You will need the correct gauge of wire for the amp rating of the charging device you purchase. I think now most are considering a 40 amp circuit which I believe will require #8 wire. You will need 8/2 wire which is two wire plus ground and a two pole 40amp breaker that will work in your panel. You can also use 8/3 but you will not need the neutral white wire in the connection for the 240v charger.
Basically 14 gauge house wiring is used for 15amps, 12 for 20amps, 10 for 30amps and 8 for 40amps capacity. The breaker you choose needs to match your panel and you need two slots together that are empty. If you do not have that, then you would be looking at adding a sub panel. You need to also assess the total load on your existing panel/supply. Most would be fine but some with lots of circuits might be at capacity.
You may also want to think about a 50amp circuit if you really want to future proof.
If there is any doubt go with the heavier gauge. The wire isn't a big cost item and there isn't any downside in having heavier wire than you need. I think the wire gauge depends on the material used as well as on the length of the run.
If you're charging at 240v at home you may not even need 240v charging at work. Charging needs are based on the miles you need to drive not on the size of the battery pack. If you're only driving 30 or 40 miles a day, packs with a capacity of 30 kWh or 60 kWh or 90 kWh would all charge in the same time, and eight hours charging at 120v will give you 40 miles. You might never need to charge at work, and if you did, charging at 120v might be just fine. Just a suggestion that might save you a few bucks.
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