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G6Tanuki · 15th Dec 2020, 5:51 pm

In the past I've done something similar using a bridge rectifier in series with the mains, a suitably-rated transistor wired as a 'super-Zener' across the DC terminals of the rectifier, and a reed-relay in parallel.

At low currents (a few milliamps) there's insufficient voltage to turn-on the Zener but there is enough to pull-in the reed-relay. At higher currents the Zener turns-on and clamps the voltage the relay's coil 'sees'.

The reed-relays I used were rated as having 2.5Kv isolation between the coil and the contacts.

15th Dec 2020, 5:51 pm	#8
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: Advice on mains current sensing, safely In the past I've done something similar using a bridge rectifier in series with the mains, a suitably-rated transistor wired as a 'super-Zener' across the DC terminals of the rectifier, and a reed-relay in parallel. At low currents (a few milliamps) there's insufficient voltage to turn-on the Zener but there is enough to pull-in the reed-relay. At higher currents the Zener turns-on and clamps the voltage the relay's coil 'sees'. The reed-relays I used were rated as having 2.5Kv isolation between the coil and the contacts.