AVTs use an automated process and single step activation, standardizing the process to avoid missteps in execution and sequence, and they are designed to be robust and fail-safe, with numerous reliability features.

Listing Requirements Help Absence-of-Voltage Testers Become a Better Way to Prevent Workplace Injuries

AVTs help reduce the risk of exposure to electrical hazards and improve worker safety by automating and simplifying the process of verifying the absence of voltage.

The importance of creating a safe workplace can't be understated. When it comes to electrical hazards, a comprehensive approach to risk control that includes not only policies and procedures, but also reducing exposure through design and use of the latest technology, is crucial. There's a lot to account for, but there's a lot at stake, and the rigorous monitoring of industry best practices can go a long way when it comes to providing workers the safe working environment they need and deserve.

Finding a Better Way to Verify the Absence of Voltage
Performing work without turning off power and verifying that a de-energized condition exists is a leading cause of electrical injuries. A study1 on common practices with voltage test instruments found that, during a five-year period, 18.3 percent of facilities surveyed had a personal injury occur when using handheld voltage-test instruments, and 11.7 percent of them experienced a plant operation interruption because of voltage testing incidents.

According to Electrical Safety Foundation International statistics,2 there were 2,210 nonfatal electrical injuries in 2017, an increase of 35 percent over 2016. Shocks accounted for 1,330 nonfatal electrical injuries, while burns accounted for 900. A study3 of the U.S. Occupational Safety and Health Administration (OSHA) injury database found that about 60 percent of incidents with key words "electric arc" and "burn" occurred at low voltages (<1,000 V), with the majority of these on three-phase systems.

A common reaction to this data is to propose more safety training, but training alone is not sufficient. In a study4 of electrical burn patients, researchers found that none of the patients followed all appropriate safety measures. It has been estimated that finding a better way to verify the absence of voltage on low-voltage systems could lead to as much as a 20 percent reduction of electrical injuries in the workplace, which equates to 10 fewer injuries per week in the United States alone.

Looking at the hierarchy of controls, the most effective measures to control risk include elimination, substitution, and the introduction of engineering controls to equipment, processes, and tools. Reducing exposure to hazards via design choices should be the first choice whenever possible, rather than relying solely on administrative policies and procedures or PPE. Absence-of-voltage testers (AVTs) are permanently mounted testing devices specifically designed with this in mind. Alternatively, an AVT determines whether a circuit part is de-energized prior to opening panels or removing covers to access and maintain electrical equipment. Panduit introduced the first absence-of-voltage tester, the VeriSafe™ AVT.

AVTs take a Prevention through Design approach to electrical safety and are an ideal option for personnel tasked with verifying the absence of voltage, whether it be for performing electrical work, mechanical maintenance or other tasks requiring LOTO, or cleaning equipment. Before the introduction of the AVT, verifying that equipment was de-energized traditionally relied on a portable handheld voltage tester. This method placed electrical workers at risk for exposure to electrical hazards while performing the test and verifying that the tester was functional, whereas the AVT allows the same test to be performed before the equipment is accessed. At the same time, AVTs helps reduce human error. AVTs use an automated process and single step activation, standardizing the process to avoid missteps in execution and sequence, and they are designed to be robust and fail-safe, with numerous reliability features. The AVT enables employees to verify the absence of voltage in a fraction of the time compared to handheld portable test instruments, and employees can move from job to job and task to task with confidence in their own safety.

Requirements for AVTs were added to UL 1436, Standard for Outlet Circuit Testers, in September 2016. This standard includes a comprehensive set of performance, functional safety, and listing requirements for AVTs.

Construction Requirements
UL 1436 references construction requirements in UL 61010 (Parts -1 and -2-030), the same standards that contains listing requirements for digital multimeters. Therefore, AVTs are evaluated to the same electrical construction requirements as your handheld tester, plus meeting additional requirements for permanently mounted equipment.

User-Initiated Test
UL 1436 requires that the user initiate the test for absence of voltage with an AVT. This is intended to help ensure that performing the step is a conscious effort and that the test occurs at the point of use, reducing the likelihood of errors due to mislabeled or look-alike equipment.

Active Indicator for Absence of Voltage
An active indicator is required to visually convey when the absence of voltage has been confirmed. Use of an active indicator is an important fail-safe feature of AVTs. This is because the lack of illumination does not guarantee that a de-energized condition exists. While the lack of illumination of an indicator may be the result of the system being de-energized, it could also be due to a faulty device, improper installation, or bad indicator.

This absence-of-voltage indicator is required to be green. No other indicators on the AVT may use green, to ensure standardization and eliminate confusion between products from multiple manufacturers.

Absence-of-Voltage Threshold
Additionally, the absence-of-voltage indicator will illuminate only if all phase-to-phase and phase-to-ground voltages are below a predetermined threshold that maintains personnel safety while operating reliably.

The threshold must be low enough to avoid any injuries to personnel and high enough to avoid nuisance indications when small amounts of residual voltage are due to radio frequency interference or noise on the ground plane. For AVTs, a de-energized condition is defined as when the voltage is measured below 3.0 V.

Installation of the AVT
If the tester is not in contact with a circuit part when the voltage measurement is taken, no voltage will be detected. To ensure reliability, it is critical that the tester be in contact with the circuit part that it is monitoring. To address this, UL 1436 listing requirements include several provisions regarding installation of the AVT. The absence-of-voltage indicator cannot illuminate if the tester is not in direct contact with the circuit part being tested or if phase and ground connections are reversed.

Test Circuit to Verify Functionality
With an installed device, the operator must have a high degree of confidence in the performance. UL 1436 requires a supervisory test circuit to verify that the AVT is functioning properly. The supervisory test circuit is activated before and after the absence-of-voltage measurements are taken and requires a known voltage source. Like the process used to validate the functionality of a handheld tester, verifying that the tester is functioning as expected before and after the test ensures that the tester was not damaged during the test, leading to a false indication. Because the AVT will normally be activated on a de-energized system, an independent power source is required. A battery is one example of such a power source, but other technologies also could be utilized.

Safety Integrity Level Rating for Safety Functions
UL 1436 also requires that electronic components related to safety functions meet IEC 61508 SIL 3. This ensures that dangerous failures are detected and controlled in a safe way. Functional safety certification requires quantitative and qualitative analyses by an accredited certification body that includes rigorous testing of the product and audits of the manufacturer’s processes.

Functional safety is measured by safety integrity levels (SILs). The SIL demonstrates the safety and reliability of the parts of the product that impact the safety functions, particularly regarding hardware and firmware. UL 1436 requires SIL 3 for safety functions of AVTs. SIL 3 means that the average frequency of a dangerous failure of the safety function is ≥ 10-8 to < 10-7 (high demand or continuous mode of operation). This is equivalent to one hazardous failure in 10,000,000 hours or 1,000+ years of continual operation. Note that the safety functions in the AVT typically operate only when the absence of voltage test is in progress (for a few seconds after the user prompt initiates the test), so this is an extremely high level of reliability.

Finding a Better Way to Protect Your Workforce
Verifying the absence of voltage is a critical step that is part of nearly every job involving electrical work. While using handheld voltage-test instruments can be time consuming and expose workers to electrical hazards, AVTs that are listed to UL 1436 can improve worker safety and the efficiency of the voltage-testing process. They have many benefits and are recognized as a method that complies with the voltage verification process described in NFPA 70E.

For plants and factories, safety pays. Electrical injuries can account for one of the highest average workers’ compensation costs, and while estimates vary, sources5 indicate6 the average direct cost of an electrical injury ranges from $50,000 to $80,000. Not to mention, the indirect cost can exceed these numbers by including lost productivity with less experienced workers and low staff morale, as well as property damage and repair.

AVTs help improve safety by design. They help make absence of voltage testing more reliable and less prone to error than the manual process, thus helping to reduce incidents related to voltage testing.

These days, smart businesses prioritize electrical safety, and it's easy to see why.

1. https://ieeexplore.ieee.org/document/567795
2. https://www.esfi.org/workplace-injury-and-fatality-statistics
3. https://ieeexplore.ieee.org/document/6165547
4. https://www.cetri.org/articles/Neuropsych_electrical_injury.pdf
5. https://aeasseincludes.assp.org/professionalsafety/pastissues/056/01/039_047_F2Manuele_0111Z.pdf
6. https://nyaspubs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1749-6632.1994.tb30455.x

This article originally appeared in the April 2019 issue of Occupational Health & Safety.

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