8 ms·

A few years ago I was working with a custom builder on a house plan (that we didn't end up pursuing), but one of the things I suggested was future proofing the

A few years ago I was working with a custom builder on a house plan (that we didn't end up pursuing), but one of the things I suggested was future proofing the garage for electric cars. Given that a Tesla can charge on 80 amps, it seemed reasonable that a two car garage in a custom home should have 160 amp service. It may not useful right away, but it would very probably be useful over the life of a home. He thought I was crazy, and maybe I was. But articles like this make me wonder.

toomuchtodo 9y ago
I would suggest 200A service as a bare minimum, with 400A being ideal (this will be heavily dependent on your electric utility service entrance). Consider two EVs, HVAC loads, and possibly electric water heaters, clothes dryers, and a stove. Also, NEC 80% derating (100A circuit required for an 80A 100% duty cycle load). The electrician's time is the most expensive part; oversize for decisions such as these (load center, EV run to outlet, subpanels, etc).
- matt_wulfeck 9y ago
  After putting up panels at my relatively modest house, I’m honestly surprised at the kind of juice I can produce. I’m ready to convert everything I have to electricity
  - toomuchtodo 9y ago
    If you didn't put a battery in at install time, there's a recent IRS determination suggesting [1] you can still receive the 30% tax credit if the battery is installed at a later date. I would highly recommend pulling the trigger right before the tax credit begins its phase out at the end of 2019, assuming costs come down further between now and then. The caveat is that your system must charge the battery from your panels, and cannot charge from the utility (trivial inverter setting). With that said, based on net metering laws in most locales, it behooves you to consume as much of your own production as possible. Exceptions abound. https://www.reddit.com/r/energy/comments/82fchy/irs_letter_on_home_batteries_could_open/ https://www.reddit.com/r/energy/comments/82fchy/irs_letter_o...
    - matt_wulfeck 9y ago
      We have net metering here, so the grid is basically my battery. It would be more worthwhile if I could charge from the grid but I’m way overproducing as is.
- jeffwilcox 9y ago
  If your utility lets you do this... in many areas, increasing your service amperage is expensive if you don't use a majority of that additional capacity.
- blattimwind 9y ago
  200+ A circuits in a residential home really makes a point for 400 V three phase (where the same load would be ok with a standard 63 A circuit, which is still a lot). [1] However, when more and more people try to have fast chargers in their homes for EVs, then not only the residential installation poses a problem, but utilities would need to rebuild ~two layers of distribution to accomodate for a 100-200 % increase in residential power consumption. [1] Not just because high currents are more difficult to handle properly, but also because you need a lot less copper.
  - lolwhatitis 9y ago
    If you live in a subdivision built within the past couple decades, your electric runs underground, making it quite expensive to run a second or third primary phase. You also then need a three-phase transformer, which is considerably larger than a typical one-phase. Oh, and your service will be commercial/industrial, which typically comes with demand and energy charges that can be quite steep: https://www.northwesternenergy.com/docs/default-source/documents/E-Programs/E-demandcharges.pdf https://www.northwesternenergy.com/docs/default-source/docum...
    - blattimwind 9y ago
      That's true, for North America, but entirely misses the point I made (i.e. when you try to push dozens of kW into a house, single phase becomes worse than a below-average idea).
      - deleted 9y ago
        [deleted]
  - hinkley 9y ago
    Which is one of the logical conclusions of products like the PowerWall. I think the current model can only run like 25 amps but an in house fast charger that can pull 10 or 20 amps during off peak hours and dump 60 amps when charging the car could be a cheaper installation. Hell if the PowerWall 3 could dump 40 amps you could pull 20 from the wall at the same time and hit your 60 amp total.
stefan_ 9y ago
160 amps alone is more than standard house connect. In any case you will likely be charging overnight, and then given the time available pumping 80 amps into your precious depreciating battery is a great way to make it lose lots of value, quick. What people need in their garage is 20 amps for the trickle charge to replenish the 30 miles lost from their commute and some grocery shopping overnight.
- newnewpdro 9y ago
  It's likely a 100% EV home would want the option to charge as quickly as possible, even if they trickle charge most of the time for the sake of battery life. It's also likely that future EVs won't have this battery limitation, just put in the heavier gauge wires and breakers while you're in there if the house is going to be around for the next century.
- manmal 9y ago
  You are right, but you forget about emergencies. Hospital is 10km away, and batteries are empty. Do you want to wait 2m for enough juice, or 10m? Or less gloomy: In between appointments, you drive home to charge. Do you want to come 15m late just because your pipe is too weak? Big pipe = freedom.
  - gambiting 9y ago
    In an emergency, you surely call an ambulance, not drive yourself.
    - TomMarius 9y ago
      Not really. Where I am that'd take at least double the time. Depends on what kind of emergency it is, of course, I'd not move someone with spinal injury, but if my girlfriend is feeling terribly sick, I'd rather drive her (that's an actual real life example that happened to me).
    - zentiggr 9y ago
      Depending on your insurance, ambulance and emergency charges can be either rather high copay or only % covered, and are NEVER cheap on their face. My wife drove me to the emergency room on a 3am Sunday morning when I felt like someone was pushing a golf ball out through my ribs and I had my gall bladder out that week. $750 copay for ambulance service.
EdwardMSmith 9y ago
When I had upgraded service run to my 1923 house, I ran 200 amps to the detached garage and 200 amps to the house. The extra cost vs a smaller service is marginal.
schiffern 9y ago
>Given that a Tesla can charge on 80 amps Note that EVs are considered "continuous loads" under the US electrical code, so the circuit actually needs to be sized for 125% of the load (ie to charge at 80 A requires 100 A service, not 80 A service).
- Filligree 9y ago
  Reasonably so. Charging it may take hours, so the line will get as hot as it's going to get.
  - tgtweak 9y ago
    I believe Tesla has 48A and 72A chargers. An 80A circuit (wired and fused accordingly) can sustain this, since the wiring standards have some overhead in them for this.
    - Waterluvian 9y ago
      That sounds like trying to needlessly get away with the minimum.
      - kurthr 9y ago
        It seems important to distinguish between wire rating (guage, junction, and length) vs fuse rating. Typically, you would fuse well below the wire rating (at least 25%) so unless you're worried about the breaker box flipping, ruining at 90% of the fuse rating is reasonable (if it is a stable 'non-inductive' load). Besides, Tesla (non-super) chargers are typically limited by the vehicle.
        amluto 9y ago
        Please read the electric code before you touch or specify any wiring. 90% is neither reasonable nor legal, and non-inductive has little to do with it.
sandworm101 9y ago
Future proofing isn't all about providing a service today for a possible need tomorrow. Plenty of fiber is sitting in walls unused because people thought in-home fiber networks were going to be a thing. Don't provide the cables. Provide the conduit for future cables. Leave the accessible passages and pull-throughs and let future generations decide exactly which cables to install.
- rb808 9y ago
  I have similar experience - you dont know what will be useful in the future. Someone put in Cat5 cables 20 years ago into my place - nice idea. There is cat5 to the kitchen which is a waste of time now that wifi is here. Meanwhile it isn't fast enough for gig ether to my server so I put a new cable in. Likewise I have analog component video wires in the wall which is useless when I want HDMI.
  - wallflower 9y ago
    As mentioned above, my builder friends will put in PVC pipe to run cables between floors and in walls. This allows cables to be replaced relatively easily if their time of usefulness is exceeded. This seems to be a common best practice, sort of like blowing in expandable foam insulation between the historic (unchangeable) facade and new inner walls to properly insulate a historic home. Electrical Metallic Tubing (EMT) conduits are similar but more stringent (fire protection). https://en.m.wikipedia.org/wiki/Electrical_conduit https://en.m.wikipedia.org/wiki/Electrical_conduit
swalsh 9y ago
As a woodworker, I'd appreciate that kind of amperage in my garage.
- poulsbohemian 9y ago
  Yes! This is exactly what I was thinking in regard to the above commentary. By the time you get an electric car, a table saw, a band saw, a dust collector... and that's before the mention of an electric tankless water heater. Throw in there some grow lights for your greenhouse or whatever other high-electric hobbies you might have and the numbers above start to look really reasonable.
gwbas1c 9y ago
You are. My custom house is almost complete and we only put a single 40 amp circuit in the garage. I've lived with an EV for a few years now. 40 amps is plenty. When we get two EVs, 40 amps will still be plenty. The garage is also close enough to the breaker box that we can run another 40 amp circuit if we need to. You don't need both of your Teslas to go from 0 range to 300+ miles in two hours everyday. If you did that much driving you'd be running a taxi service. In our case, the charger will be between both bays. Assuming that both EVs have 300 mile range, we won't need to charge both cars everyday. (Edit) I'm also assuming someone will come out with a 40-amp dual-car charger that will split the load between two cars when both are plugged in. Anyway, I did ask about 400 amp service because I wanted to use tankless electric water heaters. What he told me is that he'd have to wire in a second panel and second meter. At that point I decided that 200 amps was plenty.
- joncrane 9y ago
  >I wanted to use tankless electric water heaters Aren't these prohibitively expensive compared to natural gas? (I've considered the same but I have gas service)
  - CydeWeys 9y ago
    Not at all. A negligible increase in total cost compared to the amount it costs to build a house. You can search Home Depot's site for models.
    - miketery 9y ago
      I think he was referring to operating costs.
      - joncrane 9y ago
        Correct
      - CydeWeys 9y ago
        Ah, makes sense. Tankless gas is a cheaper ongoing way to go in the US then, though installation costs may be higher since you might need a larger diameter gas line put in.
RegBarclay 9y ago
I haven't added power to my detached garage yet, but when I do, it's getting 200 amp service. I don't have an electric car (yet) and I may not before I move out of the house, but somebody is eventually going to live in that house and have an electric car.

toomuchtodo 9y ago

I would suggest 200A service as a bare minimum, with 400A being ideal (this will be heavily dependent on your electric utility service entrance). Consider two EVs, HVAC loads, and possibly electric water heaters, clothes dryers, and a stove. Also, NEC 80% derating (100A circuit required for an 80A 100% duty cycle load). The electrician's time is the most expensive part; oversize for decisions such as these (load center, EV run to outlet, subpanels, etc).

matt_wulfeck 9y ago
After putting up panels at my relatively modest house, I’m honestly surprised at the kind of juice I can produce. I’m ready to convert everything I have to electricity
- toomuchtodo 9y ago
  If you didn't put a battery in at install time, there's a recent IRS determination suggesting [1] you can still receive the 30% tax credit if the battery is installed at a later date. I would highly recommend pulling the trigger right before the tax credit begins its phase out at the end of 2019, assuming costs come down further between now and then. The caveat is that your system must charge the battery from your panels, and cannot charge from the utility (trivial inverter setting). With that said, based on net metering laws in most locales, it behooves you to consume as much of your own production as possible. Exceptions abound. https://www.reddit.com/r/energy/comments/82fchy/irs_letter_on_home_batteries_could_open/ https://www.reddit.com/r/energy/comments/82fchy/irs_letter_o...
  - matt_wulfeck 9y ago
    We have net metering here, so the grid is basically my battery. It would be more worthwhile if I could charge from the grid but I’m way overproducing as is.
jeffwilcox 9y ago
If your utility lets you do this... in many areas, increasing your service amperage is expensive if you don't use a majority of that additional capacity.
blattimwind 9y ago
200+ A circuits in a residential home really makes a point for 400 V three phase (where the same load would be ok with a standard 63 A circuit, which is still a lot). [1] However, when more and more people try to have fast chargers in their homes for EVs, then not only the residential installation poses a problem, but utilities would need to rebuild ~two layers of distribution to accomodate for a 100-200 % increase in residential power consumption. [1] Not just because high currents are more difficult to handle properly, but also because you need a lot less copper.
- lolwhatitis 9y ago
  If you live in a subdivision built within the past couple decades, your electric runs underground, making it quite expensive to run a second or third primary phase. You also then need a three-phase transformer, which is considerably larger than a typical one-phase. Oh, and your service will be commercial/industrial, which typically comes with demand and energy charges that can be quite steep: https://www.northwesternenergy.com/docs/default-source/documents/E-Programs/E-demandcharges.pdf https://www.northwesternenergy.com/docs/default-source/docum...
  - blattimwind 9y ago
    That's true, for North America, but entirely misses the point I made (i.e. when you try to push dozens of kW into a house, single phase becomes worse than a below-average idea).
    - deleted 9y ago
      [deleted]
- hinkley 9y ago
  Which is one of the logical conclusions of products like the PowerWall. I think the current model can only run like 25 amps but an in house fast charger that can pull 10 or 20 amps during off peak hours and dump 60 amps when charging the car could be a cheaper installation. Hell if the PowerWall 3 could dump 40 amps you could pull 20 from the wall at the same time and hit your 60 amp total.

stefan_ 9y ago

160 amps alone is more than standard house connect. In any case you will likely be charging overnight, and then given the time available pumping 80 amps into your precious depreciating battery is a great way to make it lose lots of value, quick. What people need in their garage is 20 amps for the trickle charge to replenish the 30 miles lost from their commute and some grocery shopping overnight.

newnewpdro 9y ago
It's likely a 100% EV home would want the option to charge as quickly as possible, even if they trickle charge most of the time for the sake of battery life. It's also likely that future EVs won't have this battery limitation, just put in the heavier gauge wires and breakers while you're in there if the house is going to be around for the next century.
manmal 9y ago
You are right, but you forget about emergencies. Hospital is 10km away, and batteries are empty. Do you want to wait 2m for enough juice, or 10m? Or less gloomy: In between appointments, you drive home to charge. Do you want to come 15m late just because your pipe is too weak? Big pipe = freedom.
- gambiting 9y ago
  In an emergency, you surely call an ambulance, not drive yourself.
  - TomMarius 9y ago
    Not really. Where I am that'd take at least double the time. Depends on what kind of emergency it is, of course, I'd not move someone with spinal injury, but if my girlfriend is feeling terribly sick, I'd rather drive her (that's an actual real life example that happened to me).
  - zentiggr 9y ago
    Depending on your insurance, ambulance and emergency charges can be either rather high copay or only % covered, and are NEVER cheap on their face. My wife drove me to the emergency room on a 3am Sunday morning when I felt like someone was pushing a golf ball out through my ribs and I had my gall bladder out that week. $750 copay for ambulance service.

EdwardMSmith 9y ago

When I had upgraded service run to my 1923 house, I ran 200 amps to the detached garage and 200 amps to the house. The extra cost vs a smaller service is marginal.

schiffern 9y ago

>Given that a Tesla can charge on 80 amps Note that EVs are considered "continuous loads" under the US electrical code, so the circuit actually needs to be sized for 125% of the load (ie to charge at 80 A requires 100 A service, not 80 A service).

Filligree 9y ago
Reasonably so. Charging it may take hours, so the line will get as hot as it's going to get.
- tgtweak 9y ago
  I believe Tesla has 48A and 72A chargers. An 80A circuit (wired and fused accordingly) can sustain this, since the wiring standards have some overhead in them for this.
  - Waterluvian 9y ago
    That sounds like trying to needlessly get away with the minimum.
    - kurthr 9y ago
      It seems important to distinguish between wire rating (guage, junction, and length) vs fuse rating. Typically, you would fuse well below the wire rating (at least 25%) so unless you're worried about the breaker box flipping, ruining at 90% of the fuse rating is reasonable (if it is a stable 'non-inductive' load). Besides, Tesla (non-super) chargers are typically limited by the vehicle.
      - amluto 9y ago
        Please read the electric code before you touch or specify any wiring. 90% is neither reasonable nor legal, and non-inductive has little to do with it.

sandworm101 9y ago

Future proofing isn't all about providing a service today for a possible need tomorrow. Plenty of fiber is sitting in walls unused because people thought in-home fiber networks were going to be a thing. Don't provide the cables. Provide the conduit for future cables. Leave the accessible passages and pull-throughs and let future generations decide exactly which cables to install.

rb808 9y ago
I have similar experience - you dont know what will be useful in the future. Someone put in Cat5 cables 20 years ago into my place - nice idea. There is cat5 to the kitchen which is a waste of time now that wifi is here. Meanwhile it isn't fast enough for gig ether to my server so I put a new cable in. Likewise I have analog component video wires in the wall which is useless when I want HDMI.
- wallflower 9y ago
  As mentioned above, my builder friends will put in PVC pipe to run cables between floors and in walls. This allows cables to be replaced relatively easily if their time of usefulness is exceeded. This seems to be a common best practice, sort of like blowing in expandable foam insulation between the historic (unchangeable) facade and new inner walls to properly insulate a historic home. Electrical Metallic Tubing (EMT) conduits are similar but more stringent (fire protection). https://en.m.wikipedia.org/wiki/Electrical_conduit https://en.m.wikipedia.org/wiki/Electrical_conduit

swalsh 9y ago

As a woodworker, I'd appreciate that kind of amperage in my garage.

poulsbohemian 9y ago
Yes! This is exactly what I was thinking in regard to the above commentary. By the time you get an electric car, a table saw, a band saw, a dust collector... and that's before the mention of an electric tankless water heater. Throw in there some grow lights for your greenhouse or whatever other high-electric hobbies you might have and the numbers above start to look really reasonable.

gwbas1c 9y ago

You are. My custom house is almost complete and we only put a single 40 amp circuit in the garage. I've lived with an EV for a few years now. 40 amps is plenty. When we get two EVs, 40 amps will still be plenty. The garage is also close enough to the breaker box that we can run another 40 amp circuit if we need to. You don't need both of your Teslas to go from 0 range to 300+ miles in two hours everyday. If you did that much driving you'd be running a taxi service. In our case, the charger will be between both bays. Assuming that both EVs have 300 mile range, we won't need to charge both cars everyday. (Edit) I'm also assuming someone will come out with a 40-amp dual-car charger that will split the load between two cars when both are plugged in. Anyway, I did ask about 400 amp service because I wanted to use tankless electric water heaters. What he told me is that he'd have to wire in a second panel and second meter. At that point I decided that 200 amps was plenty.

joncrane 9y ago
>I wanted to use tankless electric water heaters Aren't these prohibitively expensive compared to natural gas? (I've considered the same but I have gas service)
- CydeWeys 9y ago
  Not at all. A negligible increase in total cost compared to the amount it costs to build a house. You can search Home Depot's site for models.
  - miketery 9y ago
    I think he was referring to operating costs.
    - joncrane 9y ago
      Correct
    - CydeWeys 9y ago
      Ah, makes sense. Tankless gas is a cheaper ongoing way to go in the US then, though installation costs may be higher since you might need a larger diameter gas line put in.

RegBarclay 9y ago

I haven't added power to my detached garage yet, but when I do, it's getting 200 amp service. I don't have an electric car (yet) and I may not before I move out of the house, but somebody is eventually going to live in that house and have an electric car.