Article 700 is the first in a series of NEC Articles about on-site power systems, including 700, 701, 702, 705, and 708. Each covers a different kind of system, differentiated by mission. The systems/missions include legally required systems, optional standby systems, and backup systems. All of these (except backup systems) are defined in Articles 701 and 702. The definition of a backup system depends on what you’re backing up.
What about emergency systems? Such a system is actually a special case of Art. 701 (legally required) systems. In addition to being legally required, they are classed as emergency systems by the authority having jurisdiction (AHJ). That authority might be the state codes or an agency [700.1].
Emergency systems serve a specific function. They protect human life by providing the essential power and illumination [700.1] for egress and for the operation of emergency-related equipment, such as ventilation, fire pumps, and communication systems. For this reason, you find them at hospitals (Photo 1 and Photo 2).
Emergency systems may provide power to elevators so people riding in them aren’t stuck when an event occurs. This doesn’t mean people can keep riding up and down in the elevators. Typically, the elevator control system automatically sends elevator cars to predetermined locations so the people riding them when the interruption occurs can safely reach emergency exits. These systems might continue operating so first responders can use the elevators rather than lug equipment up flights of stairs. The exact control scheme depends upon many factors, including local codes.
Size its supply to support emergency loads and other permissible loads [700.4] (those being legally required and optional standby loads).
Testing
Reliability is a key characteristic of emergency systems. For this reason, these systems must be witness-tested upon installation (and periodically afterward) [700.3]. The NEC doesn’t define this testing, and it doesn’t need to.
Each subsystem (e.g., generator, transformer) of the emergency system has its own applicable industry standards for installation and testing. The “witness” part means a third-party inspector (not the testing firm) observes the testing before signing off on it. Contact the AHJ to determine who this person can be and what documentation is required. That documentation will include such items as test equipment calibration reports, not just documentation of the actual system tests.
Obtain all of the applicable installation and testing standards well in advance, so you can properly design the witness testing program. If you wait until the installation begins, you’ll probably take a major scheduling hit.
Get it in writing
While the NEC is silent on the particulars of the acceptance tests or witness tests, it isn’t silent on documenting those tests. It requires a written record of all tests and maintenance [700.3(D)]. At one time, “written” meant ink on paper. Things have changed, however. The term “written” has always meant “entered into your information system.” But today, those systems are almost never paper.
Despite the wording, the NEC allows for the fact that we computerize our data today. One advantage inherent in paper is you have an audit trail. Make sure that advantage exists in your computerized data system also.
Bypass
You may provide a means to bypass and isolate the transfer equipment [700.5(B)]. This is beneficial for several reasons, including the ability to perform testing and maintenance without taking the emergency system offline. With a bypass, only automatic operation is offline. This poses another problem. What if the maintenance team forgets to put the system back online after conducting maintenance? Administratively, you can add a verification process in your maintenance procedures to prevent this.
Here’s one way it’s done. The lead tech must “sign out” the system for a specified period (e.g., two hours) to conduct maintenance. An operator puts the system in bypass. The operator returns near the end of the period to put it back in automatic while the tech watches. They both return to the operations desk to sign the system back in.
In power plants, status monitors show whether the system is in auto or manual. Power plants also have people assigned to monitor the status monitors. If you order a system with status monitors — and the facility doesn’t have a staffed operations room like that of a power plant — today’s technology provides a solution: the responsible party gets a notification, such as an SMS.
This problem and its solutions aren’t covered by the NEC, but having a bypass that can inadvertently be left in bypass mode defeats the purpose of having an emergency system. Also make sure the bypass doesn’t inadvertently kick the system into parallel operation [700.5(B)].
Alarming
Ensure the system provides at least the minimum requirements for visual and audio indication [700.6]. At a minimum, you need indicators to show:
• Derangement.
• Whether the battery system is carrying the load.
• If the battery charger isn’t functioning.
• If there’s a ground fault.
Well-designed packaged systems easily beat the minimum requirements for alarms and signal devices. Look into a packaged system before deciding to “roll your own.” You can, and probably should, get much more than the NEC minimums.
Think through your response strategy, and make the design support that. For example, instead of just local alarms, your system sends a text message to the plant manager, plant engineer, facilities manager, and production superintendent when Event X happens.
It’s important to locate ground faults quickly. But doing so can tie up maintenance personnel so other failures go unmet. One solution is to pre-arrange a response with a local contractor that is equipped to quickly locate and repair such faults. Your system sends a text message to the contractor, a designated plant electrician, and the plant engineer simultaneously. The plant engineer coordinates with production and other parties while the cavalry is on its way.
If the facility doesn’t have its own maintenance staff and a plant engineer, making these advance arrangements is even more critical. The facilities manager should have a response properly planned and contracted. When a fault occurs, it won’t trigger several hours of panic.
Marking
If equipment is part of the emergency system, mark it as such [700.10(A)]. That includes all boxes, enclosures, panels, transfer switches, and generators. Basically, if a piece of equipment is on the emergency system drawings, give it a permanent label saying it’s part of the emergency system. Mark the raceway, too.
One reason to mark all of these items is to help prevent mixing other system wiring or equipment in with the emergency system power wiring and equipment [700.10(B)]. There are five common-sense exceptions to this [listed in 700.10(B)].
Source it
The emergency system must have a power source in case the normal supply is lost [700.12]. Otherwise, it’s not going to be there when you need it! The requirements for this power source are in Part III. The NEC permits five classes of power source:
• Storage battery [700.12(A)]. These must meet specific requirements but are usually the lowest-cost solution.
• Generator set (gen-set) [700.12(B)]. This won’t work without also having storage batteries for ride-through while the generator comes up to power.
• Uninterruptible power supply (UPS) [700.12(C)]. These must comply with the requirements for batteries [700.12(A)]. Also with the requirements for gen-sets [700.12(B)] if the system has a gen-set. The UPS must have separate service conductors.
• Fuel cell system [700.12(E)]. Among the requirements are the fuel cell can’t serve the emergency system if it also is the normal power supply (add a separate fuel cell for that).
• Unit equipment [700.12(F)]. This includes items such as battery-powered exit lights.
Other requirements
You’ll find special requirements for lighting and power in Part IV, control of lighting circuits in Part V, and overcurrent protection in Part VI. A key theme in the lighting requirements is you must arrange the system such that only authorized personnel have control of emergency lighting, and you can’t make that control difficult for them.
The 2014 NEC added a clarifying paragraph for the selective coordination requirements. It’s no longer a DIY for the plant electrician. Now, it must be done by a licensed professional engineer or other qualified person [700.28].
No emergency here, boss
The whole point of an emergency system is to prevent corollary emergencies when a major event happens. If there’s a fire, first responders have enough on their plate without also having to free people from elevators that lost power — nor do they have time to hunt for people who couldn’t find their way out in the dark.
Complying with the NEC minimums is only part of what must be done to provide a reliable emergency system. Make sure that system reliably supports your emergency response plans.
Lamendola is an electrical consultant located in Merriam, Kan. He can be reached at [email protected].
