Low-Voltage DC Drop

DC voltage drop and percent at 12 / 24 / 48 V with application-tolerance flags.

Run the calculator

Example

You enter

System voltage 12
AWG 10
Run length one-way (ft) 20
Current (A) 10
Application led_lighting

You get

Drop 0.486 V
Percent 4.05 %
Status exceeds tolerance

No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.

Details, formula, and sources

Formula or tableVD = 2 × I × R × L for 12 / 24 / 48 V DC systems with copper resistance per NEC Chapter 9 Table 8.

Source and editionNEC 2023 (NFPA 70). Chapter 9 Table 8 (used as a copper-resistance reference, not as a low-voltage code).

Free accessFree read-only access at nfpa.org/freeaccess.

What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.

API field namessystem_V, awg, run_length_ft, current_A, application, drop_V, percent, acceptable

Application tolerance LED 3% / marine 10% / RV 5% / audio 2%engineering practice by application