How the calculation works
I = W/V; VD = 2·I·L·R/1000 with R in Ω/1000 ft (copper at 20°C, NEC Chapter 9 Table 8). This model treats the total load as a point load at the far end; LED strips are often distributed loads, so long runs may have a different real voltage drop. Consider power injection and manufacturer guidance. Class 2 circuits fall under NEC Article 725 (CEC Section 16). Limit drop to 3–5% for even brightness.
Worked example
60 W @ 12 V = 5 A over 16 ft of 14 AWG: 0.40 V (3.4%).
Common mistakes to avoid
- Powering a long strip from one end only.
- Using wire that is too thin for the current.
- Ignoring the strip's own maximum run length.
Frequently asked questions
Fix dimming?
Use heavier wire, feed from both ends, or a higher voltage (24 V halves the current).
What is the maximum run for a 12 V strip?
Many strips are specified for about 16 ft (5 m) per feed regardless of wire size, because of the strip's own copper traces.
Why use 24 V instead of 12 V?
For the same watts, current is halved, which cuts the percentage voltage drop to about one quarter on the same wire.
Read the guide
LED Strip Wiring Guide: Wire Gauge, Power Supply and Voltage Drop
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