Voltage Indicators enhance safety

Near-death experiences among paper mill electricians are all too common. On this particular day, a combination circuit breaker/welding outlet failed to provide power to the welder. The maintenance electrician began to replace the outlet. Casually, his co-worker paused and said, "Better check it with a meter." The meter revealed that one phase of the circuit breaker had failed "live" leaving the outlet energized. For these guys, this near-death experience is permanently imprinted on their minds in vivid 'Technicolor' detail never to be forgotten.

Most often, hazardous voltage violently shows up resulting in loss of limbs, severe burns, or even death. On this day, a much better result: only hearts and minds were changed. At an electrical safety training seminar, a hardened, 26-year veteran electrician stood up and said, "Until today, I never knew just how dangerous electricity really is!"

Real accidents and near-death experiences coupled with the NFPA 70E compel us to find better ways to provide safety. Accurate information and rising standards stimulate innovation. Let's discuss how one paper mill used voltage indicators, otherwise known as VIs, to enhance their electrical safety program.

Simply put, electrical safety boils down to a single question: "voltage or no voltage?" Many times a day electricians ask this question and rely on a voltmeter to provide the right answer. There is no room for error.

However, wiring a VI to the primary power source provides an independent answer to the all-critical voltage question. This pushbutton-sized device is a permanently wired voltmeter that provides electricians with a full-time, visual, independent, thru-door power indication. From a safety viewpoint, voltmeters serve multiple purposes while a VI serves has a single purpose -- to indicate the presence of hazardous voltage.

In the past, this mill used neon pilot lights installed on electrical mains that provided a similar function. On the downside, a neon indicator's intensity provided limited indication of voltage levels, and this simple voltage indicator still needed fuses and replacement bulbs. After seeing the safety benefits of thru-door voltage indicators, this paper mill went a step further and built a neon indicating light assembly with access holes that electricians used to verify zero energy after opening the disconnect. They installed these on 208V lighting panels between the Hot/Neutral.

Over time, the paper mill electricians benefited from the safety value of their home-grown, thru-door voltage indicator. Looking to improve reliability, they found a single 30mm pushbutton-sized VI that overcame the limitations of the neon pilot light assembly. This 3-phase device operates at 40-750VAC/30-1000VDC, requires no fuses, uses long life LEDs, redundant circuitry, and potted construction for high reliability. In addition, it was low cost and very easy to install. The mill maintenance manager nicknamed this device the "24/7 voltmeter" and began installing a few units into those high maintenance areas of the plant. As the days went on, the mill maintenance staff began to see the benefits of this simple reliable device and started installing them throughout the plant. Let's elaborate on some of these safety benefits.

Increasingly stringent safety requirements demanded by OSHA forced this mill to add a voltage verification step to their Mechanical Lock-Out Tag-Out procedure (LOTO). Simply put, mechanics would need to have an electrician verify a zero voltage state on the load side of their circuit breaker disconnects before performing equipment maintenance. This added manpower and downtime would greatly impact the already high costs of the paper mill's scheduled shutdowns. Someone said, "It would take our entire scheduled shutdown just to shut down!" Their solution was to use a thru door VI as a substitute 'electrician' for this zero voltage checking step.

Understanding arc flash provided the foundation for our present electrical safety culture. During an electrical fault, if energy flows too long before the short circuit device opens it will vaporize copper to 5000ºF and cause a molten copper 'shrapnel' explosion. Arc flash sends ten people a day to the hospital. The causes include dropping tools on live conductors, racking out MCC buckets or circuit breakers, and voltage checking, which is a slip of a hand that puts an electrician's face very close to this potential arc flash. Also note that most arc flashes are not anyone's fault, but rather equipment failure precipitated by an electrician just doing his job.

Most 'voltage checking' arc flash incidents center on the reliable operation of the isolator. Therefore, operating the isolator and seeing a real voltage feedback from a VI provides a secondary indication that the electrical energy has been pre-verified as isolated. Moreover, for a critical failure to occur both devices would have to fail at the same time.

Therefore, we conclude that a voltage indicator applied in this application will reduce arc flash risk because a failed isolator would be discovered while the panel door is closed.

A voltage indicator, like any safety product, must have a written procedure that insures its safe and consistent application (even cars equipped with the latest safety gadgets still need traffic laws to be safe!). The first step in applying a VI requires the electrician to verify its proper operation. Are the LEDs flashing correctly for the power system? After opening the isolator, visually inspect the VI to verify that all the LEDs cease to flash. Once the voltage returns, either planned or accidentally, re-verify proper operation of the VI.

In an eight step LOTO procedure, the electrician's voltmeter stays in his tool belt until step 6.5.(2) Think about the safety benefits when voltage information is provided to the electrician before, after, and during their entire LOTO procedure. This discussion is not complete without mentioning the first law of electrical safety: validate your voltage tester before working directly on electrical conductors.(3) In other words, test the tester, test for zero voltage, and then test the tester again (nicknamed the 'live-dead-live' procedure. The 'test the tester' principle applies to any device, whether it is a $6.95 outlet tester or high end Fluke multimeter!

In order to fully validate a VI with the 'live-dead-live' procedure, the 3-phase power must be re-applied to the device. In most cases this is impractical. Therefore, voltmeters and VI's are on the same electrical safety team, yet both provide unique safety functions.

Instantaneous and invisible electrical energy poses a unique threat to maintenance people. When electricity shows up for an accident it kills 5% of its victims. The good ol' time tested voltmeter still remains as the 'guard dog' between maintenance people and voltage. Both the voltmeter and the voltage indicator are on the same team with their own unique safety benefits; however, would our near-death experience have happened if a '24/7 voltmeter' had been installed?

From: automation.com