Switching mains power without dying

In the UK there is a free monthly magazine called Hackspace magazine, in Issue 4 (March 2018) magazine Archie Roques builds an IoT tea machine. using a mains powered kettle and some relays. One of my main objections to this article is the switching of mains current without clearly laying out the issues and risks involved. I will cover my observations at the end of this post.

I have attached the pages of the article to this post, It is an interesting project.

Spark Fun Beef Cake Relay fitted with JQX-15F 005-1Z1
Spark Fun Beef Cake Relay fitted with JQX-15F 005-1Z1

The relay board chosen for switching the mains in this project is the ‘Spark Fun Beef Cake Relay’ which is fitted with a JQX-15F 005-1Z1 which according to the QX-15F Datasheet is switched using 5V DC and the PCB mount SPDT contacts are raited to for 30 A at 240 VAC (1 Form C), but only rated to Switch 20 A, but this switching rating is not at 240 VAC, the maximum switching rating is 560 W which means that it is not designed for switching a 230 VAC 3 kW kettle (approx 13 A) on load.

Wiring diagram for the IoTea
Wiring diagram for the IoTea

I had a quick look at the Spark Fun Beef Cake Relay board to see what the PCB is like, and it looks like the tracks are a bit narrow for the full 13 A load.

I would also feel happier had Archie used bootlace ferrules on his mains wiring, as that would reduce the risk of stray conductive wires becoming lose and risking bridging or short circuitng.

You can see some of my previous experience with Mains electronic equipment on 5V ACDC Switch mode PSU or the HLK-PM01 PSU.

I would replace the JQX-15F 005-1Z1 with a solid state relay if I was to do this project. I am going to be doing something similar with my sous vide cooker but using a solid-state relay.

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