50A 240vac circuit wire and ground in conduit

Discussion in 'Electrical Forum discussion & Blog' started by jadnashua, May 22, 2014.

  1. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    I'm thinking about an electric car, and a EVCS (charging station). Looking at a 40A unit, but one that plugs in, so requires a 50A circuit since there's no 40A plug defined. As I understand it, this will require 6g power and a 10g ground. I'm also thinking I may run some 12g and install a 20A 110vac receptacle (GFCI) with supply wires in the same conduit. Thinking that THHN wire is called for in a conduit.

    Can they share the same ground, or do I need to run a 12g ground wire for the other circuit?

    What size conduit would I need for 2-6g, 1-10g, and 2-12g? Or maybe three 12g, if I must run a separate ground for it.

    Can I use black for both the power leads, or do they have to be different colors? If different, white for the second, or maybe red? For the 20A circuit, I'd run white, black, and green.

    Is there a plastic conduit I could use, or is EMT better (this would be going into a residential garage)?
  2. cacher_chick

    cacher_chick Test, Don't Guess!

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    I cannot answer all of your questions without pulling out the NEC and looking it it up, but if you were to run more that 3 current carrying conductors in one conduit, they would have to be derated, so that would be one consideration.

    If the garage is detached, only a single circuit is allowed without installing a sub panel, which would be another consideration.

    As you know, green is equipment ground and white is neutral. Hots are commonly black or red, but can be other colors, just not green or white.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    The panel is in the garage, so that's not a consideration. I think that a 6g wire is already rated for up to 60A, so using it in a 50A circuit, I'm guessing, but need to know, if that would still be okay.
  4. Stuff

    Stuff Member

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    If the charger really draws 40 amps then you multiply by 1.25 to get 50 amps for the circuit. Even with derating for 4 current carrying conductors you should be good.

    Nice fill calculator at http://www.electrician2.com/calculators/rf_calculator.html - shows you would need 3/4"

    You can share the grounding wire. Size for the largest circuit. If using EMT you technically can leave it out (topic for debate/personal preference).

    Can't use white for a hot wire when using individual wires. All hots can be black.

    PVC schedule 80 sold in the electrical department is fine for normal protection. I like EMT but go with real rigid pipe if you think that you will be driving into it with the car!
  5. bluebinky

    bluebinky Member

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    You might also want to check with your local electric company if they offer any kind of special rates for what you are planning. I've heard people talking about significant savings with off-peak rates/separate meter for the charger...
  6. Reach4

    Reach4 Well-Known Member

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    There may be no need for the white wire for the charger. The EMT can do the protective ground so no green needed with EMT.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Good to know about the EMT as ground, but I never liked to rely on that with screws and rust, etc. It would be hard to hit the EMT with the car, but I prefer EMT to PVC for strength and resistance to moving things like lumber, and sheets of ply. How resilient is the PVC?

    The car I'm thinking about can only draw 32A max, but I'd like to go with the 40A rather than a 30A one to get the max charging rate when desired, but the thing can be charged off 120, but then only draws a max of 12A (but could take forever if the battery was really low!). I'd rather go with the 7.4Kw at max available on 240-vac. Well, I'd rather go with DC high voltage, and charge the thing to 80% in 20-minutes, but those chargers and the required main circuit are way out of my price range!

    Anyway, just trying to figure out what would be needed...if I go this route, I would hire a pro, not because I couldn't do it myself, but because it is in a condo, and the rules require it. Just wanted to understand what would be required.
  8. Vegas_sparky

    Vegas_sparky Digital Billy

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    The EMT can not be considered your sole ground. You need to run a 10ga ground wire in that conduit. #8 THHN is rated for 50A at 75°. A 3/4" conduit is fine for the charging and receptacle circuits.
  9. Reach4

    Reach4 Well-Known Member

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    250.118(4) ??
  10. Vegas_sparky

    Vegas_sparky Digital Billy

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    What about 517.13(B)? How many jurisdictions have amendments regarding this exact installation requirement? I haven't met an inspector in 10+ years that'll pass a class 1 installation without an EGC. Many times that's all they look for, aside from supports.
  11. DonL

    DonL Jack of all trades Master of one

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    Are them charging ports, and is charging ION power banks in cars even allowed inside of a Condo Garage ?

    I would think the Auto should be outside. I could be wrong.

    Just don't forget the fire sprinkler and smoke detector.


    Good Luck.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Around the world, and this includes the USA, there are thousands of charge points for EV's inside closed buildings, so no, that is not an issue. They don't give off H2, like a lead-acid battery can.

    In reality, if I get one, I'd probably keep the thing outside and charge it there...the cord on some is as much as 25', but, there are no restrictions on where you can install one of the things in general...but, in a condo, you must get permission to make external modifications, which is the current holdup. No sense buying one unless it can be recharged! SOrt of like a non-rechargeable battery, they get very expensive if you need to use them lots!

    As to the wire gauge...I may have them go to 6g, should I do it, in case I needed or wanted to be able to charge faster with a new unit down the line...each new generation of EV seems to come out with higher capacity batteries and often, a bigger on-board charger (the actual voltage conversion is IN the vehicle, so that limits the max rate it can be charged regardless of how much you can provide from the mains), and while they negotiate the charge rate between the charge point and the vehicle, if the vehicle can accept more, it would be nice to be able to recharge it at whatever rate it feels it can accept. IOW, you could charge the thing at 5A, if you had to because of supply problems, but, obviously, it would take much longer than if you could do it at 40A.
  13. Reach4

    Reach4 Well-Known Member

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    I don't have a copy of the code... but references that I find to that section seem to say that applies to patient care areas, so a redundant ground is required. This application is a residence in NH.

    As to how many places don't allow EMT with suitable connectors to serve as the equipment ground in a residence, I don't know. I wonder how that number compares to the number of jurisdictions that outright prohibit Romex, even in residences.

    I have a friend that told me his inspectors won't accept the compression EMT connections for grounding but do accept the ones with a screw. The compression type look more impressive to me, but that doesn't count.

    I am not an electrician. I have run very little EMT. But for what I have seen it is normal to use it as the equipment ground, at least in residences. I had presumed that was also the case in commercial buildings, but I don't know.
  14. DonL

    DonL Jack of all trades Master of one

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    I understand they do not emit gas. Gas builds up pressure inside of the battery, and they can explode.

    Time will tell how safe they are. I think it is safe to say, Nobody knows.

    They did not seem to work very well in airplanes for one reason or the other.

    That is a lot of power in a small package, Just waiting to get out. Even when taking a high current charge.

    If you are worried about charging time, maybe gasoline would better suit your driving habits.

    I am just talking, Sorry if I hosed your thread.


    Their is a lot to think about, Before spending all of that money, For something That has not been Time Proven Safe, Yet.



    Do you really save anything ?
  15. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    EV's are somewhat off topic! But, 90% of my driving since I retired is local - easily within a 10-mile radius. Certainly, I do go further, but for instance, the grocery store I usually go to is less than a mile away (no good sidewalks, or in good weather, I'd walk), and the main regional mall is about a mile, my GP is within walking distance, and others about 3-miles. The bike trail I like to ride is the furthest, about 8-miles away. So, while I'll keep my current car (it's paid for) for longer trips, it just doesn't get warmed up on short trips which isn't great for its battery, the muffler, the engine, etc. As to actually saving money, depreciation is always the killer, and no, at least with the miles I drive in a year, it would not pay for itself. But, if you used it for regular commuting, just counting the cost of energy with a typical car, based on local gas and electric rates and what I typically get on my current vehicle, I'd save about $0.15/mile in fuel costs and have no oil changes, spark plug, antifreeze, muffler, etc. issues to deal with in regular service. On the vehicle I'm thinking about, the batteries have an 8-year/100K-mile warranty, and about the only thing that needs service are the wiper blades and maybe brakes, but with the regenerative braking, in normal circumstances, you never need to touch the brake pedal, so they should last a very long time. The vehicle actually turns on the brake lights if you lift off entirely because it slows down quite fast when the motor switches into a generator (170-Hp motor makes a pretty hefty generator, too).

    Electric cars have been around for over a century...battery tech is now getting to the point where they are a useful alternative to some people's needs. Studies have shown, the average user goes less than 34-miles/day, and the vehicle I'm thinking about can go at least twice that on a really cold day, and maybe as much as 4x that on a more temperate one (and further, if you can pre-warm the batteries and cabin while on main power before you leave to save doing that with the batteries).

    Do I need one, no, but it was fun to drive, had plenty of room for my needs, and I like the concept from an engineering viewpoint. For some, it could save as much as $8-9K/year in fuel costs over an ICE (internal combustion engine), but I do not expect to drive anywhere near that amount.
  16. DonL

    DonL Jack of all trades Master of one

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    I just know around here you can not even store a Automobile in your Car Port, In a shared Condo, Thanks to HOAs. Your Results may vary. But that is done for safety. And homeowners insurance may not cover it. The auto man may, If they are still in business.

    Just get a fuel cell, If you want to be high tek.

    Enjoy, sounds like fun. So does a motorcycle.


    I will shut up for now.


    Jim, Why do you ask these question when you know the answer and the NEC rules ?


    Who is your Test for ?
    Last edited: May 23, 2014
  17. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    If you stick around here long enough, you get many answers, but not always, and those may not cover the specific situation. I always like to be certain, and people that work in the industry will know the exceptions to the rule. Not testing, just trying to cover all bases. It's funny, in the condo, you can do HVAC stuff to include running gas lines (with permit and inspections), but you can't do plumbing or electrical - those require a licensed tradesman. Our units each have their own garage (they're townhouses), and they certainly do allow you to use it as a garage!
  18. DonL

    DonL Jack of all trades Master of one

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    Even if code does not require it, I would put a Fuse panel with a cut off at the outlet. A fuse works better and faster than a breaker, but a breaker will work better than nothing. What ever you use, should have a emergency shut off, You should not need to open a panel to kill power.

    I think you need to go beyond NEC requirements for your project.


    It is better to be safe than sorry.
    Last edited: May 24, 2014
  19. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    The charging standards for J1772 are pretty robust...no power is applied to the vehicle until the connector is locked in place and the car toggles the appropriate signal line and they negotiate the max charge rate the vehicle can accept, along with the box indicating how much it can provide. THen, there's an error line if the car senses something wrong (overheating, is just one example of what can trigger it) which causes the box to remove power as well as smarts at the charging station that will remove power. Then, it also has built-in GFCI logic. The things are pretty safe all on their own. SO, in that scenario, I'm not too worried about it. The actual charger is in the vehicle...the wall box has some logic, a small dc power supply for the logic and signal lines, and a big relay to connect the power. The fast DC charging stations (pretty much limited to commercial power) are a different story - they provide the high voltage DC at high current to recharge the vehicle and are more complex, much more expensive, and much higher current. For most cars, they limit the DC fast charge to 80-% to minimize the heat buildup in the batteries. It then, if you leave it connected, drops to a much lower current to top them off over several hours. There aren't many of these around yet. In England, they have charging stations at all service stations along their motorways, and are rolling out DC fast charging as well...for the time being, recharging is free.

    FWIW, in the USA, around me, there are about 10 free level 2 charging stations within about 5-miles. And, more are reported to be installed. I have yet to see a DC fast charging station, and if I buy the thing, that capability is an extra cost option...I'll probably get it, but not sure it is really worth it for me at $700. I might find it very convenient if over the next few years, they pop up everywhere, though, and it can't be retrofitted, so I'd probably get it.

    Some of the fancier stations have WiFi connectivity so you can remotely monitor it (as does the car over cellular), along with a meter that indicates how much power has been transferred, and you can assign a $/kwHr and have it tell you how much it cost along with how long it was on. Most, though, just have three idiot lights: power, fault, charging.
  20. DonL

    DonL Jack of all trades Master of one

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    I wish you the best on your project, Sounds like you did your home work.

    I build Lion battery chargers and even with all the safety that I build into them , I do not trust using them unattended at a fast charge rate. I avoid fast charge rates for that reason. No one wants to babysit batteries charging.

    They are fine when they work, but when the charger or battery fails, not so much.


    Good Luck to you. Enjoy your project.
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