What is the name of an electrical switch that meets the following requirements?

  1. I can plug the switch in between a 120v outlet and my device,
  2. Energizes the device (and stays energized) when I momentarily mechanically/physically engage the switch,
  3. De-energizes the device (and stays de-energized) when I momentarily mechanically/physically disengage the switch, and
  4. De-energizes the device and sets the switch to open/off when the outlet loses power.

That is, I want an energized device to be de-energized should the power go out and for the device to stay de-energized should the power come back on. When the outlet's power has been restored, the device will only be (re-)energized (and stay energized) once I momentarily engage some button.

Maybe I am looking for the opposite of an overload fuse/GFI - some "fuse" to trip when the source power is lost and I need to engaged a button to reset it.

I did find that a "relay toggle switch" might possibly describe the type of switch I'm trying to find, but there were so many varieties that I am asking for some assistance from this community to point me in a more focused direction.

Thanks in advance.

  • \$\begingroup\$ A latching relay \$\endgroup\$
    – Andrés
    Apr 1, 2018 at 14:58
  • \$\begingroup\$ "NVR" switch ((No Volt Release) is a common term for these switches in machine tools. Might be a useful search term. You can make one using a relay - but NOT a latching relay, you want it to drop out if power fails. \$\endgroup\$
    – user16324
    Apr 1, 2018 at 16:38

3 Answers 3


You can do it with two buttons and a relay, like so:


simulate this circuit – Schematic created using CircuitLab

This, or something similar, would be inside the "magnetic starter" that @st2000 mentions in his answer.


Some purchase this type of device for use with power tools such as table saws. Search for "magnetic starter" or "magnetic switch" with respect to power tools. Also, there are some power conditioning strips which contain this feature.


Edited after rereading the post. A relay latching control will do this. A pushbutton energizes the coil of a DPST or DPDT relay. In parallel with the pushbutton is a normally open contact on the same relay. When the button is pressed, the relay energizes, closing the contact mentioned. The closed contact maintains the relay in an energized state. When power is lost, the relay returns to shelf state and the contact is now open, requiring pushbutton action to reset once power is restored.

The second contact on that relay is used to switch power to your load.


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