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The Basics of Spa Electronics

Warning - Please read this section first !

This section is presented for the do-it-yourselfer who needs some help either troubleshooting or repairing their own hot tub spa. Here we are assuming that if you have chosen to work on your own unit, you have a basic knowledge of electricity.

Please remember that water and electricity DO NOT MIX. If you are not capable of performing a repair yourself, please contact a local spa professional or a licensed electrician in your area.

Also realize that the wiring and equipment described herein represents the "average" spa equipment pack. Your unit may vary significantly from the components described below. If you are in doubt as to how to properly troubleshoot or repair your specific unit, please contact a local spa professional or a licensed electrician in your area.

Use any of the information contained herein AT YOUR OWN RISK. We will not be held liable for any injuries that may result from the troubleshooting or installation of any electrical components in your hot tub spa unit.



In order for you to service any spa equipment, you absolutely must have and know how to use a multi-meter capable of measuring 120 and 240 single phase voltage, ohms, and amperage. Without this equipment, any repairs made to the electrical parts of this equipment will be strictly by trial and error or guessing which usually results in parts replaced that weren't actually bad. If you do not have a meter capable of each of these functions, either buy one at a local electrical supply house or borrow one. Either way, you must have one to work competently. Your meter instructions will explain how to hook up the test leads for each of the tests that follow.

Voltage Testing

Voltage tests of any circuit inside the equipment can be done using much the same principle as testing for good line service (covered in LINE SERVICE CHECK section of this guide). Simply decide what voltage you expect to find at a test point, set your meter (if not preset) for the scale showing this voltage, and apply your leads to the circuit in question. It is always best to put your test probes on the leads supplying the actual circuit, rather than in locations you would assume are of the same polarity.

When most people test, they conveniently apply one lead to the ground, and look for voltage with the other lead. The results of this method will easily mislead you because even a neutral wire carries electricity when a component is running. There’s no reason not to expect to see voltage when tested in this fashion. If it is a 120 volt circuit, one lead must go to a neutral connection point, and the other to the point at which there should be 120 volts. A 240 volt test must include two separate points where individual 120 volt supply leads are providing power.

Amperage Testing

An amperage test can only be conducted when a component is actually running. The components that you might test with your ampmeter are the heater (120v should read 12.5 amps, 240 volt should read 25 amps), the blower (1 Hp will read 5-6 amps, 1-1/2 to 2 Hp will read 7-9 amps), and the pumps low and high speeds (look at the plates on the motor for the amperages you should see and your actual reading should be within 10% of that). If your voltage supply to the pack is lower than the 120 volts or 240 volts as mentioned, then your amperage draw will be somewhat lower as well, (especially noticeable on heaters).

On 120 volt tests, an amperage reading should only be taken on the lead actually supplying the voltage to a component (not on the neutral). For 240 volt components, either wire supplying power will give you a good reading.

WARNING: A reading several amps higher than the component is rated for will ultimately result in a premature failure of the equipment or worse, an electrical hazard.


Using the ohms scale on your meter, you can determine whether or not you have continuity in a circuit. Continuity is the ability for electricity to pass unrestricted between two ends of a wire or circuit. Ohms is the unit of measure of that restriction or resistance. The more resistance you have, the weaker the circuit is. Therefore, when testing a switch for continuity, your meter needle should read 0 ohms if the circuit is closed or "on" (unless the battery in your meter is weak in which case the needle will move but not all the way to 0). There should be infinite resistance such that the needle does not move at all if the circuit is open or ‘off.

WARNING: NEVER CONDUCT A CONTINUITY TEST ON A LIVE CIRCUIT It is recommended that you disconnect any switch or part being tested for continuity before conducting the test.

Line Service Check

Many installations have faulty line service. Before assuming that your problem is with the equipment, always check for the proper voltage coming into the equipment.

If after testing, you find an improper line service voltage, shut the power off at the circuit breaker and contact a licensed, qualified electrician to make the necessary corrections.

Ground Fault Circuit Interruption PROTECTION (GFCI)

GFCI protection is necessary in case anything electrical should allow electricity to leak to grounded metal in connection with the spa. This is especially possible if after years of use a heater element should rupture and the ground wire (that may or may not have been originally connected) should happen to become disconnected. A GFCI will sense this leakage and shut the voltage to the power pack oft.

As of January 1, 1994, all equipment packs used with a spa or hot tub must be protected by a Class A ground fault circuit interrupter. This is called for in the N.E.C. code book in paragraph 680-42. If the equipment has a GFCI built into it, that GFCI may only protect certain components such as the blower, light ozonator, and sometimes the pump. The GFCI may not provide full protection, especially if the unit is wired for 240V service. To be sure, have a qualified electrician study the wiring diagram that came with your unit (or the manufacturer of the unit you are working on) for verification.

Keep in mind that when buying a 240 GFCI for an installation, be sure to get one that has neutral protection. The 60A Square D GFCI does not have neutral protection and therefore cannot be used on a hybrid equipment system. (Hybrid means the unit contains both 240V and 120V components.)

NOTE: Any GFCI protecting a circuit should be tested periodically to insure proper operating protection. If it fails to operate properly, it must be replaced.


There are two easily installed properly rated 240 volt GFCI breakers on the market today (as of the time this page was written). They are the Square D model QO 250GFI and the ITE Siemens model QF250, each rated for up to 50 amps. The square D 60 Amp GFCI can not be used with our equipment because it does not have load neutral protection.

Most people who install the Square D GFCI breaker do not follow the instructions accompanying it. A common mistake is made by connecting their load neutral (from the equipment), the large white pigtail on the GFCI, and the power supply neutral to the connection block on the mounting bracket. The instructions show where the load neutral is supposed to attach to the GFCI. Before suspecting a pack malfunction, check the installation of this device (when used) and make sure it was installed correctly.

The connection points for the pack on the Siemens GFCI are more obvious, but again, make sure that only the load neutral is connected where indicated and that the white pigtail is only connected to the line service neutral.


Use any of the information contained herein AT YOUR OWN RISK. We will not be held liable for any injuries that may result from the troubleshooting or installation of any electrical components in your hot tub spa unit.


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