The answer is simple - or is it?
At times, a question occasionally comes up in my electrical safety classes regarding the use of non-conductive materials, such a plastic or rubberized sheeting, as a protective barrier against electric shock hazards.
The simple answer is Yes and No because it is dependent on the materials selected. But before delving into the specifics of the “Yes” and “No” criteria, let’s first cover some basic words and definitions related to the topic.
Definitions
The word “non-conductive,” while used often by the NFPA® National Electrical Code® (NEC)¹ and by the corresponding OSHA regulations, is not defined by either. Interestingly, neither is the word “conductive” defined by the same governances. However, we can glean a general description of conductive from NFPA 70E Standard for Electrical Safety in the Workplace which simply states, “Suitable for carrying electric current.”
Obviously, the word “conductive” is related to “conductor” which has several variations defined within the NEC article 100, such as “Conductor, Bare” or “Conductor, Copper-Clad Aluminum.” But the word “conductor” itself, as previously mentioned, is not found in any of the definitions.
Therefore, we will have to rely on a basic explanation using Merriam-Webster’s online dictionary that states, “One that conducts: such as a material or object that permits an electric current to flow easily.” The prefix “non” means “not,” so when the two are combined, non-conductive can mean a material or object that does not permit electric current to flow easily. Please pay special attention to the word “easily.”
Non-conductive materials – what’s the problem?
Plastics, rubber, polymers, fiberglass, and other such materials are well known to have some level of non-conductive properties, which makes them very valuable during the fabrication and design of electrical equipment. In fact, they are often used as electric insulators in a variety of applications. But before we decide to use that roll of thick heavy plastic or rubberized sheeting purchased at Home Depot as a barrier between exposed energized parts and workers, we must evaluate its purpose.
More importantly, we must determine if it’s rated for this specific use. Very few will argue plastic or rubberized sheeting is “non-conductive,” meaning it won’t easily pass current. But all non-conductive materials will ultimately allow current to pass once the voltage exceeds the material’s ability to resist the stress imposed by the electrical pressure, i.e. voltage.
The assurance a non-conductive medium can resist the passage of electric current at a certain voltage is derived from standards addressing its chemical composition, design, and thickness, which are validated through laboratory testing that provides quantitative data to ensure the necessary parameters are not only met but exceeded.
The term “insulated” is defined by NFPA 70E article 100 as “Separated from other conductive surfaces by a dielectric (including air space) offering a high resistance to the passage of current.” And while the definition seems to imply any non-conductive material is insulation, the Informational Note proceeding it provides greater clarity:
“When an object is said to be insulated, it is understood to be insulated for the conditions to which it is normally subject. Otherwise, it is, within the purpose of these rules, uninsulated.” (emphasis added)
This means a non-conductive material may or may not be permitted to be used as insulation, depending on its designated function, its certification, its voltage rating, and whether it is used according to its instructions. This is especially important when using temporary barriers to protect people from electric shock hazards.
What Not To Do
Figures 1 and 2 show non-conductive reinforced plastic sheeting called Griffolyn® installed as a barrier to protect other workers from the open compartments housing exposed energized parts at 480 volts.
The plastic sheeting was used to keep foreign materials from entering the enclosure because the metal doors are partially opened to allow routing temporary SOOW cords into and out of the compartments. The thought process was since the sheeting is non-conductive, it should also provide an adequate insulating barrier against shock.
However, just the opposite is true. When the spec sheets for this product are researched, we find the product carries an ASTM (American Society for Testing and Materials) rating for flame resistance and other physical attributes, but not one word about a voltage rating or for use as electrical insulation.
In other words, it is not designed for electrical protection.
Other Problems Emerge
Therefore, while such plastic sheeting may be nonconductive, it cannot be considered insulation to protect workers from electric shock and must be treated as “uninsulated,” which leads us to the next quandary. If it is uninsulated, then the energized parts are technically still exposed, which will require the Restricted Approach Boundary (RAB) and Limited Approach Boundary (LAB) to be established. At 480V, the RAB is 12 inches and LAB is 42 inches.
When we review the mandatory actions necessary before crossing into the RAB according to 70E, 130.4(G), we are told no qualified person shall approach or take any conductive object closer than the RAB unless:
- The qualified person is insulated or guarded from the energized parts, or
- The energized parts are insulated or guarded from the qualified person
But let us not forget about the additional conditions placed upon unqualified persons according to 130.4(F):
- The LAB must have signs or barricades to alert unqualified workers of the danger who are not permitted to cross into the LAB unless briefed and continuously escorted by a qualified person per 130.4(F)(2) & (3), and
- Unqualified individuals are never permitted to enter the RAB under any circumstance per 130.4(F)(3).
So even with the non-conductive plastic sheeting in place, the 12-inch RAB must be respected.
Standards for Temporary Insulation
When the old adage is slightly modified from “Use the right tool for the job” to “Use the right materials for the hazard,” it aids in determining the correct abatement method to protect against electrical shock hazards, but only when the material carries a certification and voltage rating.
There are three ASTM standards for flexible sheeting or blankets that are specifically designed to provide temporary insulation at various nominal voltages, as shown in Figure 3:
- ASTM F1742, Standard Specification for PVC Insulating Sheeting
- ASTM F2320, Standard Specification for Rubber Insulating Sheeting
- ASTM D1048, Standard Specification for Rubber Insulating Blankets
The insulating sheeting will be clearly marked with their maximum use voltage and carry the same voltage classification as rubber insulating gloves consisting of Class 00 – 500Vac, Class 0 – 1kVac or Class 1 – 7.5kVac.
The rubber blankets, on the other hand, are available for higher voltage applications, such as Class 2 – 17.5kVac, Class 3 – 26.5kVac and even Class 4 – up to 36kVac.
When the correct product is used for the specific hazard, then and only then can we be assured the energized parts are insulated to protect against inadvertent contact.
What other hazards may be present?
The other safety issues shown in Figures 1 and 2 have nothing to do with the material itself, but rather the means of attachment. The photos show the use of duct tape as the securing method to the sheet metal. The adhesive has started to fail, causing it to become partially detached, thus leaving openings around its perimeter. The energized bus is now visible through these holes.
Even if the correct materials were used, if it fails to remain in place, then it can’t perform its intended purpose. HOW we install our protective barriers is just as important as its voltage rating.
The second violation is the way the temporary power cables are installed into the cubicles. The flexible cords are not provided with strain relief as required by OSHA 1910.305(g)(2)(iii) and NEC 400.14. Additionally, the installation is also contrary to 1910.334(a)(2)(i) and NEC 400.12(7), because the individual conductors are laying on the metal floor completely unprotected and vulnerable to damage after the cord’s protective jacket was partially removed.
Conclusion
Using the right material that is specifically designed and rated for use as a temporary insulating barrier and ensuring it remains in place will not only help you comply with OSHA safety regulations and avoid fines, but, more importantly, it will ensure your qualified and unqualified electrical workers are properly protected against shock hazards.
