This week’s question is another in the series about trust/confidence with various electrical protection equipment/scenarios.

It is about an Absence of Voltage Tester which is permitted (as of the 2018 Edition of NFPA 70E) to test for absence of voltage as part of NFPA 70E 120.5 Process for Establishing and Verifying an Electrically Safe Work Condition.

120.5 (7) Exception No. 1: An adequately rated permanently mounted test device 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 is permanently mounted and installed in accordance with the manufacturer’s instructions and tests the conductors and circuit parts at the point of work; (2) It is listed and labeled 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.

Here is this week’s question:
How confident are you that an Automatic Voltage Tester indicates the system is electrically safe?
-High Confidence
-Moderate/Reasonable Confidence
-Low Level of Confidence
-Not at all

Your thoughts and discussion are encouraged! What do you think?

It depends on if I was able to see it with an energized voltage first.

I understand they have some kind of self checking/verification. It sounds like a good idea, i.e. don't expose people to possibly energized parts when using a meter but this is going to take some time for people to get used to. I guess if they keep a flawless track record (i.e. no failures that lead) someday the industry might embrace this but I don't expect that to be anytime soon - Trust but verify!

I’ll trust my Fluke and do live dead live testing all the time

I have not yet seen how part 4 of the exception can be accomplished safely. Is a switch used, and if so, how can we be assured the switch did not fail during the transfer and the known source is now energizing the circuit that needs to be in a de-energized state? Is the switch part of the listed device?

I believe this is great idea but it will take a while before I have confidence in relying on this alone. Someday we may look back and think why on earth did we ever expose ourselves to potentially energized equipment to test absence of voltage - but that is off in the future for now. Like anything else, it is different and needs to develop a good track record.

Once they are proven to be installed correctly and functionally tested, then I would have a reasonable confidence level.
I have seen too many inappropriately wired voltage indicators/meters/relays. Including hand held ones.

Great comments. I also believe this is potentially a great idea but it will take some time to gain confidence and acceptance. It is telling that NFPA 70E has accepted it so someday we might look back at the "good ol" days of using test instruments.

It reminds me of the long evolution to accepting digital relays. Having worked for a utility decades ago, there was no way a utility would venture away from the time tested electro-mechanical relays. With digital relays, what if the electronics fail? What if the power supply fails, what if, what if... Then I recall they were eventually installed as backup devices - not fully trusting them. And then.... does anyone specify electro-mechanicals anymore? Granted we are talking about safety and energized conductors but with relays, it was a similar (slow moving) paradigm shift. Time will tell.

Other thoughts?

Panduit has been making an Absence of Voltage Tester for several years. They call it VeriSafeâ„¢ Absence of Voltage Tester. This device has voltage presence lights built in showing when voltage is present. When the equipment is deenergized, it is not enough to just see the lights have gone out. After pressing the test button, the AVT will go through the steps required to test for the absence of voltage. This AVT uses a battery to check itself before and after testing for the absence of voltage; thus complying with (4). I teach a lot of NFPA 70E / Arc Flash seminars and I have installed this into a safety switch to show how it operated. As long as I see the three red lights before denergizing the equipment and then see the green light after denergizing the equipment, I would trust this device.

I agree.
But what do the green lights show if it is miswired, say all three voltages supplied by the A-phase only or one phase not wired at all.

It someone is familiar with the installation instructions, they could quickly look to see where all eight conductors are terminated after the enclosure door is opened. If I saw all six phase conductors terminated in one spot on one phase, I would have serious concerns about the rest of the wiring in that facility.

It’s natural to be skeptical of new technology, but it’s also important to be informed before making a judgement. Permanently mounted testers referred to in NFPA 70E-2018 120.5(7) Exception 1 are actually Absence of Voltage Testers (AVTs) that must be listed to UL 1436. There are several construction and performance requirements built into UL 1436 that ensure the AVT test result is reliable and accurate. Some of these features include: automatically testing for AC and DC voltage phase-to-phase and phase-to-ground; active indicator to visually convey the absence of voltage has been confirmed (active indicators are important because lack of a light does not guarantee a safe condition); a test the tester function with a known voltage source activated before and after the measurements are taken; an installation check to detect open connections between the tester and circuit; SIL 3 rating for safety functions (this is a measure of functional safety that ensures electrical, electronic, or programable electronic systems are designed in such a way to prevent dangerous failure or to control them when they arise; AVTs are designed to meet the electrical requirements in UL 61010 – the same standard digital multimeters are listed to—in addition to providing isolation between the AVT and electrical system.

Opening the door should not be a requirement in order to verify the detector is displaying correctly when I was not involved in its installation.

We recently installed this one for review by our corporate safety engineers.
It has both indicator lights and test points.