TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker and becoming a Supporting Member. For more info: Support TMC

Installed my own Wall Connector, saved $848

Discussion in 'Model 3: Battery & Charging' started by RyanDe, Jun 13, 2018.

  1. RyanDe

    RyanDe Member

    Joined:
    Aug 24, 2016
    Messages:
    183
    Location:
    Massachusetts
    Lowest quote was $950. Purchased all the parts for $102. Took about 3 hours mostly fishing that large ass wire. Glad I didn't run conduit, looks better with the back install.
    IMG_0248.JPG
     
    • Like x 4
    • Love x 1
  2. EasterEgg

    EasterEgg Member

    Joined:
    Apr 5, 2016
    Messages:
    24
    Location:
    West Coast
    Looks greedy.
    Do you have a picture of the wire on the other side of the wall ?
     
  3. RyanDe

    RyanDe Member

    Joined:
    Aug 24, 2016
    Messages:
    183
    Location:
    Massachusetts
    It's in wall. Basically the circuit breaker box is about 4' to the right on the inside. Wire comes from that to the disconnect box, out of that and down 16" to the charger.
     
  4. P85_DA

    P85_DA Supporting Member

    Joined:
    Apr 25, 2015
    Messages:
    2,873
    Location:
    CA
    Nice job !
     
  5. eprosenx

    eprosenx Member

    Joined:
    May 30, 2018
    Messages:
    996
    Location:
    Beaverton, OR
    What kind of wire did you use? NM-B? What gauge? What amperage of circuit breaker?

    My install is basically the same. I had a hard time waterproofing behind my unit though. I think I need to use some more polyurethane caulk behind mine.

    I ran "rigid" (threaded) conduit through the wall.
     
  6. RyanDe

    RyanDe Member

    Joined:
    Aug 24, 2016
    Messages:
    183
    Location:
    Massachusetts
    NM, 6 AWG, 60 amp breaker. I calked behind it but I'll probably add some more just to make sure. It's soooo nice just plugging in and knowing it will be fully charged when i take off again.
     
    • Like x 2
  7. eprosenx

    eprosenx Member

    Joined:
    May 30, 2018
    Messages:
    996
    Location:
    Beaverton, OR
    So I think this is a code violation. NM cable in the walls is only allowed to use the 60c rating which is 55 amps on 6 awg. I did mine in conduit which allowed me to use the 70c rating which makes it good to 65 amps.
     
    • Informative x 4
  8. P85_DA

    P85_DA Supporting Member

    Joined:
    Apr 25, 2015
    Messages:
    2,873
    Location:
    CA
    Correct only Romex can run without conduit ...I have similarl setup but my breaker is back to back with wall connector so i was able to get away with short conduit than rest of exposed cable was in box ...the OP can probably get by with some flex conduit to bring up to code
     
  9. RyanDe

    RyanDe Member

    Joined:
    Aug 24, 2016
    Messages:
    183
    Location:
    Massachusetts
    That's right, but from what I've read is since they don't make 55 amp breakers it's fine to round up to 60. That and the wall connector will only pull 48 amps which is still below the 55. I guess in theory I could up the amps on the wall connector or install something else and it would be against cost but I think this is fine the way it is now.
     
    • Like x 1
  10. eprosenx

    eprosenx Member

    Joined:
    May 30, 2018
    Messages:
    996
    Location:
    Beaverton, OR
    So I think you are close on this logic, but missing one thing:

    You take the expected load and use it to calculate what wire size you need. Your load will be 48 amps, but it is a "continuous" load and so you must size it at 125%. So you need to size your wiring for 60 amps.

    Then you decide on the breaker. Yes, you are correct in that you are allowed to select the next size up breaker, however, your load still has to fit within the ampacity of the wire NOT the ampacity of the breaker.

    So if there was a setting for 44 amps on the wall connector (80% of 55 amps) you could protect the circuit with a 60 amp breaker and be allowed to draw 44 amps, but it is not a setting. So to make your installation code compliant you have to switch your wall connector down to position eight which is 40 amps.

    Or you can switch out to wire in conduit and keep it at 48 amps.

    (note that I am not an electrician - but this is my understanding of the code)
     
  11. RyanDe

    RyanDe Member

    Joined:
    Aug 24, 2016
    Messages:
    183
    Location:
    Massachusetts
    The continuous load is for calculating the breaker over current, it doesn't have to do with the conductor size.

    6# if fine for a 48 amp load, it's fine for up to a 55 amp load which I'll never come close to. I'm pretty confident this is safe and within code.

    Good discussion though, it forced me to look up everything I researched months ago which makes me feel better about everything. :) The code is a mess, I bet you could ask 10 electricians and you'd get 3 different answers. Same for inspectors.
     
    • Like x 2
  12. bluetinc

    bluetinc Member

    Joined:
    May 11, 2009
    Messages:
    741
    Location:
    MD
    This isn't true. The whole point of the 125% plus up on calculations continuous loads is that the original wire sizing is only set up for temporary current draws that stop, and give the wire time to cool down. Drawing continuously doesn't allow the wire (or the surrounding areas) to cool. If you want to feel more confident, instead of speaking to the local electrical guys, who only rarely work with these continuous plus up rules as they only show up in homes with solar or EV charging, stop by your local code inspectors office and discuss it with them and see what they say, just make sure they know it's a continuous draw for more than 3 hours. You can also look this up in the NEC (I'm not sure what version of the code you are required to follow, but if you say, I'm sure we can direct you to the correct sections. Even after fixing this, you will still be way ahead :) -- Peter

     
    • Informative x 1
  13. SDRick

    SDRick Member

    Joined:
    Jun 25, 2015
    Messages:
    877
    Location:
    SD CA United States
    I am no expert, but the 125% rule applies for EV charging. Also, if the Romex is going through a insulated wall cavity I believe you need to increase the wire gauge one size.
     
  14. eprosenx

    eprosenx Member

    Joined:
    May 30, 2018
    Messages:
    996
    Location:
    Beaverton, OR
    So you are absolutely correct about the 125% rule is for calculating breaker over current. Breakers are tested under "standard test conditions" where they are tested in "free air" (with no enclosure around them) at an air temp of 104 degrees. While that sounds like a pretty high temp, the reality is that when installed in a panel next to a whole bunch of other breakers drawing loads, the breaker can heat beyond this. So my understanding is that they came up with the 125% rule for continuous loads in order to prevent nuisance trips.

    Now in *addition* to that, there is a 125% rule applied to conductor sizing.

    I will direct you to 2017 NEC 210.19 - Conductors - Minimum Ampacity and Size (A) Branch Circuits Not More Than 600 Volts (1) General Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Conductors shall be sized to carry not less than the larger of 210.19(A)(1)(a) or (b).
    (a) 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.

    Then you also have Article 625 that covers "Electric Vehicle Charging System". 625.42 Rating. The equipment shall have sufficient rating to supply the load served. Electric vehicle charging loads shall be considered to be continuous loads for the purposes of this article.

    So I am pretty sure you fall into the 125% rule, however, now that I go find the actual code sections on this (rather than relying on all the reading I have done online about this), there is a little ambiguity. The section of 625 that now makes clear EVSE's are continuous loads only says they are continuous loads for the purposes of this article. Though I am pretty positive they still are to be considered continuous loads elsewhere as well (even if following the basic rule of being expected to operate for more than three hours).

    FWIW, everything I have read tells me that #6 AWG Romex (NM cable) is only allowed to use the 60c rating which means it is not good for 48 amps of continuous load EV charging.
     
  15. RyanDe

    RyanDe Member

    Joined:
    Aug 24, 2016
    Messages:
    183
    Location:
    Massachusetts
    #15 RyanDe, Jun 15, 2018
    Last edited: Jun 15, 2018
    What's confusing is the two quotes were going to use the 6#, so it's odd to say the guys that do electrical work all day every day are doing it wrong. It's also odd that if this isn't code they would do this knowing it would be inspected. Either the two electricians I spoke with suck at their job or we're reading too deep into the code. I know EV chargers are new and such so it's possible they're not fully understanding the load requirements, maybe I'll get a quote from a recommended Tesla electrician to see what they say.

    Personally, if it's safe I'm okay with it, if I need it to pass code I'll lower it to 40 amps, still better than 120v. :) From what I've read too, NM-B is rated up to 70c (or even 90c, I forget) but it gets complicated so they just rate it for 60.

    I'll probably lower it to 40 anyway, for the different in charge rate it's better to be safe than sorry. :)
     
  16. eprosenx

    eprosenx Member

    Joined:
    May 30, 2018
    Messages:
    996
    Location:
    Beaverton, OR
    Yeah, so if you had used some kind of wire in conduit or like MC/AC style flexible cable it would be fine rated to 75c and so 6 awg is the way to go. How hard would it be to swap out? That simple change would get you totally code compliant and able to charge at 48 amps.

    Did the quotes specify what kind of wire they would use?

    You are correct that the manufacturer rating says 70c or 90c, but NEC says you must use the 60c rating for NM cable. I believe you are allowed to use the higher rating for the purposes of calculating deratings for like higher ambient temperature and such, but not for the base current capacity of the wire.

    P.S. Also, from a practical standpoint, this is a somewhat low risk code violation, but the NEC is battle tested from analyzing all the house fires over like a hundred years... So presumably they had a reason to limit NM to 60c temp limits. Those edge cases they are worried about may not apply to your install, but it is just hard to say, which is why I can only recommend following the code to the letter.
     
  17. SDRick

    SDRick Member

    Joined:
    Jun 25, 2015
    Messages:
    877
    Location:
    SD CA United States
    #17 SDRick, Jun 15, 2018
    Last edited: Jun 15, 2018
    Wire size calculator...

    electrician2.com Wire Size calculator

    I could be using the calculator wrong but if you input 48 A in the continuous mode box then check the overcurrent protection box, using NM wire (60 degree) it calculates #6 wire. Does it calculate the same for you?
     
    • Informative x 1
  18. eprosenx

    eprosenx Member

    Joined:
    May 30, 2018
    Messages:
    996
    Location:
    Beaverton, OR
    Nice tool! It may not be fully up to date for 2017 NEC FWIW...

    So here is what I get.

    I selected NM wire which has a 90c insulation rating, but then I think they have you apply that code section about not being able to use it above 60c by selecting a terminal temperature of "NM - 60C". When I use that selection, it comes out exactly as I expect. It says #4 AWG would be required.

    I *think* MC cable should be fine to use without being limited to 60C (since the wall connecter terminals are rated to 75c and so should be the breaker). But now that I look at the tool you linked to, it makes me think AC (which is similar to MC) also may have some 60c limit. I have not read those code sections yet. It may depend if it is run through insulation. That has some special rules since it makes it hard for heat to dissipate.

    Calculator48amps.png
     
  19. SDRick

    SDRick Member

    Joined:
    Jun 25, 2015
    Messages:
    877
    Location:
    SD CA United States
    #19 SDRick, Jun 15, 2018
    Last edited: Jun 15, 2018
    Shouldn't the box under Special Conditions "OCPD and assembly rated for continuous loads" be checked "yes" since a 60 amp breaker is being utilized? When I tried that, I get #6 wire.
     
  20. eprosenx

    eprosenx Member

    Joined:
    May 30, 2018
    Messages:
    996
    Location:
    Beaverton, OR
    Ahh! I see the issue. No. That should not be checked. I believe that box is for if you have a circuit breaker that is rated for "100% operation" and is in the proper panel to allow it to function properly. I think this generally means there are no other breakers directly up against it that would transfer heat into that breaker. I do not believe anyone makes 100% rated breakers for residential panels as far as I know.

    My understanding of the issue is that a regular residential circuit breaker can trip in one of two ways. #1. There is an electromagnet in the breaker that is energized by the current flowing through the circuit. If a wire shorts out and a HUGE amount of current flows instantly it will cause this electromagnet to energize enough to trip the breaker. Then #2, there is a bimetallic strip that heats up more and more as too much current flows through the circuit. This is for "over current" protection for when you just put too much load on the circuit. It is not the "instant" trip that the electromagnet is for short circuits. The issue with the bimetallic strip is that it is horribly inaccurate since it is all based on heat. If your garage is hot and adjacent breakers have a lot of load on them it will trip sooner than if it is cold out and the surrounding breakers have no load.

    So when sizing wires to be protected by a regular breaker, they want to make sure that the breaker will blow (in the worst case scenario - very cold day with no surrounding breakers) before the wire melts, but then when planning how big a wire and breaker to install you need to make sure that your load won't trip the breaker even on the opposite extreme worst case scenario which is a hot day with lots of heavily loaded surrounding breakers. So hence for "continuous loads" which are likely to put lots of run time on a breaker (since time is a factor in heating up the bimetallic strip also) they want you to make sure the rating of the breaker and wire is far enough above your anticipated load such that you won't ever get nuisance trips. (which result in people doing dumb stuff like installing a bigger breaker without upsizing the wire)

    I think that most of the 100% rated breakers use electronic circuitry to decide when to blow and so they like have actual CT monitors to detect actual current flow in the circuit rather than just the temperature. So basically by having a more accurate breaker a 100% breaker lets you get more precisely closer to the capacity of the circuit without over-buying wire.

    So yeah, I think if you want to use NM cable you need #4 for 60a (48a continuous), or you can do #6 gauge if it is installed in such a way as to be allowed to use the 75c ampacity rating.
     

Share This Page

  • About Us

    Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.
  • Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


    SUPPORT TMC