Fri Dec 04, 2015 9:17 am
First, ask yourself if you want to "future proof" your installation. If you do, then you likely want to get a circuit that can handle a higher current.
If you don't, then ask what your vehicles maximum charging capacity is. Hint: if you have an SV or an SL, it is 6.6kW. If you have an S, it is either 3.6 or 6.6kW.
If your circuit is 220V, 30A, then you first have to understand that the 30A rating is not for a continuous draw. The rating must be 125% of the maximum continuous current draw. So to go the other way, you calculate 30A/1.25 = 24A. If the voltage available at the car is truly 220V, then the power that you can deliver is 220V x 24A = 5.28kW. (Note that you could only go to 6.6kW/240V = 27.5A for your vehicle, anyway...)
So, if you truly want to maximize your charging speed, you'll need to upgrade.
But first I would suggest living with your L1 charging to see how much speed you really need. My family has decided that we do want the full 6.6kW rate allowed because we want the flexibility to charge to 100%, use the full charge in the morning, recharge, and use the full charge to go out at night. You can't do that with normal L1. L1 charging is typically 12Ax120V = 1.44kW. You may find that the 1.44kW it fine for your needs, or you may find that getting an EVSE that will deliver 24A is just fine, too.
Given that you already have a plug, I might investigate an EVSE that can deliver 30A if you want it, but also has a feature that allows you to turn down the allowed current draw to 24A. That way, if you want a faster charge, your EVSE can do it, but you'll need to install a bigger circuit.
[And I just read the post that got there before I finished this one - yeah, you might check to see if the wiring can already handle 40A. Then you're good to go with a 30A EVSE.]