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Why 50 amp breaker on NEMA 14-50 if M3 incl. cable max is 32 amps?

Discussion in 'Canada' started by Rlhm3, May 20, 2018.

  1. Rlhm3

    Rlhm3 Member

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    I'm not an electrician so please forgive me if this is a stupid question but isn't a circuit breaker meant to trip if the amp rating is exceeded to protect the M3?

    It seems that Tesla has gone with 32 amps max for the included charging cable which is 80% of 40 amps so wouldn't a 40 amp breaker be better instead of a 50 amp breaker?
     
  2. rdturner0

    rdturner0 Member

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    Maybe fractionaly cheaper, but not sure I would say 'better'.

    Depends if you might use the circuit for other things. Since it's a recepticle, others things can be plugged into it.

    Technically, if all you intend to draw is 32A, then a 40A breaker is fine from a rating perspective.

    I'm not sure if there are code restrictions on what goes with a 14-50, but I don't recall any. I think my stove outlet has a 30A breaker (and those are typically 14-50). However, code has changed since that was installed.
     
  3. rdturner0

    rdturner0 Member

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    Sorry, just realized what you were getting at...

    Are you concerned that overload on the charge cable (more than its rated amperage), should be tuned to the breaker?

    You certainly could use it in that way, and it would be safe to do so. But because it's a recepticle, it's independent. The device attached would need to protect itself. The breaker is intended to protect the circuit, not the the load. The load needs to have its own protections.
     
  4. Rlhm3

    Rlhm3 Member

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    Thank you for clarifying! :)

    Yes, I thought it was there to protect the load.

    So, it's there to protect the circuit which is basically the outlet and wire to the breaker?

    That's why it's important to have thicker 6 AWG wire with a 50 amp breaker whereas it can be just 10 AWG with a 30 amp breaker for a typical clothes dryer?
     
  5. rdturner0

    rdturner0 Member

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    #5 rdturner0, May 20, 2018
    Last edited: May 20, 2018
    Yes, effectively just for the outlet and the wire. Anything plugged into it needs to take care of itself. If you had a hard-wired appliance, then it's a bit different, but still, the load would still be responsible for protecting itself.

    Wire sizing is typically determined by two main factors:
    - capacity (there are maximum limits required by code, which thusly determine minimums as well)
    - length of circuit for voltage drop

    Most of the minimums will satisfy the voltage drop requirements for around 80-100 feet (I didn't check that, but that's what I've seen when doing specific calculations of my own).

    According to Table 2 of the 2015 Canadian Electrical Code (which is being replaced at some point by the 2018 version which I've yet to get a copy of)
    6 AWG has a maximum of 55 A (maximum 60 degrees C rating)
    10 AWG has a maximum of 30 A (maximum 60 degrees C rating)

    Note that the numbers also vary depending on how cables are installed, and how many conductors are together in the raceway or cable. It's important to make sure the details are correctly understood (and there are a lot of details in the code).

    Robert
     
  6. 03DSG

    03DSG Active Member

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    The wire must to be able to support the breaker in the panel and the breaker protects the wire and the outlet. You will find almost all electric stove plugs (Nema 14-50) in Canada are powered by a 40 amp breaker using 8/3 wire and electric dryer plugs (Nema 14-30) powered by a 30 amp breaker using 10/3 wire.
    The benefit of using 6/3 wire even to a Nema 14-50 on a 40 amp breaker using the included UMC is if you decide now or later to upgrade to a Tesla WC. If your service/panel has the capacity you can switch out the 40 amp breaker for a 60 amp breaker and take advantage of full 48 amp on board charger with the WC for home charging.
     
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  7. rdturner0

    rdturner0 Member

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    To add to that, one of the major costs of a typical install is the pulling the cable through walls/floors/joists etc... so as @03DSG said, picking the bigger cable ahead of time gives you some options.

    It should be noted that you can't go too far out of range as the breakers might not take the gauge of wire, etc. So if you picked a 3/3 cable, and a 20 A breaker, I don't think the cable would fit in the breaker. That's a bit of a contrived example though.
     
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  8. svp6

    svp6 Member

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    But you can charge with the first generation mobile connector at 40A. This is what I do with my 3.
     
  9. 03DSG

    03DSG Active Member

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    Unless you have one already you can’t buy them in Canada.
     
  10. CadillacJack

    CadillacJack Member

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    Correct - I bought a 40a 14-50 Adapter in the US at a service center in Pittsburgh last year for this reason. If it’s important to you, you could try to do something similar. My dads an electrician so I had him double check the wiring and breaker to make sure I was set up for 40a.
     
  11. Rlhm3

    Rlhm3 Member

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    Thanks everyone for the helpful information!

    Luckily, my basement is unfinished and it's just a short distance from the electrical panel to the garage wall so I pretty much just have to decide which wire/breaker combo to go with:

    6/3 & 50A or 40A
    8/3 & 40A or 30A
    10/3 & 30A - I'm only considering this option because I have some leftover 10/3 cable

    For the actual wall plug I think a NEMA 14-50 makes the most sense since the car's UMC comes with that adapter already and I'm sure that all of those wire size will fit in it. However, not sure if electrical code allows it? I plan to do the install myself and then have an electrician inspect it.

    It's tempting to get the Tesla WC since the incentive on that might go away in the future.
     
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  12. akidesir

    akidesir Member

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    Do the 6/3 since you’re doing it now and your basement is unfinished. Future proof yourself.
     
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  13. rdturner0

    rdturner0 Member

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    While having an electrician inspect it isn't a bad idea, in Ontario you are required to get a permit from the ESA and have the ESA inspect it (which is not the same thing as having an electrician inspect it). (I'm not trying to tell you want to do, just making sure you are aware...)

    I'd suggest going with the 6/3 also, because pulling the cable is most of the real work -- but keep in mind that if you choose > 50A (i.e. 60A), you will also need a disconnect box close to the "appliance". Also, the cable needs suitable mechanical protection (e.g. armoured cable, inside joists, studs, or conduits), and the rules for cabling inside conduits are different that inside joists, etc. (The rules are for fire safety due to the thermal characteristics of the cables, etc. And since this is a high current circuit, thermal conditions are sort of important.)
     
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  14. Rlhm3

    Rlhm3 Member

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    True, 6/3 is probably the wisest choice long term especially if I finish the basement eventually.

    I was not aware, thank you! Wow, the ESA website and fee guide is super confusing. All I managed to find was that a homeowner's permit is $79 but not sure how much the inspection will be?

    I checked out conduit parts at the home depot yesterday. Does anyone have photos or advice on the conduit parts that they used like this one which I guess would be good for bringing the cable through the drywall into the garage to meet up with additional conduit up to the receptacle?
    IMG_4110 (1).jpg
     
  15. 03DSG

    03DSG Active Member

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    Are you positive about the disconnect? I only ask as the contractor doing my work has already installed 25m Teck 6/3 armour cable on a surface run from my basement panel to a 14-50 in the garage on a 40 amp breaker. They are returning Friday to swap out the 14-50 for the Tesla WC and swap out the 40 amp breaker for the 60 amp breaker. This is a single unbroken wire run from my panel. They didn’t spec a disconnect, however they could easily install one above the WC.
    Is this new code as it wasn’t required previously?
     
  16. rdturner0

    rdturner0 Member

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    60A+ definitely requires a disconnect in close proximity to the appliance. Could be a subpanel, or a disconnect box. I will pull up the code a bit later today and quote the specific section for you.

    Electrician should be fully aware of that requirement. The 40A run you have doesn't require it, so it was installed without issue.

    Shouldn't be too much effort to add one it though. The box only costs $20, but they might need extra cable to handle the connections, etc. Usually an extra 2-3 feet required.

    It's not new, been around since before the 2015 code for sure.
     
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  17. rdturner0

    rdturner0 Member

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    #17 rdturner0, May 21, 2018
    Last edited: May 21, 2018
    Sent you note via direct conversation to give me a call -- I can guide you through the major decision points quicker than reading the whole code book...

    ESA sheet can be confusing for sure -- fortunately there is a single code for the EV charger. The inspection is part of the permit (so long as it passes first time -- if not, there will be an additional charge for each visit).

    The wall penetration is the tricky part as there is a limit to what types of cables and conduits can pass through insulated areas. What I did was EMT (metal) between the HPWC and the disconnect, flexible non-metallic (liquid tight) between the disconnect and through the wall (stops about 1 inch after penetrating the surface), then NMD (regular cable) inside the house. The reason I chose the flexible conduit for the penetration was mostly to simplify sealing the wall penetration and making the "tight turn". Any cable in a junction box must be anchored as it enters the box, and you don't want that anchor inside the wall penetration as it's a mess to seal, etc). Inside the conduits, it must be individual conductors, so I stripped the outer sheath from the NMD for passage through the flexible, and I used individual T90 conductors from the disconnect through the metal conduit to the HPWC.

    I am not sure about poly conduits -- most of the stuff I saw suggested it was largely for outdoor, but I have seen it used indoor as well in some places (not necessarily Ontario).

    The other option is armoured cable -- which depending on the run length, might be simpler because then you don't need conduit. However, conduit isn't that pricey. I also have a few left over parts for the EMT if you are in the same end of town as me (far west end).

    You may find these other posts of mine useful:
    What is the cheapest Ontario EVIP approved charger?
    Charger Configuration and Install New M3
    220 outlet installation in garage (link to my parts list and photo of my install -- although I have added a couple of clamps to clamp the flex cable to the wall as it wouldn't have pass inspection)

    My inspection is this Wednesday -- finger crossed I got it all right. :)
     
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  18. rdturner0

    rdturner0 Member

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    Oh, and for 3-4 conductors of 6 AWG, 1 inch conduit is the minimum size (you had a photo of 3/4 inch, which isn't big enough). Also, if you run EMT (metal), I would also run a ground conductor in addition to the casing being ground (it's acceptable by code to use the EMT as ground, but most electricians prefer to also run a ground conductor in case someone comes along and sticks a plastic box in the middle...).
     
  19. rdturner0

    rdturner0 Member

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    #19 rdturner0, May 21, 2018
    Last edited: May 21, 2018
    Here's a thread where electricians are discussing the very subject, and the first post quotes the code section and requirement:
    EV charger question
    Although there are some incorrect statements from some of the posters in that thread. The code statement is the correct one -- however, the circuit rating (60A) is what actually matters in our case, because the HPWC can be set to different ratings (that's that part that was confusing the electrician). Of course, that's so long as the HPWC is set correctly to be no more than 80% of the breaker rating.

    To fully quote section 86-304 from the 2015 Canadian Electrical Code:
    86-304 Disconnecting means
    (1) A separate disconnecting means shall be provided for each installation of electric vehicle supply 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 supply equipment;
    (b) located within sight of and accessible to the electric vehicle supply equipment; and
    (c) capable of being locked in the open position.​
     
  20. rdturner0

    rdturner0 Member

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    Also be careful you do not end up going over your total load. I had to switch back down to a 50A breaker to get my house under the 160A limit for a 200A service (and I have gas for most things except the stove). I was quite surprised how tight I was on a 200A service.
     

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