Electrical
Safety is thrust into the crosshairs of every corporate safety committee
after the publication of NFPA 70e Standard for Electrical Safety in the
Workplace in 2000. Why the sudden interest in electrical safety?
Electrical accidents have the highest fatality rate of all industrial
accidents and the NFPA 70e was the tool OSHA needed to enforce electrical
workplace safety. The NFPA 70e took electrical safety from black magic
to a precise science. Furthermore, this document demanded new procedures,
added personnel protection equipment (PPE); and required rigorous training
standards, thereby making many practices obsolete.
Voltage Indicators: A Simple Concept with Striking Safety Value
Higher electrical safety standards inevitably create a need for new safety products. One of the best new products is an externally mounted VI that provides electricians with a flashing indication of voltages within a panel, before they open the panel. Elegantly simple, this product has immense safety value, because it addresses the core issue of electrical safety—Is there voltage?..does the electrician know it?
Electricity: A Unique Danger
People and electricity are a lethal mixture. Electrical safety demands the correct answer to one question: Is voltage present? Most electrical accidents happen when personnel inadvertently touch an energized conductor, which they think is de-energized. You can taste, smell, or see most other hazards (natural gas=rotten egg smell, fire=smoke, etc.), but electricity is invisible and gives no warning when it “shows-up” for an accident.
“Electrical incidents, although a small portion of the total incidents, are disproportionately fatal when they occur.”[1] Electrical accidents account for only 0.2% of all lost work days due to occupational accidents, but account for 1 in 20 (4.8%) occupational fatalities.[2] If a typical plant electrician has an electrical accident while working on 600V or below, there is a 4.1% chance that it will be fatal [3]. This is 20 times the fatality rate when compared to the leading cause of occupational fatalities- “Contact with Objects and Equipment” (fatality rate of 0.2%--873 deaths and 400,033 injuries). The National Safety Council (www.nsc.org) estimates the direct cost for the employer of a fatality is $1,070,000[4].
Why is there such a high fatality rate for electrical accidents? Electricity can flow through people instantaneously—in 1/60th of a second—and it doesn’t take much current to kill a person. The risk of fatality increases with higher voltages because there is more force to move higher currents through the body. Consider these facts:
- 2-10 mA[5]: Minor shock, might result in a fall.
- 10-25 mA: Loss of muscle control, or not able to let go.
- 25-75 mA: Painful, may lead to collapse or death.
- 75-300 mA; For a ¼ second almost always results in death.
Current passing through the heart, chest, or nervous system is the most dangerous, and current passing through limbs results in severe burns. Current that hits the chest is almost always fatal, as is current passing between the hands and feet and involving the lungs and heart.
Essential Features
The electrical design of a VI demands accurate indication of Voltage or No Voltage. Every possible electrical scenario must be designed-in to the product. Lack of one critical feature may yield a “Maybe” voltage indication, thereby nullifying the VI’s benefit. Likewise, a VI, with the required functionality and reliability, provides a second independent verification of voltage in addition to a voltmeter. In other words, a second opinion (or voltmeter) is safer.
Redundant Circuitry, Design Reliability, and Procedures
Most safety alerts
(i.e. smoke detectors) operate in a normally safe state (i.e. houses don’t
burn everyday) and require external, yet fallible, power sources (i.e.
batteries or 120VAC), and the TEST button typically activates only part of
the circuit (the horn). The only true test is creating enough smoke
to activate the smoke alarm. Conversely, a VI operates in a normally
hazardous 
state
(electrical systems are
energized), is powered and tested from the very hazard it indicates
(no separate power supply and hardwired to L1, L2, L3, & GRD).
Personnel TEST a VI by seeing all three phase indicator LED pairs flash.
External VIs, when combined with a lock-out tagout procedure must
require electricians to see the VI stop flashing after the isolator is
opened
(See Appendix A for LOTO Analysis).
Since a VI is permanently installed and hardwired to the power source, it is less susceptible to damage and offers personnel an unattended voltage check. A VI operating on either AC or DC over a wide range of voltage, warns personnel if one, two or all three phases are live.
Wide Voltage Range Operation
Electrical accidents and the NFPA 70E[6] consider voltages over 50V to be hazardous. Therefore, a VI needs to indicate if there is any voltage on any phase above 50V. Facilities with 600V (or less) power systems could standardize on a voltage warning indicator with a rating of 40VAC/30VDC to 750VAC/1000VDC. This device could be installed on any panel in the facility.
Pilot lights and other devices operate at a narrow voltage range (i.e. 480V+/- 10%). Outside this range; the device would be damaged and lethal voltage could still exist inside the enclosure.
AC/DC Operation and Stored Energy
A big concern with electrical safety is stored energy[7], which comes from several sources: 1.) Power factor correction capacitors, 2.) Machinery that “creates” electricity when slowing down, thereby feeding electrical power backwards into the electrical system. 3.) Large power supplies or UPS systems, 4.) Emergency back-up generators (stored energy is in the form of gasoline), and 5.) AC or DC drives.
In most cases, an electrical system is electrically safe when the isolator is open. However, stored energy can be a secondary lethal power source, present for a time, after the system has been electrically isolated. Stored energy, created under an AC power source, is dissipated by the flow of DC current to ground until the voltage level is zero. Because of this, the voltage-warning indicator needs to operate in a wide range of DC or AC voltage. This ensures that personnel have a visual warning until the stored energy has bled down to a safe level of 50V or less.
Visual Indication of Multiple Power Sources
Unique safety risks occur when a control panel has multiple power sources. If an electrician is greeted with flashing VIs showing the locations of all live power sources within the panel, he immediately knows how the panel is being fed. Even a de-energized voltage warning indicator provides the physical location of de-energized sources of power.
Systems that employ emergency back-up generators inherently have multiple power sources and sometimes multiple isolators. A VI installed in these systems offers voltage indication to personnel in the event the generator is energized during maintenance. 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.
Identifies Even One Phase That’s Live
Occasionally isolators (disconnect switches and circuit breakers) fail and will weld the isolator blade(s) in the ON position, thereby leaving other phase(s) live. This is highly dangerous for an electrician, because the panel may look dead, but still has a live phase(s). In this case, a voltage warning indicator needs to warn electricians if there is power just on one phase. This hazardous situation, affirms that the VI needs redundancy and exceptional reliability.
Added Safety for LOTO Procedures (See Appendix A for detailed analysis)
Safe work practices still demand testing for the absence of voltage with a voltmeter using the traditional “Live-Dead-Live” verification procedure as detailed in the NFPA 70E Annex G. However, with a VI integral to this procedure, consider the following added safety benefits:
· Provides immediate safety information before the LOTO procedure begins, such as a blown fuse, phase failure, or stored energy.
· Reliable voltage indication because a VI has only one purpose: Indicate voltage.
· A VI is not a portable device so it is less susceptible to damage.
· A VI is permanently wired, tested and validated to all 3 phases (for a typical wye-delta system).
· With correct installation, a VI is always referenced to “safe” earth ground.
· No maintenance and no batteries.
· Redundant circuit design and high surge immunity.
· Can be applied for certain mechanical LOTO not covered under NFPA 70E.
Reduced Arc Flash Risk
The probability of an arc flash explosion increases when an electrician uses a voltmeter to check for absence of voltage between phases and/or ground. Employing a VI as part of the LOTO procedure greatly increases the probability that the panel is truly dead before opening the panel door. In other words, reduced arc flash because the electrician uses his voltmeter to verify that the dead panel is dead, and not that the live panel is dead. Remember—no voltage, no arc flash.
Once electricians open the disconnect and enter the panel, they must first verify isolation with their meter. This task is done as though the panel is ‘presumed live’ and requires electricians to suit up in proper PPE. With a VI on the panel exterior, electricians can sees it flashing indicating live voltage. The indicator stops flashing, once the disconnect is open, thereby pre-verifying that the panel is dead before it is opened by the electrician.
Conclusion
“Is there voltage?” and “How can we help insure that an electrician knows it?” Voltage is the single mitigating factor to electrical safety. Installing a permanently wired VI will increase safety because it supplements the electrician’s voltmeter. One user said, “We haven’t had a single electrical accident since we started using [voltage warning indicators].” Lastly, the presence of voltage determines if an electrical accident can occur--No voltage, no accident. Therefore, the ability to ‘see’ electricity with a voltage warning indicator will increase safety and help reduce electrical fatalities.
Philip Allen is the President and Owner of Grace Engineered Products, Inc. www.grace-eng.com and can be contacted at philallen@grace-eng.com
October, 2005
