When should you choose 12V or 24V for remote heads? This guide explains how voltage choice affects run length, voltage drop, and wire size—with practical rules, example layouts, and an inspection checklist.
Last updated: October 2025
Why voltage matters (and how drop shows up)
At a given wattage, higher voltage = lower current, which reduces voltage drop on the same wire over the same distance. Lower‑voltage runs with small conductors are more sensitive—add length or load and the last head can dim or flicker late in the 90‑minute test.
Planning idea: I = P / V, round‑trip R from your AWG table → Vdrop = I × R. Aim for ≈ ≤ 5% of system voltage at the far head under emergency load.
If drop is high, shorten runs, increase wire size, split the load, or step up to 24V.
Voltage‑drop basics (simple math)
-
Current (A):
I = P / V(P = total W on the branch; V = 12 or 24). - Resistance (Ω): use copper ohms/1000 ft for your AWG; multiply by round‑trip length (out + back).
-
Drop (V):
Vdrop = I × R→ verify % drop ≤ target (~5%).
Need ready tables? See the wire gauge & distance tables (AWG 18–10).
12V or 24V? (rules of thumb)
- Choose 12V for short interior runs with a few low‑watt heads and nearby hosts; inventories and small hosts often favor 12V.
- Choose 24V for long walks, exterior canopies/corridors, higher total branch loads, or when you want smaller conductors for the same reach.
- Confirm with tables: check the wire‑gauge distance tables using a ~5% target.
Wire‑size method (repeatable)
- List each branch’s heads and watts/head → total W.
- Compute
I = P/Vfor 12V or 24V. - Estimate round‑trip length (host → far head → back).
- Pick an initial AWG from the distance tables.
- Iterate: if % drop > target, increase copper, split the run, or step to 24V.
Layout & topology
- Star (home‑run) topology: Best for long runs—keeps shared current low and drop predictable.
- Short daisies: OK for tiny loads over very short paths; keep head count per chain small.
- Aiming & spacing: Better optics can reduce head count. See the remote head spacing guide and, outdoors, IP65 spacing & aiming.
- Compatibility: Match head voltage to the host and confirm families in the compatibility matrix.
Worked examples
Example A — 12V corridor run, single head
Load: 5 W LED head. Voltage: 12 V → I = 5/12 ≈ 0.42 A.
Length: 120 ft one‑way (round‑trip 240 ft). Wire: AWG 16 (≈4.0 Ω/1000 ft).
R(run): 4.0 × 0.240 = 0.96 Ω → Vdrop ≈ 0.42 × 0.96 = 0.40 V (≈3.3%). Pass.
Example B — 12V, two heads on a long branch
Load: 2 × 5 W = 10 W → I = 10/12 ≈ 0.83 A on shared segment.
Same wire/length as A → Vdrop ≈ 0.83 × 0.96 = 0.80 V (≈6.7%). Borderline. Fix by upsizing to AWG 14 or stepping to 24V.
Example C — 24V upgrade on the same geometry
Load: 10 W at 24 V → I = 10/24 ≈ 0.42 A (half the current). Using AWG 16, same length:
Vdrop ≈ 0.42 × 0.96 = 0.40 V → as a % of 24 V ≈ 1.7%. Comfortable.
Inspection‑ready checklist
- Voltage choice documented: 12V or 24V rationale + expected distances and load.
- Wiring math on file: Current, round‑trip length, AWG, and drop target.
- Coverage: Door thresholds, landings, and first section of path are evenly lit; verify aiming on site. If outdoors, apply IP65 spacing & aiming.
- Compliance docs: Keep spec sheets and test logs; see the code requirements overview for what AHJs expect.
FAQs
Is 24V always better than 12V?
No. 24V carries load farther on the same wire, but for short runs with small loads, 12V is perfectly fine and may simplify parts and service.
What drop limit should I use?
Designers often work to about 5% as a practical planning limit. Always verify illumination at the farthest head during the 90‑minute test.
Do I need to upsize both voltage and wire?
Not necessarily. Try one lever at a time: thicker wire or higher voltage. Use both only if needed by distance and load.
This article focuses on the voltage choice (12V vs 24V) and its impact on conductor size and distance. For fundamentals and universal sizing steps, use the core guide linked above.