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National Electrical Code Explanations

Based on the 2020 NEC

by Mark Lamendola

National Electrical Code Tips: Article 701, Legally Required Standby Systems

People sometimes confuse emergency systems with other systems that aren't the main operational systems. These include legally required systems (the subject of this article), optional standby systems, and backup systems. All of these except backup systems are defined in the NEC Chapter 7 Articles 701 and 702, respectively. The definition of a backup system depends on what you're backing up. Is it backup power? Data backup? Some other type?

Our focus here is on Legally Required Standby Systems. As noted, those are covered by the NEC, Article 701.

Let's address some highlights of the Article 701 requirements:

  1. As the name implies, these systems are not optional; they are legally required. But by whom? By any governmental agency having jurisdiction; that can be state, city, county, or federal. They can also be required by the particular codes adopted by those entities. Additionally, the facility's insurer may require similar systems for the same reasons (e.g. to protect the public), but since the insurer isn't a government entity those systems are classified as "optional" (Article 702) even though the reality is the facility owners have to comply. The fact these are "legally" required just means it's a legal (government) entity that's requiring these.

    In addition to being legally required, they are classed as standby systems by the Authority Having Jurisdiction (AHJ). As with our earlier observation, that authority might be the state codes or it might be an agency [701.2].
  2. The purpose of a legally required standby system is to provide power and/or illumination [701.2] when the normal supply of electricity is interrupted. This doesn't mean emergency power for egress, it means power for continuing operations (those operations may be all of the operations at a facility or only specific ones, depending on what the AHJ specifies). The motivation for standby power is typically to protect those inside the facility (a hospital being a prime example). It may be something else, such as to keep critical operations (e.g., a sewage plant) running. In some cases, the city that grants the business license mandates that the facility have standby power to prevent the loss of jobs that would occur in the event the facility lost its main power source and suffered huge financial losses as a result (a glass plant is a good example). The actual motivation isn't the key; the fact that a government entity mandates the system is.
  3. All of these systems must be witness-tested upon installation (and periodically afterward) [701.3]. While the NEC doesn't define what this testing is, industry standards exist; the insurance company and the AHJ should insist the tests comply with these standards. So obtain the applicable installation and testing standards before beginning the installation. Also, the NEC does require a written record of all tests and maintenance [701.3(D)]. The word "written" these days pretty much means you're keeping the records in a CMMS or other computer-based system. Hand-written records are not required, despite the wording, because any competitive company has moved beyond such things and the NEC allows for that. Just make sure there's an audit trail.
  4. It's a legally required standby power system, not an emergency system. And it certainly is not a "regular" backup power system for non-essential loads. Remember the mission, and select the supported loads accordingly. Size the system to support those loads [701.4]. With an emergency system, you are going to select "essential" loads, meaning those needed to get people safely out of the building and those needed to keep processes from creating additional danger by running amok. With a legally required standby power system, the total load is nearly always much greater because generally the standby power is going to replace the normal power in the event normal power is lost; at least for identified loads.

    In a hospital, for example, you might have some load shedding of non-essential loads like the decorative fountain out front and some lighting on a selective basis. But quite often, standby power systems simply kick in to support the total existing load. Always assume that's the case, unless there is a specific load shedding scheme that is automatically implemented upon loss of main power.
  5. With emergency systems, you must provide a means to bypass and isolate the transfer equipment [700.5(B)]. But with legally required standby power, this provision is permitted rather than required [701.5(B)]. Whether you use it or not depends upon several operational parameters and engineering decisions.
  6. Ensure the system provides at least the minimum requirements for visual and audio indicating feedback [701.6]. Packaged systems from a single manufacturer come with the proper alarms and signal devices, so look into a packaged system rather than cobbling together something from various parts. These systems begin as standard designs for your type of application, and then are are engineered for your specific application; for that reason, they usually exceed the NEC minimums. Don't get caught up in cost-reduction games that involve design degradation based on a "what can we get by with" mentality. Instead, ask the question, "How can we ensure the standby system will reliably support the load and that the transfer never fails?"

    This approach also ensures your company can withstand any legal challenges in the unfortunate event that something actually does fail. Simply saying you met Code doesn't stand as a defense to the expert witness' testimony that you failed to consider operational and engineering considerations to ensure the system met the intended purpose.

  7. You can mix other system wiring or equipment in with the standby system equipment [701.10(B)]. However, the NEC does not require you to mix other system wiring and equipment in with optional standby system equipment. You may choose to keep them separate for the same reasons they are required to be kept separate when it's an emergency system [700] being installed. One consideration is your tolerance for damage to the optional standby system if work (maintenance, upgrades, etc.) is done on one of these other systems. For example, someone lifts a neutral or opens a bonding connection; do you want that to possibly affect your system?
  8. The standby system must have alternate power within 60 seconds of the loss of the normal supply [701.12]. The requirements for the various types of alternate power sources are in Part III.
  9. The branch circuit overcurrent protection devices for these systems must not be accessible by unauthorized personnel [ 701.30]. A good way to apply this requirement is to use separate panels for standby power and keep them locked.
  10. Selective coordination of the overcurrent protection devices is required [701.32]. Now, remember that these are legally required standby systems. That creates a higher standard for selective coordination than simply forcing the field electricians to interpret the installation drawings and try to do this ad hoc. Make sure you commission a selective coordination study as part of the design process. The 2014 NEC added an entire paragraph addressing this issue, and that extra text is still there in this revision.