Which voltage protection device can automatically disconnect the starter contacts when voltage levels drop below acceptable limits?

The correct choice is the undervoltage relay, which is specifically designed to monitor voltage levels in an electric motor control system. When the voltage drops below a predetermined threshold, the undervoltage relay activates, causing the starter contacts to disconnect automatically. This function is crucial for protecting motors from operating under low voltage conditions, which can lead to inefficient operation, overheating, or even damage to the equipment.

In contrast, an overvoltage relay serves a different purpose; it disconnects the circuit when voltage levels exceed safe limits rather than responding to drops in voltage. A short circuit breaker is designed to interrupt the circuit when it detects excessive current flow, which is not directly related to voltage levels. Finally, a surge protector is focused on guarding against transient voltage spikes, but it does not disconnect or monitor continuous voltage levels like an undervoltage relay does. Thus, in the context of automatically disconnecting starter contacts due to low voltage, the undervoltage relay is the appropriate device.