Cable Derating - Factors
Remember: The cable’s rating in a catalog is a promise made in a laboratory. Derating factors are the fine print of physics. Read them. Apply them. Your cables—and your safety record—will thank you.
In the world of electrical engineering and power distribution, selecting the correct cable size is rarely as simple as looking up a current rating in a manufacturer’s table. Those tables—often printed in neat, optimistic columns—assume a perfect world. They assume an ambient temperature of 30°C, a solitary cable in free air, and soil with ideal thermal resistivity. cable derating factors
A cable at 0.5m depth dissipates heat better than at 1.5m depth. Derating factors for depth are typically small (0.95–0.98 per 0.5m increase) but become significant for long, high-current runs. Remember: The cable’s rating in a catalog is
$$ I_{eff} = I_{nom} \times k_{temp} \times k_{group} \times k_{soil} \times k_{depth} \times k_{altitude} \times k_{harmonics} \times ... $$ Apply them
