Published In June 2001
The amount of maintenance work being performed by electrical contractors in a plant setting is on the rise. Corporate outsourcing of this type of work is the prime contributor to the expanding role of the electrical contractor in the maintenance and repair operations (MRO) marketplace. Having the correct test and measurement tools and using them safely is vital, especially considering national statistics that indicate electrician fatalities account for nearly 1/10 of all occupational deaths (1,000) each year. Of those, nearly 50 deaths are due to electrocution. Knowing what test or measurement tools to use can mean the difference between life and death. Since part of your job is taking electrical measurements, some of these measurements will be of live power. And even when you’re testing “inactive” circuits, chances are there’s current flowing nearby. But what if there was suddenly a lot more electrical energy in those circuits? Circuits that were designed for lightning strikes and other conditions can cause sudden power surges of thousands of volts. They don’t last long, which is why they’re also called transients. However, they’re very dangerous. The strength of the transient surge decreases as it flows through a wire system. But if the electrical contractor isn’t using the correct meter, it could mean big trouble. A surge could vaporize the tips on his test leads, increase an arc from the conductors to his test lead, explode the multimeter or even cause an arc blast. The International Electrotechnical Commission (IEC) has designed an international standard for four energy-level categories. They’re based on how much electrical energy could be present during a transient. These categories are the same, whether you’re working in Canada, the United States, Europe, or in many other countries around the world. The highest level of power—the primary supply level—covers utility lines, transformers, and lines that come to the building. This is the highest and most dangerous level of transient overvoltage that contractors are likely to encounter in working with utility service to a facility. Without safe and accurate test equipment, contractors won’t be able to comply with the proposed Category IV standard, which calls for protection up to 12,000 volts. The next-highest level an electrical contractor will face is feeders, short branch circuits, distribution panel devices, or heavy appliances with short connections to the service entrance. This is Category III. The IEC calls for overvoltage protection up to 8,000 volts. There are also Category II and Category I meters. Category II meters have 6,000-volt overvoltage protection for outlets some distance away from a Category IV or III source. Category I meters have 4,000-volt overvoltage protection, mainly for electronic devices and other low-energy equipment with transient protection. When measuring power, the electrical contractor needs a meter that’s rated to handle more than just the normal power present. The meter needs to be able to provide protection for the much higher energy that could result from a transient. Look for the international category rating that is right for the work being done. In most instances, this information can be found right on the package of the unit itself. When choosing a meter, the contractor should be wary of the rating. For example, if there is a U.S. or Canadian UL mark, the contractor would assume that the meter has been tested to the UL 3111 standard, which reflects the international IEC standard. Those assumptions are logical, but they could be wrong. For your safety, make sure any meter you choose has the right Category rating for its intended location and that the Category rating has been verified by an independent laboratory to the IEC standard. Before you head into a plant setting, review the basics. Has the electrical contractor picked a meter with the necessary features, one that can handle overvoltages that could occur where the work is? Has he or she studied the instructions carefully? If so, then he or she can use the new meter. For example, multimeters typically measure amps, voltage, and resistance. The electrical contractor can set the meter for the appropriate test. The wrong setting could damage the meter or injure the electrical contractor. Once you have tested and know the circuit is live and the meter is working properly, check the circuit you want to test. Now, go back to that known circuit and recheck. Now you know the meter is still working properly and you are confident in the test results. You just tested a live circuit. But suppose you were checking resistance? The circuit shouldn’t have been live, but are you certain? A prime example is when an electrical contractor is taking noncontact measurements. The clamp-on meter is a good example. The jaw opens and you can measure amperage without having to connect anything to a live conductor. And whenever you can take a test without contact, it’s naturally safer. There are more ways than ever to use noncontact testers. An electrical contractor can trace circuits without contact by using a circuit tracer. You can trace buried lines the same way with a buried line locator. There’s even noncontact phase indication that can keep you safer when installing or servicing three-phase motors. Remember to always wear the right safety gear, know the job site, and stay alert. Understand how much current could be present if there’s a power transient. It never hurts to use a meter that’s rated for a higher category. So when you get a new test instrument, read the instructions. Keep them for reference. Know the safety program and safety procedures specific to your job site. If you have a chance to take some additional training, go for it. And new safety technology is always being introduced. Transient surges can be very dangerous. But there’s a lot you can do to minimize risks. ELSENBACH is a product manager for Greenlee Textron. He can be reached at (815) 397-7070.