In a previous article, Shock and Arc Flash were discussed as the two primary types of hazards that present risk to an electrical worker. When we work on live electrical parts, the goal is, of course, to avoid being shocked, burned, or blown up. Because shock and arc flash are different, we must protect ourselves from both events. The PPE (Personal Protective Equipment) for shock protection differs greatly from the PPE for arc flash protection. This article will focus on shock and the specific PPE requirements to avoid this hazard. The focus of the next article will be PPE for arc flash.
Before I go any further, I want to emphasize one important point: PPE is designed to be the last level of protection for working on live electrical equipment. PPE is not intended to guarantee a worker’s safety or make the worker invincible. Working on electrical equipment in a deenergized state is always preferable.
The answer is any tool or clothing that provides insulation from live electrical parts.
Shock happens when a person comes in contact with a live conductor. “Coming in contact” can mean that the person touches the conductor. Contact can also occur when a person contacts a live part using an uninsulated tool. Nonconductive material, usually in the form of voltage-rated rubber, creates a barrier that ensures the worker does not become part of the circuit.
Electrical shock PPE is selected based on the voltage of the circuit. Shock protection, which includes insulating gloves, insulated tools, and rubber mats, is rated to protect the worker at certain voltages. You may have heard the phrase “current is what kills you”. This is true, but voltage determines the risk. The higher the voltage, the higher the risk of an incident for current to pass through a person. The chart below illustrates what different levels of current can do to the human body. Ventricular fibrillation can happen at as little as 0.1 amps.
The most common PPE for shock protection is voltage-rated gloves and insulated tools. Other shock protection includes rubber-insulated equipment such as blankets, covers, line hoses, and sleeves. Shock PPE is all about insulation.
To evaluate what PPE is required and when it is necessary, a shock risk assessment must be performed. This is outlined in NFPA 70E Article 130.4.
The shock risk assessment evaluates two approach boundaries that serve as a guide to when shock PPE is warranted. The limited approach boundary and the restricted approach boundary are often found on an arc flash label provided an arc flash risk assessment has been completed at the facility.
The highlighted area above shows the two shock approach boundaries. If there is no label on the equipment, the limited approach boundary and restricted approach boundary are easy to remember because they are strictly based on voltage. For the sake of brevity, this discussion will focus on a typical facility in which the highest voltage is 480 volts. For buildings with higher voltages, please refer to NFPA 70E Table 130.4 (D)(a) and Table 130.4(D)(b). For facilities where the highest voltage is 480 volts, the shock boundaries are as follows:
• limited approach boundary - 3’6” from 50V – 750V.
• restricted approach boundary - contact from 50V – 150V and 1’ for 151V – 750V.
Keep in mind that these are phase-to-phase voltages. For a typical facility, the limited approach boundary is going to be 3 ½ feet for most, if not all equipment, and the restricted approach boundary is going to be 1’ for most equipment, except for single phase systems <150V, which is to avoid contact.
The requirements for shock protection are outlined below.
Limited Approach Boundary – “The distance from an exposed energized electrical conductor or circuit part within which a shock hazard exists.”
• 3’6” for voltage 50V to 750V
• Only qualified personnel are allowed within the boundary. The only exception would be if a qualified person escorts the unqualified person.
Restricted Approach Boundary – “The distance from an exposed energized electrical conductor or circuit part within which there is an increased likelihood of electrical shock, due to arc-over combined with inadvertent movement.”
• 1’ for phase-to-phase voltages from 151V – 750V. Contact for single phase <150V.
• Only qualified personnel are allowed within the boundary.
• No qualified person shall approach or take any conductive object closer than the restricted approach boundary unless the qualified person is insulated or guarded from the energized conductors in the form of insulating gloves or insulating gloves and sleeves.
o The energized conductors are insulated from the qualified person.
Simply stated, a worker needs to wear voltage-rated gloves and use insulated tools when inside the restricted approach boundary and exposed to live electrical parts. The restricted approach boundary is most likely to be 1 foot the majority of the time in most facilities. The simpler the PPE program, the more likely a worker is to follow the protocol. PPE for shock is no different. Assuming you work in a typical facility in which the electrical systems are either 120/208V or 277/480V, the decision is easy.
Anytime your hands are within a foot of exposed live electrical conductors operating at 151v to 750v phase to phase, wear voltage-rated gloves with leather protectors and use insulated tools.
When dealing with voltages beyond 750V, consult NFPA 70E Article 130.4 (D)(a) or 130.4(D)(b) for DC voltage.
I won’t argue with anyone who says voltage-rated gloves are cumbersome, hot, and difficult to wear while working because this can be true. I will, however, argue with anyone who says they are impossible to wear and still get work done.
Maintenance departments make several mistakes that, once corrected, make wearing shock protection much easier. First, get the lowest rated gloves for the task at hand. If your electrical system’s highest rated voltage is 480V, then only class 00 gloves, which are rated for 500 volts, are needed. See chart below.
Secondly, maintenance departments often attempt to save money by purchasing only one or two pairs of gloves to be shared by the entire maintenance department. This is a mistake. We would never purchase one pair of work boots to be shared by several people. Why would we do that with gloves? If a manager provides each worker with the properly-rated and properly-sized gloves, workers will find them much easier to wear while working. The inconvenience and difficulty are not totally removed, but can be reduced.
If you have avoided utilizing voltage-rated gloves in the past, I urge you to rethink your position. A learning curve exists, as with anything new. Learning curves are always a part of life—riding a bike, balancing a checkbook, or using a voltmeter, for example. As we adapt and learn, the new task becomes habit and second nature. Working with voltage-rated gloves is no different. When I conduct my training sessions, I often demonstrate this point by wearing my class 00 gloves that are sized for my hands. I pick up a pen and sign my name on a piece of paper in the same amount of time it would take if I weren’t wearing the gloves and my signature even looks the same. The point of this exercise isn’t to show how talented I am at writing my name with gloves, but to demonstrate how easy it has become for me over time. Any worker who gives voltage-rated gloves a fair trial will learn and adapt.
• Shock PPE is different from Arc Flash PPE.
• Shock PPE is designed to insulate the worker from live parts.
• Shock PPE is required within the restricted approach boundary, which is 1 foot for 3 phase 480V and 208V systems.
• The most common shock PPE for workers within a facility are voltage-rated gloves with leather protectors and insulated tools.
• Consult NFPA 70E Article 130 to learn more details on other shock PPE and boundaries beyond 480V.
• It is always preferable to work on electrical equipment in a deenergized state.