Reducing a rating to account for conditions less favourable than the reference.
Every published rating assumes a reference condition: 30 °C ambient for cable ampacity, 25 °C for many component ratings, a specified mounting for power devices. Derating corrects for the difference.
Cable derating factors stack — ambient temperature, number of conductors in a raceway, and whether the load is continuous all apply at once, and the product can be well under half the nominal rating.
Applying only one derating factor. They multiply, and the cumulative effect surprises people who expect a 20% adjustment.
This site uses Google Analytics to count visits and see which pages are useful. It sets cookies only if you agree. See the privacy policy.