Testing 1, 2, 3
Knowing the right test instrument to use on an electrical system can save your life
NFPA Journal, March/April 2011
Just wet two fingers and touch them to the wires — it won’t hurt."
As primitive and unsafe as this recommendation sounds, touch testing for line voltage was discussed in early editions (circa 1930s) of the American Electricians’ Handbook, a respected and enduring document that has a place on the bookshelf of many electricians. Fortunately, discussion of that particular practice disappeared many editions ago.
The good news is that today’s electricians and others who work on electrical systems know better than to engage in touch testing and have a wide selection of test equipment available to them. The bad news is without proper training on how to safely use the test equipment, an employee can be exposed to shock, arc-flash, and arc-blast injury or death. Most of these accidents can be attributed to a lack of training on how to use and maintain the test equipment properly.
Proper use of test equipment and procedures should be part of the fundamental training for all qualified persons. Section 130.4 of NFPA 70E® states that only qualified persons shall perform testing work within the limited-approach boundary. Most, if not all, testing on 600-volt and under equipment that exposes an employee to a shock or arc-flash hazard is performed within the limited-approach boundary; more often than not, it’s performed within the restricted- and prohibited-approach boundaries. Where an arc-flash hazard exists, the testing is most likely performed within the arc-flash boundary.
Considering that one of the most important requirements in Section 130.1(A) is to work on electrical equipment only after it has been placed in an "electrically safe working condition"—and considering that a key component of establishing this condition is to test for the absence of voltage—the proper use of test equipment is tantamount to working safely. In addition, test equipment is associated with tasks such as troubleshooting, voltage measuring, and other diagnostic tests that can be performed on energized equipment without securing an energized electrical work permit.
NFPA 70E also provides specific requirements for test equipment in Section 110.9(A)(1) through (4). Included in those requirements is the provision that "test instruments, equipment, and their accessories be rated for the circuits and equipment to which they will be connected." As academic as this may appear, accidents involving test instruments used on circuits that exceed the instruments’ rating still occur.
For example, voltage testers are not generic. A voltage tester rated for 600 volts ac or dc may not be suitable for use throughout an entire electrical distribution system. The fine-print note to Section 110.9(A)(1) refers to the ANSI/ISA/UL standard, Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use–Part I: General Requirements, for considerations on the rating and design of test instruments rated 1000 volts or less.
This standard establishes four measurement categories for voltage testers. These categories relate to the level and energy of voltage impulses and establish the location in the systems where the test instrument can be safely applied. For example, a Category I voltage tester is not suitable for use with a distribution-level piece of electrical equipment, because it is not designed for the level of transient voltage impulse that may occur at that point in the system. Knowing what the measurement categories mean is essential to applying the test equipment properly.
Even though better and safer test equipment is available to us today, employees can only use that equipment safely if they have been trained to avoid the hazards associated with testing tasks.
Jeffrey Sargent is NFPA's senior electrical specilist and is staff liason for NFPA 70E.