Proper use of safety equipment on energized and de-energized circuits just might save your life.
Electrical accidents don't happen without cause. Sometimes it's equipment failure; other times, unfortunately, it's operator failure. Regardless, properly using required safety equipment might reduce the seriousness of electrical shocks. Safety must be a daily effort in which each of us continuously gains experience and knowledge.
You can prevent electrical shocks in two ways; de-energizing the circuit prior to work or using safety equipment on the energized circuit. Both methods are fairly straightforward. Unfortunately, common sense doesn't always prevail.
Working on de-energized circuits. Obviously, if you work on de-energized equipment, you greatly reduce the risk of personal injury. However, "dead" circuits have electrocuted many workers. To ensure a circuit is de-energized, you should follow these procedures.
Preliminary planning. Prior to system shutdown, you should review an updated single-line diagram of the power distribution system. Then, determine the available power sources, grounding points, switching sequencing (if any), and any equipment the proposed shutdown may affect.
Second, you should verify the nameplate callouts of affected equipment match those shown in the updated single-line diagram with this information.
Third, you should coordinate the shutdown by notifying all affected departments within the facility. Special equipment (such as elevators, computers, life safety systems, etc.) might require coordination to ensure facility operation.
Fourth, you should schedule the availability of necessary people, equipment, maintenance tools, and life safety equipment for the proposed work.
Fifth, you should write an operating procedure for the intended work and review it with pertinent facility personnel. This procedure should contain "as found" labeling information for all breakers, switches, and controls. You should also include a sequence of breaker and/or switch operation, with the sequence starting with downstream loads and working up.
Shutdown. After you de-energize the circuit, test it with an appropriate instrument, making sure you have the proper voltage rating before your work begins. Test the instrument on a known energized circuit prior to this. Test the circuit phase-to-phase and phase-to-ground on all possible sources. You should retest the instrument immediately on a known energized circuit.
Next, install safety grounds on the de-energized circuit. These grounds will protect against induced voltages from adjacent energized circuits; inadvertent circuit re-energization due to switching errors; any unusual conditions that might bring an energized conductor in contact with the de-energized circuit; and any stored charges (capacitors). When installing the grounds, you should connect to "ground" first and then to the phases.
A ground cable must be able to conduct the anticipated fault current and have a minimum conductance of a No. 2 AWG copper conductor (95A). The ground cable length should only be as long as necessary, since excess cable could "whip" in the event of a fault, causing injury to nearby personnel. Size the ground cable's clamp for adequate current flow and make certain you use it for the particular application (bus, cable, tube, special grounding knobs, etc.).
Finally, you should lockout/tagout the circuit's switching device. Each person working on the circuit should have his or her own lock and tag. Only that person should remove this lock and tag. Laminated tags with a picture of the worker are ideal.
Using safety equipment on energized circuits. The primary function of safety equipment for energized work is to increase the dielectric between the energized source and you. You can usually accomplish this with hot sticks, rubber gloves, rubber blankets, or other insulating materials. However, these products can only provide protection if you properly test, maintain, and safely use the equipment. Consider the following guidelines to increase your safety awareness.
Personal guidelines. Do not work on energized equipment with wet hands or while wearing wet clothing. Do not wear any clothing with exposed zippers, buttons, and other metal fasteners. Do not wear loose or flapping clothing. Do not wear rings, wristwatches, bracelets, or other similar items when doing work on or within 4 ft of electrical equipment with exposed current-carrying parts.
Safety equipment guidelines. Wear rubber gloves when working on energized equipment, and put them on before coming within reach of the energized parts, removing them only after you are entirely clear of these parts. Never roll down or turn the rubber gloves inside out. Wear leather protectors over the rubber gloves. And never wear two pairs of gloves.
You should test rubber gloves and other rubber protective equipment at intervals not to exceed the following.
• Rubber gloves (every six months);
• Rubber blankets (every year); and
• Rubber line hoses and hoods (every year).
You should mark the date of the testing on this protective equipment.
Store these insulating and protective devices on a flat surface in areas free of oils, chemicals, and other detrimental materials.
It's a good idea to "air-test" rubber gloves before starting work on energized equipment or circuits by grasping the glove's cuff at opposite points and twirling the glove. With the open end held closed by one hand (so the air inside can't escape), squeeze the glove with the other hand to force air into the thumb, fingers, and palm. Hold the glove to your ear and listen for escaping air, making a thorough inspection for holes or thin spots. You can also hold the inflated glove under water and check for air bubbles. If the glove is defective, tag it and replace it.
If the work requires that one hand be free of covering, you should still wear a rubber glove on the other.
You should always wear hard hats, especially when working directly under other workers. Standard hard hats must have a degree of insulation resistance to protect yourself from accidental contact with electrical circuits and equipment at relatively low voltages (less than 2200V). Electrical workers, especially those involved with transmission or distribution line installation and repair, should wear insulating safety helmets or all-purpose protective helmets proof-tested to more than 20,000V.
Use hand tools with insulated handles on energized low-voltage equipment (600V or less). Many models are available with insulation levels up to 1000V. Discard and replace any hand tools with broken, nicked, or cracked insulated handles.
Because you never know when an accident will occur, proper use of safety equipment on energized and de-energized circuits just might save your life.