Emergency light voltages - made simple. This technical note explains line (AC) input vs. battery/remote-head voltages, how dual-voltage chargers work, and what to match on labels so your units charge, transfer, and run for the full 90 minutes. Along the way, it shows how emergency light wattage, voltage (3.6 V, 6 volt emergency light, 12 volt emergency light, and even 24V emergency lighting systems), and wiring all work together so you can predict emergency light power consumption. For a broader life-safety overview, see the Emergency Lighting Guide.
Last updated: October 2025
Overview: Two Voltage Worlds
Every UL 924 emergency light lives in two voltage worlds: the line (AC) side that powers the charger during normal operation, and the battery (DC) side that drives the LEDs during a power outage. On the label you’ll see the AC input (e.g., 120/277 V) and, separately, the battery or remote-head voltage (e.g., 3.6 V, 6 V, or 12 V). Together with the listed emergency light wattage, these ratings tell you exactly how much light you get and how many fixtures or remote heads can be supported. Get both voltage and emergency lights wattage right and you’ll meet the full 90-minute runtime without surprises.
Voltage Diagram (AC vs DC)
Line (AC) Input: 120/277 V & Universal Chargers
- Dual-voltage chargers (120/277 V): most unit equipment auto-senses either voltage. Tie to an unswitched branch so the charger stays active and batteries stay topped off.
- Universal 100–240 V: some models accept global mains; still verify frequency tolerance (50/60 Hz) on the nameplate. Higher-voltage feeders may also support centralized 24V emergency lighting in larger systems, though this note focuses on unit equipment.
- Transfer: on loss of AC, solid-state transfer switches to battery in < 1 s (typ. < 0.5 s).
Tip: If a local circuit is switched, use a listed emergency transfer device so the charger remains energized while normal lights can still be switched.
Battery Circuits: 3.6/6/12 V, Wattage & Lamp Loads
Emergency lamps run on low-voltage DC from the battery pack—commonly 3.6 V (small internal packs), a 6 volt emergency light, or a 12 volt emergency light. Battery capacity is sized in watts (or volt-amps) for 90 minutes. This is where emergency light wattage and total emergency light power consumption come into play.
- Load math: add the wattage of all heads (on-board + remote). Total emergency light watts × 1.5 h must be ≤ battery watt-hours.
- Buffer: leave 10–20% margin for temperature, aging, and LED tolerances instead of running the system at its absolute maximum emergency lights wattage.
- Chemistry: SLA/Ni-Cd are common; LiFePO4 recharges faster and lasts longer in many specs.
- Voltage choice: 3.6 V for compact, internal-only units; 6 V for typical unit equipment; 12 V (and higher, like 24V emergency lighting in central systems) for longer runs and larger remote-head loads.
Remote-Capable & Remote Heads (6 V vs 12 V)
Remote-capable base units power extra lamp heads installed away from the enclosure. This is where battery voltage and emergency light power consumption matter most:
- Match voltages: 6 V heads to 6 V bases; 12 V heads to 12 V bases—no mixing. A 12 volt emergency light base must feed 12 V remote heads; a 6 volt emergency light system must stay entirely 6 V.
- Wire runs: longer runs favor 12 V to reduce voltage drop; upsize copper on long home runs, especially where total remote-head wattage is high.
- Budget wattage: remote heads consume from the base unit’s 90-minute watt rating. Re-check runtime after adds so your total emergency light wattage stays within the label rating.
Deep dive: Remote-Capable & Remote Heads Guide
Common Mismatches & How to Avoid Them
- Heads/base voltage mismatch: 12 V heads on a 6 V base (or vice versa) won’t meet runtime—match labels.
- Overloading the battery: added remote heads push beyond 90-minute capacity; either downsize spacing or choose a higher-watt base. Never assume spare capacity—always verify total emergency light watts against the unit rating.
- Line mis-tap: dual-voltage units wired to the wrong input lead; always confirm lead selection and breaker voltage.
Voltage & Wattage Checklist (Spec & Install)
- Confirm AC input (120/277 V or universal) on charger label.
- Verify battery/remote voltage (3.6/6/12 V) and match all remote heads.
- Calculate total emergency light wattage for 90-minute load (on-board + remote) and leave 10–20% margin.
- Plan conductor gauge & distance to minimize voltage drop (12 V preferred on long runs, with 24V emergency lighting used in some centralized systems).
- Connect to an unswitched branch; if switched, use a listed transfer device.
- Document initial 90-minute test with lamp aiming photos for the AHJ packet.
FAQ
Can I power 12 V remote heads from a 6 V base?
No—match the head voltage to the base unit. Mixing voltages will fail runtime and may damage components.
How do I know if my charger accepts 240 V?
Check the nameplate: it must state 100–240 V or include a 220–240 V input range. If not present, assume 120/277 V only.
What’s the fastest way to verify load?
Add the wattage of each lamp head and compare to the base unit’s 90-minute watt rating—then add 10–20% headroom.
How do I estimate emergency light power consumption?
Take the listed emergency light wattage (on-board heads) and add the wattage of any remote heads. That total is your emergency light power consumption during an outage. Make sure that total emergency light watts multiplied by 1.5 hours does not exceed the unit’s 90-minute rating.