When creating an electrically safe work condition, why are proximity detectors OK to detect the absence of voltage above 1kV, but not below? Or are we (and all the contractors we use) doing it wrong?
My explanation has been that typically MV connections are taped, so contact meters aren’t practical. Additionally, use of a contact meter above 1kV is a 2-person job (at least with the equipment we have), so we’ve now doubled the number of exposed personnel.
Article 120.1 indicates that one needs to check phase-to-phase and phase-to-ground, yet all the examples are around a 750V or less system. I’ve done a little digging and asking questions over the last year or two, but I’ve not been able to locate anything that specifically addresses this topic.
I’d appreciate some insight. Thanks!
Proximity detectors are the industry-accepted method for detecting the presence of voltages above 600VAC. The “why” question gets a little deep. Meters such as the Fluke 87-IV are rated to handle voltage measurements up to 1000VAC RMS. These meters are designed to withstand the electrical “pressure” exerted on them up to that rated voltage. Higher voltages will obviously cause damage, and a high enough voltage level will cause catastrophic failure, resulting in possible worker injury and/or death.
NFPA 70E® requires the verification of a zero-energy state, and specifically requires voltage measurements of both phase-to-phase and phase-to-ground to ensure all power is removed from the circuit in question. The standard gives no voltage range per se for when this requirement starts and/or stops. If a company claims to be voluntarily NFPA 70E® compliant, that company must follow this rule in Article 120, specifically 120.1(5), on any voltage prior to allowing work to be performed on the potentially energized circuits. NFPA 70E® compliance would thus inherently require a company to own and utilize medium voltage (up to 69KV) contact meters like the Ross Engineering Hi-Z VM25E-ALP-6 25KV Phasing Tester voltmeter. These types of meters are contact meters and typically require two electrically-qualified people to operate.
The confusion comes when we compare the requirements of NFPA 70E® and OSHA. Testing for the presence of nominal voltage in OSHA is interpreted differently than the wording in 70E. Nowhere in the OSHA electrical requirements does a statement exist that specifies that an employer must verify the absence of voltage phase to phase and phase to ground. Testing for an absence of nominal system voltage can very well be done with a proximity detector. This method should be as safe as any other method available, as long as proper safety procedures are followed, including the use of live-line tools, voltage-rated gloves, and arc-rated PPE.
If a company decides to purchase a high-voltage contact meter, which allows for testing voltages phase-to-phase and phase-to-ground per NFPA 70E®, employees using these contact meters must understand the meter limitations. For instance, several meters on the market have an accuracy limit of 1% within that voltage range. That means that a 25,000-volt contact meter can accurately display voltage only as low as 1% of 25KV, or 250 volts. Thus, even by using a properly-rated medium-voltage contact meter, the use of voltage-rated gloves and live-line tools is still required when applying personal safety grounds.
OSHA does not and will never dictate what tool to use, be it a proximity detector or a contact meter, but will always default to the OSHA General Duty clause, where it states that employers must protect their workers from known hazards. As long as company procedures do address the electrical hazard, with proximity detectors or voltage-rated contact meters; and implement proper procedures that address body position, proper safety ground application, and PPE, that company will be in compliance. Dangerous practices like using a proximity detector to verify absence of nominal voltage, then using a 1000 V-rated meter on a 15KV circuit prior to ground application, would almost always result in a citation from OSHA for failure to protect workers from these known hazards. In NO case should an improperly rated meter be used in this manner.
Are companies doing it wrong? The answer is not black and white on this one. If through a company’s procedures, the worker is protected, then no – the company is not in error. If existing work practices (even though those procedures have been in place for 40 years) do subject the employee to undue risks from a known hazard, then yes – that company is at fault and could very well be found liable.