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Incident Prevention Magazine

10 minutes reading time (2047 words)

June-July 2021 Q&A

Q: We have received some pushback from clients when setting up transmission pulling on EPZ mats that are constructed over crane mats, covered with galvanized cattle panels, overlapped, stapled down and bonded together. We follow a model passed down through our parent company’s safety research committee. Our clients have asked if the installation is certified. We did some research, found ASTM F2715 and are now wondering if that is what we should be doing. Can you help?

A: ASTM F2715, “Standard Specification for Temporary Protective Equipotential Bond Mat to be Used on De-Energized Equipment,” was established to standardize manufacturing methods for portable EPZ mats so that a purchaser can be assured of what they are purchasing. Your mat, constructed to meet proven electrical principles, is not covered by ASTM. In fact, there is no standard for constructing mats as you describe. What you are describing is a method of creating a wide area of protection for large and small operations that has been in use for decades.

The ASTM F2715 standard is for portable temporary mats, not grids. The ASTM standard itself has no conditions for use or application. Here is the scope of ASTM F2715:

1. Scope

1.1 This specification covers the manufacture and testing of the temporary protective equipotential bond mat used on or around de-energized electrical equipment.

1.2 It is common practice for users of protective equipment to prepare complete instructions and regulations to govern in detail the correct use and maintenance of such equipment.

1.3 The use and maintenance of this equipment is beyond the scope of this specification.

ASTM, just like IEEE and ANSI, devises standards through experts on committees to create best practices. Like you described, your corporate entity assembled a committee of experts and created standardization for similarly constructed EPZs across the multiple contracting companies they operate.

There are references to constructed grids. In IEEE 524, “IEEE Guide for the Installation of Overhead Transmission Line Conductors,” paragraph 5.4.1.7., “Ground Grids,” you will find reference to installation of a grid of bare conductors, metallic surface mats and/or grating arranged in a pattern over a specified area. There is no reference to a standard, and there is a sketch included depicting a grid installation.

In IEEE 1048-2003, “IEEE Guide for Protective Grounding of Power Lines,” paragraph nine, “Vehicles and equipment – Methods of protection – Workers and the public,” you will find “Grounding Equipotential Zones.” All equipment is electrically interconnected by bonding cables and grounded to a system neutral, system ground and/or grids that provide negligible potential difference across the zone. That language was revised in IEEE 1048-2016 and can now be found in paragraph 10. IEEE removed the specific language used in 2003 in favor of simply “EPZ mat,” with no reference to means or types of construction.

There are several manufacturers selling or renting units that can be assembled. They have developed their own in-house testing to offer some assurances of their product, but as noted, there is no standard that we know of. What we do know – because we have seen it over the years – is that the mat method you describe is fairly old-school, and we have seen it work both under fault conditions and in very high induction hazards.

If you build your mat, it should be designed by someone familiar with the bonding concepts necessary to provide the protection desired. The overlaps must be mechanically and electrically continuous. The equipment that is most likely to become energized by an event should have a driven rod, and the mat should be bonded to it. The designer must also be familiar with grounding and how ground rod paths should be cabled with the appropriate current-carrying capacity so that the mat has a simple task of equalizing electrical potential, not carrying fault current. As described in IEEE 524, there should also be barricades marking the protection boundaries as well as an insulating bridge to access the mat. Most importantly, all personnel should be trained on how the mat works and its limitations.

Q: We have been researching safety in and around substations and came across a 2009 article about the topic in Incident Prevention (see https://incident-prevention.com/ip-articles/what-you-need-to-know-about-substations). Given the experience of iP’s contacts and your commitment to safety, we thought you might be able to offer some guidance or sources for information. Our issue is in regard to a proposed standard concrete sidewalk with rebar that will be installed on top of 6 inches of gravel and over an existing substation grounding grid that is 18 inches below grade. Do your experts think the rebar reinforcement within the sidewalk should be grounded to the grid? 

A: This is a complex question, and we can’t address the civil nature of preference for reinforcement, but we can kick around the bonding question based on principles. One of the members of iP’s editorial advisory board is a former high-voltage research director who referred us to EPRI Project 1018976, “Touch and Step Voltage Measurements on Field Installed Ground Grid and Concrete Pads” (see www.epri.com/research/products/1018976). The project research included some test modeling, but it is based on principles of current and voltage flow in grounded systems that will be of interest to readers. There is also IEEE 80, the standard for grounding in substations. So, there are some concepts, principles and plain old observations we can consider. For years, we built tramway ducts in substations with unbonded, removable concrete tops with no issues, and those were rebar reinforced with rebar lifting eyes. 

Keep in mind that this isn’t advice, just discussion. If the walkway is not steel reinforced, that limits the conductivity to an extent, but it isn’t the same as the insulating value of the cover rock. The insulating value would be particularly hard to judge, being subject to changing over time and from weather conditions. The granite rock’s insulating value is largely due to its irregular shape and the voids between the individual stones, so even when wet, it provides a sound insulating barrier, although not as good as dry. Concrete is always wet and lacks voids. Still, it is very high-resistance, so we wouldn’t expect to find consequential step potentials for a worker standing on the sidewalk. 

The sidewalk is essentially a floating conductive object if the rock is 6 to 10 inches deep with a resistance around 3,000 ohms/cubic foot. However, if the rock degrades – and it does over time depending on wear – that means that the sidewalk is less of a floating object. If so, then we would see it as an object at a different potential than the substation floor depending on its resistance and whatever the exposure a person on the walkway is subject to. If it’s a 345-kV to a 500-kV station, the worker on the walkway will be subject to electromagnetic fields. It seems that bonding the walkway to the grid serves to ensure the grid and walkway are at a relatively equal potential, no matter the condition of the rock. Bonding to the grid, just like a switching platform, will also keep the worker on the sidewalk at ground potential in the higher-voltage substations. It seems practical, then, to use rebar for the continuity of the walkway and bond it to the substation grid, minimizing the possible potentials. 

Q: I recently participated in a grounding session and was reading over the notes I took in preparation for instituting some new best practices at my organization. During the session, we discussed that OSHA requires a spotter for buckets while working in the minimum approach distance zone (I believe that is OSHA 1910.269(p)(4)(iii)). I thought that the insulating portion of an aerial lift operated by a qualified person is exempt from this requirement. Did I get that right, or did I make a mistake in my notes?

A: The rule you bring up is the singular OSHA rule that gives you everything anyone needs to know about grounding trucks and protecting workers on the ground. That rule doesn’t mention spotters or insulated trucks. Instead, it has this criterion: If the employer cannot ensure the methods in use protect all workers from electrical exposure, then there is a list of four things the employer must do. The key word here is “methods.” This is where you heard spotters mentioned. OSHA 29 CFR 1910.269(p)(4)(iii)(C) does not describe what the methods are, only that the employer must ensure they provide protection for all workers. If you can’t ensure workers are protected, then there are OSHA-mandated requirements in (C)(1) through (C)(4) of that rule to ground, bond, EPZ mat, and insulate or barricade the vehicles. In rule 1910.269(p)(4)(ii), using a spotter is one of the things a crew can do to ensure workers are protected. The rule requires a spotter (observer) if the employer can’t assure the operator can avoid hazards without one. That rule states that a “designated employee other than the equipment operator shall observe the approach distance to exposed lines and equipment and provide timely warnings before the minimum approach distance required by paragraph (p)(4)(i) of this section is reached, unless the employer can demonstrate that the operator can accurately determine that the minimum approach distance is being maintained.” By the way, experience has shown with OSHA citations that if you had an incident and you didn’t have a spotter, this is the rule the citation will be based on.

One last thing about the insulating boom: We encourage setting up vehicles so conductive booms will not be in the energized area, but we have also learned from experience that unanticipated events occur, like loss of wire. If that wire slides down the insulating boom and reaches the truck, you have a problem.

Q: I heard in an OSHA 10-hour class that OSHA does not rule over traffic accidents, but elsewhere I recently heard that OSHA has traffic flagger rules. Where do I find those?

A: It’s true that OSHA does not investigate hospitalizations or fatalities associated with traffic or automobile use. Those are covered by the Department of Transportation or local traffic statutes and investigated by the appropriate enforcement agency. OSHA also doesn’t have maintenance of traffic rules; those are found in Part 6 of the Manual on Uniform Traffic Control Devices. OSHA uses the MUTCD occasionally as a standard of procedures. The agency does have rules that reflect the requirements of the MUTCD in 1910.269(w)(6), “Employee protection in public work areas.” These rules require signs and barricades to protect workers from traffic, but without specifications except a reference to 1926.200(g)(2). That rule, 1926.200(g)(2), states the requirements of signage that complies with the MUTCD as follows: “The design and use of all traffic control devices, including signs, signals, markings, barricades, and other devices, for protection of construction workers shall conform to Part 6 of the MUTCD (incorporated by reference, see §1926.6).”

Did you notice the phrase “incorporated by reference”? That means the MUTCD Part 6 rules are enforceable as an OSHA standard. If you didn’t know about the MUTCD, you do now, and you should also realize that if OSHA ever did claim jurisdiction over a work-zone incident, the MUTCD would be the standard upon which they would investigate the employer.

Traffic authorities don’t typically charge an employer in a work-zone accident. That can get OSHA’s interest. The most likely scenario for OSHA involvement would be a traffic-zone accident that had recordable hospitalizations or a fatality. OSHA might investigate based on violation of the rules above to see if employer compliance would have prevented the incident. If you are not compliant with Part 6 of the MUTCD, you might be found in violation of the OSHA standards and cited.

Do you have a question regarding best practices, work procedures or other utility safety-related topics? If so, please send your inquiries directly to This email address is being protected from spambots. You need JavaScript enabled to view it.. Questions submitted are reviewed and answered by the iP editorial advisory board and other subject matter experts.

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