For large commercial or industrial facilities that may not have windows or those that continue operations during the night shift, a power outage can create a kind of panic that feeds on itself and intensifies when a large crowd experiences sudden darkness — at times prompting serious injuries or even fatalities. That's where emergency lighting comes in. Without it, occupants would have to navigate great distances through rooms filled with obstacles, darkened hallways, and stairs to reach safety.
Emergency power systems are covered in NEC Art. 700, the first article in Chapter 7, Special Conditions. These systems consist of circuits and equipment that supply, distribute, and control electricity for lights, power, or both in required facilities when normal power fails. However, many occupancies require emergency lights only — no other emergency power. Although there's much to be said for a central diesel prime mover with generator plus batteries and an inverter to provide instantaneous response, it's the battery-powered unit box you see everywhere: in restaurants, schools, theaters, and other public places.
While the NEC addresses the details of emergency light installation and wiring, the Life Safety Code (NFPA 101) provides mandatory guidelines for their placement, light output, and in which occupancies they are required.
Section 7.9.1 of the Life Safety Code (LSC) requires emergency lighting along means of egress for buildings where required in Chapters 11 through 42. In other words, if you want to know whether emergency lighting is required, you have to look up the occupancy in question in individual chapters in the LSC, not the NEC. Generally, emergency lighting is required where large numbers of people may be present, such as in hotels, restaurants, theaters, sports arenas, health care facilities, etc. In addition to occupancies requiring emergency lighting because they are cited in the LSC, local building codes may add other occupancies. You wouldn't see emergency lighting in a residence because there are few occupants who are already familiar with the layout of their home.
Emergency lighting is a good example of how the LSC and NEC frequently diverge. Let's take a closer look at the differences now.
Code requirement comparison
The NEC does not discuss emergency light placement, but the LSC says illumination of means of egress shall be provided for every building required in Chapters 11-42. Exit access includes designated stairs, aisles, corridors, ramps, escalators, and passageways leading to an exit. “Designated” means designated by the authority having jurisdiction (AHJ). Light levels are specified by the LSC in terms of lux (10.8 lux equal 1 footcandle).
Where battery systems (including unit equipment) are involved, the NEC says tests shall be performed and written records kept of the results. However, there is neither mention of a specific time interval nor what the test should entail. Unit equipment always has a test button on the side or front panel. This normally on, single-pole switch cuts off incoming AC power to simulate an outage, so you might be tempted to hit the button and — if the emergency light goes on — call it good.
In contrast, the LSC provides a more detailed protocol so if your state or municipality has enacted both codes, you must observe the stricter LSC in this area. It requires:
Functional testing to be performed for 30 seconds at 30-day intervals (Photo 2).
Functional testing to be performed once every 12 months for 1.5 hours, if the system is battery powered.
Written records to be kept on file and made available to the AHJ.
Putting emergency lighting to the test
In some venues, security personnel do the testing and submit a written report to the electricians. Then, there is a space next to each location for what action was taken to repair the unit.
For the annual 1.5-hour test, it's not feasible to stand there and hold the test button. If the building has an off-season or shut-down period, it may be possible to cut the power for the whole building or individual sections and do a walkthrough after 90 minutes have elapsed. Taking advantage of an extended outage might also be an option.
Keep in mind that all of the annual inspections do not have to be done at the same time. They may be staggered throughout the year. If it's important to keep the branch circuit operational, the only other option is to open the front panel of each unit and interrupt incoming power.
An important part of all inspections is to make sure the heads have not moved and are aimed accurately. These emergency lights are simple to repair, and it is rarely necessary to purchase a whole new unit. Typically, when you push the test button and all lights fail to go on or are weak, it's a sign new batteries are needed — but not always.
Most units are 6V and have a single 6V battery or two hooked in parallel. Some models are 12V with a short jumper to connect two 6V batteries in series. It's best to check batteries, even new ones, with a voltmeter. They should read about 6.20V. Sometimes, however, a battery will test good but have excessive internal impedance and hence be unable to drive two or more bulbs. You can either test the batteries in advance with a spare bulb or put them in the unit and see if they have taken a charge after 24 hours.
Sometimes, when new batteries are installed, the unit will test good but fail to light in a subsequent monthly test — a sign that the unit is not charging. In this case, you don't have to buy a new box. Electrical distributors sell sub-chassis components that contain charging apparatus and relays, which are also fairly easy to change right in place. It is common practice to disconnect and cap off the source conductors, change over all the wires, and then restore power by reconnecting the source conductors. The better practice, however, is to be OSHA compliant by finding the right breaker and cutting off the power — or you can just pull the power cord if so equipped (Photo 1). Of course, this will put out all nearby lights, so you will need to run an extension cord and trouble light from an adjacent branch circuit, unless there is a window nearby.
Other times, if you press the test button, the lights will energize but not go out when you release the button. If this happens, then the relay is sticking. If you rap sharply on the housing, the relay will often release. In this case, realize that the problem is sure to recur in the future. There is no way to lubricate the relay, so you'll need to replace it.
Occasionally, the unit will emit a continuous AC hum. Some circuit boards have a mini potentiometer, which can be adjusted to eliminate this sound. Typically, this does not provide a lasting cure, so it's best to replace the relay.
Maximizing your investment
When troubleshooting these systems, it's important to know the ins and outs of the individual equipment components. Most unit emergency lights have two heads. Many drive one or more remote heads, and often an exit sign as well. Make sure you keep a selection of spare bulbs in stock.
When changing out a sub-chassis, a number of connections have to be made. Because some of the wires go into a wall, it's possible to make a mistake if you lose track of any of them. The basic idea is that black, white, and green are incoming AC power, with perhaps another set outgoing. Wiring to remote heads is usually 10 AWG. There may be a blue wire for the 277V option that is usually capped off and taped. The battery leads have crimped-on connectors, and the onboard lamps are connected in parallel to remote heads and exit light feeds.
You can either replace the whole sub-chassis or take it out, change out the circuit board, and then replace the sub-chassis (Photo 3). Although new replacement circuit boards may appear somewhat different, featuring an altered layout, you can figure out which connectors go on which pins, if you can read the small print on the circuit board. If you really want to be thrifty, you can solder in a replacement relay if you find it to be the faulty component. The idea is to have one or more sub-chassis on hand and rebuild them in your spare time.
The aforementioned repair procedure takes care of most problems. Occasionally, a bulb is loose in a socket, a wire nut connection has opened up, or a similar problem has developed. However, battery change typically takes care of 90% of the malfunctions, and the circuit board replacement usually works for the remainder.
Because batteries are fairly expensive, it's worthwhile to reuse them where possible. The maximum usable life is about five years so if they have been dated, you can discard the old ones by taking them to a certified recycler. If the outer case appears warped, then they have been overheated and some of the plates are too close inside. With age they become sulfated, and an insulating coat builds up on the plates, therefore increasing the internal impedance. Otherwise, put them in a dedicated test unit for about 24 hours and see if they take a charge, in which case they are the batteries that have come out of units with bad chargers, so they can be reused.
A medium-sized facility can easily have more than 100 units. That means with proper management, thousands of dollars can be saved over a period of time. It is essential to avoid a situation where you are feeding good batteries into the same units month after month. A better approach is to make an Excel program in the electrical shop computer and red flag any units that have had batteries replaced for two consecutive months, as these need new circuit boards.
In Sec. 126.96.36.199, the LSC states: Where maintenance of illumination depends on changing energy sources, the maximum delay permitted is 10 seconds. In this respect, the battery-powered unit emergency light is excellent because it's instantaneous. Another requirement is that emergency lighting must maintain 1.5 hours of illumination. Batteries are labeled with amp-hour capacity, so if there is a heavy load in terms of remote heads and exit lights, calculations may be in order. If the box will hold two batteries, it's a good policy to use both.
Although there's a lot more to troubleshooting emergency lighting than meets the eye, the NEC and LSC requirements are straightforward and clearly articulated in the relevant documents. If you follow these guidelines, universal compliance and impeccable workmanship can be achieved at any facility.
Herres is a licensed master electrician in Stewartstown, N.H. He can be reached at firstname.lastname@example.org.