National Electrical Code Explanations

Based on the 2020 NEC

by Mark Lamendola

National Electrical Code Tips: Article 700, Emergency Systems

People sometimes confuse emergency systems with other systems that aren't the main operational systems. These include legally required systems, 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 Emergency Systems. As noted, those are covered by the NEC, Article 700.

Let's address some highlights of the Article 700 requirements:

  1. These systems are actually a special case of Article 701 (legally required) systems. In addition to being legally required, they are classed as emergency systems by the authority having jurisdiction. That authority might be the state codes or it might be an agency [700.2].
  2. The purpose of an emergency system is to protect human life by providing the essential power and illumination [700.2] for egress and the operation of equipment such as ventilation, elevators, fire pumps, and communication systems.
  3. All of these systems must be witness-tested upon installation (and periodically afterward) [700.3(A)]. 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 [700.3(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 an emergency system, not a standby power system. Remember the mission, and select the supported loads accordingly. Size the system to support those loads [700.4].
  5. You must provide a means to bypass and isolate the transfer equipment [700.5(B)].
  6. Ensure the system provides at least the minimum requirements for visual and audio indicating feedback [700.6]. Packaged systems typically come with the proper alarms and signal devices, so look into a packaged system before deciding to "roll your own." At a minimum, you need visual and audio indicators to show derangement, whether the battery system is carrying the load, if the battery charger isn't functioning, and if there's a ground fault. You can get much more, and usually it's well-worth exceeding the NEC minimums.

    As an example, instead of just local alarms you can have the system send a text message to the plant manager, the plant engineer, the facilities manager, and the production superintendent when Event X happens. In the case of a ground fault, why not have a pre-arranged response set up with a local contractor that is equipped to quickly locate and detect such faults? Your system can send a text message to the contractor, the lead electrician, and the plant engineer simultaneously. If the facility has an ungrounded (floating) system, clearing that fault ASAP is vital. That's because if you get a second fault, it will be phase to phase and that typically means a massive arc blast. Ungrounded systems are outdated for this reason. Consider converting your system to a high impedance ground; you still get the continued operation in the event of one fault, but you don't get an arc blast in the event of a second.
  7. If it's 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, make sure it has a permanent label saying it's part of the emergency system. Mark the raceway, too.
  8. Don't mix other system wiring or equipment in with the emergency system equipment [700.10(B)]. There are five common-sense exceptions to this (listed in 700.10(B)].
  9. The emergency system must have a power source in the event of the loss of the normal supply [700.12]. Else, it's not going to be there when you need it! The requirements for this are in Part III.
  10. You will find special requirements for lighting and power in Part IV, control of lighting circuits in Part V, and overcurrent protection in Part VI.