Chapter 21 Electrical Test and Measurement Equipment 403 21.2 FIELD TESTING AND BENCH TESTING Th ere are two main types of troubleshooting. Assembly- level troubleshooting is usually accomplished on the plant fl oor. Component-level troubleshooting is often done at the test bench. A typical test bench has power supplies, signal generators, and test equipment to diagnose the component defect. Assemblies are often brought to the test bench for more in-depth diagnostics. Many companies keep an inventory of critical assemblies. When an assembly fails, it can be removed from service and immediately replaced with another assembly from inventory. Th is allows the equipment to continue to operate while the assembly is repaired. Without a spare assembly, the equipment cannot oper- ate until the assembly is repaired. Th e cost of having the equipment sit idle for an extended period of time can be very expensive. After the assembly has been replaced and equipment is operating, the defective assembly is brought to the test bench, diagnosed to the component level, and repaired. Often, the repair is replacement of a defective component. Th e assembly is tested to confi rm proper operation and then stored in inventory until needed for replacement. Th e time needed to troubleshoot and repair an assembly is a signifi cant factor in determining the cost of the repair. Th e reliability of the repaired assembly is also a factor. Relatively low-cost assemblies may be recycled rather than repaired. Some companies outsource their repair work. A good technician who is capable of component-level repair can save a company signifi cant money by completing repair work in-house. 21.3 ELECTRICAL MEASUREMENT TOOLS Industrial maintenance technicians use many electri- cal measurement and testing tools. Some measurement equipment can perform multiple types of tests. Other, more specialized equipment performs a single test. Learning both the operation of and uses for each type of measuring equipment is critical. 21.3.1 Test Lights Th e simplest form of test equipment is a test light, Figure 21-8. A test light is simply a lamp with two wires. It is used to test for the presence of electricity. Th e lamp lights when placed across a voltage source. A test light is a relatively limited electrical testing tool. Continuity tester Test light Klein Tools, Inc. Goodheart-Willcox Publisher Figure 21-8. Test lights and continuity testers are simple electrical testing tools with limited application for an industrial maintenance technician. Overvoltage Protection Categories Category Description Examples CAT I Connections to circuits in which measures are taken to limit transient overvoltages to an appropriately low level. Electronic circuits with overvoltage protection. CAT II Energy-consuming equipment to be supplied from a fi xed installation. Appliances, portable tools, and other household and similar loads. CAT III In fi xed installations and for cases where the reliability and the availability of the equipment is subject to special requirements. Switchgear and polyphase motors, bus systems and indus- trial feeders switches in fi xed installation and equipment for industrial use with permanent connection to the fi xed installation. CAT IV Connections at the utility or origin of installation, and all outside connections. Outside service entrance and drop from pole to building, wiring run from meter to panel. Electricity meters and primary overcurrent protection equipment. Goodheart-Willcox Publisher Figure 21-7. Standards for measurement categories are published by the IEC. Be sure the testing equipment you are using has the correct CAT level for the test being performed. If the equipment does not have an adequate CAT level, do not use the device—you could be seriously injured by a voltage spike in excess of what the device is capable of withstanding. Copyright Goodheart-Willcox Co., Inc.