Most electric hot water units use an element which draws over 16 Amps (+-4,000W on a 240V circuit). I wanted to find a way to schedule my hot water unit so that i could choose when it turned on to heat as well as when to turn off. The ultimate goal being to save electricity as i noticed that it was heating at random times thoughout the night and thus using power unnecessarily.

Using a smart switch like the Sonoff Basic R2, Deta Grid Connect inline switch or any other smart switch are generally only rated to a maximum of 10A or 2,200W. This would overload the smart switch’s circuitry and cause it to burn out. This is a serious fire hazard this is definitely something you should not do.

Even if you do find a smart switch that had a maximum rated load of 15 Amps, it would probably not be insufficient to run a hot water unit element, especially since hot water systems tend to run at high loads for extended periods of time.

How safely setup a smart switch with a load

The way to connect a high draw appliance is to use an appropriately rated contractor/replay to switch the load and a smart switch to control the contractor.

Products used

• DETA Grid Connect Smart Inline Switch – $28
• 240 Volt 25A 2Pole – 1NC + 1NO – Contactor – $25

DETA Grid Connect Smart Inline Switch

• Add the smart switch to your network and confirm you are able to control it, i use the Tuya app instead of the Grid connect one.
• Add any schedules you desire, i have the following automations setup

Connect the contactor

Connect the contactor so that the smart switch controls the relay state and connect your hot water system (the Load) to the relay.

Depending on the contactor you have purchased it could be Normally open (NO) or Normally Closed (NC), if its normally closed the smart switch would be used to open the circuit and thus turning off your hot water. Connecting to a NC relay means that if something happens to your smart switch and it stops working, the replay will close and the hot water will turn on. This means you will still have hot water even if the smart switch fails. This is a good idea so that your not in “Hot water’ with your family having cold showers!

Wiring diagram coming soon.