Multi-layer Winding

Derating is one of the most important — and most frequently misunderstood — concepts in electrical cable engineering. Many engineers view derating as an administrative requirement imposed by standards, something to be looked up in a table and applied mechanically. In reality, derating exists because of a fundamental physical law: the rate at which a cable can dissipate heat is directly proportional to the surface area exposed to the surrounding air or cooling medium, and inversely proportional to the thermal resistance of the insulating materials surrounding the conductors.