Our Permanent Electrical Safety Devices (PESDs) include an indicator for medium voltage application with the medium voltage indicator (R-1V). This PESD is installed differently than the previously mentioned indicators as it mounts directly onto a medium voltage bus to alert personnel to voltage presence with flashing LEDs. The medium voltage indicator is designed to provide sufficient illumination to be easily seen through a viewing window mounted on a medium voltage starter, transformer, switchgear, or other power distribution equipment. The R-1V indicator is built for long life and reliability with solid-state LEDs, is coated with flame-rated material, and uses capacitively-coupled resistivity to provide high surge immunity.
A medium voltage indicator is a single-phase device mounted onto each phase of a power bus. Energy from the bus flows through the indicator circuit through a capacitive ground connection. This means when higher voltages exist the air becomes slightly conductive allowing current to flow 'through the air,' which completes the flashing LED circuit. As the voltage increases, more current flows thereby increasing the flash rate. The enclosure size and the distance between the adjoining phases will also affect the flash rate.
When an electrician starts working on an energized conductor that just tested as 'dead' but is actually live, a dangerous situation called a 'false negative' indication is created. This means the voltage detector (falsely) indicated that there was no voltage (negative). The following are examples of how the design of a medium voltage indicator minimizes the opportunity for a 'false-negative' to occur:
Workers performing mechanical Lockout/Tagout (LOTO) procedures must isolate electrical energy. A voltage detector provides a means to check voltage inside a medium voltage enclosure. Without a voltage detector, a mechanic performing mechanical LOTO would be required to work in tandem with an electrician using a voltmeter to physically verify voltage inside an electrical panel. In this case, the electrician is exposed to voltage. With voltage detectors, the mechanic alone can verify zero electrical energy through a viewing window without any exposure to voltage.
Most agree that any low-cost device which simplifies maintenance and increases safety contributes to the high calling of electrical safety. The specific design and applications of medium voltage indicators increase employee productivity and enhance compliance to NFPA 70E.
Since medium voltage indicators mount inside enclosures, a viewing window will allow workers to see the flashing LEDs through the panel door without voltage exposure. Applications include:
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