shutting off) electrical systems before performing repairs. Equip voltage-regulating equipment with color-coded wiring. Train workers in CPR. A maintenance man rode 12 feet above the floor on a motorized lift to work on a 277-volt light fixture. He did not turn off the power supply to the lights. He removed the line fuse from the black wire, which he thought was the "hot" wire. But, because of a mistake in installation, it turned out that the white wire was the "hot" wire, not the black one. The black wire was neutral. He began to strip the white wire using a wire stripper in his right hand. Electricity passed from the "hot" white wire to the stripper, then into his hand and through his body, and then to ground through his left index finger. A coworker heard a noise and saw the victim lying face-up on the lift. She immediately summoned another worker, who lowered the platform. CPR was performed, but the maintenance man could not be saved. He was pronounced dead at the scene. You can prevent injuries and deaths by remembering the following points: If you work on an electrical circuit, test to make sure that the circuit is de-energized (shut off)! Never attempt to handle any wires or conductors until you are absolutely positive that their electrical supply has been shut off. Be sure to lock out and tag out circuits so they cannot be re-energized. Always assume a conductor is dangerous. Page 4 Section 1 Always test a circuit to make sure it is de-energized before working on it. Summary of Section 1
You will receive an electrical shock if a part of your body completes an electrical circuit by touching a live wire and an electrical ground, or touching a live wire and another wire at a different voltage. Section 1 Page 5 DA N G E r S O F E L E C T r I C A L S H O C K Section 2 Dangers of Electrical Shock ampere (amp)--the unit used to measure current milliampere (milliamp or mA)-- 1/1,000 of an ampere shocking current--electrical current that passes through a part of the body You will be hurt more if you can't let go of a tool giving a shock. The longer the shock, the greater the injury. The severity of injury from electrical shock depends on the amount of electrical current and the length of time the current passes through the body. For example, 1/10 of an ampere (amp) of electricity going through the body for just 2 seconds is enough to cause death. The amount of internal current a person can withstand and still be able to control the muscles of the arm and hand can be less than 10 milliamperes (milliamps or mA). Currents above 10 mA can paralyze or "freeze" muscles. When this "freezing" happens, a person is no longer able to release a tool, wire, or other object. In fact, the electrified object may be held even more tightly, resulting in longer exposure to the shocking current. For this reason, handheld tools that give a shock can be very dangerous. If you can't let go of the tool, current continues through your body for a longer time, which can lead to respiratory paralysis (the muscles that control breathing cannot move). You stop breathing for a period of time. People have stopped breathing when shocked with currents from voltages as low as 49 volts. Usually, it takes about 30 mA of current to cause respiratory paralysis. Currents greater than 75 mA cause ventricular fibrillation (very rapid, ineffective heartbeat). This condition will cause death within a few minutes unless a special device called a defibrillator is used to save the victim. Heart paralysis occurs at 4 amps, which means the heart does not pump at all. Tissue is burned with currents greater than 5 amps.2 The table shows what usually happens for a range of currents (lasting one second) at typical household voltages. Longer exposure times increase the danger to the shock victim. For example, a curr...
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This document was uploaded on 03/14/2014 for the course ECE 482 at University of Tennessee.
- Spring '09