Training Tip: Electrical

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Looking for an easier way to demonstrate the function of a PTC relay to your students? This is an easy method that uses 100W light fixtures and a PTC relay. 

A PTC has a resistance of approximately 5 to 15 Ω cold. As current passes through it, the PTC heats up and its resistance increases to 10,0000 Ω or higher. This high resistance virtually stops the current flow through the contacts. A PTC can be checked by wiring it in series with a 100-watt, 120 VAC incandescent light bulb. When power is applied, the light should be bright, and then fade out in about 60 seconds. 

An instructor can have the students wire up the bulb and relay in a lab setting. The students can monitor the current with a multimeter and record the time that passes until the light goes out. This lab can be repeated using multiple bulbs in parallel to draw more current and heat the PTC quicker. 

The students should measure the resistance of the PTC before the lab begins and record it. Upon completion, the resistance can be measured again, and the results compared. This exercise visually demonstrates the function of the PTC relay, great for visual learners!

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