How-To Guides | How to Wire a Spa for 120V or 240V

This guide shows how to wire most 240 volt hot tubs and portable home spas, including photos and hot tub schematic wiring diagrams.

This information is provided to help you to be a more informed consumer. We advise hiring a licensed electrician to wire and install a spa.

If you're not confident or qualified to do electric wiring, there's still installation preparation you can do to reduce expenses. We'll walk you through a typical project to show what's involved.

Jump to: 120V Hot Tubs

CAUTION: Electrical work and repairs can be dangerous, especially around water. There is a risk of shock or electrocution, which could result in serious injury or death. We strongly advise that hot tub electrical wiring be referred to a licensed electrician. Local code requirements for wiring vary and may differ from the educational examples on this website. The local code regulations must be followed, with permits and inspections obtained. The installer should read and follow the hot tub owner's manual and associated electrical component owner's manuals and instructions.

Shut off electrical power to the hot tub or pool at the service panel prior to any inspections or work. Improper wiring may damage equipment and void the spa manufacturer's warranty.


Your Electrical Service

Before installing a major appliance like a hot tub, determine if the electric service will handle the extra load. It's usually not a problem, since most homes built in the last 30-40 years have at least 100 amp service. 150-200A is common in most newer homes. Panel ratings are normally labeled near the main breaker at the top.

It's commonly misunderstood that the total amps of all installed circuit breakers must not exceed the service panel's indicated amp rating. This is false - capacity is determined by load calculations, not the size or number of its breakers.

Spa Wiring Basics - 240V Systems

We'll begin with an overview of the electrical requirements for wiring a spa, illustrated by our interactive wiring diagrams. A 240V spa must be supplied by a circuit that meets its load requirements (amperage) as indicated in the owner's manual.

This means that the feeder breaker (in the house service panel) must be of the specified size. Additionally, the GFCI breaker in the disconnect panel must be at least that size, and GFCI protected for safety.

The three electrical assemblies involved in this project are the:

  • House Circuit Breaker Panel
  • Outside Disconnect GFCI Box*
  • Spa Control System Box

MW Spa GFCI Load Center/Disconnect Panel for Hot Tubs up to 50A with bonus 120V Branch Circuit Expandability

*The National Electrical Code (NEC) specifies inthe stallation of an approved manual disconnect device. It must be adjacent to the hot tub, at least 5 feet away, and within line of sight.

The NEC also requires a 120V receptacle within a 10-20 foot distance from the spa.

3 & 4 Wire Spa Electrical Systems

A large portion of 240V spas manufactured today require a 50 amp 4-wire electrical service. Some hot tubs have load requirements of 30A or 40A, and a few even 60A. These requirements correspond to the size of the new feed circuit breaker installed in the house service panel. The Disconnect GFCI panel's amp rating can be equal to, or larger than the feed breaker in the main panel.

Hot tubs with mixed voltage components (such as 120V ozonator and 240V heater) require 4-wire systems. This means they require an electrical circuit providing (2) hot wires, (1) neutral, and (1) ground wire. Check the owner's manual.

hands installing wires on circuit board


The two hot legs (black + red) provide 240 volts (120V +120V). One hot leg with the neutral (white) wire provides 120V. The ground wire (green) carries no current except when a short circuit to the ground occurs. This causes the circuit breaker to trip on overload (not to be confused with the safety function of the GFCI).

Jump to: 120V Hot Tubs

Older 240V spas used 3-wire installations consisting of just 2 hot wires and a ground wire, without a neutral wire. 3-wire is obsolete and should not be used on new equipment.

Spas built within the last 25 years require 4-wire installation.

Both 3-wire and 4-wire spas must be GFCI protected. A 4-wire hot tub must not be connected to a 3-wire service. Proper grounding is also essential.

In either case, the disconnect panel must be supplied with 4-wire service in order for the GFCI to function correctly. Refer to the spa owner's manual for wire gauge, etc.

Note: Certain models of Hot Spring and Caldera spas (Watkins Manufacturing) require special subpanel disconnects. These have 2 separate 240V GFCI breakers in the load center.

Hot Tub Wiring Diagrams

Use a GFCI disconnect designed for 240V hot tubs, 4 or 3-wire spa types. The interactive schematic diagram below shows 3 and 4 wire configurations. Select the wiring configuration that your spa requires:

Black Image

Installation Basics:

Service Panel Breaker

Size the feeder circuit breaker in the service panel according to the spa's load requirement. You can find this information in the owner's manual, or an electrician can determine the value for you. The load rating of the disconnect box should be greater than or equal to the breaker in the house service panel.

The electrician can easily determine if your electric panel can accommodate the new 240V circuit required for this project. There also must be two available slots in the box for a double-pole breaker. In most homes, this will not be a problem.


When selecting an electrician, be sure to ask about experience installing hot tubs, particularly 4-wire configurations.

GFCI Tripping Due to Miswired Neutral

The most common wiring mistake occurs with 4-wire systems. Unfortunately, we've found that even a few professional electricians fail on this one.

Attach the white neutral wire to the spa's control box directly to the neutral terminal of the GFCI breaker. See our 4-wire diagrams above. Do not attach it to the sub-panel grounding bar. Miswiring it to ground instantly trips the GFCI when energized, cutting power to the hot tub.

PVC Electrical Conduit and Fittings

We prefer the protection of buried conduit in a backyard setting where future digging may occur for planting shrubbery, etc. PVC pipe is easy to install and inexpensive. 18" is usually the required depth-- check with local authorities. Secure conduit to walls with U clamps.

As an example, 4 wires are used in 1" PVC conduit, which although a bit oversized, makes pulling the wire easier. For corner bends, 90° PVC sweep elbows are used. Threaded PVC terminal adapters are cemented to the conduit for electrical box connections.

Use short lengths of flexible, liquid-tight PVC conduit for the connections to the spa control pack. From the outside wall through to the electrical service panel, use LB Condulet. The LB allows easy access for running the wires.

Frost Expansion Joints

Where local code requires, use PVC expansion joints where conduit pipe emerges from the ground and enters a wall or wall-mounted enclosures.

These slip couplings allow for changes in grade usually associated with frost heaves, to help prevent the breaking of the conduit.

Cutting & Cementing of PVC Conduit

PVC electrical conduit should be assembled prior to running the wire. It is generally easier to fish wires through the conduit in the trench before it is buried.

Cuts should be made square, using a cutting tool or PVC wire-rope saw. Remove burrs with a utility knife and medium-grit sandpaper. Dry-fit pieces before gluing.

PVC electrical conduit is joined with appropriate PVC solvent-based cement. Joint surfaces should be wiped clean before joining.

Wire Size & Type for Hot Tubs

Wire gauge requirements differ depending on the spa manufacturer's specifications, code requirements, and wire type. Unusually long runs may require a larger wire size, as determined by the electrician.

In many cases, #6 THHN-stranded copper wire is a good choice. In any event, your wire should have four individual insulated conductors: (1) red & (1) black-hot, (1) white-neutral, and (1) green-ground wire.

Although copper is not cheap, scrimping by using under-size wire is a hazardous false economy. It may violate code requirements and/or void your equipment manufacturer's warranty. Aluminum or copper-clad aluminum wire is not recommended. Sheathed cable, i.e. Romex®, is not permitted inside underground conduit.

Note: Spa control box terminals generally cannot accommodate wires larger than #6. Refer to the owner's manual.

Direct-Burial UF-B Wiring

Some localities may allow direct burial cable, at least for the run from the service panel to the disconnect box. Other jurisdictions prohibit it. UF-B cable can be cumbersome to work with, according to some electricians.

Pulling Wire

With proper preparations, pulling wire is not terribly difficult. After the conduit is assembled, electricians use a narrow spring steel fish tape to route wires through it. The first few inches of the tape are coated with wire-pulling lubricant. This helps it slide smoothly over fitting edges and around the bends of the empty conduit.

First, the tape is snaked through the empty pipe, being careful not to kink it by jamming. Then the wires are attached to the hook on its end and pulled back out.

Carefully push the wires into the conduit, keeping them separated and straight, avoiding kinks. Apply lubricant to the wires as they enter the conduit. A second person pulls from the opposite end with the fish tape tool.

Attaching Wires to the Fish Tape

A common mistake is to wrap all of the wires to the hook of the tape. This only results in a large knot that can get stuck or come undone. Here's a better method:

  • First, the fish tape is routed through the empty conduit and out the other end.
  • Then about 6" of insulation is stripped off of each conductor.
  • About 1/3 of the copper strands from each wire are separated and snipped out to make a thinner bundle. These will then fit more easily through the hook eye.
  • The bare cut-downs are then twisted snugly together with pliers.
  • Now the copper braid is looped through the hook and bent in half onto itself.
  • Finally, the bundle is double-wrapped barber pole style with electrician's tape. Starting above the hook, work down a few inches onto the insulated wires.
  • Properly done, the assembly will appear tightly wrapped and symmetrical.
  • The tape-covered bundle should be coated with wire lube for easier pulling.

NOTE: (4) #6 conductors pull much easier through 1" conduit than 3/4" diameter. An approved, non-flammable electrical wire lubricant should be liberally used.

You can fish wires from either end of the conduit. If there are tight bends closer to one end, pulling from that end sometimes provides less resistance.

It's easier to pull wires if there's room to lay them out to their full length. This helps avoid the kinks that result from spooled wire.

After the wires have been routed, the wrapped wire cut-downs attached to the fish tape are snipped off and discarded.

CAUTION: Never use a fish tape around electrified wires. Additionally, never fish into or out of the electrical service panel, even if the main breaker is off.

Terminal Wire Connections

Wherever wires are attached to terminals, the screw connections must be tight. Loosely attached wiring will inevitably result in overheating, burnt insulation, and failure of the circuit.

Spa Control Pack

Flex conduit for the power wires inside the hot tub's equipment bay is the perfect finishing touch and will allow flexibility within the cabinet for future repairs.

Things to avoid:

  • Don't forget to read your spa manufacturer's owner manual prior to installing.

  • Don't forget to get an electrical permit.

  • Don't install a hot tub under overhead power lines.

  • Don't run buried wiring under the spa.

  • Don't connect a 4-wire hot tub to a 3-wire circuit - it would be unsafe & illegal.

  • Don't use undersized wire.

  • Don't use aluminum wire.

  • Don't install outdoor lighting within 10 feet of hot tubs.

  • Don't use your hot tub until the electrical installation has been approved.

  • Don't forget to check the GFCI device frequently, using its TEST button.

  • Don't forget to maintain water balance and sanitizer.

  • Don't forget to replace & lock your spa cover after each use.

  • Don't forget to enjoy your hot tub regularly!

Spas Requiring Dual 240V GFCI Subpanel Breakers

Certain models of Hot Spring and Caldera spas (Watkins Manufacturing), require special subpanel disconnects. These contain two separate GFCI breakers: one for the heater, and a second for the pump and other components.

These spas should not be wired to a single spa circuit breaker box such as our MW disconnect panel. Consult your owner's manual, the dealer, or the manufacturer for installation information.

About 120V Portable Hot Tubs

This guide is aimed at 240 volt portable spa installations. If you have, or are getting a 120 volt plug-and-play spa, most of this information will not apply to you. However, a few spas are easily convertible to run on either voltage model.

When configured for 120V use, spas in this class use a GFCI on the end of the power cord. This then plugs into a standard dedicated household outlet. Covered GFCI-protected outlets must be used outdoors. Converting these spas to hard-wired 240V serves two purposes: faster heating time and the ability to maintain heat in cold weather.

Legal Disclaimer: assumes no liability for use nor makes any warranty as to the accuracy, suitability or usefulness of this information. This information is not intended to replace or substitute for information contained in the equipment owner's manuals. You expressly agree to hold The Spa Depot and its employees harmless. This includes property damage, personal injury and/or death, loss or damage that resulting from your use of this information. No advice or information, whether oral or written, obtained by you from this web site or our employees shall create any warranty not expressly made herein. Reader agrees to assume all risk resulting from the application of any of the information provided herein. By using this web site, including any applets, software and content contained therein, the visitor agrees that the use of this web site and its information product is entirely at his/her own risk.

Read Caution Statement

Other brands of equipment may differ from our illustrations in appearance and/or terminal configuration. Read equipment's installation instructions.

Why the MW Spa GFCI Load Center/Disconnect is the better choice:

Unfortunately, conventional load centers often perform unreliably with hot tubs due to the phenomenon called errant tripping. This false tripping is a great frustration to homeowners and electricians alike. It is often incorrectly attributed to a problem with the spa when no problem exists.

Common GFCI breakers sometimes react to a normal spa condition as if it were a ground fault. Reactive loads that spa motors present plus the resistance load of heaters make normal GFCI breakers unreliable at best.

Our Spa Disconnect GFCI panel solves these problems. It's the dependable ground fault detector designed just for hot tubs. The specially-shielded GFCI prevents false tripping due to RF interference. It is also engineered for low-voltage stability to prevent tripping due to brownouts, fluctuations, and mixed loads. If there is a ground fault, the fast-acting GFCI instantly disconnects the lines.

Note: The NEC and many jurisdictions REQUIRE the installation of a 120V outdoor GFCI outlet. It is to be located 10-20 feet away from a spa or pool, for safe operation of corded appliances.

Spa GFCI Load Center/Disconnect

"I was very impressed with the quality. I love that we were able to add the outdoor GFCI electrical outlet (required by code where we live). We didn't have to pay the electrician for wiring a whole separate circuit. That alone more than paid for it!"

Brock Hirsch
Bricktown, NJ


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