Here is a write up I did for a community/university charging parking lot that already had some Level 2 Eaton stations. It might have some useful information. I realize Tesla owner's would appreciate the NEMA 5-20, but if it's between that and 6 additional parking spaces being wired up on a 200 amp panel, I believe the 5-15 would be the way to go.:
If most of these users are working, we can assume that many of them are there for a significant amount of time. Let’s assume 8 hours. Level 1 charging is a great solution for adding as many “all day” spots as possible. This will negate the need for people to move their cars from the Level 2 stations when they are done, usually under 3 hours. Charging at level 1 for an 8 hour period will usually allow about 25 miles to be recharged. This is probably going to fit the needs of the vast majority of users. The great thing is that you already have the level 2 stations, and hopefully, these will remain open more often for traveling users, or longer distance commuters.
Now, if what I have described is close to the goal, then lets talk possible solutions. The first is what you have inquired about: 120V outlets. This is obviously the easiest and most inexpensive option to implement. If you go this route, you will want to install a 15 amp circuit for each charging space. I would suggest using 12 AWG wire instead of 14 AWG wire to reduce heat build up and voltage drop. The best combination of products to use going this route will be a weather proof enclosure and a single receptacle outlet. Using a box like this:
GE Backyard Outlet with 2-20 Amp GFCI Receptacles-U012010GRP at The Home Depot will allow you to wire up two independent circuits to the box, reducing the labor involved in mounting the boxes. I would also suggest removing the NEMA 5-20 (20 amp) outlets included with a box such as this (or ideally, get the box without the included outlets). The receptacle of choice would be something like this:
Leviton Evr-Green Base Level 1 GFCI Guide Light Receptacle for Electric Vehicles-C27-T7591-PEV at The Home Depot. The main benefits of an outlet like this will be that: 1. It is only a single receptacle. You can’t have multiple cars charging from the same circuit, and if you use a duplex outlet, cars can and will try to do this, and the result will be a tripped breaker which can’t be reset until someone with access shows up. 2. It satisfies the GFCI requirement. 3. It is only 15 amps. This last one might be a bit confusing. Your facilities manager will most likely advise you that all of their commercial outlets are 20 amp on site. This is probably the case. However, as the NEC requires that circuits dedicated to EV charging be calculated with a 100% demand, this will unnecessarily ham-string you when it comes to the number of circuits you can install. Now, if you note that previously, I stated that the use of 12 AWG wire was a good choice. 12 AWG wire is most often associated with a 20 amp circuit, but with continuos load, as in an EV charging for 8 hours, the 12 AWG wire will reduce heat build up and reduce voltage drop across the conductor. All in all, it is a best practice. The 15 amp breaker is required when using an outlet like the one I linked to earlier. This is because there is only one 15 amp dedicated outlet on that branch circuit, and you cannot place a 20 amp circuit breaker on that circuit to protect it. You may ask yourself, why don’t I just spec the 20 amp circuits? Isn’t that going to be better for the EV’s? The answer is almost always: no. Many EV’s are limited in software to only pull 12 amps from the EVSE when 120VAC is detected (my Focus Electric is an example), no matter what the EVSE advertises (i.e. 16 amps available). Tesla is one of the only makers that allows greater than 12 amp charging at 120 VAC, however, this requires a special adapter for their UMC mobile charger. Most owners will not have this, or not know about the utility. What will happen if you spec 20 amp circuits is that the highest load encountered will be 12 amps pulled from one car. However, since you used 20 amp outlets and circuits, you have now limited yourself from adding potentially more circuits since you have to calculated their load as constant demand. Therefore, it is the best case scenario to have a single receptacle, GFCI, NEMA 5-15, on a 15 amp breaker, with 12 AWG wire for charging an EV. I would also suggest, speccing all conduit and junctions so that 6 AWG wire can be pulled in the future. This will be an added expense, but if in the future you come up with more funding and want to add more level 2 spaces, it will be much easier.
Option 2 stays with Level 1 charging, but instead of supplying outlets, it supplies Level 1 EVSE’s. All of the wiring will be the same for this solution. The main advantage of this solution is that you don’t have to BYOC (Bring Your Own Charger). Some owner’s might be weary of leaving their EVSE plugged in outside where people might attempt to vandalize or steal the cord. The best EVSE I have seen for this solution would be from Clipper Creek. The ACS-15:
ACS-15, 12A, 120V charging, 25 cord | ClipperCreek Vehicle Charging Station. This uses the same 15 amp supply circuit at the NEMA 5-15 outlet, but without the need to BYOC. Now, if this route is not too expensive for you and your electrical supply is not short, I would suggest going with the LCS-20:
LCS-20, 15A, 240V charging, 22 cord | ClipperCreek Vehicle Charging Station. For the same price in EVSE, you could have all of your 3.3 kW charging Leaf’s (with the 3.3 kW charger), C-MAX’s, Volt’s, and any other 3.3 kW charging car charge at full speed, for a reduced cost. The wire for this install is the same, the only difference would be a 20 amp two pole breaker. Now, this relies on you having the sufficient panel capacity, and I have no idea what your situation is.
Finally, a 3rd option would be to add more 6.6 kW charging spaces. I know you guys have the Eaton units, but Clipper Creek makes the HCS-40:
HCS-40, 30A, 240V Charging, 25 Cord | ClipperCreek EV Charging Station | ClipperCreek Vehicle Charging Station. This is most likely much less expensive than the Eaton units. I can vouch for Clipper Creek quality as well. I have one of their units at home (a 70 amp J1772 Level 2 EVSE), and it is built very robustly.
So to wrap up, option 1 is the best route to go for the absolute lowest cost. Option 2 is a better option because it negates the need for users to bring their own EVSE’s, but the power requirements are the same. Only more money for the EVSE. Option 2 has the variant with the 3.3 kW level 2 chargers which would allow slower charging EV’s to charge up while leaving the 6.6 kW units available for faster charging EV’s. Finally, option 3 is assuming the price of the Eaton EVSE’s is what was putting you off, and it is just a much lower cost (but very good quality) 6.6 kW Level 2 EVSE.
. And the usual 80 mile BEV will be quite happy with a 25-40 mile charge during the workday. 
