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FAQ: Home Tesla charging infrastructure Q&A

Discussion in 'North America' started by FlasherZ, Jan 10, 2013.

  1. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    #1 FlasherZ, Jan 10, 2013
    Last edited: Apr 24, 2016
    Charging/Electrical FAQ for Tesla EV’s
    Maintained by FlasherZ
    Last updated 2016-04-24 15:15 CT

    The contents of this FAQ (since it's becoming very, very long) -- use your browser's search function to look for the question in which you are interested:
    • WHAT ARE THE FIRST THINGS I NEED TO KNOW?
    • HOW DO I FIND AN ELECTRICIAN WHO KNOWS ABOUT TESLA REQUIREMENTS?
    • I’M HAVING AN ELECTRICIAN HELP ME. WHAT DOES HE NEED TO KNOW?
    • I WANT TO DO THE WORK MYSELF. DO I NEED A BUILDING PERMIT?
    • I HAVE A LARGE-APPLIANCE OUTLET, BUT I DON’T KNOW WHAT TYPE IT IS. CAN I USE THIS TO CHARGE MY CAR?
    • CAN I MAKE OR USE AN ADAPTOR CORD TO PLUG MY CAR INTO A DIFFERENT TYPE OF OUTLET?
    • I HAVE AN OLD-STYLE ELECTRIC RANGE OUTLET AVAILABLE (NEMA 10-50), CAN I MAKE AN ADAPTOR CORD TO THE TESLA’S 14-50 UMC PLUG FOR IT?
    • MY FAMILY MEMBERS HAVE ONLY AN OLD-STYLE NEMA 10-30 ELECTRIC DRYER OUTLET AVAILABLE, CAN I MAKE AN ADAPTOR CORD TO THE TESLA’S 14-50 UMC PLUG FOR IT?
    • MY FAMILY MEMBERS HAVE ONLY A NEMA 14-30 ELECTRIC DRYER OUTLET AVAILABLE, CAN I MAKE AN ADAPTOR CORD TO THE TESLA’S 14-50 UMC PLUG FOR IT?
    • I HAVE ACCESS TO A NEMA 6-50 WELDER OUTLET. CAN I BUILD AN ADAPTOR CORD TO THE TESLA UMC’S STANDARD 14-50 PLUG?
    • I HAVE ACCESS TO A NEMA 6-20 AIR CONDITIONER OUTLET, AND 120V IS SIMPLY NOT ENOUGH. SHOULD I BUILD AN ADAPTOR CORD FOR THIS?
    • ALL I HAVE IS SMALLER OUTLETS AND I REALLY NEED A HIGHER RATE OF CHARGE. CAN I COMBINE MULTIPLE CONNECTIONS TO CHARGE MY CAR?
    • I HAVE SEEN A DEVICE THAT COMBINES TWO 120V CIRCUITS TO CREATE A 240V CIRCUIT. IS THIS SAFE?
    • CAN I USE AN EXTENSION CORD?
    • WHAT WIRE SIZES SHOULD BE USED FOR INSTALLING MY NEMA 14-50R?
    • IS THERE ANY SPECIAL ORIENTATION FOR THE NEMA 14-50 RECEPTACLE?
    • AT WHAT HEIGHT SHOULD I INSTALL MY 14-50 OUTLET?
    • WHAT WIRE SIZES SHOULD BE USED FOR INSTALLING MY HPWC?
    • CAN I ATTACH A CORD AND PLUG TO MY HPWC AT THE 50A SETTING?
    • WHAT DO YOU RECOMMEND IF I WANT TO INSTALL AN HPWC AND HAVE A 14-50R AVAILABLE FOR ANOTHER EV OR BACKUP?
    • SHOULD I CONTACT MY POWER COMPANY TO LET THEM KNOW THAT I HAVE AN ELECTRIC CAR?
    • AFTER VERSION 5.8.4, MY CAR "BACKS OFF" FROM THE CONFIGURED CHARGING CURRENT BY 25%. IT WORKED FINE BEFORE, SHOULD I BE CONCERNED?
    • SEVERAL TIMES IN THIS FAQ AND IN THESE FORUMS, YOU REFER TO INSURANCE AND LIABILITY ISSUES. WHAT DO YOU MEAN?
    • WHERE CAN I FIND THE NEC ONLINE?

    WHAT ARE THE FIRST THINGS I NEED TO KNOW?

    First, electricity can be as deadly as gasoline when handled incorrectly, and when installed correctly and to regulations, is relatively safe. Don’t be fooled because of your experience with normal household electricity. The Tesla, like many EV’s, relies upon a high current to charge. If you lack the skills or experience to install or modify electrical infrastructure to support the EV, call a professional. You are installing the equivalent of a gas pump in your home – and it can be just as dangerous.

    Any modifications that are made to your electrical system, whether as hard-wired infrastructure or in attaching to that infrastructure, are subject to your local regulations. Generally, this is a direct adoption of a specific version of the National Electric Code (NEC) in the US, Canadian Electrical Code (CEC) in Canada, or your specific country’s code. Local jurisdictions may amend this code, and you must be aware of these. You should ask your local inspector what you should be aware of in relation to electrical codes.

    When installing or modifying electrical infrastructure, you must assume that anyone using it has no idea of the custom modifications that you will make. While you may understand what you did, the reason the NEC governs infrastructure is ensuring that the special knowledge you possess regarding an installation isn’t required if others (your partner, children, first responders, EMT, electricians, etc.) need to use, modify, or disconnect it.

    Finally, many, if not most, homeowner’s insurance policies have exclusions and will not cover a home loss if you have failed to follow electrical code, in some cases regardless of whether or not your modification has caused the fire. For example, if your car is plugged into a 30A-to-50A adapter cord for your car, and your kitchen experiences a grease fire that results in your home being destroyed, your insurance company may deny your claim because you violated NEC rules by plugging a 50A appliance into a 30A circuit. There is a specific question near the bottom that discusses the specifics of this.

    HOW DO I FIND AN ELECTRICIAN WHO KNOWS ABOUT TESLA REQUIREMENTS?

    In late April 2015, Tesla launched a new program called "Find an Electrician" on its web site. Tesla provides specific training on installing charging equipment, and ensures that these certified electricians adhere to quality, permitting, and inspection requirements. You can find an electrician at Tesla's web site here: Find an electrician | Tesla Motors

    I’M HAVING AN ELECTRICIAN HELP ME. WHAT DOES HE NEED TO KNOW?

    Tesla provides a number of information sheets that you can hand to an electrician.

    For the UMC, you can find the installation guide here.
    The Wall Connector overview can be found here.
    For the HPWC, you can find the installation guide here.
    If you are using a J1772-based EVSE, see its installation guide.

    Your electrician will likely know the key parts of the code, but may need to (quickly) read up on the EVSE specific portions if he hasn't dealt with an electric vehicle charging install before. NEC article 625 deals with specifics related to electric vehicle charging.

    I WANT TO DO THE WORK MYSELF. DO I NEED A BUILDING PERMIT?

    It depends upon your local requirements. In the US, generally any time a new circuit is run, or an existing circuit is extended or modified, a permit and inspection are required. Call your city hall or county/parish administration for requirements.

    If you are doing the work in a multi-unit complex, be aware that local laws may require a licensed electrician to do the work. You may not be permitted to do the work yourself if it is not for your own occupied single-family home.

    I HAVE A LARGE-APPLIANCE OUTLET, BUT I DON’T KNOW WHAT TYPE IT IS. CAN I USE THIS TO CHARGE MY CAR?

    See the Tesla Motors charging page or the Wikipedia page on NEMA connectors for more information. For the Tesla site, click “adapter guide” in the "outlet" section to see the various types of adapters available and an identification guide for outlets.

    Do not bend pins on a plug or outlet to make them fit.

    CAN I MAKE OR USE AN ADAPTOR CORD TO PLUG MY CAR INTO A DIFFERENT TYPE OF OUTLET?

    It is strongly recommended that you use the appropriate Tesla adapter for the UMC, when plugging into an outlet. The adapter provides the necessary guidance to the car on how much electricity to draw.

    Using a purchased adaptor cord (typically, these are RV cords) is not always a safe route. These cords are tested and listed for specific cases, and using them for a non-listed use can be dangerous. They are likely to be constructed safely, but they may not guarantee your safety.

    If you do create an adaptor cord, there are some basic rules you should always follow:

    * LABEL, LABEL, LABEL: Label the cord “for Tesla charging only – not for any other application”;
    * Keep the cable with the car whenever possible, so that someone doesn’t pick it up and attempt to use it for another application, like plugging in an RV; and,
    * Cut it in half when you disposition the car.

    Another user, cosmacelf, has provided an illustrated guide here:
    http://cosmacelf.net/Home Made Adapters.pdf

    Always keep in mind the risks when using any adapters (and ask Tesla to create a UMC adapter too!)

    The next few questions address specific adaptor cords that are frequently considered.

    I HAVE AN OLD-STYLE ELECTRIC RANGE OUTLET AVAILABLE (NEMA 10-50), CAN I MAKE AN ADAPTOR CORD TO THE TESLA’S 14-50 UMC PLUG FOR IT?

    The NEMA 10-series outlets were installed in homes up until 1996. They are ungrounded outlets, and rely upon the neutral conductor to provide a safety ground.

    The first thing you must check is your existing breaker size. Many range outlets installed were done as 40 amp circuits, with 40 amp breakers, 40 amp wiring, and 50 amp max receptacles. If you have a 40 amp breaker, chances are that your wiring is not sufficient for the 50 amp circuit that is needed for the UMC. A good starting point / rule of thumb is that if the wires are individual wires in conduit, it is likely 8 AWG and sufficient. If the wiring is a thick cable -- usually black, a/k/a NM-B or "Romex" -- it is likely insufficient because Romex for 40A is 8/3 and 50A requires 6/3. If the wire is insufficient and must be replaced, then you may as well remove the 10-50 and use its breaker slot for a new 14-50 installed in the proper place. This is because you will not be permitted to reinstall a NEMA 10-50R on any new or modified circuits.

    Next, if the existing receptacle is not needed for an electric range, you may want to check to see if you can replace it with a NEMA 14-50R. Turn off your breaker and pull out the receptacle. Many homes built in the 1980’s and 1990’s have a ground conductor inside the box that is not connected to the NEMA 10-50, typically a bare wire that comes in with the other wires. In this case, the NEMA 14-50 can be installed in place of the 10-50, and simply connect the ground conductor to the ground terminal on the 14-50.

    If this is not possible, you can make an adaptor cord that is relatively safe from a NEMA 10-50P (plug) to a 14-50R (receptacle). Using 6/4 rubber cord (type SOOW preferred), connect each “hot” conductor (typically brass terminals) on the plug to a brass terminal on the receptacle. Connect the neutral (typically silver terminal) on the plug to the silver terminal on the receptacle. Then, on the receptacle, connect a jumper between the neutral terminal and the ground (green) screw.

    This adaptor code is against code, because in NEC 2005 a provision was adopted to require the neutral and ground conductors be tied together in only one place in the electrical infrastructure. If the cord were used for an appliance other than the Tesla – especially one that has a metal chassis and touches concrete or earth – it could create a situation where current flows through your adaptor cord to ground. The worst case of this would be a break in the neutral conductor from the meter or transformer to your home, in which case your cord may become part of the return path for electricity in your home.

    MY FAMILY MEMBERS HAVE ONLY AN OLD-STYLE NEMA 10-30 ELECTRIC DRYER OUTLET AVAILABLE, CAN I MAKE AN ADAPTOR CORD TO THE TESLA’S 14-50 UMC PLUG FOR IT?

    This is not recommended, because it has a medium safety risk associated with it. Instead, use the appropriate Tesla adapter for the UMC which will properly restrict the maximum amount of current drawn by the car.

    DO NOT make this type of adaptor cord under any circumstances if you have a Federal-Pacific Electric or Zinsco/Zinsco-Sylvania circuit breaker panel – CHECK THIS! The potential for the car accidentally drawing too much current, and the high failure rate of breakers in these panels is of high risk!

    If you insist upon making a cord, follow the same instructions for the 10-50 adapter cord but use a 10-30P plug instead, and you may use 10/4 cable instead of 6/4. Follow the instructions above for using adaptor cords.

    You will need to set the charge current down to a maximum of 24A in the Tesla (80% of rated circuit) and ensure it remains there when you charge. While technically you could set it to 30A, plugs and receptacles rated for 30A are not intended to be used for continuous loads at full rated capacity, and members of the forum have reported burned/destroyed plugs from running the circuits this hot. If the car is not set down to a lower charging current, it is likely that the circuit breaker will trip if the car tries to draw the full 40A across the circuit.

    Again, this carries a medium risk, and in case of fire you are likely to find that your homeowner’s insurance company will not cover you in case of a fire, regardless of whether or not the cord is the cause.

    MY FAMILY MEMBERS HAVE ONLY A NEMA 14-30 ELECTRIC DRYER OUTLET AVAILABLE, CAN I MAKE AN ADAPTOR CORD TO THE TESLA’S 14-50 UMC PLUG FOR IT?

    This is not recommended, because it has a medium safety risk associated with it. Instead, use the appropriate Tesla adapter for the UMC which will properly restrict the maximum amount of current drawn by the car.

    DO NOT make this type of adaptor cord under any circumstances if you have a Federal-Pacific Electric or Zinsco/Zinsco-Sylvania circuit breaker panel – CHECK THIS! The potential for the car accidentally drawing too much current, and the high failure rate of breakers in these panels is of high risk!

    If you insist upon making a cord, obtain a short length of type SOOW cable, 10/4. Connect the red and black wires of your cord to each of the brass terminals on the plug and the corresponding brass terminals on the receptacle. Connect the white wire of your cord to the silver terminals, and the green wire of your cord to the green terminals. Follow the instructions above for using adaptor cords with regard to labeling and storage.

    You will need to set the charge current down to a maximum of 24A in the Tesla (80% of rated circuit) and ensure it remains there when you charge. While technically you could set it to 30A, plugs and receptacles rated for 30A are not intended to be used for continuous loads at full rated capacity, and members of the forum have reported burned/destroyed plugs from running the circuits this hot. If the car is not set down to a lower charging current, it is likely that the circuit breaker will trip if the car tries to draw the full 40A across the circuit.

    Again, this carries a medium risk, and in case of fire you are likely to find that your homeowner’s insurance company will not cover you in case of a fire, regardless of whether or not the cord is the cause.

    I HAVE ACCESS TO A NEMA 6-50 WELDER OUTLET. CAN I BUILD AN ADAPTOR CORD TO THE TESLA UMC’S STANDARD 14-50 PLUG?


    Tesla has discontinued its NEMA 6-50 adapter, and therefore there is no longer an option to connect to NEMA 6-50 (welder) outlets using a native UMC adapter.

    While one of these cables can be safely used with the Tesla EV, you must be careful as it carries a significant risk to someone who would try to use it for another application. In particular, this adaptor might be used by someone looking to connect an RV. RV’s typically have many 120V loads, and as a NEMA 6 series connector does not provide a neutral conductor, 120V appliances can be destroyed if this adapter cord is used for an RV. Other appliances that require 120V (electric ranges, for example, for timer and clock circuits) may also not work properly if this adapter is used. Always properly label any adapter cords that you make for the Tesla as "FOR TESLA CHARGING ONLY".

    To make such an adaptor, use a short length of type SOOW 6/3 cord. Connect the black and white wires (if using 6/3 cord), or black and red (if using 6/4) to the respective brass terminals on the NEMA 6-50P and NEMA 14-50R, and the green wire of the cord to the green terminals of the plug and receptacle. Label and store this cable per the above instructions, and add “NO NEUTRAL – DO NOT USE FOR RV’S” to the label. Under no circumstances should you ever connect the neutral pin of a NEMA 14-50 receptacle to the equipment grounding conductor (ground) - this is unsafe and dangerous.

    You may want to consider filling in the neutral pin of your 14-50R with epoxy, and cutting off the neutral pin of the UMC’s 14-50P (it is unconnected and unused by the UMC) to prevent this cord from being used with an RV. This will invalidate your UMC’s warranty but will provide an added level of protection in that the 14-50 cannot be used for appliances that need a neutral.

    This type of adapter carries potential liability and insurance implications, but is operationally safe to use.

    I HAVE ACCESS TO A NEMA 6-20 AIR CONDITIONER OUTLET, AND 120V IS SIMPLY NOT ENOUGH. SHOULD I BUILD AN ADAPTOR CORD FOR THIS?

    Given the high risk associated with using the Tesla 14-50 plug on a 20A circuit, this is not recommended at all. It is possible, but carries so many risks that it should be avoided at all costs:

    * Making a 6-20 to 14-50 adapter would create a situation where too much current could be drawn (if someone forgot to adjust the car’s current) over a very small wire size (12 AWG).
    * A 6-20 to 14-50 adaptor will not have a neutral wire and carries the same risk mentioned in the previous question, if an RV were to be plugged into it.

    If you insist upon making such an adapter, follow the same instructions as the 6-50 to 14-50 adapter, above, and ensure that the car’s charging current is adjusted down to a maximum of 16A. Do not use 20A, because most connectors are not rated for continuous loads at the circuit maximum and you are likely to burn the connectors.

    Again, this carries a high risk, and in case of fire you are likely to find that your homeowner’s insurance company will not cover you in case of a fire, regardless of whether or not the cord is the cause.

    ALL I HAVE IS SMALLER OUTLETS AND I REALLY NEED A HIGHER RATE OF CHARGE. CAN I COMBINE MULTIPLE CONNECTIONS TO CHARGE MY CAR?

    NEC 2011 article 310.10(H)(1) prohibits connecting equipment using paralleled conductors less than size 1/0 AWG. Technically, you are not permitted to do this.

    Invariably, though, the next question that is asked is whether it is safe or not. The answer is that it is complicated and can be made safe to use, but there are many factors that come into play. For the most part, for the average user, you should not do this.

    First, the circuits must be entirely phase-aligned. This means that the two circuits used must be connected from the same legs of the same transformer. Some commercial & industrial areas, large multi-unit apartment buildings, and RV parks are fed with a three-phase power distribution, and multiple circuits are likely to be on different phases of the service.

    Second, the circuits must have the same length. A longer circuit has a higher resistance, which will create an imbalance of current. If circuit 2's resistance is twice as much as circuit 1, circuit 1 will receive 66% of the load and circuit 2 will receive 33% of the load. In this case, if we were charging at 80A, circuit 1 would try to pass 53A (which should trip the circuit breaker), and circuit 2 would only carry 27A.

    And then, you will likely require some intelligence to make sure that the charging can back off if one circuit is unavailable. In the example above, circuit 1 is likely to trip its 50A breaker after a short period, at which point circuit 2 will try to handle the full 80A draw, tripping its breaker, and resulting in no charging at all.

    Finally, if the circuits are protected with GFCI devices, it adds another complexity in that the current draw must be symmetrical across the legs of each circuit, or the GFCI detects a difference and trips.

    Anecdotal evidence suggests that while this does work occasionally, it does require a lot of knowledge, some intelligent devices that can handle multiple inputs, and there are many times when it simply will not work because two circuits cannot be found that can be paralleled easily.

    As mentioned, be sure to understand any insurance implications of using a non-compliant means to power a vehicle.

    I HAVE SEEN A DEVICE THAT COMBINES TWO 120V CIRCUITS TO CREATE A 240V CIRCUIT. IS THIS SAFE?

    This is similar to the question immediately above this one, and many of the same requirements apply. It adds a twist, though, in that it uses two opposing 120V legs to create a 240V connection.

    The NEC does not permit a device to be connected to multiple branch circuits at once, so this approach would be non-compliant. However, again many times the question is whether it is safe...

    First, you must find two receptacles that are located on opposite legs of the building's electrical service without needing to use very long, very expensive extension cords that prevent significant voltage drop. This can be difficult in some homes.

    An additional point with this type of equipment is that many times, the 120V receptacles that would be used are shared with other receptacles on the same circuit. For example, circuit 1 might be in the garage where a freezer is connected, while circuit 2 is just inside the door, in the laundry room, where the washer and gas dryer are plugged in. As the 240V load must be symmetrical, the existing load plus additional charging load cannot exceed either of the circuits, or a circuit breaker will trip and cut the charging completely.

    As above, this approach is certainly not recommended and may have insurance implications.

    CAN I USE AN EXTENSION CORD?

    Tesla Motors makes it clear that an extension cord is not to be used with its UMC. The NEC requires that you follow manufacturer’s instructions, so technically you violate the NEC by using one.

    The NEC contains some rules for using extension cords. Some of the rules state that extension cords are not permitted to be used as a substitute for the fixed wiring of a structure; run through holes in walls, structural ceilings, suspended ceilings, dropped ceilings, or floors; run through doorways, windows, or similar openings; or be concealed behind building walls, structural ceilings, suspended ceilings, dropped ceilings, or floors.

    However, as to the question of whether it is safe or not… Technically, yes. With the right size conductors, an extension cord, whether 120V or 240V, is relatively safe in limited lengths.

    For 120V, to keep the voltage drop within range, you can use a 14 AWG cord if your TOTAL one-way circuit length from the car to the breaker panel is < 50 ft., 12 AWG if your total is < 100 ft., and you'd need to go to 10 AWG if you're at 150 ft. or greater.

    For 40A charging @ 240V (NEMA 6-50, 10-50, or 14-50), you should use 6 AWG, and your total one-way circuit length can be 300 ft, with voltage drop at reasonable levels.

    For 24A charging @ 240V (NEMA 6-30, 10-30, or 14-30), AWG 10 is good to 200 ft. one-way from breaker panel to the car, go one gauge up (AWG 8) if you need more.

    As mentioned, keep your cord to the smallest length possible to reduce voltage drop and increase your charging efficiency.

    Keep in mind the potential insurance implications of this, as mentioned above. You are violating the NEC in the US by doing this.

    WHAT WIRE SIZES SHOULD BE USED FOR INSTALLING MY NEMA 14-50R?

    Note: All wire sizes assume copper conductors!

    For wire-in-conduit, 8 AWG THHN (dry locations) or THWN (wet locations) is sufficient to carry 50 amps, but many electricians will use 6 AWG to ensure that there is enough headroom. The ground conductor must be a minimum size of 10 AWG.

    For “Romex” (NM-B cable), it must be sized for the 60 degC rating. This means that 8/3+ground NM-B may not be used for 50A, and 6/3+ground NM-B must be used. Note that type NM cable must be protected from damage (e.g., must be run inside a wall) and cannot be exposed. If you must run wiring on the outside of a wall, below 7' above the floor, you must use conduit. Type NM cable may be run in conduit as long as it does not run outside.

    If these conductors will ride in the same conduit as another circuit, they must be “de-rated” and 6 AWG is required.

    IS THERE ANY SPECIAL ORIENTATION FOR THE NEMA 14-50 RECEPTACLE?

    Most electricians will install a NEMA 14-50R with the equipment grounding conductor "up", as most plugs and cords are oriented this way. However, some electricians will place the receptacle ground pin at the bottom of the receptacle. If this is the case, you should ask to have it changed, as the UMC is oriented so that the ground pin is at the top of the receptacle. The ground pin is the round hole in the receptacle, not the rectangular blades.

    AT WHAT HEIGHT SHOULD I INSTALL MY 14-50 OUTLET?

    The NEC does not specify a minimum nor maximum height, although article 625 requires a disconnect means to be easily accessible. I have observed that many inspectors will take this to mean below 7' from the floor. Section 86-404 of the Ontario Electrical Safety Code requires that EVSE equipment -- including HPWC, EVSE's, and UMC's -- be located no more than 1.2m above the floor.

    Most electricians install these outlets 48" high, to support the Americans with Disabilities Act section 4.2.5/4.2.6 requirements. This is required in commercial settings, and desirable in residential.

    There is a little quirk in the NEC EVSE article 625 - the "coupling means", which is the J1772 or the "Tesla end" of the UMC or HPWC, must be installed and stored between 18" and 48" from the floor. Tesla's HPWC instructions (required to be followed by the NEC) also specify this as the maximum height. Violating this provision is unlikely to be an issue with inspectors for the UMC, but it's primarily intended to ensure the connector is accessible and you may want to consider that.

    WHAT WIRE SIZES SHOULD BE USED FOR INSTALLING MY HPWC?

    Note: All wire sizes assume copper conductors!

    For wire-in-conduit, 3 AWG THHN (dry locations) or THWN (wet locations) is sufficient to carry 100 amps, but many electricians will use 2 AWG to ensure there is enough headroom, and it’s carried more widely on electricians' trucks. The ground wire must be a minimum of #8 AWG.

    If these conductors will ride in the same conduit as another circuit, they must be “de-rated” and 2 AWG is required.

    2/3 NM cable available in the US (3 conductors of 2 AWG) is insufficient for the 80A charging / 100A breaker setting, because that cable is rated only at 95A per articles 334 and 315, and article 210 requires that an 80A charging load use a conductor with minimum ampacity of 100A. Likewise, I am told that Canadian consumers have the option of type NM cable (3/3+ground) for this installation, but NEC does not permit this (because 3 AWG must be used at the 60 degC rating, only 85 amps).

    This tends to generate a lot of confusion, since there is a "next size up" breaker rule, but not a wire/conductor rule. Here is the applicable NEC code:

    • Section 625.40/625.41 states that vehicle charging loads are always to be considered continuous loads.
    • Section 210.19(A)(1)(a) says that "Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch circuit conductor size shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load." An HPWC configured for an 80A continuous load, then, requires a conductor with an "allowable ampacity not less than" 100A.
    • Section 334.80 requires you to use the 60 degree column of 310.15(B)(16) when determining allowable ampacity of the NM cable.
    • Allowable ampacity of conductors is defined in section 310.15. The 60 degC column of 310.15(B)(16) states that the ampacity of #2 copper conductors is 95 amps.
    • As 95 amps is not "not less than" 100 amps, 2/3 NM cable would not be usable for this application.
    • The 240.4 "next size up" rule, for breakers only, doesn't apply to conductors, so it cannot be used.

    CAN I ATTACH A CORD AND PLUG TO MY HPWC AT THE 50A SETTING?

    In several threads on this forum, some have asked whether they may use their HPWC plugged into a NEMA 14-50 receptacle; this would allow them to unplug it and use their UMC in case of a wall connector failure.

    Technically, there is nothing in the NEC that prohibits the practice; Tesla's instructions don't explicitly call for only permanent wiring methods, and article 625 permits 240V devices to be plug-and-cord devices as long as they're "fastened in place". The only restriction is that the segment of cord prior to the ground fault protection (HPWC) must be a maximum of 12 inches in length (NEC 625.17(A)(3)(a)). Proper connectors, clamps, and strain relief connectors must be used.

    When consulted on the compliance of such a solution, several municipal and county inspectors have determined the practice to be legal based on the current instructions published by Tesla, and the NEC's requirements.

    However, when consulted, Tesla expressed concerns about the practice. The charging team responded to an inquiry with an explanation that the HPWC is designed to be mounted on a wall or post and wired using permanent wiring methods. There are concerns that a power cord could be yanked from the HPWC's terminals and expose live wires if, for example, someone or something grabbed the cord and yanked.

    A suggestion was made that Tesla note in the instruction/installation manual that permanent wiring methods are required, which would then be required by the NEC per section 110.3.

    WHAT DO YOU RECOMMEND IF I WANT TO INSTALL AN HPWC AND HAVE A 14-50R AVAILABLE FOR ANOTHER EV OR BACKUP?

    My recommendation is to install a 125A subpanel in the garage somewhere near where you will install the HPWC. From a 125A double-pole breaker in your home’s main panel or a subpanel, run 1 AWG (black, red, and white) and a 6 AWG ground (green) in a 1-1/4" conduit. Use a small 125A panel with lugs (without main breaker), GE type TL412CP or Square-D type QO148L125GF or similar. In this subpanel install 2 circuits, a 50A circuit to a NEMA 14-50R receptacle in 3/4” conduit, and a 100A circuit to the HPWC in 1” conduit.

    One of the reasons for this is that the NEC EVSE Code (article 625) requires that any EVSE using more than 150v have a disconnect in a "readily accessible location". Some jurisdictions require this to be in the same room, others are okay with it being in the same building. Canada appears to be even tighter about this -- section 86-304 of the Ontario Electrical Safety Code requires that it be within view and accessible.

    For the UMC, the 14-50 plug and receptacle are considered a "disconnecting means". For the HPWC, however, installing it without some type of switch for it in the same room may fail inspection. This subpanel fulfills the requirement. 625.23 requires the ability to lock the disconnect to the "open" or "off" position with a non-portable means (ruling out temporary circuit breaker locks), but I have been told by various inspectors that they are ok with the circuit breaker as the disconnect. You should ask your local inspector if you have questions.

    Note: There is one caveat here. Technically, if you insist upon the HPWC and 14-50R being able to charge at precisely the same time, you will be violating the continuous load provisions of subpanel feeders with this setup. It is legal at installation, because the 14-50R can carry varying types of loads; it's only when both cars are plugged in and charging at the same time that this creates a violation. This is because the HPWC's continuous load (80A) and the 14-50R's continuous load (40A) makes up more than 80% of a 1 AWG feeder (rated for 130A). In this type of setup, you should be staggering your charge times. If you are concerned about this and require both cars to be able to charge simultaneously (say, for time-of-day provisions in rates), you should upgrade the wire feeder size to #1/0 AWG, your feeder breaker in your main panel to 150A, and get a 150A rated subpanel for your garage (a good example might be an Eaton CH8B150RF). The trade-off you'll have to make here is that there are few small 150A rated subpanels, so you'll have a very large enclosure for a couple of circuits. The Eaton comes with a main breaker, but is a small panel. If you want one with main lugs, you'll have to settle for a larger (20-space) panel.

    SHOULD I CONTACT MY POWER COMPANY TO LET THEM KNOW THAT I HAVE AN ELECTRIC CAR?

    It is a good idea to call your power company; you should explain that you are going to be adding a significant continuous charging load of 40A (in the case of a 14-50) or 80A (in the case of an HPWC). They’ll likely ask what time of day you plan to see this load.

    The reason you want to do this is that the transformer or service entrance wiring into your home may not be appropriate for the new load that you will be placing on it. Many homes were connected to the grid many years ago, when electricity use was considerably reduced. Since then, general household electricity use has increased and adding a significant load may be the “tipping point” that causes an outage.

    There are signs that your current service is being strained: if lights dim significantly when your air conditioning or heating unit starts or your electric range or oven is turned on, you may need to have the power company assess your service – in the US, they should do this for free.

    Also, if you have your Tesla, pay attention to the difference between the voltage reported when the car is not charging (0 amps) and at full charging current. If the voltage difference between the two is more than 10V or so, you will want someone to take a look.

    AFTER VERSION 5.8.4, MY CAR "BACKS OFF" FROM THE CONFIGURED CHARGING CURRENT BY 25%. IT WORKED FINE BEFORE, SHOULD I BE CONCERNED?

    Yes, you should be concerned. If you have charged successfully for a while at full current, you are likely not in imminent danger (this is why the car's chargers back off, to protect you); however, it does mean that to the car, a component of the electrical system appears to be under duress. This condition is triggered when the car sees an abnormal voltage drop or fluctuation. Tesla has not released the specifics of its algorithm, so measurements cannot determine whether you will see this condition or not. The best that you can do is to perform some troubleshooting steps if you see this "backing off" behavior.

    It could be the result of a number of things:

    • The UMC/HPWC/J1772 connector contacts to the car could be dirty or loose, causing a higher resistance in the connection, which will generate significant amounts of heat. Check to see if the connector to the car is hot to the touch (warm is ok, hot is not).
    • The UMC or its adapter contacts at the NEMA 14-50 receptacle could be dirty or loose, causing a high resistance connection. Check to see if the UMC plug is hot to the touch (warm is ok, hot is not). Note that 14-50 adapters shipped after April, 2014 contain a special thermal protection component that will stop charging completely if it gets too hot.
    • Wiring at the branch circuit receptacle or breaker may be loose. Be alert for hot electrical smells or melting plastic smells as your car is charging.
    • The branch circuit conductors / wires may be undersized if there is a very long run (> 100 ft.) from the location's electrical panel, causing a larger-than-normal voltage drop. Voltage drop as seen by the car between 0A charging and the maximum charge current should be less than 5%.
    • Another high-current appliance in the home may be experiencing a problem. For example, a bad start capacitor in an air conditioning compressor or furnace blower may result in a very high load during start-up for a longer-than-usual period of time. The Tesla may respond to this by backing off.
    • Service conductors feeding the location from the power company may be undersized or damaged. These cables do not have to follow the same rules as wiring for the inside of the home, and sometimes are undersized. As an example, prior to my upgrades for the Tesla, my home had a 200A rated service being delivered over 2/0 AWG ("two-aught") aluminum cable; the NEC's tables determine that cable is sufficient only for 135A. Undersized cables, or those even slightly damaged by digging or other causes, will create a voltage drop at high loads that may trigger the Tesla to back away.
    • Utility transformers feeding the home may be undersized or failing. These transformers are sometimes very old (in some cases, transformers have been in place for 50 years) and typically serve two or more homes. They are typically replaced by the power company when they fail, and in many cases have not kept up with the electrical load growth over time. As an example, prior to my upgrades for the Tesla, my 200A rated service was fed from a 15 kVA-rated transformer, which was rated only at 62A. While these transformers are robust (the power company said they had calculated occasional load spikes of over 200%), they do cause abnormal voltage drops under higher loads.
    • The distribution lines from the nearest substation to your transformer may be overloaded due to highly fluctuating loads.

    Other than troubleshooting the specific branch circuit that feeds the Tesla charger, finding the source of this fluctuation can be complicated, and speaking with a competent electrician and the power company may be your best course of action. They have special test equipment that can monitor the voltage found at the point of entry to the home, and can help isolate the problem.

    If you want to be prepared before speaking with an electrician or a power company representative, you can take some of the first troubleshooting steps:

    • 1. First check the connections to the car from the UMC/HPWC. Are they hot to the touch? If so, contact the Tesla service center.
    • 2. If UMC, check the UMC adapter and plug for any signs of melting. If you see any, contact the Tesla service center. If your receptacle shows signs of melting, you should also have the connections checked.
    • 3. You might try charging at another good AC source -- a friend's home, an RV campground, a good J1772 charger. You may need the hardware in your car checked if it still backs off.
    • 4. Check that the connections on the receptacle, HPWC, and breaker that feeds the branch circuit to ensure they are tight. An electrician can help with this (or a handy relative or friend).
    • 5. Start by turning off every other breaker than the Tesla and start a charge. If the car still backs off from charging, then you know that the back-off is not caused by an appliance or other loads in the home, and it's highly unlikely it's due to aggregate load from the home. At this point, calling the power company is probably the best cause of action.
    • 6. Slowly add the breakers in the home, starting with the largest appliances first. If the Tesla backs off after adding a particular breaker, you'll want to see if you can isolate it to a specific appliance on that circuit. Does it only back off when the air conditioning starts, for example? Or when the well pump runs? If you turn that breaker off, but the rest of them on, does it not back off? This will point to a problem with an appliance in the home.
    • 7. If it can't be narrowed to a specific breaker or appliance, and seems to happen intermittently only at a certain amount of load, it may point to undersized conductors or transformer feeding the home. Only the power company can help you here.

    In any case, walk the electrician or power company engineer through your troubleshooting steps and results so that they might be able to help find the problem.

    One other note: it has been noted that if you make an in-car change to the charging current while it has backed off, that it will retain that current as the default charging setting for that location. For example, if your car has backed down from 40 amps to a maximum of 30 amps, and you hit the arrows on the charging screen in an attempt to ramp it back up, it will keep 30 amps as your new normal charge current. Once you've checked and/or corrected your infrastructure, you should ensure that you reset your charging value to the maximum again in the car.

    In any case, the Tesla is backing down the charge current to protect property from overloads or loose connections, and is the result of an anomaly seen in voltage characteristics. It should not be ignored - even if it worked at full current prior to v5.8.4, it doesn't mean that it was safe or that there aren't problems in the infrastructure.

    SEVERAL TIMES IN THIS FAQ AND IN THESE FORUMS, YOU REFER TO INSURANCE AND LIABILITY ISSUES. WHAT DO YOU MEAN?

    Just as in most subject areas, connections to an electrical system cover a wide range of solutions. When considering these potential connections, there are three important factors to consider: 1) Will it work? 2) Is it safe? 3) Is it legal?

    Some solutions will work but are unsafe and/or not legal. An extreme example is that in theory, bare wires could be used to transmit electricity to our cars, but it is not safe, and it is prohibited by most electrical codes, including the US National Electrical Code (NEC) and other appropriate country standards. There are some solutions that will work and are mostly safe - such as connecting your Tesla UMC to a receptacle via an extension cord, or using a J1772 extension cord - that are not legal, according to the NEC. Most jurisdictions in the United States adopt a form of the National Electrical Code, whether as-is or with specific local amendments; most countries outside the US have similar codes; the adoption of the NEC is codified in law with specific performance requirements and penalties for failure to comply.

    Many homeowners' and auto insurance policies in the United States have clauses that preclude payment of a claim in the case of unlawful behavior in various ways. My own homeowner's insurance has a clause that requires me to make any improvements to my property only in accordance with appropriate construction standards and take appropriate action when a deficiency is discovered to protect my property. Technically, my use of an extension cord could violate that.

    The stated implications of these clauses have been challenged on these forums, and other forums by those who design and market EVSE equipment and accessories. A post here explains one person's report after calling his insurance company for a determination.

    To obtain an independent opinion, I contacted the claims department of a "top 5" homeowners' insurance company (as measured by premiums revenue) with whom I have no business relationship, and asked to speak to a supervisor who would take part in claims decisions. I asked the following question verbatim:

    The answer I received had several parts:
    This means that the homeowner will assume all risks of using a solution that does not comply with electrical codes; and that should the insurance company decide to deny a claim, recovery would be suspended until completion of legal challenge via arbitration or lawsuit. Several states have found certain provisions like this to be unenforceable, yet others have found them unenforceable only in certain situations (for example, only if the bad wiring wasn't the direct cause of a fire), and if you suffer a loss and have a denied claim you should contact appropriate legal professionals to determine whether you have additional rights. My first-hand experience leads me to an opinion that no shortcut is worth the risk of loss of life or property, or having to fight insurance companies for several years.

    One final note: complicating this topic is the open question of whether EVSE equipment is considered part of the electrical infrastructure governed by the NEC, or an appliance which is not governed by the NEC. This question may take a legal challenge to resolve, but it is likely going to be solved only after a claim is denied and a homeowner takes legal action to have the claim approved. It is a gray area that may be a defense for using the solutions that will work and are safe, but not legal according to the NEC.

    WHERE CAN I FIND THE NEC ONLINE?

    The NEC is available online via the NFPA web site, but it requires registration and has a restrictive reading application. However, because the NEC is used as law in many jurisdictions, it is freely available. Archive.org hosts the 2011 NEC here.

    However, you should be careful when interpreting it – it is like interpreting law. One example is that what most people call the “neutral” is referred to as the “grounded conductor” in the code, while what most people call the “ground” is referred to as the “equipment grounding conductor”. As you can see, it is relatively easy to get confused.

    *** END OF FAQ ***
     
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  2. Lloyd

    Lloyd Active Member

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    great post! Links not working.
     
  3. PeterW

    PeterW Member

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    Hi FrasherZ, this is awesome thank you.

    Can you check the links you have provided, none of them work for me
     
  4. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Should be fixed. I wrote it externally and for some reason using the direct URL code for the forum didn't work.
     
  5. ElSupreme

    ElSupreme Model S 03182

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    I have a question. Do you have to put THHN wire in conduit? Or can you run it together in a bundle inside a wall.
     
  6. clea

    clea Member

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    It is perfect timing for this as I have an electrician dropping by tomorrow. Thank you.
     
  7. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    THHN must be run in some type of a raceway/conduit.

    Romex (NM) can be run inside a wall and doesn't need a conduit.
     
  8. dennis

    dennis P85D

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    Terrific! Thanks for posting.
     
  9. ElSupreme

    ElSupreme Model S 03182

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    Thanks. Guess I need to get some conduit then.
     
  10. swegman

    swegman Member

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    Thanks for all your work on this.
     
  11. Johan

    Johan Took a TSLA bear test. Came back negative.

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    Fantastic FAQ! Great job!
     
  12. tdiggity

    tdiggity Member

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    awesome stuff!
     
  13. montgom626

    montgom626 Active Member

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  14. W.Petefish

    W.Petefish Active Member

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    If you use 2-3 SO cable, you don't need a conduit either.

    Sent from my Galaxy S3 using Tapatalk
     
  15. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    This is correct, but service cord (SO/SEO/SJO/etc.) cannot be used for permanent installation; portable or pendant only. You don't need conduit for armored cable/BX or a few other types. I just post the most commonly used mechanisms -- THHN in conduit or NM-B.
     
  16. Doug_G

    Doug_G Lead Moderator

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    Nicely done, and thanks for adding a few words about Canadian differences.
     
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  17. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    I'd like to add more, but I can barely keep a handle on the US NEC much less a completely different codebook - and then there's the CSA (UL equivalent). Anyone who submits information, I'll edit and stuff it in there. And I'll clean some more of it up over time.
     
  18. mknox

    mknox Well-Known Member

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    Thanks FlasherZ for putting this together. I am pasting in below an extract from the Ontario Electrical Safety Code (Supplement to the Canadian Electrical Code) pertaining to EV issues:

    Section 86 — Electric vehicle charging systems
    Scope

    86-000 Scope

    (1) This Section applies to the installation of the electrical conductors and equipment external to an electric vehicle that connects an electric vehicle to a source of electric current by conductive or inductive means, and to the installation of equipment and devices related to electric vehicle charging.
    (2) The requirements of this Section supplement or amend the general requirements of this Code.

    General

    86-100 Special terminology

    In this Section, the following definitions apply:

    Electric vehicle (see Appendix B) — an automotive-type vehicle for highway use that
    (a) includes passenger automobiles, buses, trucks, vans, low-speed vehicles, etc., powered by an electric motor(s) that draws current from a rechargeable storage battery, fuel cell, photovoltaic array, or other source of electric current; and
    (b) excludes electric motorcycles, scooters for persons with disabilities and similar types of vehicles, and offroad self-propelled electric vehicles, such as industrial trucks, hoists, lifts, transports, golf carts, airline ground support equipment, tractors, and boats.

    Electric vehicle charging equipment — the apparatus and conductors, including the electric vehicle connectors, attachment plugs, and all other fittings and devices, that are specifically used to deliver current supply from the premises wiring to the electric vehicle.

    Electric vehicle connector — a conductive or inductive device that, by insertion into an inlet on the electric vehicle, establishes connection to an electric vehicle.

    Electric vehicle inlet — a conductive or inductive device that is permanently affixed to the electric vehicle into which the electric vehicle connector is inserted for charging and information exchange (see Appendix B).

    86-102 Hazardous locations (see Appendix B)
    Where electric vehicle charging equipment or wiring within the Scope of this Section is installed in hazardous locations as specified in Section 18 or 20, it shall comply with the applicable Rules of those Sections.

    86-104 Voltages
    The nominal alternating-current system voltages used to supply equipment covered in this Section shall not exceed 750 V.

    86-106 Permanently connected and cord-connected equipment
    Rules 86-300 to 86-404 apply to installation of permanently connected and cord-connected electric vehicle charging equipment.

    Equipment

    86-200 Warning sign
    Permanent, legible signs shall be installed at the point of connection of the electric vehicle charging equipment to the branch circuit wiring, warning against operation of the equipment without sufficient ventilation as recommended by the manufacturer’s installation instructions.

    Control and protection

    86-300 Branch circuits
    Electric vehicle charging equipment shall be supplied by a separate branch circuit that supplies no other loads except ventilation equipment intended for use with the electric vehicle supply equipment.

    86-302 Connected load
    The total connected load of a branch circuit supplying electric vehicle charging equipment and the ventilation equipment permitted by Rule 86-300 shall be considered continuous for the purposes of Rule 8-104.

    86-304 Disconnecting means
    (1) A separate disconnecting means shall be provided for each installation of electric vehicle charging equipment rated at 60 A or more, or more than 150 volts-to-ground.
    (2) The disconnecting means required in Subrule (1) shall be
    (a) on the supply side of the point of connection of the electric vehicle charging equipment;
    (b) located within sight of and accessible to the electric vehicle charging equipment; and
    (c) capable of being locked in the open position.

    86-306 Receptacles for electric vehicle charging equipment (see Appendix B)
    (1) Each receptacle for the purpose of electric vehicle charging shall be labelled in a conspicuous, legible, and permanent manner identifying it as an electric vehicle charging receptacle and shall be
    (a) a single receptacle of CSA configuration 5-20R supplied from a 125 V branch circuit rated not less than 20 A; or
    (b) of the appropriate CSA configuration in accordance with Diagram 1 or 2 when supplied from a branch circuit rated at more than 125 V or more than 20 A.
    (2) The receptacle in Subrule (1)(a) shall be protected with a ground fault circuit interrupter of the Class A type, when the receptacle is installed outdoors and within 2.5 m of finished grade.

    86-308 Electric vehicle as electric power production source
    (1) Electric vehicle charging equipment and other parts of a system, either on board or off board the vehicle, that are identified for and intended to be interconnected to a vehicle and also serve as an optional standby system or an electric power production source or provide for bi-directional power feed shall be specifically approved for that purpose and so marked.
    (2) When an electric vehicle is used as described in Subrule (1), the requirements of Section 84 shall apply.
    (3) Electric vehicle charging equipment installed in commercial garages or on premises of flammable liquid and gas dispensing and service facilities as described in Section 20 shall comply with Rule 20-114.
    (4) Where electric vehicle charging equipment is installed in commercial garages as described in Rule 20-100, the electric vehicle charging equipment shall be located outside the hazardous areas identified in Rule 20-102.

    Electric vehicle charging equipment locations

    86-400 Indoor charging sites (see Appendix B)
    (1) Indoor sites shall be permitted to include, but not be limited to, integral, attached, and detached residential garages, enclosed or underground parking structures, repair and non-repair commercial garages, agricultural buildings, and similar rooms or locations where the electric vehicle connector can couple to the electric vehicle.
    (2) Where the electric vehicle charging equipment requires ventilation,
    (a) adequate ventilation shall be provided in each indoor charging site as specified in Rule 26-546;
    (b) the electric vehicle charging equipment shall be electrically interlocked with the ventilation equipment so that the ventilation equipment operates with the electric vehicle charging equipment; and
    (c) if the supply to the ventilation equipment is interrupted, the electric vehicle charging equipment shall be made inoperable.
    (3) Electric vehicle charging equipment installed in commercial garages or on premises of flammable liquid and gas dispensing and service facilities as described in Section 20 shall comply with Rule 20-114 and shall not be located in the hazardous areas described in Rule 20-102.

    86-402 Outdoor charging sites
    Outdoor charging sites shall be permitted to include, but not be limited to, residential carports and driveways, curbsides, open parking structures, parking lots, commercial charging facilities, and similar locations.

    86-404 Height of electric vehicle charging equipment
    Electric vehicle charging equipment shall be located at a height of not less than 450 mm and not more than 1.2 m above the floor level.
     
  19. jeffrey.begens

    jeffrey.begens New Member

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    What should I expect to pay an electrician to install an electrical outlet for my 40KW Model S? (He quoted me a price of $650.00).
     
  20. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    It's hard to say exactly -- it depends upon how long the run is, because the wire itself is expensive and then you have the cost for conduit and fittings (or you have to put 6/3 NM-B into the wall). Then there's the labor -- whether he/she needs to move circuits around to make room in the panel, does he have to work in the walls, fish wire, go through the attic, etc. I would say that $650 sounds pretty reasonable as a normal install price, unless you have an exceptionally short run with no tough spots.
     
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