Cable Size & Voltage Drop for LED Installations
The single most common cause of "dim LEDs at the far end" is not the driver — it is the cable. Undersize the wire and voltage drop steals brightness before the light ever sees it. This is the sizing method we use on every install.
The law that decides it
Voltage drop = Current × Resistance of the cable. Resistance rises with length and falls with cross-section, so a longer or thinner cable drops more volts. Keep total drop under 5% (0.6V on 12V, 1.2V on 24V) and the far end stays bright.
How far can you run at 12V vs 24V?
At the same wattage, 24V draws half the current of 12V, so it drops roughly a quarter of the loss and runs about twice as far:
| Load | Cable | Max run @ 12V | Max run @ 24V |
|---|---|---|---|
| 24 W | 1.5 mm² (16 AWG) | ~8 m | ~16 m |
| 48 W | 2.5 mm² (14 AWG) | ~8 m | ~16 m |
| 96 W | 4 mm² (12 AWG) | ~7 m | ~14 m |
| 192 W | 6 mm² (10 AWG) | ~5 m | ~10 m |
Three ways to beat drop
- Go to 24V. For any run over ~5 m, 24V removes the problem in most rooms (see the 12V vs 24V guide).
- Feed from both ends. Halves the effective length and the drop.
- Thicken the cable. One size up costs little and fixes a dim far end; two sizes up if the cable is buried or bundled with mains.
Two mistakes we see constantly
- Sizing cable for the driver, not the run. The driver rating is fine; distance is what kills brightness. Use the table, then go thicker if in doubt.
- Using speaker wire. Thin "lamp wire" looks tidy but doubles the drop. Use real mains-rated flex at the section the load needs.
Worked example: 10 m of 14.4W/m strip = 144W on 24V = 6A. Through 2.5 mm² that is about 1.0V drop — under the 1.2V (5%) budget, so it stays bright. The same load on 12V would need roughly 4 mm² to hit the same drop.
What we need from you
Send the load in watts, the output voltage (12V or 24V), the cable length and the section you plan to use. We will confirm the run is safe — or tell you to step up to 24V or a thicker cable before you install.
Worried about dim LEDs at the far end?
Send the load, voltage, cable length and section. We will confirm the run is safe — or tell you to step up to 24V or thicker cable.
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