It makes sense if the relay is rated for momentary contact that the switch should be as well. How this "holds" the contacts in the opposite position of either NO or NC alludes me.
On a Magnetically Latched contactor, along with the magnetism created when the pull in coil is energized, there is also a permanent magnet in the background that comes into play.
Through a control relay, when you send power to the coil, that magnetism closes the contacts, then, the permanent magnet takes hold and keeps the contacts closed.
Once the permanent magnet takes hold, there Is no longer any need for the coil to remain energized and can be removed from the control circuit by the coil clearing contacts incorporated into contactor itself.
That way the coil doesn't remain energized and burn the coil out.
Even in a loss of utility power without a 2 wire control relay in the circuit , a magnetically latched contactor would remain pulled in forever since the permanent magnet has got it held.
To "unlatch" a magnetic contactor a signal must be sent to the permanent magnet through a rectifier to reverse its polarity of the magnet so it will let the contactor fall open.
A mechanically latched contactor works in much the same manner except instead of a magnet, it uses a mechanical means to latch and unlatch the contactor by sending a control signal to a "Latch" or an "Unlatch" solenoid to activate it.
The momentary signal instead of a maintained is so you wont be needlessly be burning up the coil.
JAP>
