I have a hypothetical question in regards to phase conversion and transformers, more specifically on their combination. I am not a certified electrician or engineer, so I don't know what all goes into something like this, but I am very much so interested in learning, so I welcome any constructive input.

My question is: if you have (I believe it is) single phase 120v from a residence, is it possible to use a transformer to step that up to 480v, which in turn goes into a 1-3 phase converter, to provide 3 phase 480v output? Would this be a single device, or multiple units linked together? The resulting power would then be used for something like a Tesla Supercharger, which I understand requires a 3 phase 480v supply. And money being no factor, would it be possible to install something like this in a residential setting? Why or why not? What would go into building something like this?

Again, this is a hypothetical question, driven by a conversation between my EV enthusiast friend and I late at night, of which neither of us has an electrical background, so I thought I would consult the great minds of Stack and see what may or may not be possible. I am very well aware of the dangers working with voltage, especially when it comes to mains power, and I have no intention or desire to make this type of system myseld, I'll leave that to those learned and certified to do so, much safer that way.


  • 2
    \$\begingroup\$ For any conversion, you always put in at least as much power as you get out. Superchargers take up to 120kW, so you would have to supply about 1000A from the 120V circuit. Residential 120V circuits are usually 15 or 20A in US, so this is not a good plan. \$\endgroup\$ – mbedded Sep 25 '20 at 21:03

Approach I'd Take

I know you are discussing Tesla EVs and their supercharger systems. But I'm going to start out generally and then work towards your specific situation nearer the end, below.

If I were looking to get 3-phase 480 (and I wouldn't mind it, but I don't exactly need it either), I'd just call up the power company and ask them what's involved on their end in providing it to my home.

You can coordinate this with both the power company and a certified electrician to get your entrance panel changed out and appropriate breakers and sub panels arranged for you.

It's not cheap. But it's not a fortune, either.

The Process as I Understand It

You can usually work through the electrician, who will take care of the necessary notifications to the local county office with respect to any needed inspections they may require and also with the power company, as well. So you don't usually need to worry about those details.

The electrician will be responsible for getting all this done in such a way that you are without power for the shortest possible time. This means they need to coordinate their own time along with the inspectors' time so that the power company can re-connect sooner than later.

Disconnecting your power is relatively easy to do. You can just call the power company and ask them to disconnect you. At least in my area, that is really easy and I don't think it costs any money, either. They just pull the plug and go away.

It's the re-connection part where everyone in the world wants a piece of you. The electrician will work quickly to get your entrance panel arranged the way it needs to be, prior to re-connection. There will probably need to be a county inspector who runs out and verifies that everything looks correct. They will certify the work and leave a "sticker" of some kind, signed by the inspector. The power company sends someone out to reconnect you and checks the inspection papers to make sure that part was done. They will also inspect what was done, too. (They aren't going to just trust a piece of paper from the county.) If they see that an inspection was done and that what they also see there looks sensible to them, then they will re-connect your power and then it is up to you and your electrician to work on the inside and re-engage the main breakers and hope nothing goes "bang."

You will pay for the county inspection. But it's usually not a large number. In fact, you usually won't notice the price when compared to the rest. The new panel, breakers, and electrician work will set you back several thousand US dollars. This depends on a lot of factors, but I would not expect it to be any cheaper than $2k (and that would be a bargain) and likely a fair bit more than that. And the power company will want something. Some power companies are really nice about it (mine is) and they charge you less than their own costs. Other power companies may literally rip you off for it. You'll have to call them and ask.


For this, you really will need to call the power company, directly. They usually offer different options depending upon whether or not the service will be above ground or below ground. So that's step 1.

For example, in my area, they offer the following nominal services:

  • Underground: split-phase 240/120 VAC, 3-wire, grounded.
  • Underground: split-phase 480/240 VAC, 3-wire, grounded.
  • Underground: 3-phase 208Y/120 VAC, 4-wire, grounded, wye.
  • Underground: 3-phase 240/120 VAC, 4-wire, grounded, delta.
  • Underground: 3-phase 480Y/277 VAC, 4-wire, grounded, wye.
  • Underground: 3-phase 480/240 VAC, 4-wire, grounded, delta.
  • Overground: split-phase 240/120 VAC, 3-wire, grounded.
  • Overground: split-phase 480/240 VAC, 3-wire, grounded.
  • Overground: 3-phase 208Y/120 VAC, 4-wire, grounded, wye.
  • Overground: 3-phase 240/120 VAC, 4-wire, grounded, delta.
  • Overground: 3-phase 480Y/277 VAC, 4-wire, grounded, wye.
  • Overground: 3-phase 480/240 VAC, 4-wire, grounded, open-delta.

Others can be requested. But they would be subject to a different approval process with the power company, as well as at the county level, probably.

But as you can see, 480 VAC 3-phase is a nominal service and can be readily provided by the power company.

In my area, there are current/power limitations with respect to the above services. For example, they may not offer 3-phase 480 VAC service unless your need is 50 kW or higher. (Above 100 A, though they do make irrigation pump exception cases for a single motor of at least 20 HP.)

Also, if you are considering using your own conversion system (your own customer-supplied transformer, for example), then my power company would need to pre-approve it before you could use it. Even if it is on your side of the service entry to the home.

EV Applications

If you are considering a fast charging service, of some kind, then there may also be special provisions that are directly related to that specific usage. Often, their tariffs (the rates they charge as agreed by local gov't) may be cheaper (or more expensive) for the specific case of charging up an EV. Usually, it's cheaper. They also may have an experimental program where you allow them to use your EV to temporarily store energy or to recover it, at their control. You'd need to provide them with details about when you want to use the vehicle (a calendar of your usage, in effect) so they wouldn't interfere with your intended uses of the EV. (Some will offer a still steeper discount if you allow that.)

I'm sure there are NEC code requirements with respect to fast chargers for EVs, by now. But fast charging systems in residences is a relatively new activity and it's possible the code is still playing catch-up in your area. Just be aware that there are fire risks unique to this situation. They may affect your home fire insurance policy, too. Make sure everyone is on the same table when considering the right way to get this done.

Telsa has a special group that you can get into contact with. I have their number, but I probably shouldn't give it out here. They are highly technical and they can answer most questions with respect to their 480 VAC charging stations. Make absolutely certain that you contact them and ask them to help you work with your local power company as well as with a local electrician who has the right skillsets to make this happen, correctly. (Most electricians will not have adequate experience in this area because so few residences are setting themselves up, this way. -- Except perhaps in California where you may have better access to appropriately trained electricians.)

And yes, I know it is possible to consider a Tesla Supercharger in a residential home situation because I've had this exact conversation already with my local power company specialists. It's not a slam-dunk. It will take some time on their part to consider how it may be done and if it may be done, at all, as they also need to look at their entire system leading up to my home for its capacity and my proposed demand requirements. If I do decide to move forward, then they will take the time to evaluate their own system and their staff's willingness to support providing that service directly to my home. And I'm told that until they check things out, it's not a sure thing. But they didn't discourage me, either. So it appears the door is open, at least here, for the Tesla supercharger system. But Tesla doesn't expect many residential installations and the power company doesn't, either. For the most part, it's expected mostly to be used in a more commercial setting. (Check with Tesla for availability when purposed for a residence.)


The upshot of all this is that you need to involve all interested parties and make sure that everyone is on the same page about what is to be achieved and how it can be safely achieved.

Asking here is not a means of avoiding any of that. Even if you get really good information that helps you get closer to understanding your situation, you still need to involve all of the appropriate groups. There are many ways this can go wrong and the amount of power and size of the energy transfers are unusually large and therefore deserve the best informed attention you can muster for the project.


if you have (I believe it is) single phase 120v from a residence, is it possible to use a transformer to step that up to 480v, which in turn goes into a 1-3 phase converter, to provide 3 phase 480v output?

Well, most modern trains do it very much that way...

example of a german train I know as I helped building that thing during my studies:

15kV at 16 2/3 Hz --> transformer to ~6kV then we have a 2QS which converts the power into DC for the intermediate circuit which then feeds a 4QS which is connected to the 3Phase asynchronous motors...

So Your concept is something you might see in a real installation, yes.

If the semiconductors are available for your voltage and current, you will rather leave away the transformer... it is big, heavy, expensive,...

And money being no factor, would it be possible to install something like this in a residential setting?

Of course... your electric company might charge you some decent digging a new cable to the next medium voltage transformer... sometimes these need an upgrade to. (OK, in the US and other countries which prefer installation on weather proof wooden pylons [?] - it might be a little cheeper)

To my personal amazement nobody seems to talk about fire protection and such, when it comes to high power charging at home...

  • \$\begingroup\$ Detatched garage \$\endgroup\$ – DKNguyen Sep 26 '20 at 1:54

You may want to take a look at https://www.tesla.com/en_AU/support/home-charging-installation/faq#supercharger in particular Tesla makes the statement:

Why is Supercharging faster than charging at home? Superchargers skip the onboard charger of the vehicle, providing up to 120kW of direct current (DC) power to the battery. This level of power requires dedicated transformers and utility connections which are not available in residential situations.

Tesla do produce a home charger, the "Tesla Wall Connector" which can run on a 3 phase supply. It appears that it would take about 4-5x as long to charge a vehicle (based on the model). The question becomes is the time saving worth the extra cost of the installation. For comparison plugging the car into a standard single phase outlet at 10A is going to take 28-35x as long to charge the vehicle.

You can convert a single-phase supply to 3 phase (with a specialised unit, essentially a single-phase mains powered 3 phase generator) but it clearly involves extra equipment, installation and maintenance costs which may likely be more expensive that just having your electricity supplier upgrade your domestic supply to a 3 phase connection.

  • \$\begingroup\$ "This level of power requires dedicated transformers and utility connections which are not available in residential situations." Premium Car manufacturers are already thinking how to provide charging at power levels beyond typical wall chargers, they also are into wireless charging - despite the bad efficiency factor of the whole chain of devices... And there are enough people around who easily can afford to pay the value of a normal house for such a toy \$\endgroup\$ – schnedan Sep 26 '20 at 6:51
  • \$\begingroup\$ I agree. There's not much economic sense in electric cars yet but it will come eventually... \$\endgroup\$ – mhaselup Sep 26 '20 at 6:56

Stop. Provisioning time.

The first thing you have to do is provision the power. Conversion isn't going to matter until you've done that.

A SuperCharger V1 draws 150 kilowatts (kW). Since you're dealing with 480 VAC, you're in North America so we have to look at readily available North American power. Mind you, I'm looking out the window at my own facility which has enough 480VAC delta to power four Supercharger stations (8 parking slots).

Note that NEC requires you provision 125% of the amount of power an EVSE requires. So your 150KW now becomes 187.5 KW.

The minimum US residential service is 100 amps @ 240V = 24 kW.
The more common residential service is now 200A @ 240V = 48 kW.
Often seen is 320-class (400A) service: 400A @ 240V = 96 kW.
I have seen a 600A installation: 600A @ 240V = 144 kW.
None of this is even close.

We need to talk to the power company.

Realistically, though, the power company gets cranky when you ask them to deliver that much 120/240V. 600A makes for some rather fat wires, because of thermal derates - increasing wire cross section isn't enough, you must also increase wire surface area if you want the wire to cool. Really, you're at a dedicated transformer anyway... so you might as well just ask the power company for the power you actually want, rather than do a costly double conversion. (go price 200kVA transformers and you'll grasp the "costly" thing. VA ~= Watts). Also the wires: 800A of service @ 240V will require six 1000 kcmil copper wires @ $20/foot each.

The power company gets EXTREMELY cranky if you ask to put that much load on a single phase. They really want balanced power, especially in a residential branch or rural circuit where your load will be the biggest for miles around. At this power level, they want to serve you 3-phase so it loads the distribution lines evenly.

All this to say, you are really, really, really better off asking the power company to provision the power you actually need for the thing: 480V 3-phase. They would much rather provide the 3-phase! And it's "six of one, half dozen of the other" whether they install a 480V transformer or a 240V one.

225A @ 480V/3-phase is served by common 4/0 AWG aluminum wires sold at Home Depot: 3 wires @ $2.50/foot each.

Depending on the power company, they may cheerfully sell you 2400V or 12KV directly, and let you run your own transformers. You can run that on 6 AWG aluminum ACSR... dirt cheap.

Well, that took care of conversion

The provisioning conversation has already brought us to the destination of the "conversion" issue. We are getting either 480V from the PoCo (at 225A provisoned for our 187.5kw)... or we are taking 2400/12kV off the poletop and running our own plant.

But, in case you're curious, how would you convert single-phase to 3-phase for a Tesla Supercharger? You wouldn't. The Supercharger couldn't care less; it just turns it into DC. The only reason the Supercharger takes 3-phase is because that's what the power company wants to deliver. Doing a 3-phase conversion is like giving car keys to a cat. So you'd call up Tesla and have them walk you through jumpering the Supercharger to take single-phase power.


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