Any “modern-day” pump motor has either a ground screw or ground wire. We all acknowledge that motors should be grounded, but many do not know why.
Grounding is used for the protection of anyone who could come in contact with the motor or piping that is attached. Keep in mind that although a pump may be connected to a plastic pipe that does not carry current, the fluid inside can very likely carry current.
Ground wires act as a conductor to ground (literally) — any stray current that escapes a motor due to a breakdown of the manufacturer’s built-in insulation.
New and re-wound motors are tested to be sure they have no current leakage before being sent to any installers and end users. If this insulation could never be broken down as is the case of power surges, high heat, overloaded motors and so on, there would not need to be any grounding. However, this is not the case. Nature, aging and changing conditions of service all lead to eventual insulation breakdown.
So, what makes a good grounding system? As mentioned earlier, the stray current needs to get to ground. A ground wire coming from the motor needs to be large enough to carry current from the motor to the earth at a point where the earth is suitable to attract it. It should go deep enough to contact moist soil because very dry soil sometimes does not attract electrical current.
In addition to the earth, the ground wire at some point should also be connected to the ground furnished by the power source of the electric company. A ground is always brought into a service when power is provided. The electric company has their system grounded to earth throughout the system.
The pump installation should always include a ground wire that feeds all the way back to the point of electric service entrance. This includes submersible well pumps. Many argue that the motor is already in the ground, and it is true that can be a great source of grounding. The motor does rest in water that separates it from earth.
In some cases, the quality of that water may not carry current as expected, or no better that the water coming through the pipes and may still lead stray current to someone opening a faucet. It is recommended that all well pump motors have the ground wire connected to the same service ground as any other motor would be.
Grounding is a safety issue and offers protection from electric shock or electrocution due to leaking current. Grounding should never be ignored, and it is wise to verify that the ground service brought to the motor is properly connected as well.