Electrical Safety -- Don't Be Shocked!
One challenge that's got many electricians, safety trainers, and frontline workers confused is the definition of low voltage. Another question regards the difference between alternating current (AC) and direct current (DC) in terms of the risk of shock and/or electrocution. These two areas are linked, since the potential of shock from low-voltage, both AC and DC, is dependent on the amperage involved.
In one case, a computer industry client had low voltage direct current exposures to exposed terminal strips on devices on racks under test. The equipment normally operated at 48VDC, but many had variable capacity to operate between 48-73VDC. The devices were changed out frequently as testing was completed. Some of the equipment came with terminal covers, which were frequently left off. Note that the engineers did not work on live circuits. Any exposure to these terminals was incidental, when walking between the rows of racks or when installing a new unit for testing. Monthly facility inspections lead to the discovery of many exposed terminals. Two questions arose:
- Were these exposed terminals regulated if operated at no more than 48VDC?
- Was there a potential risk since the exposures were direct current, and not alternating current?
"Low-voltage" is not specifically defined in OSHA regulations for electrical safety, although there are references to requirements related to "50 volts or more," such as 1910.303(g)(2)(i) for guarding of live parts, which states that "live parts of electric equipment operating at 50 volts or more shall be guarded against accidental contact".
Another regulation covering the use of work practices and specifically deenergizing parts (§1910.333(a)(1)) states "Live parts that operate at less than 50 volts to ground need not be deenergized if there will be no increased exposure to electrical burns or to explosion due to electric arcs."
The training requirements specified in 1910.322 include a table (Table S-4) of typical at-risk occupations, with the footnote, Workers in these groups (all except electricians and welders) do not need to be trained if their work or the work of those they supervise does not bring them or the employees they supervise close enough to exposed parts of electric circuits operating at 50 volts or more to ground for a hazard to exist."
There are also frequent references in the OSHA regulations and elsewhere that refer to high-voltage as being anything greater than 600 volts. The National Electrical Code (NEC) does cover installations operating at less than 50 volts, including both DC and AC.
Overall, these references seem to imply that the regulatory ranges are as follows: >600 volts = high voltage; 50 – 600 volts is low voltage; and <50 volts (sometimes referred to as "extra-low voltage") is generally not regulated except by NEC.
Direct Current vs. Alternating Current
Is there a different risk when working with direct current as opposed to alternating current at the same voltage? Research indicates that direct current (DC) is more likely to "freeze" a victim in a shock scenario, but the victim is more likely to recover afterwards. This is one reason that automatic defibrillating devices (AEDs) operate using DC power to halt fibrillation and then give the heart a chance to recover.
Alternating current (AC) is more likely to cause a heart fibrillation, which is a more dangerous condition for the victim after the shocking current has been halted. The fluctuating AC current is less likely to cause the "freeze" effect. Exposure to both types of current poses risks, albeit different, and both should be avoided. In both cases, the level of risk depends on the amperage of the circuits. Higher amps equal higher risk.
These issues present ongoing problems for many electricians. A combination of training and work practices will safeguard potentially exposed employees, especially those engineers directly involved in the installation and testing process.
Site-specific training should address:
- General electrical safety topics
- OSHA applicability and applications for both AC and DC current
- Types of exposure and methods to reduce the exposures
- The effects of amperage on electrical shock involving low voltage
- Proper grounding techniques
- Daisy-chaining (plugging one extension cord or power strip into another), which can overload wiring
- Site specific issues and solutions for exposed terminals
- OSHA requirements for "qualified persons."
The best approach is to understand both actual risks and potential risks based on your specific situation. OSHA regulations and NEC guidance provide dependable methods for determining work practices. These include:
- Regular site inspections of areas and processes prone to electrical risk
- Site- and process-specific procedures, or SOPs, that require employees to safeguard the equipment being worked on
- Proper wiring and grounding methods, including wire sizing, use of ground fault circuit interrupters
- Installation of guards to ensure inadvertent exposures
- Use of approved cabinets and enclosures
- Proper use of flexible cords and power strips
- Installation of required signage for guarded locations. OSHA has stated that entrances to rooms and other guarded locations containing exposed live parts must be marked with conspicuous warning signs forbidding unqualified persons to enter.
- Application of equipment labels
Through diligence, persistence, and follow-up inspections, my client's exposed terminal problem has decreased dramatically.
Application of these work practices and development of an electrical safety and LOTO program will help employees avoid injuries, shock, and electrocution.
Chuck Paulausky, CP Safety & Environmental, is a Certified Hazardous Materials Manager. He has worked as an Environmental, Health & Safety professional for more than 24 years, providing EH&S management and compliance services for manufacturing facilities in Arizona, Texas, Utah, California, Europe, and Asia. For more information, visit www.cpsafety.net.
Jack Rubinger, Graphic Products, contributes to industrial safety blogs and publications worldwide. Graphic Product is the global leader in workplace labeling and signage. For more information about electrical safety and industrial labeling systems, visit www.GraphicProducts.com or email [email protected].
Posted by Chuck Paulausky, Jack Rubinger on May 02, 2014