Shelly 1L causing current leakage when used in a borrowed neutral configuration in a landing light.

  • My 20yo home has a landing light, with a switch downstairs, and a switch upstairs. There are no neutrals at any of the switches. The live is fed from the downstairs lighting circuit into the downstairs lightswitch, and the neutral is provided at the light fitting from the upstairs lighting circuit. (A borrowed or stolen neutral configuration, it is common in older houses in Ireland and the UK).

    A few weeks ago, I installed a 1L at the downstairs switched live, and used a high load halogen bulb to save me adding a bypass to the light.

    Then, this week, after receiving a pile of new bypasses, I installed a bypass as I may use an LED bulb in the near future.

    After adding the bypass, when the landing light was on, the Shelly dimmer 2 in the living room (downstairs) and the manual dimmer switch in the kitchen (downstairs) started to flicker. Turning off the landing light stabilised the dimmers.

    There's a shelly dimmer 2 upstairs also, in the ensuite. With the landing light on it was flashing really badly. With the landing light off (and the bypass installed), it overheated and crashed at 30% brightness. It had to be set to 100% brightness all night until I could remove the bypass in the landing.

    After removing the bypass, the downstairs lights all behaved but the upstairs dimmer2 still behaved erratically. Today I removed the 1L also and restored the original wiring configuration and the ensuite dimmer 2 is behaving as expected.

    - How much current leakage should I expect from a Shelly 1L installed across a borrowed neutral?

    - How much should I expect with the bypass in place?

    - Is there any solutions to automating the landing light that don't require knocking holes in the walls to run new cables?