Estimate feeder voltage loss using current multiplied by the complete circuit resistance, including the return path. Then check the strip's own voltage behavior separately. A cable calculation alone cannot establish the maximum usable strip length.
Use loop resistance rather than one-way resistance
For a simple two-wire DC feeder, the current travels out and returns. If the complete loop resistance is 0.4 ohm and the current is 4 A, the estimated feeder drop is 1.6 V. Against a nominal 24 V supply that is about 6.7 percent. Whether it is acceptable depends on the product's input limits and the project requirements.
This example uses an assumed resistance, not a recommended cable size. Actual resistance depends on conductor material, cross-section, length, temperature and connections. A qualified designer should select the cable and protection using the applicable rules and installation conditions.
Keep feeder and strip calculations separate
The voltage available at the strip input is the source voltage minus feeder and connection losses. Along the strip, copper tracks and product circuitry introduce further behavior. Some products regulate output over a range; others show a visible brightness change. Obtain data for the exact model and proposed branch length.
Do not fix an inadequate circuit by increasing the source above the product's allowable range. Equipment near the source may then be overvolted. Review shorter branches, supported voltage options or a different supply position instead. Any multi-feed design must account for isolation and compatible power equipment.
Make calculation assumptions visible in the RFQ
Give the supplier feeder distances, expected load and minimum supply condition. Ask whether stated watts per meter are typical, maximum or measured under a particular setup. For long routes, identify each branch rather than presenting one total length. This makes it possible to assess the most demanding section.
At commissioning, compare predictions with loaded measurements at defined points. Record the operating temperature and any changes from the drawing. A calculation that looked satisfactory before installation may need revision if the feeder route became longer or extra sections were added. Keep the accepted branch limits in the maintenance documentation.
Values needed for a defensible calculation
- Source voltage range, not just its nominal label.
- Load current and its stated measurement basis.
- Complete feeder loop resistance at relevant conditions.
- Connector losses and product input limits.
- Strip branch length and the manufacturer's performance evidence.
Questions buyers ask
Is five percent voltage drop always the correct target?
No. Use the applicable design rules and equipment limits; a generic percentage is not universal acceptance evidence.
Does higher voltage eliminate the problem?
No. It may reduce current for the same power, but cable, connection and strip limits still apply.
Related engineering guides
- Tunnel strip lighting: the system design overview
- Segmenting Tunnel LED Strip Circuits for Easier Isolation and Repair
- Factory Acceptance Tests for Tunnel LED Strip Orders
Technical references
Use the following source alongside the project specification; it does not certify a ZBL product or replace site engineering approval.
