by , on May 18, 2015
red background with burning question

Q: Your recent answer to the question about EEWP for applying grounds jogged my memory about a different question that has come up during our in-house training.

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!

A:

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.

In speaking with OSHA on the issue, e-Hazard meets the intention of OSHA in our training. What we must address at all times is the electrical hazard(s) that exist(s). In this case, the hazard is the exposed electrical conductors that could result in an arcing or shock event, and employers must mitigate hazards through methods that provide the worker a safe working environment.

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 nothe 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 yesthat company is at fault and could very well be found liable.

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Ken Sellars
About author:
Ken Sellars is an instructor of electrical safety, NEC, Grounding/Bonding and Arc Flash Safety courses nationwide. Read more about Ken.

10 Comments on "Why are Proximity Detectors OK to Detect Voltage Absence above 1kV and not Below?"

R Grant - 29 May 2015 Reply

Can anyone comment on the following extension of the above article (very interesting question by the way): after using the non-contact voltage detector to identify lack of nominal voltage (say on a 15kV system) and taking into account that there would be a possibility of voltage below the accuracy of NCVD (double the 1% example just to be extra safe so 300V possible), prior to discharge and the application of grounds the above suggests requiring the use of a voltage meter (now does it have to be rated for 1K for the 300V possibility or the full system voltage of 15kV) p-p, p-g. So what would the person be wearing in terms of PPE at this point? Is one wearing class 00 gloves since the max v based on the accuracy of the meter is 300V, or class 2 gloves due to the system nominal (maybe taking into account induced, or stored energy). How about arcflash. Is the lack of system voltage enough to confirm that the feeding breakers are open, which obviously severely limits the fault current available, or do we assume original fault level just to be extra safe?

    Kenneth Sellars
    Kenneth Sellars - 29 May 2015 Reply

    R Grant, great questions. The idea of using a 1000 volt-rated meter on a 15KV system is NEVER warranted. This is mentioned in the article as a bad work practice - in effect, a very dangerous work practice. 1910.269 requires grounding to be performed to ensure that the system voltage is kept at ground potential, or if accidentally re-energized, an upstream safety device operates to immediately remove the power source. E-Hazard recommends the approach of verification of removal of NOMINAL voltage with a proximity detector, and then hanging grounds in full PPE, but never using a volt meter not rated for full nominal system voltage on a circuit. I have been involved in an investigation of that exact fatality investigation with a 1000 volt-rated multimeter used on a 15KV lockout/tagout incident where the system was thought to be de-energized, and the 25-year veteran electrician checked the system with a category 3-rated 1000 volt multimeter, creating a phase-to-phase arc flash, which destroyed the meter and instantly killed the electrician. He suffered both internal (shock) injuries and horrible external (arc flash) injuries and was pronounced dead at the scene. I cannot stress enough to NEVER use an under-rated volt meter on any system to verify zero energy state. Also, keep in mind that when using a medium-voltage-rated meter, the meter is checking for lack of nominal voltage, but the system may still have induced voltage. Again, ground the system with properly sized and rated personal safety grounds, rated for the system's fault current. If you do not know the available fault current, check with your engineering department PRIOR to installing a set of grounds. Undersized grounds are nothing more than an expensive and long-acting fusible link to a medium or high voltage power source.

      Kenneth Sellars
      Kenneth Sellars - 29 May 2015 Reply

      PPE levels should stay the same until the grounds are properly applied. No reduction of PPE should be allowed by your company procedure until the system is isolated, absence of nominal voltage verified, and the system is properly grounded. The nominal system voltage-rated gloves must be worn with leather protectors. This provides both shock and arc flash protection while grounds are installed/removed. We always suggest wearing voltage-rated gloves while testing for absence of nominal voltage (on medium-voltage systems), installing, and removing safety grounds as an added safety measure.

        Mark Rucker - 1 June 2015 Reply

        Good thread. Static charge left behind or built up is one more reason to require full PPE on medium voltage systems while checking for voltage and applying grounds. Static or d-c voltage can be left behind by vacuum interrupters or switch bounce while opening a circuit, or induced by nearby conductors, lightning, hi-pot testing, etc. This is one more of the several things that personal grounds guard workers against. But most non-contact meters _cannot_ detect the presence of d-c voltage, only a-c. This is very definitely a shock hazard and can be quite lethal. One should always assume lethal d-c voltages exist until proven otherwise, such as by attaching grounding conductors using appropriate PPE.

      R Grant - 29 May 2015 Reply

      Thanks for the follow-up Kenneth. I completely agree, and my company policies and work procedures reflect the above. My post was based on the types of questions that I have had from the field (shop lawyers with their what-if scenarios) and your post will be very useful for others as it steps the logic out.

Ken Sellars
Ken Sellars - 8 June 2015 Reply

Mark, Excellent point. The reasons for personal safety grounds are just as you stated - to prevent build-up of voltage - be it ac or dc, static, induced, impressed, etc. The key factor is properly-sized and properly applied grounds with the electrical potential zone maintained to prevent these totally unnecessary shocks and electrocutions of our medium and high voltage work force. We are allowing way too many injuries and deaths due to poor electrical safety practices. This is very unfortunate, especially since most, if not all, of these types of injuries are in fact preventable.

safetyben101@gmail.com - 8 July 2015 Reply

Other than the 70E requiring a phase to phase check, is there other reasons why a proximity tester should not be used to declare absence of voltage in LV (below 600v)?

Hugh Hoagland
Hugh Hoagland - 10 July 2015 Reply

Other than the phase to phase check, OSHA requires for LV to be tested with a "contact type tester" which is capable of measuring 0 Volts. This is required since <600V is typically not grounded. Absolute verification is critical.

Ken Sellars
Ken Sellars - 12 July 2015 Reply

SafetyBen, Great question. NFPA 70E Article 120.1(5) dictates that an "adequately rated test instrument" is used to test each phase conductor "phase-to-phase and phase-to-ground." This test is impossible with a proximity detector. The proximity detector only tests for presence of voltage through capacitive coupling, and cannot sense phase to phase or phase to ground voltage. It only sees the presence of a field. Here is a great link to how these detectors function from Fluke's website: http://www.fluke.com/fluke/uses/comunidad/fluke-news-plus/articlecategories/electrical/capacitivevoltage

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