Here is an example: 80A EV charging load that should never go over 80A since that is the limit of the chargers. Current code requirements dictate #3 line wires, #8 ground, 1" conduit with 100A breaker.
Since the load "never" goes over the 80A a #4 wire with the proper insulation material, that has an ampacity of 85A, should be sufficient if we look at the wire operation. Ampacity is defined as maximum continuous current at the specific temperature. So #4 will not even reach 75C regardless of how long the car is charging. But since the breaker does not like 75C at its terminals we cannot use an 80A breaker and need to use 125% breaker.
The 100A breaker will protect the #4 wire and the EVSE and the car charger from any short-circuit and ground-faults. But if the car decides to draw 100A then the 100A breaker will not trip and the #4 wire will overheat, destroy the insulation and cause a fire/fault.
If the EVSE will act as a motor overload set at 100% and additionally asked the car to reduce current if it reaches 80A then the EVSE is protecting the #4 wire from overheating or overloading.
If all EVSEs would be designed to act this way, for me this is a perfectly safe solution: #4 wire, 100A breaker, and 3/4" for a 80A EVSE.
Disclaimer: No, I do not plan to do this installation and I do not plan to burn the house down. This discussion is just theoretical since the EVSE behavior at 81A is not known nor standardized.
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