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, doesn't smell and can't be seen, so electrical maintenance personnel need to be constantly aware of its potential danger.
NFPA 70E and sections of OSHA 1910.147 and 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 lockout/tagout (LOTO) 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), and
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. In a standards interpretation dated Nov. 16, 1999, the agency stated: "Due to the complexity of the situation, few workers can fully determine whether all of the appropriate energy isolating devices have been
LOTOed." 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, NFPA 70E states that "the employer shall be responsible to ensure that an equally effective means of locating sources of energy is employed." 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
Electrical panels are "live until proven to be dead," and it is the employee's responsibility, according to OSHA's interpretation, to "personally verify" that energy sources are isolated. NFPA 70E 3-1 requires that personnel use personal protective equipment (PPE) when "working in areas where there are electrical hazards." If a main disconnect has been open, the panel is still considered "live" until workers 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. (Once the panel has been open, the maintenance personnel still need to personally verify isolation.)
Isolation is a critical safety issue, so the door-mounted voltage awareness device performing this function needs to be redundant. RemLive voltage awareness devices, for example, have independent phase indicator circuit and independent flashing circuits. Failure of either circuit still provides voltage indication on the unit. Be aware, however, that 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 the presence of an energy source.
Stored Residual Energy
Electrical and non-electrical stored energy is a recognized hazard. OSHA states in 1910.147(a)(3)(I) that one purpose of LOTO is to prevent the "release of stored energy in order to prevent injury to employees." AC and DC drives, power factor correction capacitors and mechanical loads that backfeed electric and magnetic fields (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, in 1910.147(d)(5)(ii) 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." To sense this type of energy, the voltage awareness device needs to constantly monitor AC or DC voltage at any voltage range.
Failure of an Isolating Device
When disconnects or circuit breakers fail, they may leave one, two or three phases live. Therefore, on a three-phase system, the voltage awareness device must operate if there is a voltage on one, two or three phases.
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. OSHA in 1910.147(c)(3)(ii) 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." A voltage awareness device is a valuable "additional means" when it comes to electrical safety.