Voltage Awareness Devices Increase Electrical Safety

Abstract
Increased awareness and better safety procedures increases safety.  The NFPA 70E and OSHA 1910[2] describe electrical maintenance safety procedures for employer and employee.  The object is to isolate and identify all sources of electrical energy (inside or outside the electrical panel) prior to performing electrical maintenance.  Verification of isolation, energy control programs, lock-out/tag-out (LOTO), and issues related to stored energy, currently offer personnel suitable protection.  However, personnel may still be at risk if there is a failure of the procedures, a failure of an isolation device (disconnect or circuit breaker), or other energy control problems.  A voltage awareness device that is wired into electrical panel main isolator and/or other incoming power sources will increase safety for electrical maintenance personnel.  This device(s)[3] provides maintenance personnel constant awareness of all sources of electrical energy by constantly flashing when voltage is present.
 
Awareness is safety’s “best friend.”  A device that provides constant “flashing” awareness of hazardous voltage within electrical panels will increase safety.  Electricity has no “taste,” it doesn’t “smell,” and can’t be “seen,” so electrical maintenance personnel need to be constantly aware of its potential danger.  The NFPA 70E and sections of OSHA 1910.147 & 1910.333 were written to provide safe maintenance procedures while working on systems with electrical energy. These documents reiterate both the employer’s and the employee’s responsibility to follow procedures during electrical maintenance activities.  The main issues related to voltage awareness are:
  1. Multiple power feeds into electrical panels and systems that require a complex LOTO[4] procedure
  2. Breakdown in the LOTO or energy control procedure
  3. The hazards of stored residual energy
  4. Failure of an isolating device (disconnect switch or circuit breaker)
  5. Other applications where a voltage awareness device will increase safety. 
Multiple Power Feeds
The purpose of LOTO is to keep electrical energy away from personnel.  Complex LOTO involves multiple energy sources, crews, crafts, locations, employees, different disconnecting means, particular sequences, and work that may continue for more that one work period.  OSHA recognizes that a hazardous power source may be “lost” in a complex LOTO.  “Due to the complexity of the situation, few workers can fully determine whether all of the appropriate energy isolating devices have been LOTOed”[5].  A voltage awareness device installed permanently or temporarily at each power source clearly identifies all sources of energy and verifies that the complex LOTO is successful. 
 
In addition, the NFPA 70E states that “the employer shall be responsible to ensure that an equally effective means of locating sources of energy is employed.”[6]  This requirement would be met, if electricians were “greeted” with a flashing indicator(s) that clearly identifies all power source(s) feeding a panel.
 
Systems that employ emergency back-up generators inherently have “multiple” power sources.  A voltage awareness device installed in these systems offers protection to personnel in the event the generator is energized during maintenance or the back-up power feed comes from a separate isolator.  The safety issues are further exacerbated, because emergency generators are tested regularly.  This means that the emergency power feed is energized intermittently, thereby providing an opportunity for an unsafe condition due to “unexpected energization.”
 
Verification of Isolation--LOTO or energy control procedure
Electrical panels are “live until proven to be dead” and it is the employee’s responsibility to “personally verify”[7] that energy sources are isolated.  The NFPA 70E requires that personnel use personnel protective equipment (PPE) when “working in areas where there are electrical hazards”[8]  If a main disconnect has been open, the panel is still considered “live”, until personnel don their PPE and personally verify the panel is de-energized.  A door mounted voltage awareness device does not eliminate the need for personnel to verify isolation.  However, personnel will not need to use PPE to perform this verification, because the voltage awareness device has pre-verified that the system is de-energized[9].  Isolation is a critical safety issue, so the door mounted voltage awareness device performing this function needs to be redundant.[10]The device is not a substitute for personally verifying isolation with a meter.
 
When it comes to verifying isolation, one electrical contractor in the Midwest trains his electricians to: 1) Open the isolator, 2) Verify that the meter is functional on a known source (i.e. 120V outlet), 3) Put on the appropriate PPE, 4) Open the enclosure door, 5) Verify with a meter that all three phases are “dead”.  A door mounted voltage awareness device saves time by eliminating the PPE in step 3. of this process.
 
Lastly, if an employee inadvertently violates the LOTO procedure, and a “dead” panel becomes “alive” without the maintenance personnel’s knowledge, the voltage awareness device will “rise from the dead” and alert personnel to presence of an energy source.
 
Hazards of Stored Residual Energy
Electrical and non-electrical stored energy is a recognized hazard[11]. OSHA states that one purpose of LOTO is to prevent the “…release of stored energy in order to prevent injury to employees.”[12] AC & DC Drives, power factor correction capacitors, and mechanical loads that backfeed EMF into systems are the common sources of stored energy.  Stored energy is particularly dangerous because it dissipates energy “at its own pace,” thereby inducing a variable voltage over a variable time back into the panel.  Furthermore, OSHA states, “If there is a possibility of reaccumulation of stored energy to a hazardous level, verification of isolation shall be continued until the servicing or maintenance is completed, or until the possibility of such accumulation no longer exists.[13]”  To sense this type of energy, the voltage awareness device needs to constantly monitor AC or DC voltage at any voltage range[14].
 
Failure of an isolating device
When disconnects or circuit breakers fail, they may leave one, two, or three phases live.  Therefore, on a 3-phase system, the voltage awareness device must operate if there is voltage on one, two or three phases.
 
Other Application for a Voltage Awareness Devices
  • Explosion-proof Purged Panels: A door mounted voltage awareness device gives personnel visual indication if voltage is present in the panel before they open the enclosure door.
  • This device can be installed at strategic overhead cranes locations with exposed DC bus work to remind personnel that the bus work is live.
  • Carbon Build-up: In rare cases carbon builds up around disconnect switches or contactors.  This allows voltage to “leak” around the device and cause exposure to hazardous voltage even though the isolator is “open”.
  • AC Drive Panels:  A 480 Volt AC drive has an internal DC bus capacitor that operates at 700VDC (typical).  A voltage awareness device wired into this DC bus will provide indication of voltage until the DC energy is at a safe level.
One maintenance supervisor said, “If I install voltage awareness devices in control panels, then my electricians will become complacent and rely on the device for safety”.  OSHA has the same concern with a tagout procedure “Tags may evoke a false sense of security”.[15].  Safety alerts and awareness products should enhance safety, but there is no substitute for alertness and following the proper safety procedures.
 
Conclusion
A vast majority of safety products are awareness devices such as signs, audible alerts, and flashing lights.  Even employee safety training can be considered an “awareness device”.  School buses, fork trucks and earth moving equipment employ a beeping and/or flashing back-up alarm to give people audible and visual indication that there is “increased danger” when these vehicles are backing up.  Open electrical panels fall into the category of “increased danger” and are good candidates for an awareness device.  Lastly, OSHA also recognizes that “Additional means to be considered as part of the demonstration of full employee protection shall include the implementation of additional safety measures.” [16] A voltage awareness device is a valuable “additional means” when is comes to electrical safety.
 
Note: With the current regulatory environment in Europe, Voltage Awareness Devices are becoming a standard electrical item in Europe.
 
Credits
This article was contributed by Philip Allen, Grace Engineered Products.  Grace Engineered Products manufactures RemLive® family of Voltage Awareness Products and GracePort™ Convenience Interfaces, brings connections from the inside to the outside of control panels. Grace provides 1000’s of different combinations of cables, connectors, and outlets in NEMA 1/12/4/4X, stainless steel, and Nema 7/9 housings. All ports are clearly marked as to their function. Orders are processed on a one-piece minimum with a typical 3-5 day delivery.  For more information, please visit www.grace-eng.com
 
FAQ’s about the RemLive® family of Voltage Awareness Products
 
1.)      What if RemLive® fails?
RemLive® is a Voltage Awareness product – a flashing reminder of live voltage. It is NOT a substitute for normal safety procedures.  The RemLive label clearly states "Danger Live equipment can kill – other safety procedures still apply – test before touching." TEST POINTS are clearly identified on each unit.
A good analogy: Construction vehicles [dump trucks, fork trucks, etc.] have a beeping back-up alarm. If the alarm fails, the driver is still responsible; however, the alarm acts as a constant reminder of potential danger and is no substitute for alert personnel. RemLive® is built with redundant circuits – dual flashing LED indicators and independent phase/line indicator LED’s.
 
2.)      What if the Flashing LED’s fail?
The dual sets of Flashing LED’s are controlled by a power supply on the PC Board; however, the (4) phase/line indication LED’s are fed directly from the panel input power. Those LED’s will be illuminated whenever a voltage greater than 24 volts exists in the panel. (The product has been tested to a sensitivity of 19 volts!)
 
3.)      How does RemLive® differ from other methods of voltage indication?
RemLive® is built for safety & reliability from the highest quality components. It’s dual set of flashing LED’s will illuminate if it senses 24 volts or more between any (2) terminals. The phase/line indicator LED’s will visually show if a disconnecting means (disconnect switch or circuit breaker) fails to clear all lines properly when opened.
 
4.)      What is the MTTF (Main Time To Failure) for the LED's?
The 3 phase RemLive® has is total of (6) High Intensity LED's. Each LED has a rating in 100,000 hours when operated at 30mA continuously. It is important to note, that RemLive intermittently and only draws 5mA, which would greatly increase the MTTF rating.
 
 
[1] US Department of Labor http://www.bls.gov/news.release/cfoi.t01.htm
[2] 29 CFR 1910.147 and 29 CFR.1910.333
[3] A device would be needed for each power source feeding the panel.
[4] NFPA 70E 2000 Edition 5-1.3.3
[5] OSHA Standards Interpretation 11/16/1999 Verification procedure for group lockout/tagout http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=22824
[6] NFPA 70E 2000 Edition 5-3.
[7] Paragraph 8 in the same reference as footnote 6???
[8] NFPA 70E 3-1
[9] Once the panel has been open, the maintenance personnel still needs to personally verify isolation
[10] RemLive® voltage awareness devices have independent phase indicator circuit and independent flashing circuits. Failure of either circuit still provides voltage indication on the on the unit.
[11] OSHA 1910.147(a)(3)(i), 1910.147(c)(i), 1910.147(c)(4)(i), 1910.333(b)(2)(ii)(C), 1910.333(b)(2)(ii)(D), NFPA 70E 2000 Edition 5-4.2.2
[12] OSHA 1910-147.(a)(3)(I)
[13] OSHA 1910.147(d)(5)(ii)
[14] RemLive® R-3P operates (flashes) at 24VDC/AC to 1000VDC or 700VAC.
[15] OSHA 1910.147(c)(7)(ii)(E)
[16] OSHA 1910.147(c)(3)(ii)

About The Author


Philip Allen is President/Owner of Grace Engineered Products

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