Thinking Like an Engineer
Safety Factors & Derating
12 min · 2 worked examples · 3 questionsFree
Why engineers never run anything at its stated limit.
After this lesson you can
- Apply a safety factor and justify the number
- Derate a component for temperature
- Say what an absolute maximum rating really means
Margin is not waste
A resistor rated 0.25 W will survive 0.25 W, in ideal conditions, at room temperature, briefly. Run it there continuously and its life shortens dramatically.
So engineers design in margin deliberately. A common rule of thumb is to operate below 50% of a rating for continuous duty. If your calculation says 0.2 W, fit a 0.5 W part. The cost difference is pennies; the reliability difference is enormous.
This is not timidity. It is recognition that ratings are measured under specific conditions, and the real world rarely matches them.
In the full lesson
- Margin is not waste
- Safety factor
- Derating with temperature
- Absolute maximum ratings
Free with an account. Read it, work the examples, answer the questions, then build it in the simulator.