Need a straight-shooting guide to emergency light voltages and voltage drop? This spoke walks through system voltage (6V/12V/24V), wire sizing, and quick field math so your remote heads stay bright. For a broader overview of code, fixture types, and maintenance, see the Emergency Lighting Guide. When you’re ready to compare units, browse the parent collection: Emergency Lights.
Last updated: October 2025
Emergency Light Voltage
Most standalone emergency light units operate on 6 volts DC. In practice, the building’s 120/277V AC is stepped down and converted to low-voltage DC to charge the battery and power the lamps during outages. Larger or centralized systems often use 12V or 24V DC, which is especially helpful when driving multiple remote heads or longer wire runs. The key planning variable is distance: long cable runs introduce resistance and voltage drop, which can dim the lamps if not addressed. For related electrical context on signage circuits, see Exit Signs Voltage & Wattage Explained.
Understanding Voltage Drop
Any conductor has resistance, so voltage falls as current flows over distance. Short runs barely move the needle; long runs (hundreds of feet) can materially reduce lamp brightness. In egress lighting, designers commonly target ≤ 5% voltage drop to preserve illumination. Thicker copper (lower AWG numbers) reduces resistance and helps the remote heads see full voltage. This practice aligns with general NEC guidance to limit branch-circuit voltage drop for performance and efficiency.
Calculating Voltage Drop
You can compute drop with Ohm’s Law, but quick reference tables are faster. The table below shows approximate % voltage drop per 100 ft for common wire gauges at several load currents (assuming a 6V DC system). Find your wire gauge and total current (amps) to estimate percent drop per 100 ft of run; scale linearly for total length.
| Wire Gauge | 0.5 A | 1 A | 2 A | 4 A | 10 A |
|---|---|---|---|---|---|
| 10 | 0.10% | 0.20% | 0.40% | 0.80% | 2.00% |
| 12 | 0.16% | 0.32% | 0.64% | 1.27% | 3.18% |
| 14 | 0.25% | 0.50% | 1.01% | 2.02% | 5.04% |
| 16 | 0.40% | 0.80% | 1.60% | 3.20% | 8.00% |
| 18 | 0.64% | 1.27% | 2.54% | 5.08% | 12.71% |
| 20 | 1.01% | 2.02% | 4.03% | 8.07% | 20.17% |
| 22 | 1.60% | 3.20% | 6.40% | 12.81% | 32.02% |
Formulas: Amps, Volts, Watts
Use these to translate between power, current, and voltage:
- Watts = Volts × Amps
- Volts = Watts ÷ Amps
- Amps = Watts ÷ Volts
Example: a 6V emergency lamp with a 9W head draws 1.5A (9 ÷ 6). Two 9W heads on 6V total 18W, i.e., 3A. Modern LED heads (1–5W) cut current—and drop—versus legacy incandescent (7–12W).
Voltage Drop Examples
Scenario 1: One 12W remote head at 300 ft on 6V draws 2A. 18 AWG yields about 7.6% drop (too high). Upsize to 16 AWG and you’re ~4.8% (acceptable).
Scenario 2: Same lamp and distance on 24V draws 0.5A. 18 AWG is ~1.96% at 300 ft—well within target. Even 22 AWG stays just under 5% (~4.8%).
Scenario 3: A 25W remote at 300 ft on 24V draws ~1.04A. 18 AWG is ~3.1%; you could run ~475 ft before hitting ~5%.
Need to verify runtime too? Use our Battery Runtime & Load Calculator to confirm 90 minutes under UL 924. For a broader comparison of when to rely on dedicated emergency lights vs exterior illumination, see Emergency Lights vs. Wall Pack Lights.
Conclusion
Picking the right voltage and wire size is the simplest way to keep remote heads bright over distance. As a rule of thumb, higher-voltage (12/24V) systems make long runs easier because they move the same watts with less current. If you must stay at 6V, plan for thicker conductors or shorter runs. When in doubt, check the table, run the numbers, and document a nighttime aim/reading at handover.
Need a straightforward, code-ready solution? Explore our Emergency Lights to find UL 924 fixtures matched to your voltage, run length, and environment. For onboarding or a quick refresher, pair this article with the Emergency Lighting Guide—it covers the big-picture code basics while this page tackles the voltage-drop details.