About the Cable Route Length
Cable route length calculation measures the actual cable run length between two points in a solar plant — accounting for horizontal distance, vertical rises, bends, and entry/exit loops — to accurately size cable cross-sections, estimate voltage drop, and budget cable quantities.
How to calculate it
- 1Measure straight horizontal distance between the two endpoints on the plant layout drawing.
- 2Add vertical rises: each metre of height change adds one metre of cable length.
- 3Add bend allowances: each 90° bend adds approximately 1–2 m to the effective route length.
- 4Add entry/exit loops at each end: 0.5–1 m per termination for strain relief and future maintenance.
- 5Add a 5–10% contingency for unforeseen route deviations.
- 6Total route length = Σ(horizontal + vertical + bends + loops) × 1.05–1.10.
Worked example
A DC cable from AJB to inverter room: horizontal distance 28 m, one 90° bend up a wall (2 m vertical rise + 1.5 m bend allowance), exit loop at AJB (0.5 m), entry loop at inverter (0.5 m). Subtotal = 32.5 m. With 10% contingency: 35.75 m → order 36 m per polarity (72 m total for + and −).
What you can calculate
- DC + AC routes
- 10–15% contingency
- Total m
- Cost estimate
Frequently asked questions
Why does cable length matter more than direct distance in solar plants?
Voltage drop is proportional to cable length — a longer actual route causes more resistive loss and lower inverter input voltage, both reducing yield. Cable sizing is also based on route length: a 25 m route vs a 15 m direct distance may require the next larger cable cross-section to stay within the 1% voltage drop limit. Accurate route lengths prevent under-sizing errors that are expensive to fix after installation.
How do I measure cable route length on a rooftop plant?
For rooftop plants, route length cannot be scaled from a 2D plan — it must account for the actual 3D path: across flat sections, down parapet walls, up risers, around obstacles. The best practice is to walk the route with a measuring wheel during site survey, or use a string/tape to trace the proposed path. Add 15% to measured rooftop routes (vs 5–10% for ground-mount) due to the higher frequency of obstacles.
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