Wire Fill for Submersible Well Pump
Submersible well pump wire fill: 1.5 HP at 240V uses 12 AWG copper on 20A breaker, larger pumps need 10-8 AWG. NEC Article 430 motor sizing applies.
Wire fill for submersible well pump circuits is governed by NEC Article 430. A typical residential 1/2 to 1.5 HP single-phase 240V submersible pump uses a 20A breaker, 12 AWG copper THWN-2 (or 10 AWG for long runs), and 3/4-inch PVC for the buried home-run from house to well head. Larger pumps (3-5 HP) need 30-40A breakers with 10 AWG or 8 AWG copper. Motor sizing follows NEC 430.6, 430.22, and 430.52 using Table 430.250 full-load currents.
Load characteristics
Submersible pumps are inductive loads with significant starting current:
| Pump HP | NEC 430.250 FLA (1ph 240V) | Starting current (LRA) | Breaker | Motor overload |
|---|---|---|---|---|
| 1/2 HP | 4.9A | ~30A | 15A | 6.0A |
| 3/4 HP | 6.9A | ~40A | 15A | 8.6A |
| 1 HP | 8A | ~45A | 20A | 10.0A |
| 1.5 HP | 10A | ~55A | 20A | 12.5A |
| 2 HP | 12A | ~65A | 25A | 15.0A |
| 3 HP | 17A | ~95A | 30A or 40A | 21.3A |
| 5 HP | 28A | ~150A | 50A | 35.0A |
Starting current can be 5-7× FLA, so NEC 430.52 lets the breaker be up to 250% of FLA for inverse-time circuit breakers (or 175% for fuses) to handle starting without nuisance tripping.
NEC code references
- NEC 430.6 — sizing using Table 430.250
- NEC 430.22 — single motor circuit conductors at 125% of FLA
- NEC 430.32 — motor overload protection (heater elements at 115-125% of nameplate)
- NEC 430.52 — branch circuit short-circuit and ground-fault protection
- NEC 430.102 — disconnect within sight of motor
- NEC 300.5 — burial depth for direct-buried cable or conduit
Conductor sizing
Conductors at 125% of Table 430.250 FLA (NEC 430.22):
| Pump HP | FLA | × 1.25 | Min copper THWN-2 |
|---|---|---|---|
| 1/2 HP | 4.9 | 6.1A | 14 AWG |
| 1 HP | 8 | 10A | 14 AWG |
| 1.5 HP | 10 | 12.5A | 14 AWG (or 12 for headroom) |
| 2 HP | 12 | 15A | 14 AWG |
| 3 HP | 17 | 21.3A | 12 AWG (or 10 for VD) |
| 5 HP | 28 | 35A | 10 AWG |
| 7.5 HP | 40 | 50A | 8 AWG |
Voltage drop is critical for well pumps because runs are often 100-300 ft from house to well head, then another 100-400 ft of drop pipe to the pump. Most pump manufacturers publish wire size tables based on total length:
| Pump HP | 100 ft | 200 ft | 300 ft | 500 ft |
|---|---|---|---|---|
| 1/2 HP | 14 AWG | 14 AWG | 12 AWG | 10 AWG |
| 1 HP | 14 AWG | 12 AWG | 10 AWG | 8 AWG |
| 1.5 HP | 12 AWG | 10 AWG | 8 AWG | 6 AWG |
| 3 HP | 10 AWG | 8 AWG | 6 AWG | 4 AWG |
Follow the pump manufacturer's chart — they're more conservative than NEC code minimum because pump motors are sensitive to under-voltage.
Conduit sizing
Pump cable typically has 3 conductors (L1, L2, EGC) for 2-wire 240V submersibles, or 4 conductors (L1, L2, EGC, control) for 3-wire 240V pumps with start capacitor in the control box.
| Pump | Conductors | Total area | 3/4" PVC Sch 40 | 1" PVC Sch 40 |
|---|---|---|---|---|
| 1.5 HP, 12 AWG | 2 × 12 + 1 × 12 EGC | 0.0399 in² | 9.8% | 4.5% |
| 3 HP, 10 AWG | 2 × 10 + 1 × 10 EGC | 0.0780 in² | 19.2% | 8.8% |
| 5 HP, 8 AWG | 2 × 8 + 1 × 10 EGC | 0.0855 in² | 21.1% | 9.6% |
| 5 HP, 3-wire control | 3 × 8 + 1 × 10 EGC | 0.1228 in² | 30.3% | 13.8% |
3/4-inch PVC handles essentially every residential well pump installation, with margin.
Special requirements
- Submersible pump cable: Listed twisted assembly (yellow or black) — direct-buried-rated or fed inside the well casing for the down-hole portion.
- Pitless adapter: Buried fitting connecting drop pipe to lateral water line at frost-free depth. Electrical cable runs along the drop pipe inside the casing.
- Pressure switch and control box: Located in well house, basement, or near pressure tank. Provides motor overload and (for 3-wire pumps) start capacitor.
- Disconnect: Required within sight of pressure switch / control box per NEC 430.102. A simple snap switch or breaker in sight works.
- Bonding: Bond well casing to grounding electrode system if metal casing is exposed.
- GFCI: Not required on the motor circuit itself, but any 120V receptacle in the well house needs GFCI per NEC 210.8.
Worked example — 1.5 HP submersible, well 175 ft from house, pump 200 ft deep
- Total wire length: 175 + 200 = 375 ft (down and back)
- Manufacturer chart (1.5 HP, 375 ft): 8 AWG copper recommended
- NEC 430.22 minimum: 14 AWG. Use 8 AWG for voltage drop.
- Breaker: 20A 2-pole (NEC 430.52 allows up to 25A but 20A is standard for 1.5 HP)
- Home-run from house to well head: 8 AWG copper THWN-2 × 3 in 3/4" PVC Sch 40 buried 18 inches
- Pitless to pump: 200 ft of 8 AWG submersible pump cable
- Fill check (PVC home-run): 2 × 0.0366 + 1 × 0.0366 EGC = 0.1098 in² in 3/4" PVC Sch 40 (40% limit 0.213) = 27.0% pass with margin.
- Pressure switch: 30/50 PSI standard, includes the disconnect for the pump motor.
Quick reference
| Pump HP | NEC 430 FLA | Breaker | Copper wire (short run) | Conduit |
|---|---|---|---|---|
| 1/2 HP | 4.9A | 15A | 14 AWG | 1/2" PVC |
| 1 HP | 8A | 20A | 12 AWG | 1/2" PVC |
| 1.5 HP | 10A | 20A | 12 AWG | 3/4" PVC |
| 2 HP | 12A | 25A | 12 AWG | 3/4" PVC |
| 3 HP | 17A | 30A | 10 AWG | 3/4" PVC |
| 5 HP | 28A | 50A | 8 AWG | 3/4" PVC |
| 7.5 HP | 40A | 70A | 6 AWG | 1" PVC |
Always cross-check with pump-manufacturer voltage-drop tables for the actual run length.
Related
FAQ
This page's figures are transcribed from NEC 2023 (NFPA 70) Chapter 9, Tables 1, 4 and 5, and checked by a version-controlled automated test suite — they are not signed off by a licensed professional. WireFillChart is an independent reference, not affiliated with or endorsed by NFPA. Always verify against the code edition adopted by your local authority having jurisdiction (AHJ).