Which term describes reducing the rating of standard motor control contacts when used to switch loads with high inrush, such as filament-type lamps?

Which term describes reducing the rating of standard motor control contacts when used to switch loads with high inrush, such as filament-type lamps?

• A. Derated
• B. Overrated
• C. Underrated
• D. Normal

Answer: (A)

When switching loads that create a high inrush, such as filament-type lamps, the current spike at switch-on is much larger than the running current. That surge subjects the contacts to more stress, which can shorten life or cause arcing. To reflect this extra stress, the contact rating is reduced for these conditions—that reduction is called derating. So the term that best describes adjusting the rating downward for high-inrush loads is derated. The other options don’t fit because overrated would imply increasing the rating beyond capability, underrated would imply using a rating that’s too small by default, and normal means no adjustment at all.

When switching loads that create a high inrush, such as filament-type lamps, the current spike at switch-on is much larger than the running current. That surge subjects the contacts to more stress, which can shorten life or cause arcing. To reflect this extra stress, the contact rating is reduced for these conditions—that reduction is called derating. So the term that best describes adjusting the rating downward for high-inrush loads is derated. The other options don’t fit because overrated would imply increasing the rating beyond capability, underrated would imply using a rating that’s too small by default, and normal means no adjustment at all.