Using Single, Two And Intermediate Switches To Control A Water Heater?

In our series on wiring electric water heaters we will show how to control a water heater using single, two, three and four way (intermediate) switches.

Using a single switch to control a water heater

To control a non-continuous (non-simultaneous) water heater using a one-way or unidirectional switch we must use a 10 gauge wire and a circuit breaker of at least 30 amps.

Depending on the rating, for 240V, 30 amp circuit breakers, always use 10 gauge wire. Depending on the appliance rating, meter 12 can be used for single phase 120V.

Use minimum 30A switch for 240V and 30A protection CB.

240V circuit breakers or switches can be used for 120V, while 120V rated breakers and switches cannot be used for 208, 240, 277 or 480V.

Switches must be installed on the line (fire or phase) only and not on the zero line. 

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  Water Heater Switch

Double cutter switches to control water heaters

A double pole switch can also be used to control the on/off operation of an electric water heater. In our 240V water heater case we use a 30 amp double pole switch protected by a 30 amp circuit breaker to form the main power panel.

In this way, both wires (Fire or Phase) are switched off by the switch. As the only way to work perfectly is to disconnect the single line, we can still use a double pole switch instead of a single pole switch as it ensures that the water heater is completely disconnected. In this way, the double pole can also be used as a safety switch.

Safety switches are required for tankless water heaters, HVAC (heating, ventilation and air conditioning), commercial water heaters or when the main breaker box is not in sight.

 Water Heater Switch     

In the case of a single phase 120V supply, the neutral wire is connected directly to the water heater, where the fire wire (fire or line) is connected to the common end of the 3-way switch. Both 3-way switches are connected via a wire loop (blue) and the common end of the second 3-way switch is connected to the water heater. For 240V, a correct earth and a 30 A circuit breaker with a #10 wire should be used. For 120V, a 12-gauge wire should be used according to the rating. Only one fire wire is sufficient to disconnect the power supply via the 3-way switch. In general, it is referred to as a three-way circuit. Both the switch and the circuit breaker are rated at 30 amps.

The circuit breaker and all switches (both 3-way and 4-way) are rated at 30 amps. You can use the appropriate rated switch and breaker size for single phase 120V. Don't forget to properly ground the water heater and switches.

Follow the manual instructions, your local area code or contact a licensed electrician for correct installation.

The author cannot be held responsible for any loss, injury or damage caused by the display or use of this information or by attempting any circuit in the wrong format. So, please! Be careful, because it's all about electricity and it's too dangerous.