DC cable voltage-drop planning

For a simple two-conductor DC feed with equal outgoing and return conductors, cable drop can be estimated from loop resistance and current. Keep that cable calculation separate from strip-PCB loss, connector loss and the final conductor/protection design.

Decision and input record

Decision	What to check	Record or boundary
Input length	One-way route in metres	The model includes the return conductor
Resistance	One conductor in ohm/km	Use actual cable data and stated conditions
Output meaning	Estimated cable-only voltage loss	No ampacity or safety approval

Use the resistance for the actual cable

Obtain conductor resistance from the cable data sheet and note its stated conditions. Enter one-way route length, not the sum of outgoing and return lengths, when the formula already multiplies by two. If the conductors differ or the route branches, model the separate paths instead of forcing them into this simple equal-conductor calculation.

Worked example with declared assumptions

Assume a one-way length of 10 m, equal-conductor resistance of 8 ohm/km, 3 A DC current and a 24 V source. Loop resistance is 2 × 10 × 8 / 1000 = 0.16 ohm. Estimated drop is 3 × 0.16 = 0.48 V, or 2% of 24 V. Estimated cable dissipation is 3 × 3 × 0.16 = 1.44 W. All inputs are hypothetical; the result is not a rating for a named BEXLIGHT model or cable.

Decide what the answer does not cover

The calculation excludes connections and variation in conductor resistance with operating conditions. It does not predict brightness variation along the source, check ampacity, select protective devices or establish compliance. An acceptable voltage budget must come from the system design and source requirements. A low calculated percentage alone does not approve the installation.

Use the estimate to ask a better question

Compare realistic route alternatives or conductor data at the same design load. Identify which assumption dominates the result. Then ask the electrical designer to review the selected cable, routing and terminations against the installation conditions. If the design changes, update the load and path rather than reusing the old percentage.

Verify an installed section

Record measured source and load-end voltage under the defined operating scene using an appropriate measurement procedure. Keep the measurement locations with the drawing. If a dim end remains, investigate the strip and connections as separate sections of the circuit rather than attributing every loss to the feed cable.

What to include in a technical inquiry

Use the cable-drop worksheet to make assumptions visible, then include the route, cable data and design load with the electrical review.

Discuss the application and supply scope

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