A water pump, whether it is cord and plug connected or straight-wired, should be the only load on that circuit. A water pump draws between 8 and 15 amperes when running. The water pump pulls several times its running amperes when starting up, so you need to have it wired to a circuit dedicated to the pump alone. Residential water pumps have 110-volt, 220-volt or dual-voltage motors. Wire residential water pumps with 12/2 Romex with ground wire and protected with a 20-ampere circuit breaker. Most water pumps have a dual-voltage motor and should be wired for the higher voltage.
Mount the safety disconnect switch on a wall, within sight of the water pump location. The National Electrical Code requires that a safety disconnect switch be visible from the appliance it is disconnecting.
Install a run of cable between the safety disconnect switch and the main service panel. Cut the cable long enough at the service panel end to reach any area inside the panel box. You will trim the wires to length when you install the circuit breaker.
Position the battery-powered work light to shine on the service panel. Turn off the main service breaker on the panel and remove the outer and inner panel covers. Remove a metal knockout slug from the side of the panel box and install one of the cable connectors in the hole.
Install the new circuit breaker. Circuit breakers either snap in place or are secured to the bus bars by screws.
Push the cable through the connector and tighten the clamping screws securing it in place. Remove the cable's outer covering with the razor knife. Route the black and white wires to the circuit breaker, cutting off the excess wire. Run the bare copper wire down to the ground bar, securing the wire under a screw on the grounding bar.
Remove 3/4 of an inch of insulation from the black and white wires. Tape the full length of the white insulation to re-identify it as a current-carrying conductor. Secure the stripped ends under the screws on the circuit breaker.
Replace the panel box covers. With the new branch circuit breaker in the off position, turn the main breaker to the on position.
Install a cable connector in the top of the safety disconnect switch. Install the cable as you did at the service panel. Connect the black and re-identified white wire to the top switch terminals. Connect the ground wire to the ground bar.
Install a flex connector in the bottom of the safety disconnect switch box and another in the pressure switch housing on the pump. Cut a length of flex to run between the pump and the switch box. Push lengths of black, red and bare or green insulated wire through the flex. Connect the red and black wires to the bottom terminals on the safety switch. Connect the bare or green insulated wire to the ground bar.
Connect the red and black wires to the "L1" and "L2" terminals on the pressure switch. Connect the ground wire to the green screw. Replace the cover on the pressure switch. Turn on the safety disconnect switch. Turn on the branch circuit breaker.