Leviton EVSE, do I need to upgrade my panel to 250 or 300A?

[fooljoe]

I just hope htey put a 40A breaker on it, not a 30A as that would mean 6kw charging instead of 10

A 40A breaker means ~7kw charging - you want a 50A breaker to do "10kw" (actually more like 9.5.)

 

[TonyWilliams]

I just hope htey put a 40A breaker on it, not a 30A as that would mean 6kw charging instead of 10

You need a 50 amp breaker for 40 amps continuous.

40 * 1.25 = 50

40 is 80% of 50

 

[jscgvnc]

I just hope htey put a 40A breaker on it, not a 30A as that would mean 6kw charging instead of 10

You need a 50 amp breaker for 40 amps continuous.
40 * 1.25 = 50
40 is 80% of 50

And your wiring would have to be capable of carrying 50A as well.

This 125% rule applies to all EVSEs, so if it's a 30A charger, then it would be 30x1.25 or 37.5A, so a 40A breaker and wire.