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TEST INSTRUMENT SAFETY
WARNING
Normal use of test equipment exposes you to a certain amount of danger from electrical shock because testing must sometimes be
performed where exposed voltage is present. An electrical shock causing 10 milliamps of current to pass through the heart will stop most
human heartbeats. Voltage as low as 35 volts dc or ac rms should be considered dangerous and hazardous since it can produce a lethal
current under certain conditions. Higher voltages pose an even greater threat because such voltage can more easily produce a lethal
current. Your normal work habits should include all accepted practices to prevent contact with exposed high voltage, and to steer current
away from your heart in case of accidental contact with a high voltage. You will significantly reduce the risk factor if you know and
observe the following safety precautions:
1. Don't expose high voltage needlessly. Remove housings and covers only when necessary. Turn off equipment while making test
connections in high-voltage circuits. Discharge high-voltage capacitors after removing power.
2. If possible, familiarize yourself with the equipment being tested and the location of its high voltage points. However, remember that
high voltage may appear at unexpected points in defective equipment.
3. Use an insulated floor material or a large, insulated floor mat to stand on, and an insulated work surface on which to place
equipment; and make certain such surfaces are not damp or wet.
4. Use the time proven "one hand in the pocket" technique while handling an instrument probe. Be particularly careful to avoid
contacting a nearby metal object that could provide a good ground return path.
5. When testing ac powered equipment, remember that ac line voltage is usually present on some power input circuits such as the on-
off switch, fuses, power transformer, etc. any time the equipment is connected to an ac outlet, even if the equipment is turned off.
(continued on inside back cover)
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