Introduction

Electricity is an efficient and effective means to move energy to where it is needed to power a device or perform some sort of work. It is simply the movement of electrons, energy containing atomic units, along a path to the point at which that energy is consumed, or used, by a device. Like any energy source, if the energy is released in an uncontrolled or unexpected way it may become hazardous. Knowledge about electricity and electrical power is perhaps the most powerful hazard prevention method. This article will provide some background on electricity that every person should know to protect themselves and others from electrical hazards at work and at home.

Understanding Electricity

There is some terminology associated with electricity and electrical power. This section provides definitions for the characteristics of electricity and other basics of electrical power. It is important to understand these concepts well when working with electricity so that you can respect the energy source and not fear it. Each of these terms is considered relative to their electrical hazard. More information on electricity, electrical circuits and components can be found in the Basics of Electricity and Basics of Electricity 2 articles.

Voltage: This is typically how electricity is referenced. The most common voltages found in the United States at the facility level are 120-V, 220-V and 480-V. 600-V, 1,200-V and 4,600-V are also found in industrial facilities, and higher voltages are used for transmission of power from the plant to local substations. Voltage is essentially the driving force of the electrical power. It is analogous to the pressure in a pipe that moves water along or a hand pushing an object across the table. Therefore, the higher the voltage, the more the push. Just as higher pressure hydraulic systems move water and fluids up an incline, higher voltages are more likely to arc or "jump" between non-touching conductive surfaces, creating an electrical hazard.

Current: If voltage is the pressure in a pipe, then current is the flowing water. Current is simply the number of electrons, or energy containing atomic units, passing through a certain area, such as a cross section of wire, in a certain amount of time. Since current carries the energy that when released in an uncontrolled manner causes damage, it is the more dangerous component of electricity. Current is typically classified as alternating (AC) [from a plug outlet] or direct (DC) [from a battery]. This describes how the current changes over time, as shown in the figure below.

Circuit: An electrical circuit is simply a continuous path or loop. A circuit must be closed to operate properly. Thinking of a kitchen sink — the water (current) moves through the pipes to the faucet because of pressure (voltage) in the system. However, for the sink system (circuit) to operate properly, you must have a drain to take the used water away or the sink will overflow. This is analogous to the return path of the circuit. Therefore, when looking at a circuit diagram, you should always be able to move your finger along the loop in a continuous manner, returning back to the source without going over any point more than once.

Occasionally, circuits are formed unintentionally. This is general called a short circuit. Short circuits allow power to flow into areas that it would not be expected, such as the outer casing of a piece of equipment or even part of a person’s body. Other times, components reserve power in the circuit, so simply unplugging may not eliminate the electrical hazard. As an example, use the exercise below to understand open and closed circuits and electrical components, and notice how the open switch removes the AC power supply from the circuit, but a battery or capacitor, potentially holding a charge, still powers the circuit. It is important to be aware of where power is flowing and prevent incidental formation of a hazardous circuit.

Electrical Safety

There are two principles of electrical safety: Protect yourself and others and protect your equipment. Many concepts of the basics of electrical safety are common sense.

The most important thing is to respect electrical power, and not fear it. When a person is nervous about a situation, there is a tendency to focus too narrowly on the particular task and lose sight of your surroundings and the total circuit. This can make the situation more dangerous. Therefore, if you are unsure how to accomplish a task or uncomfortable working with or around electricity or electrical circuits, find a knowledgeable and experienced person or certified electrical professional to complete the task or seek out the appropriate training.

Protect Yourself & Others

• When at all possible, remove ALL energy sources from the system. This practice greatly reduces the hazard when working on equipment. To ensure that all energy is dissipated from the system, it is recommended that the system is checked appropriately with a multimeter (voltmeter/ammeter/ohmmeter combination tool). OSHA requires all facilities to develop a lockout-tagout procedure and train all employees, regardless of job function, on how to recognize and react to a locked or taggd energy source. This system requires the person working on a system to apply an active locking device, such as a key lock, or other method of communicating that the system is not to be powered "on" to ensure that no other person inadvertently energizes the system while he is working on it or before the task is completed.
• Use appropriate personal protective equipment. Safety glasses, while not necessarily intuitive for electrical work, are recommended in all situations. Insulating gloves (linesman gloves) and many tools are rated for a maximum safe voltage. For most facilities, Class 00 or Class 0 is sufficient since they protect to 600-V and 1000-V, respectively. However, some tools are only rated to 240-V or 480-V. Additionally, there is a need to protect a worker from powered tool failures, such as if a reciprocating saw short circuits or otherwise fails. Equipment such as ground fault circuit interrupters (GFCIs) is available and provides this protection.

In addition to protecting parts of the body that may come into direct contact with electricity, it is important to protect against arc flash hazards. Arc flash is when a high amperage current arcs through the air to another surface, like lightning, causing heat and pressure waves and launching projectiles. All electrical systems are susceptible to arc flash, and so the National Electric Code recently adopted a standard requiring persons working on live systems to use protective clothing in addition to safety glasses and proper hand protection. The type of outfit required depends on the activity, as shown in the table below. OSHA requires all employees be trained in which situations require what level of personal protective equipment as part of their job function at the start of the job with annual retraining.

Protect Your Equipment

• Properly ground all systems. Grounding reroutes fault and over currents back to the power source before it generates a high voltage on the surface of the equipment, harming people and other systems. Proper grounding can also alleviate power quality and signal reference problems. For grounding to work effectively, check that the grounding wire is appropriately and tightly bonded to a conductive (metal) surface with a positive locking mechanism, such as a bolt. For other resources, please check the Progress Energy website.
• Properly utilize fuses and circuit breakers. Fuses and circuit breakers should be appropriately sized to the equipment being operated so that when there is an irregularity in the system or equipment failure, electric power is immediately disengaged by blowing the fuse or opening the circuit breaker. This equipment can prevent damaging fault currents from reaching the equipment and developing hazardous voltages on the surface of the equipment. Periodically test the circuit breakers and make sure nothing impedes them from opening when tripped. Also, make sure that the equipment is properly wired, particularly that the ground leads back to the expected circuit breaker or fuse to ensure the equipment will be de-energized when current exceeds expected levels.

References

Additional and in-depth information about electricity and electrical safety can be found at the following websites, including codes and regulations, facility training and policy examples, and much more.