The numbers in this question are for jurisdictions where the voltage delivered by electricity companies (confusingly called "hydro companies" in some places) is at 110V or 120V, and where every power outlet around a home will supply a typical 15A of power. Feel free to ask a question with the status in jurisdictions where the voltage is 220 or 240, or to provide an answer relevant to these jurisdictions.

I am hearing and reading conflicting rumors about the way, looking forward, to prepare a garage to have a power outlet that makes it possible to charge an electric car the fastest.

A salesperson (for the leading T-branded electric vehicle) mentioned that one can contact one's Hydro company and, rather than the usual 110-120V / 20A that is commonly available at kitchen counters and near the clothes dryer, one can request installing a 120V / 90A outlet in one's garage. Doing so may be expensive since the hydro company may not have 90A near one's home.

In government flyers and news magazines, the talk involves not increasing the amperage, but the voltage. Installing either 240V (A?) or, best, 480V (A?) outlets in one's garage is the way to go.

Where is the truth? I understand that high voltage is most useful for moving electricity over long distances. But in this scenario it makes more sense to have higher power through wattage. Could this be an evolving standard—one that may not crystallize for a while?

  • 1
    For those in other locations - "hydro" means "electricity" as jargon in some parts of the world, despite being a prefix meaning "water-" elsewhere.
    – Criggie
    Commented Oct 23, 2016 at 6:21

3 Answers 3


Since you are talking about, on the base side, an outlet having 120v/20A, I'll assume you are talking about here in the States, as I don't know what's going on with the rest of the world, but voltages and amperages are going to be different elsewhere.

I don't know what's going to be standard here for electric vehicle plug-ins, but I believe part of your assumptions about what is or could be available is off-base. If an electric vehicle needs a 120v/90A circuit to get charged adequately, this shouldn't be an issue as most homes today have at least a 240v/200A feeder coming into the house. If my recollection serves me correctly, you should be able to take the three-phase wiring at the 240v level, cut it in half down to the 120V level and double your amperage figure to 400A worth of circuit running off of the feeder. Taking 90A off of this would be a large chunk of the overall available amperage, but it is doable. Mind you, there would be the need for higher gauge wiring and the standard three-prong outlet does not accommodate 90A.

On the Tesla Home Charging Installation Page, they talk about what connector power options are usable by the Tesla Model X/Model S vehicles. These range from 15A to 100A at 240V. Even so, you have to get the High Amperage Charger Upgrade on the vehicle for anything over 60A. Plugging the vehicle into 120V/90A will only give you the equivalence of 240V/45A charging. It seems as though 240V would be the way to go, using the NEMA 14-50 connector. This would give you the 40A charging capability and about as good as you are going to get at home under normal circumstances.

Unless you get a special line ran into your home, the standard residential voltage you can get in your home is 240V/3-phase. It would be of huge expense to get anything higher as it is not standard. Due to this, 480V would be a huge cost burden and would be hard to accommodate. With the higher demand in amperage on a normal feeder, there may be need to run a second line into the home in order for a higher than 50A circuit to work for a charging station.

The rest of what you ask is truly conjecture at this point and anyone's guess as to what's going on in the industry for electric vehicles. It would seem Elon Musk is blazing the path in this arena, so there's no telling where we'll end up.


This is why concepts like Tesla's Powerwall will be valuable. Instead of uprating the socket and wiring to your garage, a storage battery will only need a "standard" utility power connection and then a relatively short big-fat lead to the car's power receptacle.

So the battery slowly charges up at cheap rates, and has a lot of spare power to dump into the car as soon as its connected. Once the internal storage is used, the car cab be trickle charged to capacity.

It may not be the most optimal in terms of energy usage, but it will make installation in a home cheaper, and the infrastructure costs to the power company become much lower.

  • Intriguing. Thanks for the keyword—which makes me wonder. Why not build the Powerwall as a duplicate battery to be swapped physically in and out? I'm pretty sure I read about a startup working on exactly such a concept, with batteries that can be swapped at a "gas station". Getting stuck with a battery with little or no recharge cycles left would be a worry, but then duplicating the most expensive part of a car also sounds dubious.
    – Calaf
    Commented Oct 23, 2016 at 10:27
  • Because car batteries will weigh more than a person can safely move - likely order of hundreds of kilograms. And some vehicles use them as structural components in the floor, so they have to be bolted in properly, not easily removed.
    – Criggie
    Commented Oct 23, 2016 at 18:55

In North America where 120V is standard, lots of gearheads have 220V outlets in the garage for huge compressors. Electric dryers and electric ovens run on 220V also, so there's nothing new here. As Paulster mentioned, a residential service running 480V is uncommon.

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