Understand the mechanics of electrical shock and arc flash hazards.
By Ed Butts, PE, CPI
Although workplace safety is always important when working around or with a component of any well or pumping system, there is no more critical time to practice safe working procedures than when working with or around electrical power or circuits.
In fact, electrical safety is so important to jobsite safety it occupied one of the places in OSHA’s top 10 most cited safety violations list in 2018:
- Fall Protection
- Hazard Communication
- Respiratory Protection
- Lock Out–Tag Out
- Powered Industrial Trucks
- Fall Protection—Training Requirements
- Machine Guarding
- Eye and Face Protection
This does not mean lock out–tag out safety violations were added to the list only last year. As a matter of fact, lock out–tag out violations have been cited on OSHA’s top 10 list for the last six years in a row!
Working Safely Around Electricity
Many technicians mistakenly believe they can only be seriously harmed when they are exposed to or directly contact high voltage AC circuits. Unfortunately, there are too many cemeteries currently occupied with people who felt this way. The fact is virtually any value of electrical power can cause serious injury, including severe burns and tissue damage—and a current of less than one amp can actually kill you!
It is imperative a technician who plans to work with or around electrical power fully understands the fundamental relationships of electrical voltage and current, ground path, and safety hazards, including electrical shock potentials.
Since June is National Safety Month, this month’s Engineering Your Business is related to Water Well Journal’s focus on safety in the workplace and offers a review of five basic rules of electrical safety.
Rule #1: Know how much and where contact with electricity can kill you.
Voltage can be considered as the fundamental force that pushes electrical current through a circuit. As an analogy to hydraulics, voltage is the same as water pressure. In low voltage systems, alternating current (AC) power is used for most residential and industrial pumping purposes in the United States and is generally available in 120, 240, 480, and 575 volts.
Current refers to the amount of electricity (electrons) flowing through a circuit each second. Current is measured in amperes or milliamperes (1 mA=1/1000 of an ampere) and is analogous to the flow rate in hydraulic systems. The amount of electric current that flows through the body determines the various effects from an electric shock.
Resistance is the value of pushback the circuit offers to impede or slow the flow of current (amps) against the applied pressure (voltage). Resistance is measured in ohms and is analogous to friction losses in hydraulic systems.
Combining these three factors yields the following word relationship: Depending on the resistance of a circuit, a certain amount of current will flow for any given voltage.
Or mathematically (Ohm’s law): Volts = Amps × Ohms or Amps = Volts/Ohms
The volts and ohms in an electrical shock potential will play a role, but it is the current flow that determines the physiological effects. Most current-related effects result from heating of tissues and stimulation of muscles and nerves.
Stimulation of nerves and muscles can result in problems ranging from a slight fall due to recoiling from pain to serious respiratory or cardiac arrest. Relatively small amounts of current are needed to potentially cause these physiological effects.
The body has or offers resistance to the flow of current. More than 99% of the body’s resistance to electrical current flow exists at skin level.
As previously stated, resistance is measured in ohms. Thus, a calloused, dry hand may possess more than 100,000 ohms of resistance because of a thick outer layer of dead cells in the skin, while a wet skin displays a resistance closer to 1000 ohms. The internal body or hand-to-foot resistance is about 300-500 ohms and is related to the wet and relatively salty tissues that lie beneath the skin.
The skin resistance can be effectively bypassed if there is a breakdown in the skin from high voltage, a cut, a deep abrasion, or immersion in water.
The International Electrotechnical Commission offers the values for the total body impedance (resistance) of a hand-to-hand circuit for dry skin, large contact areas, based on 50 Hz, AC currents. The columns in Table 1 contain the distribution of the impedance (AC resistance) in three percentiles of the total population. For example, at 100 volts AC power (VAC), 50% of the population had an impedance of 1875 ohms (Ω) or less.
Therefore, at a voltage level of 25 VAC and average (50% percentile) hand-to-hand resistance, an individual receiving an electrical shock may easily encounter 25 VAC/1875 ohms = 0.013 amps, which is 13 times greater than or well above the perceptible level of 1 mA (0.001 amps) and just below the maximum current an average man can grasp and then release from 16 mA or 0.016 amps shown in Table 2.
This demonstrates how little voltage is needed to generate an electrical current flow and resulting shock. The skin acts like an electrical device such as a capacitor in that it allows more current to flow if a voltage is changing rapidly. A rapidly changing voltage will be applied to the palm and fingers of one’s hand if it is holding a metal tool that suddenly touches a voltage source. This type of contact will give a much greater current amplitude in the body than would otherwise occur. The level of AC current and the degree of potential damage are illustrated in Table 2.
As seen in Figures 1A and 1C, a current path through the heart—regardless of the actual path taken to ground, the foot, or arm—can cause defibrillation of the heart, rapidly leading to serious injury or death. A current path that flows straight through the right arm and then out the right foot, as in Figure 1B, may result in much less damaging injuries since the current does not travel through the heart.
A technician must always be mindful that electrical voltage must have a path for electrical current to flow from an electrical source through a human body and back to a ground before bodily damage or injury can occur. Disrupting, shielding, or preventing this route of current flow will usually avoid serious injury.
Additional factors such as skin condition (sweaty or clammy), ambient temperature, duration of contact, whether the power source is AC or DC voltage, and humidity can all impact the flow of electrical current through a body.
Rule #2: Understand the basics of electrical circuits.
This column assumes the reader has a basic understanding of alternating current (AC) and direct current (DC) principles, including the relationship between voltage (electrical pressure or force), amperage (current), ohms (resistance), and watts (power) as well as the basics of AC and DC circuit theory.
If not, I suggest going back and taking the time and effort to learn the basic concepts of electrical power and circuits. Without this basic knowledge of electrical theory, even the most talented service technician will have great difficulty deciphering and identifying even the simple problems and associated hazards related to electrical circuits.
This level of understanding is also needed to become a successful and efficient electrical troubleshooter. Effective troubleshooting of electrical equipment requires not only a firm understanding of the fundamentals of AC and DC electrical power, but also an ability to grasp how and why electrical circuits work—and just as important, the probable reasons they don’t work.
A full understanding of the basics of electrical theory and terminology also includes reading and understanding electrical symbols, schematics, line diagrams, and process narratives. Troubleshooting will often require extensively evaluating as-built drawings and electrical schematics to assist in locating and identifying the most likely cause of a system problem.
Rule #3: Understand the different types of hazard exposure.
Electrical safety hazards present a potential list of exposure to hazards that are unique. Electrical safety hazards aren’t simply present if you happen to engage a live conductor. Rather, numerous hazards are associated with working around electrical equipment that many people never consider.
The following list, in order, comprises the most common hazards associated with exposure to electrical power:
- Worn, frayed, or broken conductor (wire) insulation
- Exposed live or loose parts or connections
- Improperly maintained or defective switches/circuit breakers
- Obstructed access paths to disconnects or panels
- Water or other liquids near or next to energized electrical equipment
- Working with high voltage equipment.
Every type of exposure shown on the list represents a potential hazard. Related to the water well industry, the four most common types are likely carelessness, worn or broken conductor insulation, exposed live or loose parts or connections, and water near electrical equipment.
Every item on the list can be eliminated or greatly reduced by observing fundamental safety procedures, as simple as taking a little more time to check or lock out a circuit, verifying there is no voltage at a supposedly dead connection, or cleaning up spilled water in front of an electrical panel.
The bottom line is that almost every electrical hazard exposure or risk comes down to the first item on the list: carelessness. They can all be avoided by using just a few more seconds to fully examine the potential risks and ways to prevent electrical hazards before beginning any actual work on the circuit.
Rule #4: Know how to use your meters or test instruments.
This rule is actually more important than it sounds. No matter how much fun it may sound like to use the old-fashioned method of troubleshooting by wetting your finger and placing it into a light socket to see if power is present, it is much safer to use the proper test meter to do the same test. (Obviously, this is just a joke. Never use your finger or any other body part to test an electrical circuit.)
I can’t overemphasize the importance of owning and knowing how to use the appropriate tools and meters when troubleshooting electrical problems. In fact, I have personally seen more than one case where several days were wasted in the firm belief there was no power present at a wellhead—when the real reason power was not indicated was because the test meter needle was locked!
In fact, verifying the presence of electrical voltage at a specific site is easier than it’s ever been due to the recent addition of non-contact sensors to the troubleshooter’s arsenal. These handy pocket-size instruments allow a service technician to visually detect the possible presence of electrical voltage at a connection before actually needing to touch the circuit in any way.
They are low-cost, reliable, and quick alternatives to having to fetch the meter, plug test leads into the meter, and then engage the test prongs to the circuit to verify or determine source disconnection or deactivation.
Lock Out–Tag Out
There is likely no more important electrical safety procedure than an effective lock out–tag out program. This is particularly true for those of us who regularly work in the water well industry where remote offsets from the electrical panel or control box to the well can exceed 1000 feet or more.
The severity and causes of electrical hazards are varied, but the best protection is to de-energize or disconnect equipment before working on it.
The most effective lock out–tag out program requires each service technician to possess a personal locking-out mechanism. A padlock is usually used; see the circuit breaker example in Figure 2. The technician has the only key and a visible tag to secure to the equipment disconnection—alerting all other personnel the equipment is being serviced and is otherwise unavailable for energization.
Combining these two elements into a standard protocol and policy will help avoid many unnecessary accidents . . . and electrocutions.
If equipment cannot be de-energized for any reason, electrical workers must be properly qualified and trained, wear appropriate personal protective equipment, and follow all applicable OSHA and NFPA (National Fire Protection Agency) standards. This type of situation generally calls for a licensed electrician to do the work.
As a general rule, no unlicensed pump installer or water well driller should ever attempt to work on energized electrical circuits.
Arc flash results from a rapid release of electrical energy due to an arc fault that occurs between a phase busbar and another phase busbar, neutral, or a ground. During an arc fault the air becomes the conductor. Therefore, anybody within the vicinity of the impacted air becomes a possible victim.
Arc faults and flashes are generally limited to systems where the bus voltage is in excess of 120 volts; lower voltage levels will normally not sustain an arc.
An arc fault is similar in nature to the arc obtained during electric-resistance arc welding. And as with arc welding, a fault has to be manually started by something creating the path of conduction or a component failure like a breakdown in insulation or an equipment short.
The cause of a short normally burns away during the initial flash, with the resulting arc fault sustained by a highly-conductive plasma. This plasma will conduct as much energy from the electrical source that is available and is only limited by the impedance of the arc.
This massive energy discharge burns the busbars and vaporizes the copper, thus causing an explosive increase in the volume of the heated air. Arc blasts have been conservatively estimated to contain an expansion of 40,000 to 1. The fiery explosive blasts usually devastate everything within their paths, creating and spraying deadly shrapnel as they dissipate from the source, which can generate multiple injuries and acute health-related problems.
For example, the pressure created from the blast may exceed 2000 pounds per square foot, which has been known to knock workers off ladders, shatter windows, or collapse the lungs of nearby personnel.
These events also occur rapidly with speeds often exceeding 700 miles per hour, making it virtually impossible for a worker to get out of the way in time. The hot gases expelled from the blast also carry the products of the arc with them, including small droplets of molten metal, similar to the effects of buckshot delivered from a fired shotgun. These small droplets can readily travel through workers’ clothing and become lodged underneath the skin and in the body cavity, sometimes causing severe internal damage.
The sudden and intense blinding light emitted by the blast will undoubtedly result in weld type flash burns to the eyes of nearby observers and can lead to temporary or permanent blindness in the worse cases.
Lastly, the sound these blasts create are known to exceed 160 decibels. This is louder than standing next to and hearing an airplane take off, which can easily rupture eardrums and cause permanent hearing loss.
The arc fault current is usually much less than the available bolted fault current and below the rating of most circuit breakers. Therefore, unless these devices have been selected to handle the arc fault condition, they will generally not trip and the full force of an arc flash event will occur.
The electrical equation for energy emitted from an arc fault is equal to volts × current × time.
The transition from an arc fault to arc flash takes a finite time, increasing in intensity as the pressure wave develops. The challenge is to sense the arc fault current and shut off the voltage in a timely but expedient manner before it develops into a more serious arc flash.
Employees working within the flash protection boundary must wear nonconductive head protection wherever there is a danger of head injury from electric shock or burns or from the flying debris resulting from the electrical explosion.
NFPA’s “Standard for Electrical Safety in the Workplace” (NFPA 70E) states both the employer and the worker have specific responsibilities for safety, training requirements, the establishment of an electrical safety program, and the establishment of an electrically safe working condition.
Arc flash hazard considerations are covered in NFPA 70E, Article 130: “Working On or Near Live Parts.” The basic requirement is that live parts more than 50 volts to ground to which an employee might be exposed should be put into an electrically safe work condition before working on or being near them unless the employer can demonstrate the equipment has been disconnected or must be worked on live. In this case, live work requires an Energized Electrical Work Permit, for which the requirements are stated in Article 130.1(A)(2).
Some exemptions are given to the requirement for an electrical work permit, such as testing and troubleshooting performed by qualified personnel.
Typical approach boundaries to “live parts” are illustrated in Figure 3. These form a series of boundaries from an exposed, energized electrical conductor or circuit parts. The requirements for crossing each of these boundaries become increasingly restrictive as the worker moves closer to the exposed live parts. The limited, restricted, and prohibited approach boundaries are shock protection boundaries and are defined in NFPA 70E, Table 130.2(C).
Qualified individuals can approach live parts 50 volts or higher up to the restricted approach boundary and can only cross this boundary:
- If they are insulated or guarded and no uninsulated part of the body crosses the prohibited approach boundary
- If the person is insulated from any other conductive
- If the live part is insulated from the person and from any other conductive objects at a different potential.
Unqualified personnel must remain outside the limited approach boundary unless they are escorted by a qualified person.
Keeping out of the individual boundaries and using personal protective equipment are the best ways to avoid personal injury from arc flash and general electrical hazards.
The most common cause of electrical accidents is carelessness. No matter how well a person may be trained, exterior distractions, weariness, pressure to restore power, or overconfidence can cause an electrical worker to bypass safety procedures, work unprotected, drop a tool, or make inadvertent contact between energized conductors.
Never—I repeat NEVER—allow yourself or a coworker to practice any electrical troubleshooting procedures without clearly understanding and comprehending the dynamics of electrical power along with knowing and implementing proper precautions necessary to work safely around electrical power.
This includes knowing the basic procedures such as the use of insulating tools, gloves, safety glasses, test meters, and hardhats, as well as the basic OSHA and state safety rules that apply to lock out–tag out procedures, barriers and shields, personal protective equipment, and grounding procedures.
If necessary, insist your employer send you to the appropriate electrical safety class or seminar before beginning any practice of electrical troubleshooting.
The most important safety rules I can relate to you are: Always de-energize and test live electrical circuits before approaching or working on them as if they were live. Always use the proper safety precautions and meters when working around electrical power of any kind. Continually verify the proper operation and accuracy of your test meters. Never trust anyone who tells you the power is off without checking it yourself.
Another important factor for all troubleshooting procedures is not to allow yourself to get in over your head or try to take on more than your level of skill, knowledge, and licensing. In other words, don’t allow your ego to write a check the rest of your body cannot cash!
If necessary, enlist the assistance of a qualified electrician when the situation warrants, especially whenever energized equipment must be examined or serviced. If you’re questioning as to whether or not you are qualified to perform electrical troubleshooting, chances are you aren’t. After all, being a little bit embarrassed for a few minutes is a whole lot better than being dead forever!
This wraps up this month’s column on electrical safety. Next month, we will return to our series on the fundamentals of irrigation system design.
Until then, work safe and smart.
Ed Butts, PE, CPI, is the chief engineer at 4B Engineering & Consulting, Salem, Oregon. He has more than 40 years of experience in the water well business, specializing in engineering and business management. He can be reached at email@example.com.