Electrical Code Question

Discussion in 'Prime Plug-in Charging' started by m8547, Jan 10, 2020.

  1. m8547

    m8547 Active Member

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    My garage has a single 15A circuit that's shared with the kitchen lights. I want two circuits so that I can run a power tool at the same time as the shop vac, and I want 240V so I can charge my car faster. Ideally I'd run something like a 50A circuit to a sub panel, but installing the sub panel is a fair bit of work and cost to do it correctly. For example since it is a detached garage my understanding is it requires grounding rods pounded into the ground for a sub panel.

    I had an idea to limit the scope of the project. If I run a single 10/3 wire (oversized from 12/3 minimum) out there on a 20A two pole breaker, I could install two 20A circuits (multi wire branch circuit style) and also a 240V NEMA 6-20R or 14-20R for charging the car. Is there anything in code that prohibits this arrangement? It's a little unusual, but I think it should be safe as long a I use a GFCI protected breaker. I would just have to not use power tools at the same time as charging the car, but that's no different than now. The 2017 NEC is in use in my area.
     
  2. Matt73

    Matt73 Junior Member

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    Disclaimer: I am not an electrician or electrical inspector. Just a DIYer that tries to do things right.

    2017's 210.11(C)(4) requires one 20amp circuit dedicated to 120v outlets in the garage and can have "no other outlets" beyond an exception for "readily accessible outdoor outlets". I think that will prohibit what you intend, even though it is intended to ensure there's an outlet suitable for EV charging in the garage.

    Besides, if you are using a 16a 240v charger on that 240 outlet, you really don't have any current capacity left for anything in the garage, not even lighting, without risking slowly tripping a breaker (80% loading of breaker).

    That said, you can do the multiwire branch, use one for the dedicated 20amp garage outlets and charge your car on that, and the other can be a mix of lighting and outlets for your tools. It doesn't get you the 240 charging you want, but you could at least 120v charge your car while using tools, which is at least a little better than what you have now.

    If you want 240 charging, run a sub panel, and consider making it at least a 60a. This makes good long-term sense, as someday you may get a full EV, and want something beefier than 240/16a charging. (i.e.: consider that you might want a 30 amp or 50 amp circuit for charging someday)
     
  3. Elektroingenieur

    Elektroingenieur Senior Member

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    Yes, at least this:

    625.40 Electric Vehicle Branch Circuit.
    Each outlet installed for the purpose of charging electric vehicles shall be supplied by an individual branch circuit. Each circuit shall have no other outlets.
     
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  4. m8547

    m8547 Active Member

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    Thanks for the detailed replies.

    Technically it sounds like if I need to meet 210.11(C)(4) and 625.40, then I need three circuits because I need another one for the light.

    How does the code know if my outlet is installed for the purpose of EV charging? Could it just be a generic 240V receptacle that I happen to plug an EVSE into? I'm planning on using a portable EVSE not a permanently installed one.

    To meet 210.11(C)(4) (ignoring 625.40) and also have 240V available, could I make an adapter cable that plugs into two 15-20R receptacles on opposite hot legs, and converts that to a 240V receptacle? For example something like this. Making my own adapter sounds more dangerous than just putting in a 240V receptacle, and taking it out if I ever move.
     
  5. Elektroingenieur

    Elektroingenieur Senior Member

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    That’s true, but it’s because there would be more than one branch circuit, not because of the subpanel. See 250.32(A) and its Exception “where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure.” If you leave the existing 15 A circuit and add new circuits, then you’d also need the grounding electrode system.
    If I were going to the trouble to get an electrical permit, install new wiring between the buildings, do the branch circuit wiring for the new receptacles, and drive the ground rods, I’d probably go ahead and do the panelboard, too. A small one wouldn’t add all that much to the cost.
    I know why the code-making panel added 625.40, but in my opinion, it’s not especially well drafted: the difference between a compliant and non-compliant installation shouldn’t depend on anyone’s state of mind. If you decide that you’d like a 240-volt outlet in the garage for unspecified cord-and-plug connected equipment, and you don’t say anything to the contrary, then 625.40 wouldn’t apply, of course.
    I’m not sure I’d agree that 210.11(C)(4) would be a problem. If the garage is existing, its wiring met the code in effect when it was installed, and that wiring will remain, then you might not be required to bring the garage fully up to the current code, depending on your state or local laws.

    Whether you install one circuit or more, think carefully, however, about the requirements of Article 220, Part II, Branch-Circuit Load Calculations, and Part III, Feeder and Service Load Calculations. Would the existing service and main panelboard be able to accommodate the added load (1) calculated according to the code-required procedures for existing dwelling units, and (2) in practice?
    I definitely wouldn’t do this.

    All of this is, of course, just general information—I haven’t seen your installation and don’t know your local regulations. I’d encourage you to discuss your requirements with an electrician or electrical engineer; your local building department may also be able to explain what they require when existing installations are upgraded.
     
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  6. m8547

    m8547 Active Member

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    Thanks! I am an electrical engineer, but I work on electronics not building wiring.

    I'm aware of the requirement for grounding. I'm not planning on leaving the existing 15A circuit. It also serves the kitchen lights and range hood. I think the range hood precludes much else from being on the circuit, but I can't remember which requirements apply.

    I'm confident that I could run a MWBC and add receptacles in the garage. But a subpanel adds just enough complexity that I should probably hire an electrician. That significantly increases the cost. I'm not sure how long I plan to live in this house, so I don't want to invest a lot in garage wiring. Maybe having an EV charging outlet in the garage would be a selling point, but it's probably not a significant consideration.

    For load calculations it looks like I can use 220.83 "Existing Dwelling Unit" which is much more generous than the rest of 220 III. I'll have to do more research. I only have 125A service, and I'm strongly considering replacing the electric water heater with gas to free up capacity, free up space in the main panel, and to save money on water heating. I would also like to add another mini split air conditioner in the future if I stay in this house.

    Regarding whether 210.11(C)(4) applies, I am never sure how much the latest code applies to new work in existing buildings. I am assuming that since I plan to redo most of the wiring in the garage, that it would fall under the current code. But this requirement does seem like it's intended to be a standard for new buildings.

    The only local amendment that appears to be relevant is that AFCI requirements apply to new panels and subpanels. Luckily that doesn't require my main panel to be upgraded to AFCI, since that would be a lot more expensive. I don't mind putting AFCI breakers in a new subpanel (I'm a fan of safety devices).
     
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