LED strips are low-voltage loads, so even a short run on thin wire can cause visible dimming. Wire gauge and feed layout matter more than most people expect.
Size the power supply
Add up the strip wattage and add about 20% headroom. A 60 W strip load needs a supply of at least 72 W. Class 2 supplies are power-limited (commonly around 100 VA), so larger installations use multiple supplies.
Calculate current
Current = watts ÷ volts. A 60 W load is 5 A at 12 V, but only 2.5 A at 24 V.
Pick the wire gauge
Voltage drop = 2 × current × length × resistance per 1,000 ft ÷ 1,000. For 5 A over 16 ft one-way at 12 V:
- 16 AWG (4.016 Ω/1,000 ft): 0.64 V, 5.4% drop
- 14 AWG (2.525 Ω/1,000 ft): 0.40 V, 3.4% drop
- 12 AWG (1.588 Ω/1,000 ft): 0.25 V, 2.1% drop
Aim for 3% or less, and no more than 5%, to avoid noticeable dimming and color shift.
Avoid dimming on long strips
- Choose 24 V strips; the same watts at half the current gives about one quarter of the percentage drop on the same wire.
- Feed long runs from both ends, or add extra feed points.
- Respect the strip's maximum run length; many 12 V strips are limited to about 16 ft (5 m) per feed regardless of wire size.
- Keep the supply close to the strip and run the heavier wire on the low-voltage side.
Safety notes
Use a listed power supply, keep the mains wiring in proper enclosures and follow NEC Article 411 for low-voltage lighting systems and Article 725 for Class 2 circuits.
Try the calculators
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