Integrating electrical safety with design
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.
Functional and operational considerations
Designing an electrical system for a facility requires several considerations in order to make the electrical system functional, address the operations of the facility from a production and safety standpoint, and make it cost-effective. This includes how the electrical equipment is maintained, operated, and modified. Another important consideration would be continuity of electrical power service. This could include the facility’s tolerance to power shutdowns and interruptions in service, and frequency of modifications to the electrical system to support company operations.
Continuity of service: A primary concern of many facilities is providing an uninterrupted source of electrical power to the entire facility. The designer should solicit input from the operations and maintenance groups to understand the critical functions that must be protected from scheduled and/or unscheduled power outages. Under the OSHA general industry rules, infeasibility is not justified based on economic considerations such as production schedules, interrupting a manufacturing process, or data processing operations. The feeders and branch circuits of a facility’s electrical system may require additional design steps to maintain continuity of service and provide worker safety.
Maintenance: Workers that maintain electrical systems encounter electrical exposures on a daily basis in the course of their work. A review of their assigned work tasks could lead to enhanced design to eliminate or minimize the worker’s exposure. The properly designed electrical system could provide increased safety with a minimum amount of interruption to the operation of the facility.
If a company performs infrared testing on electrical equipment as part of a preventive maintenance program, specifying and installing site window(s) on the equipment to perform the infrared task is a cost-effective design consideration. This site window would remove the hazard to the worker. This would also reduce maintenance time for removing covers and wearing electrical PPE. If installing site windows is not a practical solution, specifying hinged covers on electrical panelboards versus bolted covers is another consideration. The worker would still require the electrical PPE to open the cover, but it would reduce the potential exposure to an arc flash.
Modifications and additions
Modifications and additions to electrical systems and equipment are a major obstacle to the operation of a facility. Taking a proactive approach to consider the operation of the facility and taking steps to design the electrical hazards out of the work task could result in actual cost savings for operations and increased safety for the worker.
Some facilities have production equipment that requires the equipment’s computer program to be modified to accommodate production processes. To reprogram or modify a program requires opening the control panel door, exposing the worker to electrical hazards. A resolution to this hazard is to relocate the computer port to the exterior of the control panel. This would permit the equipment to be programmed by the worker without wearing electrical PPE and without specialized electrical safety training, thus eliminating the worker’s exposure to a hazard.
Another design technique to facilitate maintenance, repair, and electrical installation is to install an overprotection protective device adjacent to or upstream of the power or control panel. This changes the design specification from a main circuit breaker type panel to a main lug only panel. This provides the capability for the worker to disconnect power to the power or control panel, providing a safe environment to make modifications on install new circuitry or components. It also is cost effective and facilitates a lockout/tagout procedure.
An installation technique that provides both safety and efficiency is to incorporate the use of wireways with electrical power and control panel installations. This design concept provides numerous benefits to the facility for both efficiency and safety. Figure 3 shows a typical design that could be used. The basic design would be to install the power of control panels as shown. The wireway would be installed above the panelboard at a distance not to exceed 24 in. Conduit nipples would be installed between the power or control panels to facilitate installing the conductors into the electrical panel. These conduits would be of an adequate size to accommodate the installation of the number and size of the wires to the power panel. Limiting the length of the conduit nipples to 24 in. between the wireway and the panel(s) would permit the installation of a large number of conductors without having to de-rate them. This is permitted in section 310.15(B)(3)(a)(2) of the 2011 NEC. The space above the wireway would be used to run the individual feeder or branch circuit cables or conductors and conduit to feed substation equipment.
The most significant benefit of using wireways is after the electrical system has been commissioned and energized. When an additional feeder or branch circuit has to be installed, the worker can remove the wireway cover and ensure that there is adequate clearance to enter the conduit or cable in the top of the wireway with the equipment energized. The worker can then install the cable or conduit, and pull in the wire from the equipment to the wireway, leaving the conductors long enough to be installed and terminated in the panel. The worker can then schedule an outage and make the final terminations of the conductors. This would minimize the disruption to the continuity of service for the facility.
This design technique could also be used for data centers. If the installation has a raised floor, the wireway would be located in the plenum space below the raised floor. Many data installations are designed with an ample amount of spare circuit capacity in the power distribution units (PDU). If the majority of the circuits in the PDUs are 120 V/20-amp circuits, it provides an opportunity to proactively prewire the PDU. The strategy would be to install the spare branch circuit wiring from the PDUs to the wireway. The conductors would be marked in the wireway and designated as a spare circuit on the panel directory. The ends of the conductors in the wireway would be made electrically safe.
When an additional circuit is required in the data center, the worker would remove the cover, ensure that there is adequate clearance to enter the conduit or cable in the wireway, and install the branch circuit to the substation equipment. The worker would then determine spare circuit number in the PDU that would be used. The applicable circuit breaker could be locked out and verified, de-energizing the circuit in the wireway. The conductors in the wireway could then be re-energized. The entire task can be performed with no interruption to the operation and electrical power in the data center. It also prevents the worker from being exposed to electrical hazards.
Electrical product design
U.S. electrical product specifications are developed in correlation with the NEC. While this can permit a safe electrical installation, it may not address worker safety issues when equipment has to be accessed or maintained after it is commissioned. While product standards are designed to provide guarding from electrical shock, in most cases they may not provide adequate safety from arc flash and arc blast. Once a cover or panel trim is removed, the equipment is not in compliance with the product standards and the worker could be exposed to electrical hazard.
Electrical distribution equipment could be designed to isolate sections of the equipment in order to permit work on them without exposure to electrical hazards. Consider, for example, an electrical power panelboard. Typically, the main circuit breaker is unguarded and is located in the same compartment as the branch circuit breakers and wiring. If a listed and labeled design were approved so that the panel cover could be removed and be classified as de-energized with the main breaker in the panelboard locked out (see Figure 4), it would permit modifications and additions to the electrical panel in accordance with OSHA regulations. This would be an exceptional benefit for the residential market.
OSHA enforcement regulations forbid compliance officers from approving products or installations. They have to conduct inspections and review products in accordance with their listing and labeling. In the case of a residential panelboard, if there is electrical power on the line side of the main circuit breaker and the main breaker is in the off position, the panelboard is still classified as the worker could be exposed to live parts. Under the listing and labeling criteria, the employer would have to demonstrate that the equipment would be listed and labeled with live power inside and the cover removed. The manufacturers require all trims and covers be installed when there is power above 50 V present. The trims and covers act as guarding from live parts.
The past 20 years have seen a marked evolution in the electrical industry’s awareness of electrical safety issues and increased requirements for electrical safety-related work practices. Building inherently safe design into electrical products for maintenance and modification as well as installation purposes is the next step.
Engineers can design the hazard out of work tasks by specifying electrical products that have enhanced safety features, by specifying products that address both design requirements and operation of the facility, and by incorporating improved installation techniques is a strategy that will not only increase worker safety, but also increase productivity and profits.
Kenneth Mastrullo is president of MES Consulting Services. His many years in the electrical construction industry include: 7 years in OSHA’s New England Regional Office (Region I Electrical Technical Expert), 6 years in the NFPA (Secretary, NFPA 70E Electrical Workplace Safety), and 11 years as a facilities engineer.