Smart Switch Upgrade for Immersion Heater

This is a project to convert an existing hot water immersion tank from a simple on / off manual switch to a configurable system with remote access. The challenge is to keep it electrically safe; a simple design; whilst on a budget.

Option A

Install a smart switch directly to the immersion heater.

Option B

Install a smart switch to the consumer unit feeding electricity to the immersion heater.

Option C

Save myself the bother.. and get a plumber/electrician to do the job. Not an option for a curious DIYer – or particularly easy in France!

Chosen Approach

• Option A requires a smart switch rated for a high current (~16 amps for a 3000W heater) and ‘wet contact’ plus opening up the internal workings of the heater.
• Option B makes use of an existing relay switch on the water heater circuit. This is electrically safer since the switching can be triggered from the low current side of the relay. However, it meant working on a consumer unit for the first time.
• Option B is chosen.

Contacteur Jour/Nuit

In France, this relay switch is called the Contacteur Jour/Nuit. It is designed to allow hot water tanks to make use of cheaper electricity at night.

It has 3 settings: I, Auto and 0. Since our electricity tariff with EDF is a basic tariff, this Jour/Nuit facility is not installed. Fortunately, this meant the Auto setting of the relay could be re-purposed for a smart switch installation.

Circuit Breaker

The Contacteur Jour/Nuit sit downstream of the circuit breaker for the hot water heater. This proves to be convenient later as the spare terminals are used to power the smart switch.

Purchases

• Shelly 1 Gen 3 smart switch
  • This is suitable for a dry contact installation. Dry contact is defined as a switch that controls electrical circuits without supplying the power itself. Gen 3 can be accessed via WiFi.
• DIN Rail Holder for Shelly smart switch
  • This is a 3D-printed device to secure the smart switch inside of the consumer unit.
• 2.5mm gauge solid core electrical wire.
  • This is consistent with existing electrical cabling within the consumer unit.
• 2 * Wago 221 connectors

Total Cost ~€30

Wiring