Need confirmation of level 2 charging with 10 gauge wire

Question

My condo was built in 2021 and the builder told us it was wired for automobile charging. Now we are finding out that the wiring provided is only 10 gauge. Since our garages are downstairs and under neighbor's condos, rewiring to a 6 or 8 gauge wire is very expensive. Also, the wiring is probably 50 feet from my breaker box. My understanding is that 10 gauge wires will support a continuous 24 amps (30 amps x 80%). I found a chart on the internet that shows at 24 amps, the Tesla Model 3 charges at 22 miles per hour. Using a range of about 300 miles, it will take 13.6 hours to fully charge. Can someone confirm my math? Can a level 2 charger be set to deliver a specific amperage? If not, the circuit breaker would trip, or I can imagine the wire would heat excessively at 30 amps.

Answer 1

Using a range of about 300 miles, it will take 13.6 hours to fully charge.

So if you leave it plugged in overnight (let's say 8 hours on the low end) it will charge 60% of the battery. Which gives you a daily range of 180 miles without needing to stop at another charger. That should be plenty in most places. and the remaining capacity can be used as a reserve which can be topped up on any day you don't need to commute to work by car.

Can a level 2 charger be set to deliver a specific amperage?

yes, The charger will have a setting to limit the current. You will need to check the installation manual for the specifics.

Answer 2

Can a level 2 charger be set to deliver a specific amperage?

Most of them can, yes. The "charger" is not a charger at all. It is simply a smart GFCI which sends a signal telling the car how many amps it can take. The car's onboard actual charger obeys that signal. It's an ingenious standard, not surprising since it's SAE's fourth major design of a charging standard (after so many false starts). And hey, SAE isn't in the business of selling service upgrades. They're in it to sell cars.

Anyway, most chargers- sorry, EVSE's, allow you to set that "amps" signal either by cracking the case and setting DIP switches, or by a 'soft setting' done by a special procedure. (To approve a soft setting, UL wants it to be weird and difficult to do, so homeowners don't tamper with it). A few do not - ClipperCreek comes to mind. So watch out.

Since you will probably not be able to use Grid Limiting in your condo space, a unit with that feature is probably off the table. That means your best bet might actually be the Tesla Wall Connector (Tesla socket), because the industry will be switching to it over the next 2 years.

only 10 gauge

You don't need 40-50A. Really. We get a lot of questions about this. An excellent video by Technology Connections can set you straight. And feel free to wind back to 18:30 or even the beginning if you'd like more of a backgrounder.

Alec's words: A big charger is expensive, and may come with more headaches than you bargained for. And there are plenty of those.

Alec breezed over this but my #1 is "Don't set your panel on fire". Only a NEC Article 220 Load Calculation (pref: 220.82 alternate method) can determine the headroom in your panel. That x 80% is your max charge. (others: a grid-limit EVSE like Wallbox can beat this, but that may be impractical to install in a condo).

#2 is not blowing up your condo's transformer, and you will probably need to report the EV charging setup to the power company. The power company may limit your charge rate anyway, so don't go putting in a 60A circuit only to get told you're limited to 20A anyway.

#3 is city permits - one person in Maryland, their town had a brutal permit process, but waived it for 15-20A circuits. *NEC does not distinguish 120V vs 240V circuits... so super easy!

My condo was built in 2021 and the builder told us it was wired for automobile charging. Now we are finding out that the wiring provided is only 10 gauge.

So if you listened to the video, the builder made the right call. They're up against panel limits - I bet your panel is 100A. They're up against transformer/provisioning limits from the utility. And their assumptions about your commute pattern are entirely reasonable: high density housing is found in urban cores: Oakland, Pasadena, Little Five Points, etc. People who buy such condos commute within that same metro - typically 30-50 miles tops each way, since traffic is pretty bad. (BTDT). So yes, if I was asked to make a blank sheet recommendation, I'd say 30A breaker myself out of a concern that for some people 20A might be too little.

Cars take a lot of power, yes, but not as much as you'd think.

My understanding is that 10 gauge wires will support a continuous 24 amps (30 amps x 80%). I found a chart on the internet that shows at 24 amps, the Tesla Model 3 charges at 22 miles per hour.

Yeah, that's about right. Teslas are more efficient generally, and the Model 3 particularly so.

Using a range of about 300 miles, it will take 13.6 hours to fully charge. Can someone confirm my math?

The error is in assuming a) the car's battery is totally empty at the end of the day, and also b) that it will need to be totally full by morning. Neither is true: just look at your experience in gas cars. You might leave with 3/4 tank and arrive back home with 1/2 tank. EV batteries work the same way, except home charging is like having an uncle who owns a gas station pour a can of gas into your car every night (as much as will fit). The size of the can corresponds to the charge capacity.

Who's kidding who? You'd game that. :) You'd deliberately arrive home from travel on empty, and let your car slowly recover back to full over days, since "gas given" > "gas used in a typical day".

Answer 3

I have Tesla and charge it with 30A circuit.

That would be 24A continuous charge.

Tesla is clever and knows (detects) that I am on 30A circuit so it only uses 24A limit, without you doing anything.

I use Tesla Mobile Charger.

That gives me 264 miles range if charging for 12 hour overnight (8 PM to 8 AM).

I only drive 150 miles per day (round trip) so it works for me.

My settings on Tesla is to charge to Max 90% (to protect battery) and I newer go below 10 % to prevent getting stranded.

PS, the cable newer gets warm.