App note from Vishay on the changes to the load dump test condition and defines the maximum surge suppressing capability for Vishay load dump TVS series in these conditions. Link here (PDF)
As more trucks and buses are built with complex electrical systems, load dump protection is becoming an important safety feature for vehicles with 24 V powertrains.
The function of a load dump protection device is to keep the clamping voltage under the maximum input voltage of the power regulator, or other electronic components in the circuit, without halting or powering down the system. The protection device will not operate until the line voltage reaches 36 V for 1 to 10 minutes or longer, as specified by the vehicle’s manufacturer or as required in withstand test conditions. This means the device does not perform at 36 V in any kind of status in either high or low temperature environments.