Working hot

Proper protective equipment, tools and training are required to work on live lines. It's best to power off circuits before beginning repairs or upgrades.

Accident reports show that workers often do not turn off the power before installing or working on electrical equipment. This is a major safety concern to the electrical industry, reports the National Electrical Manufacturers Association (NEMA). It shares why it’s so important to de-energize electrical systems before working on them.

Good reasons to turn off power
An electrical accident can’t happen if electrical power is not present. Even with power locked off, workers need to wear proper protective clothing and be trained in the hazards — and safe working practices — needed around electrical components.

NEMA identifies what can happen when installers work on energized systems:

• Short-circuit arcing faults. A short circuit happens when conductors of opposite polarity are bridged by a conductive object or to grounded metal.

The arc will continue until the circuit breaker, fuse or ground fault protection device on the line side of the fault opens the circuit. That’s the good news; the bad news is even if the short-circuit protective device opens as it is supposed to, the conductors and other metallic materials in the path of the arc may explode violently, showering the area with molten metal that can cause severe burns or death. The bright arc flash can cause permanent eye damage.

• Switching dangers. Most live electrical system components must be in an enclosure designed to prevent accidental contact.

When a switch, circuit breaker or contactor opens, hot gases are produced when the arc travels across the device’s contacts. Metal particles may also shoot from the device. This is normal and enclosures are designed to contain them. The enclosure is also designed to protect workers from live current. If the enclosure is open and the circuits are hot, it cannot protect you from these dangers.

• Shock and electrocution dangers. The human body is conductive and the circuit path may go through any body part in its search for ground.

Electrical circuits carrying 120V can be just as lethal as 240V, 480V, 600V or higher voltage circuits because the current through the body depends on the body’s resistance. If the current passing through the body is high enough, humans experience “no let-go current” that can cause serious burns and death by electrocution. Electrical shock can also cause involuntary muscular reactions that may cause falls that result in other injuries.

Poor reasons for working hot
So why don’t workers turn off power? According to the NEMA report, there are many reasons, but they are all poor ones.

• Poor or no training. If workers are not aware of the inherent dangers of working around energized power sources, they can become victims. Witnesses of electrical accidents are amazed at the violent and explosive nature of electrical energy, which may express itself as a fire ball, bright flash, acrid smoke and hot, molten metal.

Do not allow unqualified and unlicensed people to work on live circuits. Safety training should be completed on a formal basis and completed by instructors with good work habits.

• Workers believe electrical service can’t be interrupted.

Invariably, this philosophy causes major shutdowns, outages and the need for equipment replacement, so what could not be shut down is shut down.

With planning, almost any piece of electrical equipment can be taken out of service. It may take additional time and cost, but the risks of not doing it may be an accident that causes massive equipment damage and personal injury or death. The time and cost of an accident will far exceed the time and cost of a properly planned outage.

• It’s a fast-track job. When the pressures of time dominate any work activity, mistakes and accidents will happen because caution and good judgment are replaced by haste.

• Working hot has not caused a problem before. It’s a common misconception that if a known safety practice is violated without resulting in an accident, then a future safety violation won’t result in an accident either.

Many electricians get safety training on 120V/240V circuits because much of their work deals with 120V to ground. It is possible to be injured or killed by 120V/240V systems, but workers may lose their fear after a few shocks, sparks, and burned wires. Applying that 120V experience to 480V and greater systems can be fatal.

• The equipment needs to be energized to perform tests. Some measurements can only be taken if equipment is energized. In these situations, workers must follow safe working practices.

The National Electrical Code (NFPA 70) is the law most states and government bodies follow. It mandates that only qualified persons have access to live electrical components.

NFPA 70 states a qualified person is “one familiar with the construction and operation of the equipment and the hazards involved.” An electrical license may not be sufficient to qualify a person to work on live equipment; additional training may be needed.

Lockout/tagout helps assure safety
Electrocution is not the only hazard of working on energized equipment. Built-up mechanical, hydraulic, pneumatic or other energy may be released during installation or repair.

Check the circuit with a voltmeter before working on equipment that’s presumed to be powered down, especially if it has tie breakers, double-throw disconnect switches, automatic transfer switches or is connected to an emergency generator circuit.

Always use lockout/tagout practices on all energized equipment. Lockout/tagout systems can help assure that the power is off and stays off.

Published in the May/June 2002 issue of Contractor Tools and Supplies magazine.

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