G&D SMART / Professional outdoor lighting

Voltage Drop in Roofline Lighting

Calculate and test cable voltage drop before selecting a roofline branch length. Include fixture load, extension gaps, wire resistance and connector losses.

What causes voltage drop?

Current flowing through cable resistance reduces the voltage available at the fixture. Long extensions, small conductors and high branch current can increase the drop. Connector resistance and temperature also affect the installed result.

A useful first calculation

For a simple two-conductor supply path: voltage drop = current × total loop resistance. If cable resistance is quoted per conductor per unit length, include both the outgoing and return paths.

Illustrative example: at 4 A and 0.20 Ω total loop resistance, the calculated drop is 0.8 V. That is about 3.3% of a 24V supply. This is a calculation example, not an approved cable or system rating.

Distributed loads need a branch calculation

A roofline has fixtures distributed along the run. The first cable segment carries more current than the segment near the final fixture. Calculate each segment with its downstream load, then add the drops along the path. Include unlit extension gaps.

Check the installed system

• Use the selected fixture revision and its maximum tested load.
• Record conductor size, conductor material, length and connector count.
• Measure supply voltage and voltage at the most distant fixture under the planned maximum-load scene.
• Check color consistency, controller stability and connector temperature.

Changing to a higher-voltage system also changes the fixture, power supply and accessory requirements. Do not substitute voltage while keeping incompatible components.

Continue to power injection planning.

Apply this to your project

Send the fixture model, voltage, layout, cable lengths and intended control platform to G&D SMART. Request the current model documents and validate the selected configuration before production or installation.

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