How to Wire a 120V Water Heater Thermostat?

How to Wire a 120V Water Heater Thermostat? . A properly functioning water heater thermostat ensures a steady supply of hot water in your home. Wiring a 120V thermostat may seem daunting, but with the right knowledge, tools, and safety measures, you can complete the task efficiently. This guide covers everything from tools required to troubleshooting common issues.

What Is a 120V Thermostat?

A 120V thermostat controls the temperature of your water heater by regulating the power supply to the heating elements. These thermostats are standard for smaller water heaters or those used in residential settings.

Components Overview:

Thermostat Body: The main control unit.
Terminals: Connect wires to the heating element and power supply.
Heating Element: Converts electrical energy into heat to warm the water.

Types of Thermostats:

Single Thermostat Systems: For smaller water heaters.
Dual Thermostat Systems: Typically found in larger units with upper and lower heating elements.

How to Wire a 120V Water Heater Thermostat

Single Phase 120V Non-Continues Dual Element Water Heater Thermostat Wiring

In the electric water heaters and thermostat wiring and installation series, we will be showing that how to wire and install a non-simultaneous (non-continuous) dual element water heater and thermostat for 120V AC single phase (US) and 230V AC single phase (EU/UK).

Non-Simultaneous or Non-Continuous Operation of Water Heater

Non continuous or non-simultaneous heating elements are dependent on each other i.e. both elements are not “ON” at the same time. In other words, the upper heating element will turn “ON” and heat the top of the water tank first. The redundant or lower element will turn on when cold water enters the tank. This is an automatic process due to the thermostat wiring connection where the lower thermostat and element is controlled by the upper thermostat which automatically turns on the lower element when needed..

This way, both elements won’t operate at the same time. In very simple words, either the upper or lower heating element is “ON” or both are “OFF”. Keep in mind the same thermostats can be wired for simultaneous or continuous operation where both elements are operational at the same time in case of more hot water consumption.

Tools and Materials Required

Before starting, ensure you have the following tools:

Essential Tools:

Screwdrivers (flathead and Phillips)
Wire strippers
Electrical tape
Multimeter

Safety Gear:

Insulated gloves
Safety goggles

Recommended Materials:

120V thermostat
Proper gauge wires (typically 10 AWG or 12 AWG)
Wire nuts

120V AC Single Phase Dual Element Water Heater Thermostat Wiring

In non-simultaneous water heater thermostat wiring, the Phase or Hot “L” is connected to the left terminal L₁ of the upper thermostat and Neutral “N” is connected to the right terminal L₃. Two wires are outgoing from L₄ as neutral to the upper and lower heater elements. The upper heating element is connected through T₂ and L₄.

The lower thermostat is connected through T₄ of the upper thermostat which is wired to the terminal “1” of the lower thermostat. The second terminal “2” is connected to the lower heating element.

Since there are two heating elements each rated about 1900 watts, the total wattage rating of this heater is 3800 watts. We will be using the breaker and switch sizes for half rating of the total wattage i.e. 1900 watts as only one element is operating at a time.

How-to-Wire-an-Electric-Water-Heater-120V-AC-Dual-Element-Non-Simultaneous-3800-Watts

Now in case if 120V AC, a 20A circuit breaker and single way switch is suitable for both wires having 12 gauge size. How? Let’s see as follow.

Total wattage: 3800 / 2 = 1900 Watts.
Load Current = 1900 / 120V = 15.83A.

Breaker Size should be 1.25 (125%) of the load current:

15.83 x 1.25 = 19.79A

Another way, the safe limit of circuit breaker is 80% (0.8), this way 20A x 0.8 = 16 Amp which is safe for load current.

This way, a 20A circuit breaker for over current protection is suitable in case of dual element non-continuous water heater circuit for 120V AC.

230V AC Single Phase Dual Element Water Heater Thermostat Wiring

The following wiring diagram shows the same connection as above despite the breaker and switch size rating according to the NEC and IEC. The wiring connection and working is the same as above for 120V configuration.

Electric-Water-Heater-Wiring-Diagram-Non-Continuous-1900-Watts-Heating-Element

Non-Simultaneous Thermostat Operation

In this case, the power enters through L1 and L3 (upper thermostat) which operates the upper element. Once the temperature in the upper portion of the water tank rises to the desired (according to the rating i.e. 150° to 180°F) , the bimetallic strip in the upper thermostat releases and separates the T2 from T1 and connects T1 to the T4 terminal. This way, the upper element is turned off and power continues to the lower element through L4 and T4.

This process is shown in the following fig. fig (a) shows the upper element operation while fig (b) shows the lower thermostat and element operation when they are active.

Water-Heater-Thermostat-Wiring-and-Working-dual-Elements

Note: In the above diagram, the Red color illustrates the Line or Phase wire and Black color shows the Neutral Wire in the above figures. You may follow your regional wiring color codes i.e. IEC or NEC.

Warning:

Disconnect the power before replacing, repairing, troubleshooting, maintenance and installation electrical appliances and equipment.
Use the suitable voltage and ampere rating of switch with appropriate wire size and proper size of breaker according to the load rating.
Failure to do so can result in electrical shock, serious injury, fire or even death.
Please follow the manual instruction, local area codes or contact a licensed electrician for proper installation.
The author will not be liable for any losses, injuries, or damages from the display or use of this information or if you try any circuit in the wrong format. So please! Be careful because it’s all about electricity and electricity is too dangerous.

Step-by-Step Guide to Wiring a 120V Water Heater Thermostat

1. Disconnect Existing Wiring:

Remove the access panel and unscrew the cover to expose the thermostat. Carefully disconnect the old wires.

2. Connecting the New Thermostat:

Connect the line wires to the “Line” terminals on the thermostat.
Attach the load wires to the “Load” terminals leading to the heating element.
Secure each connection with wire nuts or screws.

3. Securing the Connections:

Ensure all wires are tightly connected and insulated using electrical tape.

Read More : How to Wire a Three-Phase Meter?

Troubleshooting Common Issues

Common Wiring Errors:

Loose Connections: Can cause overheating.
Crossed Wires: Results in malfunction or no power supply.

Fixing a Non-Working Thermostat:

Double-check the wiring diagram and connections. Replace faulty components as needed.

FAQs About Wiring 120V Water Heater Thermostat

1. Can I wire a 120V thermostat myself?

Yes, with the right tools and knowledge, you can wire it safely.

2. How do I know if my thermostat is working?

Test with a multimeter or check if the water heats consistently.

3. What gauge wire should I use?

Typically, 10 AWG or 12 AWG wires are recommended for 120V systems.