Suspected earth loop

Projects General Guidance
15

Not sure what the device in the top of the controls box is.

I would suggest:

  1. Add at least 1µF on the output of the Power supply.
  2. Connect all your grounds to one physical place (suggest the power supply common).
  3. Replace the Relay board with a commercial grade SSR (Solid State Relay)

Why SSR.

  • The Songle "hobby" relay and has a long history of failures. I would not rely on it for any heating device.
  • An SSR will turn on and off when the voltage on the mains is zero. This reduced much (if not all) the electrical switching noise. Especially in my home.
  • I would verify the heater has a overheat device to act as a failsafe. These are usually a two leaded silver device located in the heating element area.