No matter how many times our mothers tried to protect us from electric shock, few of us have avoided it completely. You may have the scars to show for it, either on your skin or on your tools. You may have lost the skin off your elbow when you jerked back in reflex from a shock and encountered an immovable object such as a rough stucco wall or a sharp corner of heater sheet metal.
Each of your toolboxes should contain an inexpensive tool that is one of the best defenses against electrical shock. This tool takes up very little room and can be found for a few dollars at any respectable hardware store. This small neon light bulb, with two wire leads attached, will show you if a circuit is live without the more expensive and delicate volt-ohm meter. The bulb lights up if the voltage is between approximately 50 and 600 volts, either AC (alternating current) or DC (direct current). AC is the power that most houses and businesses run on. AC can be transformed to a higher or lower voltage and rectified (changed from AC to DC). DC power can come from a battery or from rectified AC house current, but you’re unlikely to see DC voltage high enough to light the bulb. DC is usually used at low voltages to run electronics. Nonetheless, if the DC voltage is high enough to be dangerous, the bulb will light — alerting you to its presence.
If you make a habit of carrying this neon test light with you at all times, it’s easy to check each wire before you touch it with either your fingers or tools.
When checking for voltage on a motor or other 220V loads, always check between both lines (or all three lines, two at a time, in the case of a two-speed or three-phase motor). Then, check between each line and ground. On a light, or other 110V loads, there will only be one line and one neutral wire. The procedure is the same. First check between the line and the neutral, then from the line to the ground, and finally from the neutral to the ground. If you’re thinking this is crazy, as there is no voltage from neutral to ground, you’re right in theory. However, all too often systems are wired incorrectly — connections run to the wrong place, wires are improperly colored, or the neutral wire may be damaged, broken or disconnected. If this is the case, you may measure no voltage between the line and the neutral even when the line is live.
Some older remote control units use single-pole relays to switch double pole (220V) loads. Turning off one line leaves the load live but not running. Testing between the lines will not show any voltage, but testing from either line to ground will. Touching either line will remind you of your mother’s warning — in shocking fashion!
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