Over the past decade, a deeper understanding of arc-flash energy underscored the risk of voltage exposure to health and safety managers. Since then, many Fortune 1000 companies mitigated this risk by installing hundreds of thousands of PESDs into electrical equipment as part of their safety programs as aids for isolating electrical energy during lockout/tagout (LOTO).
The collective experience of PESDs led to the creation of another device in the PESD family: the AVT. An AVT automates the process of creating an electrically safe work condition that might ultimately eliminate the manual six-step voltmeter test required by OSHA 1910.333(b)(2)(iv)(B). The minimum requirements for this device are described in the 2016 version of the UL-1436 specification.
Once AVTs earn industry acceptance, perhaps AVTs will be standard features on every electrical disconnect or circuit breaker. However, industry acceptance doesn’t happen overnight, as evidenced by the history of other pioneering electrical devices such as the Ground Fault Circuit Interrupter (GFCI) outlet and the circuit breaker. Each one of these devices labored through years with improvements and modifications before earning their place as standard electrical devices.
These questions will be answered eventually. For now, guiding principles are in place to fuel innovation and determine the future for AVT product standards. The consensus standard processes, new product engineering innovations, and better product certifications will create AVTs that will meet the rigors of daily use in the field by workers who depend on them for safety.
The Laborious Code and Standard Cycle
As a teenager in the 1970s, I saw my friend’s mom freeze with a hedge trimmer in her hand, unable to move because ground fault current paralyzed her. Luckily, she avoided injury because her quick-acting husband unplugged the trimmer from the 120VAC outlet.
Today, these incidents rarely occur, because the codes require GFCI outlets on every outdoor outlet without exception. The unquestioning reliability record of GFCI outlets also did not just happen; it was a result of five major and many numerous minor revisions to the original 1971 UL-943 GFCI outlet specification. As the GFCI’s safety and reliability reputation grew, standards committees subsequently responded with 20 new code references from 1971 to 1999.
A similar situation surrounds the development of the circuit breaker. After Thomas Edison invented the first circuit breaker in 1876, it took until 1898 to be used in an application. In 1904, ITE (formally Cutter Manufacturing Co.) became the first circuit breaker manufacturer. The first published circuit breaker product standard wasn’t until 1922 and almost 40 years later circuit breaker panels replaced fuses, at least for residential construction in the 1960s.
My point is, both the circuit breaker and GFCI outlet were welcome electrical safety innovations, but only after they earned acceptance by users through years of design improvements, technical advancements and manufacturing innovations — all of which were supported, encouraged and inspired by code revision cycles, standards and safety.
At this early developmental stage of AVTs, fully vetting and understanding the foundational principles of operation helps verify that AVTs might eventually become the de-facto standard equipment on all electrical isolation devices.
A Look at NFPA 70E 120.5(N)
Exception No. 1: An adequately rated permanently mounted test device (a) shall be permitted to be used to verify the absence of voltage of the conductors or circuit parts at the work location, provided it meets the all following requirements:
(1) It’s permanently mounted and installed in accordance with the manufacturer’s instructions and tests the conductors and circuit parts at the point of work (b);
(2) It’s listed and labeled (c) for the purpose of verifying the absence of voltage;
(3) It tests each phase conductor or circuit part both phase-to-phase and phase-to-ground;
(4) The test device is verified as operating satisfactorily on any known voltage source before and after verifying the absence of voltage (d).
- (a) A robust high-impedance design combined with an overvoltage rating of CAT III(1000V)/IV(600V) ensures that voltage surges do not damage the device and create an unsafe or dangerous condition. Power distribution systems are good applications for permanently mounted test devices but require a minimum of a CAT IV(600V) overvoltage rating.
- (b) The phrase “installed in accordance with the manufacturer’s instructions and tests the conductors and circuit parts at the point of work” reaffirms that permanently mounted test devices require a validated installation procedure documented by the end user for every installed device. The concept of “proper installation” is a common theme in each new edition of the NFPA 70E. Obviously, permanently mounted test devices are both dangerous and useless if installed incorrectly or not at the “point of work.”
- (c) A suitable “listed and labeled” AVT also needs a listing and labeling for the correct environmental enclosure rating (UL type and IP) and a suitable overvoltage rating.
(d) To verify voltage from outside the enclosure, users began installing UL Listed (Measuring, Testing and Signal-generation Equipment [PICQ]), CAT III/IV UL 61010-1 rating) test points protected with internal impedance onto their enclosures. These UL listed “meter lead extensions” used in conjunction with an adequately rated voltmeter in lockout/tagout (LOTO) provide a way to verify absence of voltage. This combination of a portable device and permanent adequately rated devices is an example of an innovation that meets the intent of requirements of NFPA 70E 120.5(N)(3)-(4).
A SIL-3 Reliability Primes the Innovation Pump
However, the most important far-reaching effect of the UL-1436 specification is the introduction of a reliability standard based on a Safety Integrity Level 3 (SIL-3) for absence-of-voltage testing systems. Notice that the term “system” is used because only a system, not a device, can be SIL-3 rated.
In addition, a SIL-3-rated “system” doesn’t require all, or any, SIL-3 components. It must be engineered to both fail safely and meet a minimum uptime reliability performance measure. With the foundational principles of PESDs laid out in NFPA 70E 120.5(N), the door is now wide open for plenty of advancements on absence-of-voltage systems.
Unseen Influences
What forces will affect today’s accepted practice of creating and verifying an electrically safe work condition? Getting back my GFCI story, I can’t remember the last time I used an electric hedge trimmer with an extension cord. Why? Because all my yard tools now are battery powered, so l have less need for GFCIs.
In the case of AVTs, forces such as product standards, consensus standards and field experience application will inevitably collide with other yet unknown forces to help answer this question in the years to come. At least for now, permanent AVT devices are recognized in a consensus standard and also has a product specification with a nationally recognized testing laboratory.
Grace Engineered Products, Inc., based in Davenport, Iowa, is a participating Encompass™ Product Partner in the Rockwell Automation PartnerNetwork™ program. Grace makes Permanent Electrical Safety Devices (PESDs), which allow for thru-door electrical safety, and a line of customizable PLC ports, called GracePorts.
The Journal From Rockwell Automation and Our PartnerNetwork™ is published by Putman Media, Inc.
