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[Garage Charger] How should we go with the cable?

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Here is a simple picture to explain our garage situation; in order to have a 50A cable from the small garage (where the main breaker box is) to the 2-car garage (where we park our model 3), how would you recommend us doing this?

Thanks for your time.

Charger.png
 
Presumably, your question is about how expensive it will be to run the needed wiring to have an EVSE in the two car garage?

Or the alternative is to install the EVSE in the one car garage at lower cost, then park the EV in the one car garage or next to it for charging.
 
Presumably, your question is about how expensive it will be to run the needed wiring to have an EVSE in the two car garage?

Or the alternative is to install the EVSE in the one car garage at lower cost, then park the EV in the one car garage or next to it for charging.
Thank you. Yes, I’m wondering in this case, what is the best way to run wire from small garage to the two car garage for installing EVSE. Should it be underground through the lawn next to it or go though the roof? Or is there any alternative? I have normal outlets in the two car garage, can I convert them to higher current and change the switch in breaker box? Thank you.
 
You may want to ask electricians about cost of various options.

If you know someone with a less expensive EV, you may want to borrow it to leave it parked in the driveway while hiding the Tesla when you have electricians visit.

Normal outlets are presumably only 15A, suitable for at most 12A charging if there is nothing else on the circuit. Converting them to higher amperage would require larger wire (and separating them from other things on the circuit if that exists).
 
FYI: You'll need a 60amp circuit to charge at 48amp for the continuous derate.

I think the electrician is going to prefer going through the lawn. If you trench it yourself (just rent the tool), or source a handyman, you can save the 150/hr labor for the work. I would do it this way to also save on labor for pulling the massive cable through multiple stories and buildings, as well as the cost of copper.

But either way the electrician will make the call. If you run it outside you'll probably need an external junction box for disconnecting the circuit plus all sorts of hoops to jump through for doing it properly to code. The electrician may not want to deal with that.
 
There are many methods depending on your structure and aesthetic goals. For example:
  • You could bury 6/2 UF cable right in the dirt (50A circuit / 40A charge).
  • You could drag 6/2 NM cable (Romex) thru the upstairs floorspace or go all the way up to the attic and back.
Or for 60A/48A:
  • You could run 3/4" conduit (rigid or "smurf" flex) with #6 or #4 AWG wires in the dirt, floorspace, attic, or along the outside of the walls.
Tips:
  • The conduit option provides the best performance and protection with no increase in material cost, but it's a lot more work to deal with 3/4" conduit and fittings and then pull a bunch of wire thru it so the labor costs should be much higher than simple "Romex" cable.
  • Save money with a 2-conductor circuit "/2" if you're feeding a wall charger or 6-50 outlet. You'll need 3 conductors "/3" for a 14-50 outlet.
  • Use a wall charger instead of a portable one for the best bang/buck.
As for converting your existing outlet, you can simply double the power by replacing the 120V breaker with a 240V version but this is only practical if you have a single circuit going directly from the panel to a single outlet in the garage that is not needed for anything else. In other words, forget it. But you certainly can charge at 120V with your existing garage outlets and for many people this is adequate.
 
  • Helpful
Reactions: Rocky_H
So much depends on how hard it is to run the cable through that second story area. What, if anything, is directly in between the two garages? A suggestion I haven't seen here would be running conduit on an outside wall or maybe on the underside of the second story, or perhaps there's a shade structure there it could be run across (or maybe you'd like to add one :) )?

Another question is whether there are any existing subpanels that might have room and be closer to that garage.
 
FYI: You'll need a 60amp circuit to charge at 48amp for the continuous derate.

I think the electrician is going to prefer going through the lawn. If you trench it yourself (just rent the tool), or source a handyman, you can save the 150/hr labor for the work. I would do it this way to also save on labor for pulling the massive cable through multiple stories and buildings, as well as the cost of copper.

But either way the electrician will make the call. If you run it outside you'll probably need an external junction box for disconnecting the circuit plus all sorts of hoops to jump through for doing it properly to code. The electrician may not want to deal with that.
Thank you very much
You may want to ask electricians about cost of various options.

If you know someone with a less expensive EV, you may want to borrow it to leave it parked in the driveway while hiding the Tesla when you have electricians visit.

Normal outlets are presumably only 15A, suitable for at most 12A charging if there is nothing else on the circuit. Converting them to higher amperage would require larger wire (and separating them from other things on the circuit if that exists).
Thanks for your suggestions.
 
FYI: You'll need a 60amp circuit to charge at 48amp for the continuous derate.

I think the electrician is going to prefer going through the lawn. If you trench it yourself (just rent the tool), or source a handyman, you can save the 150/hr labor for the work. I would do it this way to also save on labor for pulling the massive cable through multiple stories and buildings, as well as the cost of copper.

But either way the electrician will make the call. If you run it outside you'll probably need an external junction box for disconnecting the circuit plus all sorts of hoops to jump through for doing it properly to code. The electrician may not want to deal with that.
Thank you very much, could you please help me understand what you mean by "You'll need a 60amp circuit to charge at 48amp for the continuous derate". So I need a 60amp outlet to charge the model 3?
 
There are many methods depending on your structure and aesthetic goals. For example:
  • You could bury 6/2 UF cable right in the dirt (50A circuit / 40A charge).
  • You could drag 6/2 NM cable (Romex) thru the upstairs floorspace or go all the way up to the attic and back.
Or for 60A/48A:
  • You could run 3/4" conduit (rigid or "smurf" flex) with #6 or #4 AWG wires in the dirt, floorspace, attic, or along the outside of the walls.
Tips:
  • The conduit option provides the best performance and protection with no increase in material cost, but it's a lot more work to deal with 3/4" conduit and fittings and then pull a bunch of wire thru it so the labor costs should be much higher than simple "Romex" cable.
  • Save money with a 2-conductor circuit "/2" if you're feeding a wall charger or 6-50 outlet. You'll need 3 conductors "/3" for a 14-50 outlet.
  • Use a wall charger instead of a portable one for the best bang/buck.
As for converting your existing outlet, you can simply double the power by replacing the 120V breaker with a 240V version but this is only practical if you have a single circuit going directly from the panel to a single outlet in the garage that is not needed for anything else. In other words, forget it. But you certainly can charge at 120V with your existing garage outlets and for many people this is adequate.
Thank you very much, could you please help me understand what you mean by 60A/48A?
 
So much depends on how hard it is to run the cable through that second story area. What, if anything, is directly in between the two garages? A suggestion I haven't seen here would be running conduit on an outside wall or maybe on the underside of the second story, or perhaps there's a shade structure there it could be run across (or maybe you'd like to add one :) )?

Another question is whether there are any existing subpanels that might have room and be closer to that garage.
Thank you Dave. Yes, I think running conduit on the outside wall underside of the second story can also be a good method.

As for subpanels, :) I do have two panels but unfortunately, they are next to each other in the small garage, haha.
 
Thank you very much, could you please help me understand what you mean by 60A/48A?

Long range models can accept a maximum AC charge current of 48A and coincidentally Tesla's current "Gen 3" wall charger can supply a maximum of 48A. Building codes require you to oversize the circuit by 125% if the load will be "continuous" as it is with EV charging. Hence, you'd need a 60A circuit for 48A charging, or 50A for 40A, etc. but you can choose whatever you want - run a 20A circuit if you like and charge at 16A.
 
  • Informative
Reactions: Rocky_H
Thank you very much, could you please help me understand what you mean by "You'll need a 60amp circuit to charge at 48amp for the continuous derate". So I need a 60amp outlet to charge the model 3?
For continuous loads like EV charging, you can use up to 80% of the circuit's capacity.

So if you want to charge at 48A (which a Model 3 LR or P can do; a RWD can do 32A), you need a 60A circuit. This generally requires a hardwired EVSE.

However, even if your EV can charge at 48A, you do not have to charge at that -- it will charge just fine on a lower amperage circuit, although not as quickly.

Charging amperageCircuit capacityNotes
48A60AHardwired
40A50AHardwired or NEMA 14-50 or 6-50 outlet
32A40AHardwired or NEMA 14-50 or 6-50 outlet
24A30AHardwired or NEMA 14-30 outlet
16A20AHardwired or NEMA 6-20 outlet (or 5-20 outlet for 120V)
 
Thank you very much, could you please help me understand what you mean by "You'll need a 60amp circuit to charge at 48amp for the continuous derate". So I need a 60amp outlet to charge the model 3?
Other people have answered this but whenever you have a circuit designed for a continuous load, like charging, it needs to be beefed up to handle the extra heat. Most electronics aren't taking the full load from a circuit at all times, so all the wiring is designed for that in mind. This is why when you charge from a 120v outlet the car takes 12 amps instead of the 15 amps that it is rated for.

Even if you don't get a car with a 48 amp charger (the charger is built into the car) it's always good to future-proof. Copper isn't going to get cheaper and many newer EVs have beefier (72 amp) onboard chargers. That's why I ran a 100 amp circuit to my garage rather than 60. You can save a bit of money on the run by using aluminum SEU if it's inside. Just make sure that your electrician doesn't cheap out on the junction. Copper can't be mixed with aluminum willy-nilly (this has been the cause of many house fires).
 
I would appreciate if people wouldn't do that thing that sounds like fear mongering of telling everyone they need a 60A circuit. They don't necessarily, and as we saw here, it scared someone that they were about to do something wrong. A 50A circuit is fine, or a 40A. Whatever people have capacity and cost effectiveness to fit in their house's system is fine.
 
We're only being helpful as a 50 amp circuit is too much for a 32 amp charger and too little for a 48 amp charger. Adding nuance and insight isn't fear-mongering; he asked for our recommendations and we're providing them. :)