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I have low voltage dry contact closure switches rated to handle 32V AC/DC. I want to use these to control standard 120VAC lighting. So I need a device that can take 120VAC, supply a low voltage signal to the momentary switch that in turn will control the 120VAC latching relay.

This all has to fit into a single gang switch box behind the wall mounted momentary switch. Budget is not an issue, just want something that works and is of course safe in that environment.

Any thoughts on simple solutions to this? Thanks..

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Generally it's normal for controls like this, including latching relays, to run on 24V - either AC from thermostat transformers, or DC from batteries if reliability is required. Lower than 24V isn't practical because you typically need to carry these control signals some distance.

You can't switch 24V with an Arduino, but you can operate a fairly small relay that can switch 24V.

This would be boring old trade electrical work, except that you made it harder on yourself because of your parts bin mismatch - 120V latching relay coils, vs low voltage switches. So here you are. What's the budget on this project?

The preferable option would be latching relays with 24V coils, which are avout $30 each... Or if you're willing to do every inch of the control wiring in Class 1 wiring methods, you can get listed line voltage switches for about $10/pop (but this will do nothing to allow automation).

If it were me, I would put 24V relays right in front of the latching relays, in the same cabinet. That way you're doing the control wiring in 24V under the more relaxed low-voltage rules.

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  • \$\begingroup\$ Thank you for your feedback. I realize I should have given a bit more detail. This is to go inside a light switch box, so needs to be small. Given its location it rules out a battery. I need to get the 120VAC down to 24V AC/DC. I guess you're suggesting a thermostat transformer for that? Budget is not an issue, really just looking for something that works, is safe and fits in a switch box behind the momentary switch that will control it. Thanks! \$\endgroup\$ – George Basco Oct 4 '17 at 16:22
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    \$\begingroup\$ it also needs to comply with the electrical code, then... You might stop by a local electrical supply house (the kind for electricians which stocks huge piles of conduit and wire in every size from #14 to 1000kcmil) and see what they have in their parts bin. Some thermostat transformers mount in a knockout and sit outside the box. Can any of the gear go under the ceiling rose ( fascia piece) for the light? \$\endgroup\$ – Harper - Reinstate Monica Oct 4 '17 at 17:03
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These parts have been around for a century. Now they come in a wide range of DC coil voltages , single coil with bipolar voltage pulses applied or dual coil for set and reset. They come in a wide range of currents from amps to thousands of amps.

But it will take more than a logic level to move the coil. ;)

https://www.digikey.ca/products/en/relays/power-relays-over-2-amps/188?FV=ffe000bc%2Ca8c0003%2C1f140000&mnonly=0&ColumnSort=1000011&page=1&stock=1&pbfree=0&rohs=0&cad=0&datasheet=0&nstock=0&photo=0&nonrohs=0&newproducts=0&quantity=&ptm=0&fid=0&pageSize=500

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