Yes, the EVSE has to be over 40 amps for the second charger to kick in. When it does, it splits the current between the two. This means, for home charging, that if you charge at 50 amps, each charger is only charging at 25 amps so they run cooler than a single one at 40 amps. With the new "hardware is always there" system, I'm not sure if that still applies.
