Avoiding Electrical Contact
Last year in February and March of 2024, I presented a two-part discussion titled, “Avoiding Electrical Contact” on the e-Hazard podcast “Plugged into Safety.” You can listen to Part 1 here and Part 2 here.
The main point I made on that podcast was the phrase “avoid contact” when used as a shock protection boundary as found in both NFPA® 70E® as a Restricted Approach Boundary (RAB) and the Minimum Approach Distance (MAD) according to OSHA. The podcast was later proceeded by a paper (ESW 2025-08) titled Avoid Contact – The Shock Boundary Without a Distance presented during the IEEE® Electrical Safety Workshop (ESW) conference in Jacksonville, FL, in March of 2025.
Since many individuals could not attend the IEEE ESW conference, I felt an article covering this very important safety topic had to be developed and shared to help you improve your electrical safety programs. At face value, the subject of ‘Avoid Contact’ seems like an easy open-and-closed discussion, but once we start digging into the basis according to the safety standards and regulations, we will find the correct answers. It will take some diligence.
In Part 1, we begin with the basics of where to find the physical distances and how maintaining a physical distance from exposed energized parts offers proven safety measures.
RAB & LAB: NFPA 70E
Those familiar with NFPA® 70E® Standard for Electrical Safety in The Workplace®1 will recall there are now only two electric shock boundaries designated the Limited Approach Boundary (LAB) and the Restricted Approach Boundary (RAB).
However, the 2012 and prior versions of 70E contained a third shock boundary known as the Prohibited Approach Boundary (PAB), which was removed with the release of the 2018 version. This is because the PAB and RAB were essentially identical, which led to unnecessary confusion and frustrations by users.
The 2024 edition of 70E houses the LAB and RAB distances in Table 130.4(E)(a) for alternating current (AC) and Table 130.4(E)(b) for direct current (DC).
Minimum Approach Distance: OSHA vs NESC
On the other hand, those individuals working within industries that traditionally limit their safety programs with only the OSHA regulations of either 1910 Subpart S and/or 1910 Subpart R/1926 Subpart V will often scratch their heads when they hear the terms LAB or RAB. This is due to OSHA’s use of an electric shock boundary called the Minimum Approach Distance, better known as the MAD.
OSHA’s general industry regulations pursuant to 1910 Subpart S, Table S-5, for non-electric utility locations (electric utilization) during operations list various distances for voltage ranges up to 140kV. Unfortunately, 1926 Subpart K, which covers electrical safety practices during construction in non-utility environments, does not have a MAD table. So, the use of Table S-5 from the General Industry standard is highly recommended for construction work.
The main reason for the delta between OSHA’s General Industry and Construction standards is the retirement of their author, David Wallis, from OSHA. Mr. Wallis revised 1910 Subpart S in 2007 but retired before the same could be completed for 1926 Subpart K.
Due to one being revised and not the other accounts for significant differences between the two OSHA regulations covering electric utilization equipment. This is a good reason why employers should voluntarily incorporate NFPA 70E into their electrical safety programs, as it provides exceptional safety practices when conducting either maintenance or construction activities.
On the other hand, electric utilities operating under 1910.269 Subpart R and/or 1926 Subpart V are aligned with nearly identical information. Electric utilities are allowed to calculate their company specific distances through an engineering study of their systems. However, many power companies favor the use of the preestablished distances shown in Tables R-6 and V-5 for voltages up to 72.5kV and Tables R-7 and V-6 from 72.6kV to a maximum of 800kV.
MAD in NESC
If you also incorporate the National Electric Safety Code® (NESC®) into your electrical safety program, you will notice it, too, uses only the MAD. NESC Table 441-1 for AC and Table 441-5 for DC houses these distances.
It should be noted that neither OSHA nor the NESC has an equivalent to the LAB as used in NFPA 70E.
The OSHA and the NESC distances for the MAD are nearly identical to the RAB in 70E. And while there are slight differences in the actual measurements between the RAB and MAD, they serve the same purpose by establishing a physical gap between an exposed energized part and the unprotected worker.
Any differences are insignificant in relation to this article, so they will not be elaborated upon. Our main point for this article is the purpose of these shock distances. Therefore, for the remainder of this article, we will focus our attention on only the RAB and MAD.
Regardless, if you use the RAB or MAD, both are safety zones that mandate physical space in traditional feet and inches, or metric values based on the nominal system voltage. The sole purpose of the RAB and MAD is to prevent unintentional contact or unsafe encroachment to exposed energized parts during work activities by qualified electrical workers.
The Science Behind RAB and MAD
Using air as the dielectric medium to protect workers from electric shock is a historic and scientifically proven safe practice that’s been effectively employed for decades. This is because air is an effective insulator offering excellent resistance against the passage of electric current.
If we look at today’s modern-day design of overhead transmission and distribution (T&D) power lines and open-air bus segments, we see ambient air is used to prevent short circuiting of exposed parts energized at not only tens of thousands but also in the range of hundreds of thousands of volts. The greater the voltage, the greater the air gap needed between the phases to prevent an arc over, as illustrated by Figure 1.
Using air to minimize the disruption and maintaining the reliability of electric infrastructure is one thing, but expecting air to save lives, while related, is a completely different matter. Based on this limitation of air alone for people safety, most of the distances established for RAB or MAD contain two very important factors: the electrical component of air combined with an ergonomic component.
Minimum Air Insulation Distance
Let us first look at the electrical component of air, which is also called the “Minimum Air Insulation Distance,” or “MAID.” The MAID is designed to prevent an arc over/spark over/flashover where the voltage stress is greater than the dielectric strength of a certain amount of air. When an arc over or flash over occurs, it’s known as the “voltage breakdown of air.”
The electrical component of air is founded on five key factors:
The maximum system voltage,
The voltage wave form,
The electrode configuration forming the end points of the gap,
The insulating medium of the gap, and
The atmospheric effects.
According to ANSI C84.1-2020, Electric Power System Voltage Rating at 60 Hz, the breakdown of air can be affected by voltage spikes or transients when circuits are energized at medium to ultra-high voltages. This is caused by things such as switching, faults, heavy inductive loads or storms. OSHA’s electric utility regulations pursuant to 1910 Subpart R for general industry and 1926 Subpart V during construction require additional correction factors for systems energized at greater than 72.5kV to compensate for any unexpected voltage swells.
But the elevation of the worksite can also impact air’s insulating properties. Studies indicate that standard air at sea level has a dielectric resistance of about 3kV per millimeter but lessens as the air thins at higher altitudes.
As an aside, when speaking of thinner air offering less insulation, I find an interesting paradox with the science. Because, when air molecules are completely absent, such as in a vacuum chamber, then it offers incredible dielectric strength. But as air density thins, its dielectric value decreases; that is, until a vacuum is established where it becomes a super insulator, making this a very interesting phenomenon.
Ergonomics
The second important safety factor built into the RAB and MAD is the Ergonomic Component, which is a buffer to add safety margin in the event of human errors on the part of the workers. Often called the “Inadvertent Movement Factor/Adder,” it compensates for any unexpected movement by the worker, like misjudging the actual distance between himself and the energized part, swatting at flying insects, or reaching for tools or equipment. Figure 2 depicts the worker’s position in relation to the MAD.
From 751 volts to 72.5kV, the electrical component is smaller than the ergonomic component, but above 72.6kV we see the reverse.
Conclusion
In Part 2, we will start looking at the RAB and MAD from a position of compliance. More importantly, we will look at the safety practices required when qualified workers cross into these boundaries.
Other Resources
Listen to e-Hazard’s podcast Plugged Into Safety.
Visit OSHA’s FAQ page for more on Minimum Approach Distance.
