Voltage tester offers proof that power is really off
Satisfying NFPA 70E, this built-in absence-of-voltage tester confirms the power is off before the technician opens the cabinet door.
Your maintenance technician needs to add some wiring to the MCC, but since you have an older facility, the main power switch is not immediately in sight. Though the three-phase power is shut off and has a lock-out, tag-out notice placed on it, the cabinet should still be checked to make sure it is no longer live. NFPA 70E requires that workers verify equipment is in an electrically safe state before working on it. Until proven otherwise, equipment must be treated as energized, and necessary precautions must be observed.
To verify the equipment is in an electrically safe state requires a test for the absence of voltage (AoV). That process requires opening the cabinet and then following several prescribed steps with a digital multimeter—often a tedious and not exactly safe process. Wouldn’t it be nice to know, before opening the door, the power has been completely removed?
That was the thinking of Rachel Bugaris, Panduit business development manager and inventor of Panduit’s VeriSafe absence-of-voltage tester (AVT). Bugaris, with a BS in mechanical engineering from the University of Notre Dame, has experience in R&D and designing products. She is a member of the IEEE and SWE, has multiple patents and has written several technical papers on electrical safety topics.
FE: What inspired the creation of the VeriSafe AVT?
Rachel Bugaris: The concept for an AVT was inspired by observing electrical workers and networking with people at industry events like the IEEE Electrical Safety Workshop. As best practices for electrical work, like NFPA 70E, began to place more emphasis on the importance of verifying the absence of voltage, I noticed that the process was prone to human error, and many people were unsure of how to do it properly. I firmly believe in the importance of safety by design and was surprised that although there have been huge advancements in technology over the years, the absence-of-voltage testing process had not really changed and relied primarily on procedures and PPE to protect workers. With the emphasis on de-energizing equipment before performing electrical work, this process is one of the most frequently performed by electrical workers. Therefore, it seemed like a great opportunity to look at ways to innovate.
FE: How does it work?
Bugaris: After de-energizing equipment and locking and tagging it out, an electrical worker can use the VeriSafe AVT to verify the absence of voltage. Pressing the test button on the AVT initiates a series of tests that include verifying the tester is functioning [“test-the-tester” with a known voltage source], confirming that the AVT sensor leads are in contact with a circuit part, testing to verify voltage is below a 3-volt threshold phase-to-phase and phase-to-ground, re-testing the installation and re-testing the tester. If all these tests pass, a green indicator will illuminate to indicate a safe condition.
FE: With such a novel device, what was involved in getting approvals from standards bodies?
Bugaris: This required significant work and involved collaboration with several organizations. I began by researching injury statistics and case studies that involved voltage testing, which helped justify the need for a safer process. This research was presented at the 2015 IEEE Electrical Safety Workshop. Existing standards for portable voltage testers did not address all of the necessary requirements to ensure an installed tester could operate in a safe and reliable way. Recognizing this, we worked with UL to define requirements specifically for permanently mounted absence-of-voltage testers, or AVTs. AVTs are a new product listing category that was added to UL 1436, the Standard for Outlet Circuit Testers and Similar Indicating Devices, in September 2016. With the addition of the new AVT requirements in UL 1436, products can now be listed and labeled as an absence-of-voltage tester. This is important, because the listing is a key aspect of complying with NFPA 70E 120.5 (7) Exception 1.
FE: Why are current manual AoV tests potentially unsafe? How many steps are involved?
Bugaris: When using a handheld tester, the process is complex, and there are many opportunities for error. Handheld testers must be tested on a known voltage source before and after testing for absence of voltage. On a three-phase system, this is a total of eight time consuming measurements [testing the tester on a known source, testing for voltage between A-B, B-C, A-C, A-ground, B-ground and C-ground, and re-testing the tester]. While testing the tester and testing for absence of voltage, the user may be exposed to electrical hazards. The process is also time consuming, which may lead to workers taking short cuts or skipping it all together.
There are several other limitations when using a handheld tester. For example, the tester may not be rated for the equipment, portable testers and probes can be susceptible to damage, incorrect settings may be used, and there is a human error factor when applying test probes, as possible interruptions or distractions may occur during the process. An installed tester with an automated test sequence eliminates many of these failure modes.
FE: How many steps does the VeriSafe eliminate?
Bugaris: Actually, it performs the same sequence of steps that are used with a portable voltage tester, plus a few additional steps to ensure that the tester is in contact with the circuit. The main difference is that the steps are performed automatically and without exposure to electrical hazards. An AVT dramatically improves the efficiency of the process and provides results in about 10 seconds.
FE: Can VeriSafe be set up to show loss of both DC and AC voltages in a panel?
Bugaris: Each time the test button is pressed, the AVT tests for voltage phase-to-phase and phase-to-ground. AVTs listed to UL 1436 are required to verify both the absence of AC and DC voltage before the absence-of-voltage indicator is illuminated.
FE: Can the tester detect whether a ground fault exists?
Bugaris: The product is designed specifically to test for absence of voltage, which is a completely different function than ground fault indicators. If a difference in potential greater than 3V AC or DC is detected between any phase and ground, the absence-of-voltage indicator on the AVT will not illuminate.
FE: What powers the VeriSafe AVT?
Bugaris: The absence-of-voltage test is powered by a battery. The AVT needs to have its own power source, because the absence-of-voltage test is normally conducted when the equipment is de-energized, so it cannot draw power from the line. We also wanted to make sure the test could be conducted regardless of how long the equipment had been de-energized. The battery used in the VeriSafe AVT is a long-life industrial battery, so maintenance should be minimal. The battery can be changed from outside the equipment without exposure to electrical hazards and does not require the equipment to be de-energized. In addition, the AVT has three red LEDs that indicate the presence of voltage in each phase. These are powered directly by the circuit being monitored and will operate even if a battery is not installed.
FE: Does the VeriSafe AVT have any outputs, potentially for monitoring?
Bugaris: A set of redundant dry contact signal outputs are included on the isolation module for optional use with control systems. The outputs are normally open. They close only when the green absence-of-voltage indicator is illuminated.
For more information, visit www.panduit.com/verisafe