Wire Fill Chart for Swimming Pool Wiring
Wire fill for swimming pool circuits: 20A pump on 12 AWG THHN, 50-60A heater on 6 AWG, all in 3/4-1 inch PVC Sch 80 above grade per NEC Article 680.
Wire fill for swimming pool circuits is governed by NEC Article 680. A typical residential pool installation has a 20A 120/240V pump circuit on 12 AWG THHN copper, a 50-60A 240V heater circuit on 6 AWG copper, and a low-voltage lighting circuit. All conductors above grade at the equipment pad must be in PVC Schedule 80 or other approved corrosion-resistant raceway per NEC 680.23(B)(2). GFCI protection is mandatory on pump and lighting circuits per NEC 680.21(C).
Load characteristics
Residential pool loads are mostly continuous during operation:
| Equipment | Voltage | Typical FLA | Breaker | Continuous? |
|---|---|---|---|---|
| Single-speed pump (1.5 HP) | 240V | 8-10A | 20A | Yes |
| Variable-speed pump | 240V | 5-8A | 20A | Yes |
| Electric heater (small) | 240V | 50A | 60A | Yes |
| Salt cell / chlorinator | 120V | 3A | 15A | Yes |
| Underwater light (line voltage) | 120V | 4A | 20A GFCI | No |
| Underwater light (low voltage) | 12V via xfmr | 2A primary | 15A GFCI | No |
The pump is the workhorse. Most modern variable-speed pumps are sized at 16A or 20A circuits per the manufacturer instructions.
NEC code references
- NEC 680.21 — pool motor branch circuits, GFCI requirement
- NEC 680.23 — underwater luminaires, raceway for transformer secondary
- NEC 680.24 — junction boxes (brass, listed for pool)
- NEC 680.25 — feeders to pool equipment panels
- NEC 680.26 — equipotential bonding (8 AWG solid copper)
- NEC 680.42-44 — separately covers hot tubs and spas (see Wire Fill for Hot Tub)
Conductor sizing
Use 75°C column of NEC 310.16 for terminations (most breakers and disconnects are rated 75°C):
| Load | Copper THHN | Aluminum |
|---|---|---|
| 20A pump | 12 AWG | 10 AWG |
| 30A small heater | 10 AWG | 8 AWG |
| 50A heater | 6 AWG | 4 AWG |
| 60A heater | 6 AWG | 4 AWG |
| 100A pool sub-panel | 3 AWG | 1 AWG |
For runs over 100 ft, check voltage drop separately with the Wire Ampacity Calculator and consider stepping up one gauge.
Conduit sizing — PVC Schedule 80
PVC Sch 80 is the standard above grade at the equipment pad. Use NEC Chapter 9 Table 4 for PVC Sch 80 internal area (slightly less than Sch 40):
| Circuit | Conductors | Conductor area | 3/4" Sch 80 fill | 1" Sch 80 fill |
|---|---|---|---|---|
| 20A pump (2-wire + EGC) | 3 × 12 THHN | 0.0399 in² | ~14% | ~9% |
| 30A heater (3-wire + EGC) | 3 × 10 + 1 × 10 | 0.0848 in² | ~30% | ~18% |
| 50A heater (2-wire + EGC) | 2 × 6 + 1 × 10 | 0.1115 in² | ~39% — over | ~24% |
| 60A heater (3-wire + EGC) | 3 × 6 + 1 × 10 | 0.1622 in² | over 40% | ~34% |
| 100A pool sub-panel (4 conductors) | 3 × 3 + 1 × 8 | 0.3199 in² | over 100% | ~68% — over |
For the 50A and larger heater feed, use 1-inch PVC Sch 80. For the 100A pool sub-panel feed, step to 1-1/4 or 1-1/2 inch.
Special requirements
- GFCI — All 15A and 20A 125V receptacles within 20 ft of pool wall, all pool motor branch circuits per NEC 680.21(C).
- Equipotential bonding — Solid 8 AWG copper connecting pump motor, ladders, handrails, reinforcing steel, perimeter surfaces (NEC 680.26).
- Junction boxes — Listed brass or PVC Type FS within 10 ft of pool, raised to grade per NEC 680.24.
- Wet location conductors — THWN-2 is preferred over THHN when conductors enter underground or wet portions of raceway. THHN/THWN-2 dual-rated is standard.
- Disconnect — Within sight and at least 5 ft horizontal from pool wall per NEC 680.13.
Worked example — 1.5 HP pump + 50A heater
A typical equipment pad has both circuits run from a sub-panel in the garage to the pad in separate raceways:
- Pump feed: 12 AWG THHN × 3 (L1, L2, EGC) in 3/4" PVC Sch 80, 20A 2-pole GFCI breaker.
- Heater feed: 6 AWG THHN × 2 + 10 AWG EGC in 1" PVC Sch 80, 60A 2-pole breaker (50A heater nameplate, breaker per heater spec).
- Equipotential bond: 8 AWG solid bare copper run separately to pump motor, heater chassis lug, ladder anchor, and structural rebar.
Verify fill with the Conduit Fill Calculator and check the PVC Conduit Fill Chart for quick lookup.
Quick reference
| Equipment | Breaker | Wire (Cu THHN) | Conduit (PVC Sch 80) |
|---|---|---|---|
| 1.5 HP single-speed pump | 20A | 12 AWG × 3 | 3/4" |
| VS pump | 20A | 12 AWG × 3 | 3/4" |
| 50A heater | 60A | 6 AWG × 2 + 10 EGC | 1" |
| Low-voltage lighting xfmr | 20A GFCI | 12 AWG × 3 | 1/2" |
| Pool sub-panel 100A | 100A | 3 AWG × 3 + 8 EGC | 1-1/4" |