How to wiring a well pump

Sizing the Circuit and Conductors

Most residential well pumps run 1/2 HP to 1.5 HP on 230V single-phase, pulling 6 to 10 amps at full load. Always size from the motor nameplate FLA, not the horsepower rating. Per NEC 430.6(A)(1), use the tables in 430.248 for single-phase motors when the nameplate is missing or unreadable.

Branch-circuit conductors must be rated at least 125% of the motor FLA (NEC 430.22). For a typical 1 HP, 230V pump at 8 FLA, that is 10 amps minimum, so 14 AWG copper handles the load, but most installers pull 12 AWG for voltage drop on long runs from the panel to the well head.

Voltage drop kills pumps. Keep it under 3% on the branch circuit per NEC 210.19(A) Informational Note No. 4. On runs over 100 feet, bump to 10 AWG. A pump that sees 200V instead of 230V draws more current, overheats the windings, and trips the overload, or worse, cooks the motor.

• 1/2 HP, 230V: 12 AWG up to 150 ft, 10 AWG beyond
• 3/4 HP, 230V: 12 AWG up to 120 ft, 10 AWG beyond
• 1 HP, 230V: 10 AWG up to 180 ft, 8 AWG beyond
• 1.5 HP, 230V: 10 AWG up to 130 ft, 8 AWG beyond

Overcurrent Protection and Disconnect

Motor branch-circuit protection is not the same as overload protection. The breaker or fuse protects against short circuits and ground faults, sized per NEC 430.52 and Table 430.52(C)(1). For a single-phase motor on an inverse-time breaker, you can go up to 250% of FLA, rounded up to the next standard size per 430.52(C)(1) Exception No. 1.

An 8 FLA motor can land on a 20A breaker. Do not undersize thinking you are being conservative, the starting inrush will nuisance trip and you will be driving back out to the job. Overload protection lives in the pressure switch box or control box, sized at 115% to 125% of FLA per NEC 430.32.

NEC 430.102(B) requires a disconnect within sight of the motor, or lockable if out of sight. For a submersible with the motor 200 feet down the casing, the disconnect at the well head or pressure tank qualifies as "in sight" of the driven machinery, which is the pump itself. A fused pull-out or a 2-pole switch in a raintight enclosure is standard.

Grounding, Bonding, and GFCI

The well casing, if metal, must be bonded per NEC 250.112(M). Run a bonding jumper from the casing to the equipment grounding conductor at the pressure tank or service. Use a listed bronze ground clamp, not a hose clamp with a lug jammed under it.

The 2020 NEC added 210.8(F) requiring GFCI protection for outdoor outlets, and 422.5 covers specific appliances. Submersible well pumps themselves are not on the GFCI list, but any 125V receptacle at the well head for a control box or convenience outlet is. Check your adopted code cycle, some jurisdictions on the 2023 NEC now require GFCI on all outdoor single-phase branch circuits 150V to ground or less.

If the pressure switch chatters or the pump short-cycles after a GFCI is added upstream, check for a neutral-to-ground bond past the service. Submersible pump leads can develop leakage over years, and a brand new GFCI will find it immediately.

Wiring the Pressure Switch and Control Box

Two-wire submersibles have the starting components down in the motor and land directly on the pressure switch: L1, L2, and ground. Three-wire pumps require a control box with a start capacitor and relay, mounted above ground within the manufacturer's maximum cable length.

Match the control box to the exact pump model. A Franklin 1 HP box will not run a Goulds 1 HP correctly, the capacitor values differ. Land the yellow wire on Y, red on R, black on B, and the green ground to the box chassis and the pressure switch ground lug.

1. Kill power at the breaker and verify with a meter, not a tic tracer alone
2. Land incoming L1 and L2 on the line side of the pressure switch
3. Run load side to the control box line terminals
4. Land pump drop cable on the control box load terminals per color code
5. Bond the well casing, pressure tank, and equipment ground together
6. Megger the pump leads to ground before energizing, minimum 1 megohm cold

Submersible Cable and Splices

Drop cable is flat-jacketed, twisted, or individual THWN in conduit down the casing. Size it for the total run from the control box to the motor, not just the depth. A 200 ft well with 80 ft of lateral to the house is a 280 ft run for voltage drop calculations.

Every splice below the pitless adapter must be waterproof. Use heat-shrink splice kits with adhesive liner, or a listed submersible potting kit. Wire nuts with electrical tape will fail within a season, and pulling a pump to redo a splice is an 800 dollar mistake.

Tape each splice individually before bundling. If one conductor fails, you can identify which leg without cutting all three apart, and water ingress into one splice will not wick across to the others.

Commissioning and Documentation

Before closing the well cap, record the megger reading, the static water level, and the amp draw on each leg at steady state. Amps should match the nameplate within 10%. A high reading means binding, sand, or low voltage. A low reading means a dry well or a stuck check valve.

Label the disconnect with the pump HP, voltage, and FLA per NEC 110.22. Leave the control box cover and pump manual with the homeowner, taped inside the pressure tank enclosure if there is no other dry spot. The next tech to troubleshoot will thank you, and half the time that next tech is you, two years later.