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Interesting. I’ve not seen this, though I’ve also not done loads of wiring!
I have had a dimmer module fail to switch fully off tho.
I was indeed thinking take the known good one off and try it on the other, checking they’re the same spec
Hefty-
It's fairly common. I see it more often on newer installations. I guess there's a lot more wiring installed on new builds or refurbs and it tends to run in the same spaces and then split out to individual circuits.
How electrical current actually works is fascinating. It's not vibrating molecules inside a cable. The cable basically directs the electrical field which travels around it.
I have known dimmer modules to stop clicking on and off but that usually exhibits different symptoms. It's complicated though because there are lots of combinations of lamp types and dimmers these days.
Airhead
It's because they require so little energy to power them that there's enough parasitic power (energy picked up from adjacent cables) in the circuit to give a very small amount of light.
Usually nothing to do with the dimmer as in the off position it's disconnecting power completely.
Sometimes you see 'phantom' power on circuits when you're testing to see if they are dead. If you use a normal tester it gives you a warning. A 'real' meter will apply enough load to the circuit that the phantom power disappears.