Integrating electrical safety with design
Integrating maintenance requirements into the design of an electrical system is an important first step to provide workplace safety.
By Kenneth Mastrullo, MES Consulting Services Inc., Weymouth, Mass.
Safety-related maintenance requirements for electrical equipment are outlined in Chapter 2 of NFPA 70E: Standard for Electrical Safety in the Workplace, but they are often overlooked to the detriment of both worker safety and a company's reputation. Using the concepts and strategies in Chapter 2 can enhance the company’s worker safety, productivity, and positive image.
Integrating maintenance requirements into the design of an electrical system is an important first step to provide workplace safety. There are two elements that comprise maintenance tasks at a facility: technical expertise and safety considerations. Chapter 2 provides a great foundation to understand the fundamentals of what every company requires to operate and maintain the electrical system in a safe manner after it has been commissioned. Lack of proper maintenance could not only affect the operation of production at a facility, it could have a catastrophic effect for worker.
In difficult economic times it is common to eliminate or decrease the frequency intervals of preventive maintenance for electrical systems. However, lack of adequate maintenance often results in the failure of overcurrent protection devices to operate within the prescribed range for opening. An elongated opening time, which can be measured in a few tenths of a second, can have a significant difference in the arc flash exposure to a worker. The idea is that the calculations assumes a certain opening time, if the device fails to operate in that time, then the arc flash study/values are incorrect, and the worker may not have the proper personal protective equipment (PPE). If the worker is not protected for the magnitude of the exposure, it could result in a significant injury or death.
An example of what can happen when electrical equipment is not properly maintained occurred in 2010. In this case the electrical equipment was installed in the 1970s and was never maintained, calibrated, or exercised. When the arc flash occurred, the main breaker in the switchboard did not trip. The circuit eventually opened at a fuse located on the primary side of the site transformer. This is an example of the difference in magnitudes that could result in an actual event compared to what could be anticipated using the NFPA 70E tables or arc flash calculations. The difference in actual and anticipated tripping time of the overcurrent protection device due to failure to maintain equipment resulted in an exposure to the worker of 15 Cal/cm2. A typical protective worker strategy for this installation would be Category 2 in accordance with Table 130.7(C)(15)(a) of NFPA 70E. This would require 8 Cal/cm2 outer layer arc rated clothing with 100% cotton underlayers.
Understanding the regulatory framework
Both the safety and the efficiency of electrical equipment maintenance and modifications can be greatly enhanced if equipment systems were designed to facilitate the use of safe work practices under both Occupational Safety and Health Administration (OSHA) regulations and NFPA 70E during maintenance and modifications. That is why an understanding of the regulatory framework and the interplay between OSHA's electrical safety regulations, NFPA 70 (National Electrical Code, NEC), and NFPA 70E should be basic to design, installation, and maintenance of electrical equipment.
OSHA regulations are federal and are the law nationwide. Historically, OSHA's electrical safety regulations have drawn heavily on the NEC and NFPA 70E, but there are important distinctions. Compliance with the NEC and 70E does not always equate to compliance with the OSHA regulations.
When designing electrical systems, there are two different considerations: installation, and maintenance and modifications after the equipment is commissioned.
With regard to installations of electrical equipment, there is a long and successful history of equipment that permits a safe installation for persons and property if performed in accordance with the overlapping OSHA regulations that cover installations. U.S. electrical product specifications are developed in correlation with the NEC, which has led to this success. OSHA's electrical construction regulations (29 CFR 1926, Subpart K) apply to new electrical installations. This could be classified as any addition, enhancement, or upgrade to an electrical system. Examples could include a new electrical system, adding a feeder or branch circuit to an existing power panel, or adding components in an existing control panel.
As to maintenance and modifications of already installed electrical equipment, it must be emphasized that all OSHA regulations are based on the task that the worker performs, rather than the worker's job title or the classification of the company he/she works for. Overlapping but different regulations apply to the construction industry (29 CFR 1926) versus general industry (29 CFR 1910). Determining whether OSHA's construction or general industry regulations apply is not always as simple as it sounds. For example, when a maintenance worker employed at an existing facility adds a feeder or branch circuit for a new piece of electrical equipment, the task would be classified as a construction activity and would be covered under the requirements of OSHA's construction regulations (because it's an installation). Another example: When the employee of a construction company is changing defective lighting ballast on an existing fixture, it would fall under the general industry standard (because it is maintenance).
Most of the electrical safety-related work training that is currently given to workers is based on NFPA 70E, rather than the applicable OSHA electrical regulations. The energized work wording in NFPA 70E differs from OSHA's general industry electrical regulations, creating some misinterpretations of whether the job task is permitted to be performed live at a worksite.
It is critical to remember that any place where OSHA regulations set a more stringent rule than NFPA, the OSHA regulations must take precedence. As federal regulations, they have the force of law.
For example, Section 29 CFR 1926.416(a) of the OSHA electrical construction regulations says:
No employer shall permit an employee to work in such proximity to any part of an electric power circuit that the employee could contact the electric power circuit in the course of work, unless the employee is protected against electric shock by de-energizing the circuit and grounding it or by guarding it effectively by insulation or other means.
This regulation does not contain any exception, for example, for infeasibility to perform a task. Note that this regulation was promulgated in the 1980s, before arc flash was recognized as a hazard in the industry. Of course, from a practical aspect, you would have to de-energize the equipment to attempt to install what would "[guard] it effectively." If that were the case, you could perform the task while the equipment is de-energized.
Some design criteria involve the use of a technique called “finger safe.” The finger safe concept is used with the intent of protecting a worker from electrical shock by enclosing/isolating exposed parts. However, it may not protect the worker from all recognized electrical hazards in a piece of electrical equipment. There are two issues with this concept. When the equipment cover is removed or the equipment door is open, it would not comply with the listing requirements of the product. Additionally, finger safe design would not protect the worker from an arc flash or arc blast.