Sometimes you want to energise a relay to stay on instead of only momentarily staying on. For example you may want to make an electric motor, or a solenoid to stay on for some time. You can do this with the circuit shown.
The key to this is a momentary push button switch (there are many in this catalogue.)Pressing the push button switch (S1) activates the relay and closes the N O (Normally Open) and COM(Common) contacts. These contacts form a parallel connection across S1. Even if S1 is now opened, the relay will stay ON, or latched.
To turn the relay off, you must interrupt power to the coil, in other words, switch V+ off, even momentarily. Even if you switch V+ on again, the relay will remain off, until you push S1 again.
Note: While the relay is energized, it will continue to draw coil current. True mechanical latching relays do not do this.