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This guide shows how most 240 volt hot tubs and portable home spas are wired, with photos, a step-by-step hook-up movie & 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 and qualified to do electric wiring, there's still installation prep work you can do to reduce expenses. We'll walk you through a typical project to show what's involved. About 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 web site. 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.

Regardless of who performs the work, be sure that power to the spa circuit is switched off at the house service panel prior to inspections, wiring, or repairs. 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 a 100 amp service, with 150-200A common in newer homes. Panel ratings are normally labeled near the main breaker at the top.

Electric Service Panel
     Service Panel

It's a common misconception that the sum total of the amps of all the circuit breakers installed 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 hot tub, as illustrated by our interactive wiring diagrams below. A 240V spa must be supplied by a circuit which meets its load requirements (amperage) as indicated in owner's manual.

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

We're using a typical outdoor portable home spa installation for our example.

The (3) electrical assemblies involved in this project are the:

  • House Circuit Breaker Service Panel
  • Rainproof Spa GFCI Load Center/Disconnect Panel*
  • Spa Control System (box inside the hot tub enclosure)

MW Spa GFCI Load Center/Disconnect Panel
for Hot Tubs up to 50A

120V Branch Circuit

GFCI Disconnect Panel

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

The NEC also requires a 120V receptacle within 10-20 feet from the spa. Our MW Panel provides this branch circuit expandability with no need for a separate wiring run!

Installing our Backyard Spa

Now let's take a look at a typical backyard installation. In our movie below, we've already poured a level cement slab and placed our new, energy-efficient Belize portable hot tub on it. For a quick, easy, and lower cost alternative to concrete, check out Handi Spa Pads.

Concrete spa pad

Per the owner's manual, our example hot tub requires a 240V, 50 amp 4-wire electrical hook-up, using AWG #6 copper wire. The electrician is running all buried wiring in 1" rigid Sch-40 gray PVC electrical conduit.  Refer to your owner's manual and a qualified electrician for your wire requirements.

Click the tabs below to follow the project from Planning through Hook-up:

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, which should correspond to the size of the new feed circuit breaker installed in the house service panel. The Spa 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, which means they require an electrical circuit providing (2) hot wires, (1) neutral, and (1) ground wire. Check the owner's manual.


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 ground occurs, causing the circuit breaker to trip on overload (not to be confused with the safety function of the GFCI). About 120V hot tubs.

Some 240V spas (and many older ones) use three wire systems with (2) hot wires and (1) ground wire, without a neutral wire. 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 a 4-wire service in order for the GFCI to function as required. Refer to the spa owner's manual for wire gauge, etc.

Note: Some spas, such as certain models of Hot Springs and Caldera (Watkins) spas require use of a special subpanel with 2 separate 240V GFCI breakers in the load center.

Hot Tub Wiring Diagrams

Our MW Spa GFCI Load Center/Disconnect is designed for 240V hot tubs, 4 or 3 wire spa types, with specified loads up through 50 amps or less. The interactive schematic diagram below shows 3 and 4 wire configurations. Select the wiring configuration that your spa requires:

Other brands of equipment may differ from our illustrations in appearance and/or terminal configuration. Read equipment's installation instructions.
Why our MW Spa GFCI Load Center 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, often incorrectly attributed to a problem with the spa, when no problem exists.

Because of the reactive loads that spa motors present along with the resistance load of heaters, and the fact that parts of the spa including ozonators may run on 120V, common GFCI breakers sometimes react to a normal spa condition as if it were a ground fault. They can be very unreliable.

Our Spa GFCI Disconnect 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, located 10-20 feet away from a spa or pool, for safe operation of corded appliances.

Weather-proof covered outdoor outlet
GFCI Outdoor Outlet Example

Our GFCI load center provides for expandability for a 120V branch circuit outdoor outlet. This alone pays for itself! (Be sure to use a GFCI outlet receptacle for this circuit). Schematic & instructions included.



Note: Voltage specifications on our site: 220V, 230V, and 240V are interchangeable because actual line voltage will vary somewhat across the USA. 110V, 115V, and 120V are also interchangeable.


Installation Basics:

Service Panel Breaker

The feeder circuit breaker in the service panel must be sized according to the spa's load requirement, per the owner's manual or as determined by an electrician. The load rating of the disconnect box should be at least equal to, or larger than this limiting breaker in the house service panel.

240 volt double pole circuit breaker

Removing Knockouts
The electrician can easily determine if your electric panel can adequately 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, but always check with a qualified electrician.

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


GFCI Tripping Due to Mis-wired Neutral

Flunking Grade The most common wiring mistake occurs with 4-wire systems. Unfortunately, we've found that even a few professional electricians sometimes get a flunking grade on this one:

The white neutral wire to the spa's control box must be attached (as shown in our 4-wire diagrams above) directly to the neutral terminal of the GFCI breaker, NOT TO THE SUB-PANEL GROUNDING BAR. Mis-wiring it to ground instantly trips the GFCI when energized, cutting power to the hot tub.

Non-metalic conduit

PVC Electrical Conduit and Fittings

We prefer the protection of buried conduit in a backyard setting where future digging may occur for planting scrubs, 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.

In our example, 4 wires are used in 1" PVC conduit, which although a bit oversized, makes pulling the wire easier. For corner bends, wide 90° PVC elbows are used.

PVC clampsTerminal adapter Threaded PVC terminal adapters are cemented to the conduit for electrical box connections.  

Our electrician used short lengths of flexible liquid-tight PVC conduit for the connections to our spa control pack and from the outside wall LB Condulet through to the electrical service panel. The LB allows easy access for running the wires.

Flexible conduit
Flex Conduit
LB Condulet
LB Condulet
PVC expansion joint Frost Expansion Joints

Where required by local code, a PVC expansion joint must be employed at points where conduit pipe emerges from the ground and enters a wall or a wall-mounted enclosure.

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

Cutting & Cementing of PVC Conduit

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

PVC pipe cutters Cuts should be made square, using a cutting tool or saw. It is important that burrs are removed, and that pieces are dry-fit prior to gluing.

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

More information:
NEMA Guide Solvent-Cementing PVC Nonmetallic Conduit

PVC cement

Wire Size & Type for Hot Tubs

After reviewing the hot tub owner's manual, our electrician determined that #6 THHN stranded copper wire was the right choice for our project needs, and used four individual insulated conductors: (1) red & (1) black hot, (1) white neutral, and (1) green (insulated) ground wire in our project example.

Wire guage Your wire gauge requirements may differ from our example, depending upon the spa manufacturer's specification, code requirements, type of wire, and other factors. Unusually long runs may require larger wire size, as determined by the electrician.

Although copper is not cheap, scrimping by using under-size wire is a hazardous false economy, and 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 wire larger than #6. If using larger wire, a separate junction box near the spa (not to be confused with the Disconnect Panel) may be required for splicing short lengths of #6 wire (or as prescribed) between that junction box and the spa controller. Refer to the owner's manual.

junction box
UF-B Direct Burial Cable 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 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 to help it slide smoothly over fitting edges and around 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

Fish tape
Fish Tape            
One person pushes the wires, carefully keeping them separated and straight without twisting or kinks as they enter the conduit, while applying wire lubricant. 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, resulting in a large knot which 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 which will 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, from above the hook 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.
tape wrapped Wiring lubricant 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.

Wires can be fished from either end of the conduit, but if there are very tight bends nearer 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:  A fish tape must never be used around electrified wires, or fished into or out of the electrical service panel, even if the main breaker is shut off.

Tightening terminal screws 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.


Hooking Up Spa Pack Control for hottub

Spa Control System Pack

In our example, the electrician installed flex conduit for the power wires inside the hot tub's equipment bay, referring to the owner's manual hookup instructions. Replacement Spa Packs


  • 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!

Hot Tub Safety  Water Chemistry  Routine Maintenance  Spa Selector

Spas Requiring Dual 240V GFCI Subpanel Breakers

2 GFCI Subpanel Example
Subpanel Example
Some hot tubs, such as certain models of Hot Spring and Caldera spas (Watkins Manufacturing), require a special subpanel disconnect containing 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

Indoor electrical outlet
Indoor Outlet
This guide is aimed at 240 volt portable spa installations, so if you have a 120 volt plug-n-play spa or are planning on getting one, most of this information will not apply to you. However, a few spas are easily convertible to run on either voltage, such as the popular Belize Oval II and Trinity Spa models.
Weather-proof covered outlet
Outdoor GFCI Outlet
When configured for 120V use, spas in this class are equipped with a GFCI on the end of the power cord, which plugs into a standard dedicated household outlet. (Covered GFCI-protected outlets must be used outdoors). Advantages in converting these hot tubs over to hard-wired 240V include: faster heating time and ability to maintain set temperature in very cold weather.

Legal Disclaimer:
The Spa Depot assumes no liability for the use nor makes any warranty as to the accuracy, suitability or usefulness of the information provided herein, which 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 FOR ANY PROPERTY DAMAGE, PERSONAL INJURY AND/OR DEATH, OR ANY OTHER LOSS OR DAMAGE THAT MAY RESULT FROM YOUR USE OF THE INFORMATION PROVIDED. 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

spa customers write Consumer Reviews
Spa GFCI Load Center/Disconnect
"I was impressed with the quality. And I really like the fact that we were able to add an outdoor GFCI electrical outlet (which is required by code where we live) at the same time we installed this box, just by adding another breaker in one of the extra slots. This saved me the expense of a separate electrical run for the outlet. This feature saved me more than the cost of the load center!"

Brock Hirsch
Bricktown, NJ

Spa Depot, The, Spas & Hot Tubs - Dealers, Olympia, WA

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