Nate Electrical Practice Exam

What is the function of the resistor wired across the terminals of a start capacitor?

1. For the safety of the technician

2. To prevent arcing and damage to start relay contacts

3. To increase the life of the start capacitor

4. To protect the capacitor from back-EMF

The correct answer is: To prevent arcing and damage to start relay contacts

The function of the resistor wired across the terminals of a start capacitor is primarily to prevent arcing and damage to start relay contacts. When the start capacitor is energized, it allows the motor to start by providing an initial boost of energy. Once the motor reaches a specific speed, the start capacitor is taken out of the circuit by the start relay. However, there is a risk of arcing occurring at the relay contacts when they open if the capacitor is still charged. The resistor helps in this process by discharging the capacitor quickly after the relay opens, which minimizes the chances of arcing. Without this resistor, the charged capacitor could create a high-voltage situation at the relay contacts, leading to wear, potential welding of contacts, or even failure of the relay over time. This protective measure ensures that the relay operates reliably and prolongs the life of the motor control circuit. In contrast, while other options might touch on pertinent topics within electrical circuits, they do not specifically address the role of the resistor in the context of start capacitors and relays. For instance, the safety of the technician and protection from back-EMF are critical considerations in electrical work, but they are not the primary functions of this resistor in the specific application of