What could cause a sump pump motor to continue running after the sump pump is empty?

A sump pump motor continuing to run after the sump pump is empty can often be attributed to contacts in the switch being welded closed. When the contacts of the float switch, which controls the pump operation, are welded closed, they create a continuous circuit, allowing power to flow to the motor regardless of whether the sump is full or empty. This situation can lead to overworking the pump, potentially causing motor failure due to running without adequate water for cooling and lubrication.

Understanding the role of the contacts in the float switch is crucial. They are designed to open and close based on water levels in the sump; when they do not operate correctly, it can lead to the pump running unnecessarily. This can happen due to excessive wear, overheating, or even electrical faults that cause the contacts to fuse in a closed position, resulting in the described situation.

In contrast, the other options highlight potential issues but do not directly explain the continuous operation of the pump motor once the sump is empty. For instance, welded open contacts would stop the motor from running, a plugged suction line would typically cause the pump to cycle on and off, and low supply voltage would generally cause insufficient power to the motor, leading it to malfunction or fail to start.