394 CHAPTER 14 Working with electrical power FIGURE 14.6 An easy way to shop-test continuity in a cable is to twist the wires together at one end and read continuity at the other end, as shown (A). If you get a beep, both wires are good. (Use a jumper wire or make a testing plug to short out the conductors when the cable has connectors attached.) You can also use the continuity meter to check for shorts between wires (B) by touching a meter probe to one wire, then checking each of the other wires. If you get a beep, there is a short between those two wires. Wattmeter or power meter A wattmeter or power meter has a clamp-on device like an ammeter, and probes like a voltmeter. It reads true power (W) in a circuit. This meter can account for the phase difference between current and voltage when there is inductive or capacitive reactance in the circuit. Some power meters require you to turn off power to the circuit when connecting and disconnecting the meter, then turn on power to take readings. A wattmeter also reads amperage and voltage separately, which together give you the apparent power (see section on "Power Factor"). You can determine the efficiency of power use by dividing true power by apparent power (which gives you the power factor), and multiply by 100 to get pf as a percentage. ELECTRICAL SHOCKS AND MUSCLE FREEZE Some important rules to live by when working with electricity: · · · · · Whenever possible, plan so that you can work with de-energized circuits. Follow lock-out/tag-out procedures to prevent someone from inadvertently energizing a circuit while it is being worked on downstream. Use well maintained, properly rated tools and test equipment. Use appropriate personal protection equipment. Don't work alone. In the event that an electrician comes into contact with a live wire and completes a circuit, the biggest danger is that his muscles will contract and freeze, and he will not be able to pull away from it. If this happens, the most important thing is to turn off the electricity and get him away from the current as quickly as possible. The severity of an electrical injury and the likelihood of cardiac arrest and death is directly proportional to the length of time a person is shocked. Do not touch someone who is being electrocuted. Unless you can move faster than 186,000 miles/second (the speed of