Step-by-step: wiring exit signs

Exit signs are life-safety equipment. They have to work when the power is out, when the building is full of smoke, and when no one is paying attention. Wire them like you mean it.

Know what code applies before you pull a wire

Exit signs fall under NEC Article 700 (Emergency Systems) when they are part of a legally required emergency system, or Article 701 (Legally Required Standby) or 702 (Optional Standby) depending on the AHJ's classification. Most jurisdictions also enforce NFPA 101 Life Safety Code and IBC 1013 for placement, illumination, and visibility. Verify with the local inspector before rough-in.

Per NEC 700.10(B), emergency wiring must be kept independent of all other wiring. That means no sharing raceways, boxes, or cables with normal branch circuits except in transfer equipment, exit/emergency luminaires fed from two sources, or a common junction box where listed. Plan the homeruns accordingly.

Illumination duration is set by NFPA 101: a minimum of 90 minutes on battery or generator backup. Light level on the egress path must average 1 foot-candle and not drop below 0.1 foot-candle anywhere along the route.

Pick the right fixture for the job

Three common types show up in the field: self-contained battery-backup (most retail and small commercial), AC-only fed from a generator-backed emergency panel, and combination exit/emergency units with integrated heads. Match the fixture to how the building is backed up. A self-contained unit on a generator circuit is fine; an AC-only unit on a normal lighting circuit is a code violation.

Check the listing. Look for UL 924 on the label. If it is not listed for emergency use, it does not belong on an egress path, no matter what the catalog says.

Field tip: if the spec sheet does not show UL 924 and a 90-minute runtime, put the fixture back on the truck. Inspectors will reject it and you will be back to swap them out on your own time.

Circuit and conductor requirements

Exit signs are typically fed at 120V or 277V depending on the building's lighting voltage. Per NEC 700.15, no appliances or lamps other than those specified for emergency use shall be connected to the emergency lighting circuits. Do not tap a receptacle, an HVAC control, or a sign transformer off that homerun.

Per NEC 700.12, the source of power must be capable of supplying the load within 10 seconds of normal power loss. For generator systems, that is the transfer switch timing. For unit equipment per 700.12(I), the internal battery handles it. For inverter systems per 700.12(F), the inverter must be listed for emergency use.

• Conductors: 12 AWG copper minimum is standard for 20A branch circuits feeding exit/emergency lighting.
• Identification: emergency circuits, boxes, and enclosures must be permanently marked per NEC 700.10(A). Red marker, red boxes, or labeled covers all work if consistent.
• Wiring methods: use a wiring method permitted by 700.10(D) where fire protection is required, typically MI cable, MC-rated for emergency, or in 2-hour rated construction.
• Switching: 700.20 prohibits any general-purpose switch from controlling emergency lighting. The unswitched hot from the lighting circuit ahead of any local switch is what feeds the sense leg.

Step-by-step rough-in and termination

For a typical self-contained UL 924 unit fed from a normal lighting circuit, you need three conductors at the box: hot, neutral, and an unswitched hot for the sensing leg. The sensing leg tells the unit when utility power has failed so it can kick over to battery.

1. Pull your homerun to the nearest emergency-classified panel or, for self-contained units, to the lighting circuit that serves the area. One circuit per NEC 700.15 rules.
2. Land the unswitched hot ahead of the local wall switch. Pigtail it through the switch box and continue to the exit sign location.
3. At the exit sign, identify the leads: black is switched or sensing hot depending on the manufacturer, red is often the unswitched sense, white is neutral, and green or bare is ground. Read the wiring diagram on the back of the canopy. Do not assume.
4. Wire the unswitched hot to the sense lead, the neutral to white, and ground to ground. Cap unused leads per the manufacturer.
5. Mount the fixture per IBC 1013, generally within 80 inches of the floor on or near the door, with letters visible from 100 feet or the listed distance on the fixture.
6. Energize, verify the AC pilot light is on, then press the test button. The sign should run on battery for the test cycle.

For AC-only fixtures fed from an emergency panel, skip the sensing leg. Land hot, neutral, and ground from the emergency circuit only. The transfer switch handles the source change.

Testing, labeling, and turnover

NFPA 101 7.9.3 and NEC 700.3 require functional testing. Monthly: 30-second function test. Annually: 90-minute full discharge test. Self-testing/self-diagnostic units per UL 924 satisfy the monthly test automatically, but the annual is still on the owner. Document everything.

Field tip: before you leave site, kill the breaker feeding each unit and time it. If any sign goes dark before 90 minutes, the battery is bad or the fixture is failing. Better you find it than the inspector.

Label the panel directory clearly: "EMERGENCY, EXIT LIGHTING, DO NOT DISCONNECT." Mark every junction box on the emergency circuit. Hand the owner a copy of the test schedule, the fixture cut sheets, and the as-builts. That paperwork is what closes out the job and keeps you out of a callback when the AHJ shows up next year.