PEC Voltage Drop

PEC Voltage Drop: A Worked Example on a Long Residential Feeder

A 35-meter feeder run pushed to the edge of the PEC voltage drop limit — walked through step by step.

Ampacity checks tend to pass comfortably on long residential feeders — it's voltage drop that quietly becomes the real constraint. Here's a worked scenario.

The Scenario

Parameter	Value
Load	40A, single-phase, 230V
Feeder length	35 meters, one-way
Cable under test	10mm² copper

Why Length Dominates Here

At 35 meters, the resistive voltage loss along the conductor accumulates enough that a cable comfortably rated for 40A ampacity can still land close to or past the PEC's percentage limit. This is the exact scenario where "the ampacity table said this size is fine" leads someone astray if voltage drop isn't checked as a genuinely separate, independent step.

What Changes the Outcome

• Upsizing the conductor reduces resistance and therefore voltage drop, even though ampacity was never the binding constraint
• Splitting a long run with an intermediate distribution point (where feasible) shortens each individual run's voltage drop contribution
• Reducing load current, where possible, has an outsized effect since voltage drop scales linearly with current

Run your own feeder length and load through the PEC Voltage Drop calculator rather than assuming a "big enough" cable is automatically compliant.

Engr. Jason Morales — Founder, SolarEnergyPH & OhmWorks

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