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I'm doing a remodel on my house which involves building a new garage. I have no plans to get a new car soon but presumably will in 1-5 years. How should I wire for an undetermined electric vehicle (Leaf? Tesla?). What current should I wire for? What gauge? Should it be an independent circuit? What receptacle? Any other advice?

Follow up question: I realized I have a 50A 240V run to behind my stove which I capped and put a blank on when I remodeled the kitchen and switched to a gas range. This appears to be 6/3 (+ ground) and has a 50A breaker-pair. So if I splice to a new 6/3 cable and run that to an empty box at the front of the garage, does that seem like a good (and up-to-code) plan?

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See National Electrical Code 2014 Article 625 - Electric Vehicle Charging System. –  Tester101 Nov 29 '13 at 11:08
    
@Tester101: Please see follow up –  ThePopMachine Nov 30 '13 at 4:46
    
@Tester101: Got a link to that article? –  ThePopMachine Nov 30 '13 at 5:04
    
No link, I have the book. It could be yours for the low low price of ~$90.00. –  Tester101 Nov 30 '13 at 12:47
    
Ventilation may also be required, depending on the car, charging station, and where it's installed. –  Tester101 Dec 2 '13 at 13:42
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3 Answers

See SAE J1772

In the 2009 standard, two charging levels are defined.

            Voltage  Phase          Peak current
AC Level 1  120 V    Single phase   16 A
AC Level 2  240 V    Split phase    32 A (2001)
                                    80 A (2009)

Nissan say

Most Nissan LEAF owners recharge their cars at home. The 6.6kW charger option lets you charge your Nissan LEAF at home in just 4 hours using a 32A Home Charging Unit

For that option you'd need a dedicated 240 volt 32 amp circuit.

Until you actually have an electric car it may be best to leave that circuit terminated in a junction box of some sort and leave the fitting of a charging-unit until later. You probably shouldn't fit a regular 240 V 32A outlet because the J1772 system requires some intelligence be built in to the supply side (the charging unit).

In some countries the government will pay you up to $1600 to have a charging point fitted in your garage. If you live in such a country, it might be worthwhile taking advantage of such offers whilst they are still available.

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Run conduit to a box capable of 60 amp service and leave space in the CB panel for appropriate breakers. Any vehicle capable of long distance and quick turnaround will need the capacity. Pull the cable and install the socket when that time comes. You won't know till you get there. –  Fiasco Labs Nov 29 '13 at 17:02
    
@RedGrittyBrick: Please see follow up in original question –  ThePopMachine Nov 30 '13 at 4:46
    
@FiascoLabs: See my follow up -- I can do 50A (6/3) -- should I do it? –  ThePopMachine Nov 30 '13 at 5:07
    
@RedGrittyBrick: I'm in California -- any luck here? –  ThePopMachine Nov 30 '13 at 5:07
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First you have to know what car requirements and what amperage service. Second, you need to know if the service is going to require 4-wire (Hots, Neutral, Ground). Also, you can't just splice 240V service, if there's any NEC requirements to meet new standards, you're limited to not changing what is in place unless you bring the whole circuit up to new code levels, i.e. pull the full length of cable. Hence my recommendation to conduit it in until you truly need the service. It's easy to over size the conduit to take up to 110A if that was necessary. –  Fiasco Labs Dec 1 '13 at 0:28
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Tesla's "High Power Wall Connector" option should have a 90 amp/240 volt breaker to serve 70 amps for a 4 hour recharge time. The same charger can be set to use less.

Breaker     Draw        Approximate  
(Amps)     (Amps)   Charge Time (hours)  
90           70             4  
80           64             4.2  
70           56             4.7  
60           48             5  
50           40             6  

It comes with a 25 foot cord, so placement is not critical. The connector is on the driver's side of the vehicle.

enter image description here

I note that the Nissan Leaf has the charger connection at the front of the car (below the hood front), so an outlet at the end of the garage is probably more convenient if there is a choice.

enter image description here

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For a Nissan Leaf, your best bet is a 240V 40 amp circuit to run the charging station. The car will only draw ~32 amps but you need to derate the circuit so you'd use 40A. No neutral is required or used. Your best bet would probably be to extend the 6/3 circuit to a box. Don't actually install any outlet until you get the charging station: some use a direct connection.

You'll also need to replace the breaker with a 40A.

If you're looking at a Tesla S, you may want a larger circuit. I'm not sure how high they go but I'm pretty sure it would be able to use the 40A circuit, just for slower charging.

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Why derate the 50A? Conduit runs? The breaker protects the wiring from overheating, not the end device. –  HerrBag Nov 30 '13 at 17:44
    
AFAIK, the charging stations require that the breaker match. I could be wrong about that,though. –  DoxyLover Dec 1 '13 at 3:36
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According to NEC, overcurrent protection must be rated at 125% labeled load. Which means if the charger draws 32 amperes, the overcurrent protection must be at least 40 amperes (32 * 1.25 = 40). If you have cable in place that can support higher currents, there is no reason to switch out the breaker. –  Tester101 Dec 2 '13 at 13:35
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