Hot tubs & spas

Electrical — NEC Article 680, Part IV

The National Electrical Code treats hot tubs and spas as a special occupancy with its own article. Part IV of NEC 2023 §680 covers spas — outdoor at NEC 2023 §680.42, indoor at NEC 2023 §680.43.

• Receptacle setback (outdoor). NEC 2023 §680.42 — a 125 V, 15 or 20 A receptacle is required not less than 6 ft and not more than 20 ft from the inside wall of the spa. Any receptacle within 20 ft must be GFCI-protected.
• Receptacle setback (indoor). NEC 2023 §680.43 — required receptacle 6 ft to 10 ft from the inside wall. Other receptacles within 10 ft rated ≤ 30 A require GFCI protection.
• Disconnect. A readily accessible disconnecting means, in sight of the spa, at least 5 ft away — so a bather can reach it without touching energized equipment. Locking the panel breaker does not count.
• GFCI on the feeder. NEC 2023 §680.44 requires GFCI on all outlets supplying a self-contained, packaged, or field-assembled spa. Exception: a listed self-contained / packaged unit with integral GFCI protection for all its own components is already covered. Cord-and-plug portable units are limited to 15 or 20 A, 125 V single-phase per NEC 2023 §680.42(A)(2).
• GFCI trip level. A Class A GFCI trips at 6 mA within approximately 25 ms (must not trip below 4 mA). This is the UL 943 §Class A personnel-protection standard — the same device you'd see on a bathroom receptacle.

Equipotential bonding — 680.26

Bonding is the reason a hot tub is safe even when everything around it is wet. The goal is to keep every metal surface, every wet surface, and the water itself at the same electrical potential so a person can't become part of a current path.

NEC 2023 §680.26 requires bonding of the shell's metal parts, perimeter surfaces within 3 ft horizontally of the spa, metal fittings, pump and motor housings, metal raceways and piping, ladders, and luminaires. The bonding conductor must be ≥ 8 AWG solid copper — insulated, covered, or bare. When a perimeter grid is used, it is 8 AWG on a 12″ × 12″ grid tied to the equipotential bond.

Bonding is not the same as grounding. Bonding equalizes; grounding provides a return path to earth. Both are required. A hot tub installed without bonding can pass a plug-in leakage test and still be a lethal step-potential hazard.

Foundation & base

Manufacturers universally require a level, non-flexing surface. There are three common approaches:

1. Reinforced concrete slab. Minimum 4″ thick at 3,500–4,000 psi. 6″ is commonly specified for larger tubs or expansive/soft soils. Reinforce with #3 or #4 rebar on a 12–18″ grid (or 6×6 W1.4×W1.4 welded wire mesh), chaired to mid-slab depth. Full 28-day cure before installation.
2. Compacted paver base. Per the ICPI / CMHA hardscape guide spec (PAV-GSP-004-21): 4–6″ of compacted crushed stone, compacted to ≥ 95% Standard Proctor (ASTM D698) for cohesive soils, or 95% Modified Proctor (ASTM D1557) for granular soils. Pavers set on a 1″ bedding course of ASTM No. 8 stone, with edge restraint on all sides.
3. Manufactured spa pad. Interlocking polymer pads (Handi-Spa, EZ Pad, etc.) sit on a compacted base. Fastest install, works for many models — but check whether your specific manufacturer accepts it before you commit.

A filled 7'×7' hot tub with four bathers weighs roughly 4,000–5,000 lb. Distributed over 49 ft², that's under 100 psf — but concentrated at the corners it can be much higher. Use the calculator below to sanity-check your specific model.