Meeting the challenge of electrical system protection
Certain requirements in the 2005 National Electric Code have electrical engineers throughout the country scrambling to design emergency and legally required standby systems in aging buildings affordably and efficiently. Sections 517.26, 700.18, and 701.27 were added as part of the 2005 NEC and require selectively coordinated design of these essential systems’ overcurrent protective devices in both new construction and renovated structures. While such a system is relatively easy to design conceptually, implementing it into an existing hospital or healthcare facility with often antiquated equipment can be a logistical and economical headache.
In any new or existing building, a series of overcurrent protective devices are organized in a descending fashion, leading from the main distribution system all the way down to the branch circuit that feeds the load, such as overhead lighting or electrical wall outlets. In a preferred scenario, these overcurrent protective devices are specified such that the device closest to, and ahead of, the fault will open first, keeping the remaining portions of the distribution system operational.
The “selective coordination” code makes sense—its aim is to minimize the impact of a short circuit to a system fault event and keep it from disrupting the entire distribution system, thus hampering a healthcare facility's ability to function. However, in older buildings, existing electrical systems are not always so accommodating toward accomplishing this goal. Renovations, tenant improvements, additions, and space reconfigurations over the years frequently result in uncoordinated systems. Some systems are very old and utilize circuit breakers that do not have adjustable trip capabilities, as these systems were designed with load flow, short circuit bracing, and the ability to isolate the smallest blocks of load possible in mind.
In these cases, compliance with the selective coordination requirements often means detailed engineering investigations and additional electrical work beyond the initial budgeted scope of work. Owners are realizing that what they thought would be a straightforward tenant improvement to a few offices or patient rooms could end up requiring a time-consuming selective coordination study, creation of additional space to house new, larger pieces of electrical equipment, the purchase of costly new transformers and breakers, and use of fuses and fewer levels of distribution.
Selective coordination studies also become expensive because they require the design engineer to model how a distribution system responds to a fault current condition by selecting the exact type, configuration, and accessories for each overcurrent protective device in the system. To put this in perspective, the budget to complete a comprehensive study for a recently completed 45,000-square-foot college classroom facility was $14,000. Clearly, costs can quickly spiral out of control.
Open for interpretation
Depending on the geographical location of the facility, the NEC codes are interpreted in a number of different ways. It's up to the agency overseeing the electrical work to use the NEC code as a guideline, applying the code as it deems appropriate. Some “authorities having jurisdiction,” or AHJs, have “grandfathered” existing facilities, excusing them from compliance with the NEC's selective coordination requirements. Others are following the code to a certain degree, requiring a system to be selectively coordinated one level back from the load. Still other jurisdictions, however, are sticking to the letter of the law, requiring full compliance even among antiquated systems despite additional costs, extended schedules, and questionable benefits.
The Portland, Oregon, office of electrical engineering and technology consulting firm Sparling has been faced with an unbending AHJ in the case of a 200,000-square-foot, complete campus renovation at a healthcare facility in Eugene, Oregon. The aging structure's electrical systems must comply with the current NEC's selective coordination codes, requiring Sparling to perform a detailed study to determine the extent of work to be done. This has entailed a thorough and detailed site investigation of the entire electrical system that will remain in the building and identification of existing equipment interrupting ratings.
Designers have also provided a design of new and existing systems to meet the plan for the buildings and performed short-circuit calculations for all branches of the emergency system. This included selectively coordinating existing equipment with added equipment. While much of this effort would be part of a normal design process, the added professional fees of modeling the entire essential distribution system and reconfiguring the entire essential system has proved to be a cost burden to the project.
For reasons such as these, many in the design community question the need for complete selective coordination. While most everyone agrees that minimizing the impact of a short circuit to the operation of a facility is essential to protecting human life, mandating selective coordination and completely removing engineering judgment from the process can be more detrimental to the distribution system than an uncoordinated system. By allowing fuses to play a more significant role in the electrical distribution system, are we hindering or helping the reliability of the system? By minimizing the number of overcurrent protective devices to selectively coordinate the system, have we improved the reliability, or simply increased the amount of the system impacted by a short circuit?
As electrical engineers consider the impact of selective coordination, a consensus is growing that this is the wrong direction for the NEC, and that this area of design should be returned to engineering judgment. In fact, there have been more than a dozen proposed changes to the 2008 NEC to delete these new requirements or better define them.
Taking the initiative
To ease the burden on its healthcare facility clients, Sparling initiates meetings with the local AHJs early in the design development phase to propose mutually agreeable design solutions. A proposal Sparling recently made to the AHJ overseeing a 20,000-square-foot healthcare facility expansion in Gresham, Oregon, for example, resulted in an equivalent safety design for the building occupants, saving the owner thousands of dollars in potential system study and electrical redesign costs, not to mention valuable program space.
Early, up-front discussions with the owner and architect are also important, so the owner knows what to expect down the road. If an extra 100 square feet may be required for new equipment, the idea is much better received during preliminary designs than in the midst of construction.
Sparling has streamlined the process of approaching AHJs with code change proposals through its use of a jurisdictional matrix that outlines previous projects that have been approved as complying with an alternate version of the selective coordination code. This refreshes the memories of the decision makers and allows for a more streamlined and less complicated decision-making process.
On a higher level, Sparling has helped lead the charge to bring about a change to what is seen by many as a burdensome code restriction. Members of the firm sit on several NEC boards and have joined other electrical engineers in writing numerous articles and essays on the topic.
Despite the electrical engineering community's efforts, it's unlikely that much relief is in sight anytime soon. The changes that were proposed to the 2005 NEC were overturned, and only minor modifications were made to the 2008 code, released this past September.
In the meantime, electrical engineers must continue to address the selective coordination issue with owners and architects, work with local jurisdictions to create a working solution and remain flexible and open-minded during the entire design and construction process. TCV
Kimberly Krull has more than 16 years of electrical design experience in healthcare, medical office building, laboratory, and clinic projects. As a principal of Sparling, she has the unique ability to conceptualize designs and set budgets at the earliest stage of a project. As a LEED-accredited professional, Krull is adept at developing innovative and flexible design solutions to protect and preserve the environment.
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