Re: Advice on mains current sensing, safely
Current transformers don't mind a short on the secondary, but they object to being open-circuited.
I'd suggest a CT with permanent load consisting of a bridge rectifier feeding an electrolytic capacitor and your 24V relay coil.
If your TV takes 400W, that's about 1.6A, and the relay needs 50mA, then you need a current ratio of 32:1.
So, I'd suggest a 240V:9V mains transformer, (ratio 26.7), rated at about 20VA. Connect the bridge rectifier to the 240V winding. Connect the 9V winding in series with your TV. It's now working as a current transformer. And the insertion drop will be around 24V / 26.7 which is less than a volt.
And of course, you get your isolation. Twice, once in the transformer, once in the relay.
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