Why must standard motor control contacts be derated if used to control filament-type lamps?

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Prepare for the NCCER Electrical Level 2 Control Systems and Fundamental Concepts exam. Utilize flashcards and multiple choice questions with hints and explanations. Ensure success on your exam!

Multiple Choice

Why must standard motor control contacts be derated if used to control filament-type lamps?

Explanation:
When a filament-type lamp is switched on, the filament is cold and has a much lower resistance, so a large inrush current flows for a brief moment. This startup surge can exceed the contact rating of standard motor-control devices, causing stronger arcing and faster wear, which shortens life. So the need to derate is due to those high initial currents. The other ideas aren’t the main issue: running current is lower once the filament heats up, cooling isn’t the primary concern here, and the startup surge does affect life through arcing.

When a filament-type lamp is switched on, the filament is cold and has a much lower resistance, so a large inrush current flows for a brief moment. This startup surge can exceed the contact rating of standard motor-control devices, causing stronger arcing and faster wear, which shortens life. So the need to derate is due to those high initial currents. The other ideas aren’t the main issue: running current is lower once the filament heats up, cooling isn’t the primary concern here, and the startup surge does affect life through arcing.

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