PEC Derating
PEC ampacity tables assume a reference ambient temperature that many Philippine installations exceed daily.
Cable ampacity tables are built around a standard reference ambient temperature. In much of the Philippines — especially enclosed rooftop or ceiling spaces during the hot season — real installation temperatures regularly exceed that reference, which means the table's headline ampacity figure isn't the cable's real, usable capacity without correction.
| Location type | Why it runs hot |
|---|---|
| Rooftop conduit | Direct sun exposure heats the conduit well above surrounding air temperature |
| Enclosed ceiling space | Poor ventilation traps heat generated by the building and by the cables themselves |
| Outdoor switchboard enclosures | Metal enclosures in direct sun can reach surface temperatures far above shaded ambient |
Skipping the temperature correction factor because "it's close enough to standard conditions" is a common but risky shortcut in tropical climates specifically, since the gap between reference and real conditions is often larger here than in temperate-climate codes' typical assumptions.
Enter your installation's real ambient conditions in the PEC Cable Sizing calculator and let the correction factor do its job.
Engr. Jason Morales — Founder, SolarEnergyPH & OhmWorks