NFPA 70E: Key Terms Electricians Should Know, Part 6

The definition of “electrically safe work condition” from Art, 100 seems straightforward enough, but it is often misunderstood. Here’s the definition straight from NFPA 70E:

“A state in which an electrical conductor or circuit part has been disconnected from energized parts, locked/tagged in accordance with established standards, tested for the absence of voltage, and, if necessary, temporarily grounded for personnel protection.”

Let’s unpack this and look at each piece of the definition.

• “Electrically safe” does not mean safe. There are other kinds of energy that you could encounter. These include steam, kinetic energy (e.g., the raised ram on a 10-ton press), and hydraulic pressure. You also may encounter high noise, poor light, high temperature (e.g., in a kiln), toxic fumes, low oxygen, strong acids or bases, radiation, or oil. The only aspect of safety you are addressing here is electrical.
• Is it the right electrical conductor or circuit part? Just because you open a breaker doesn’t mean you have de-energized the equipment in question.
• Lockout/tagout doesn’t always follow established standards. A plant in southern Illinois had a lockout/tagout program that failed on several counts. Instead of gang locks on a hasp, only the operator would hang a lock, violating OSHA 29CFR.1926.147(f)(3)(i), and leave it there across shifts, which violates OSHA 29CFR.1926.147(f)(4). The tags never bore the name of the worker, equipment, or circuit being worked on, a violation of 29CFR.12926.417(c). People followed this program assiduously, but it was not in accordance with any established standards. If you are familiar with those standards, you can see how dangerous this plant was.
• One way to test for the absence of voltage is to look for a light to go off. But is that light off because the lamp failed or because the circuit is actually open? The smart thing is to test with your “wiggie,” right? No, that is not a reliable method. Test with your DMM? Yes, but it depends. It is possible to take a null reading even though the circuit is energized. Maybe one test lead is open, or it’s connected to something other than the intended return path. To solve this problem, the three-step test method is used. First, test on a known energized conductor or terminal to test that the meter is correctly set and functioning properly. Then test the “dead” circuit for the absence of voltage. Finally, go back to your known hot and test the meter again to ensure it was still set and working right when you tested for absence of voltage.
• Did you know that you can stand with one foot on a ground rod and still receive a lethal shock? Due to soil impedance, there is a difference of potential between that rod and a nearby metallic object. A ground rod doesn’t bring metallic objects to the same potential unless they all connect to the rod via a metallic conductor. Be careful when attaching safety grounds that they are actually eliminating differences of potential. You want a dead circuit, not a parallel one.