JadeshayAC Current Sensing Switch, SZC23-NO-AL-CH Adjustable 0.2-30A Normally Open Self-Powered Current Sensing Switch

Used it to monitor if one of two small heaters failed, so it had to change state if the load dropped by 2 amps, which it does reliably after tuning it in. Used the output to turn on a relay when the current was correct, and the NC contact on the relay to flash a light if the current dropped by 2 amps or more. Works great even in winter in an unheated Michigan garage!

Does the job.

I use one of these on each tool (table saw, jointer, planer, etc) to turn on my vacuum and open the tool’s blast gate. Very inexpensive compared to the other options.

Used with relay to control dust collection for table saw

Used to control one circuit without having to cut into the second circuit. This self powered relay allows you to switch a load on and off, without ever connection the two separate circuits. Simply loop one leg of the circuit you want to "detect" and the relay will turn on/off whenever that circuit is turned on/off respectively. But this switch can only handle small loads, so buy an additional 10 amp, 20 amp or 40 amp relay (with appropriate voltage ... the same as the voltage of the self powered relay) and you are all set. Green light shows current detected, and red light indicates the solid state relay has switched to "on" ... which is N.O. or N.C, depending on the one you buy, double check before purchase. Would recommend!!

I need to be able to sense when a heating and cooling unit was in demand by the thermostat but have no access to the control board to get my relay signal I need. This device allows me to just sense the primary feed current and adjust thee trip point I need. When the "contacts" close I measured about 4.5 ohms which was fine for a remote relay that will do the real work of what I need to turn on. When this "contact" opens you will get a blink of the green LED. The LED only stays on in the closed condition. This was a simple inexpensive way to do this.