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Electrical Help

Discussion in 'Model 3: Battery & Charging' started by Glamisduner, Jul 9, 2018.

  1. Glamisduner

    Glamisduner Member

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    I had a 10-30 outlet in my garage, chained to another 10-30 outlet. It's for my washing machine and this is how it has been since I moved in 8 years ago. It was behind a 20 amp breaker. !?!

    After some discussion on this forum and after I verified a floating ground wire and that the wire's were in fact 10/3 romex I upgraded both outlets to 14-30's, grounded the boxes they were in, and instead of daisy chaining them, I used wire nuts to run to the second outlet which is right next to it. Grounded the electrical boxes (they were not grounded previously!).

    Then I changed the breaker to a 30 amp breaker, and re-wired the dryer to use a 14-30.

    I ran into some issued with the breaker tripping when I was done, not sure where the short was :(, I did tape over a wire that split insulation while cramming everything into the metal box, but still had an issue. After a few attempts I finally got everything in there without tripping the breaker (maybe a hot screw was hitting the ground or something I'm not sure, it's a really tight fit!)

    I realize it's not great to have 2 outlets, but it allows me to not have to plug and unplug the washing machine all the time, and is a temporary solution until I have have a 14-50 or tesla wall charger installed at a later date.

    Currently I'm charging my volt off a 16 amp charger using the new outlet and have not had any problems.

    My concern is that the 10/3 wire run may be too long (box is on the far side of the house). I read that if it is over 50ft I should have 8awg, but I also read that if the run is less than 100ft I should be ok? Is there a way to test resistance (between black and neutral, or red and neutral) to ensure the run isn't too long? What should the resistance measure to be safe with the 30 amp breaker?
     
  2. ewoodrick

    ewoodrick Member

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    If the wire was indeed a ground, then the size is not as important. It really shouldn't be carrying any current.

    Your story doesn't make me feel too confident though. If something was intermittent, then the heating when charging will tend to find it.
    I hope you really do need this amount of current to charge daily.
     
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  3. Glamisduner

    Glamisduner Member

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    I would prefer higher power, but need to work on getting a 14-50 or better. Commute is about 82-100 miles a day.
     
  4. mongo

    mongo Well-Known Member

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    One way to do a rough check is to use the charging display in the car. It will tell you the voltage at the charger, so you can check voltage drop by doing a super low charge rate, recording the voltage, then doing a normal rate. The change in voltage is proportional to the wire resistance.

    Note: this change is the loss of all wire up to and including the power company transformer. You should have less than 5% drop from 0 amps to full load.

    I'm a little woried about the breaker tripping, if the problem wasn't fixed it could become a resistive short and create heat/ fire.
     
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  5. Glamisduner

    Glamisduner Member

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    I think I fixed it, I took everything apart and put it back together and no more tripping? I examined all the wires and couldn't find anything fishy other than the one wire which had the sleeving split due to being forced into the small box (which I fixed with liquid electrical tape and regular electrical tape). Still pretty strange but I did examine all my connections and they seemed ok. Maybe there was another split somewhere I couldn't find though..., but it's also not like there are not hot wires in the box already? (which is now grounded at least). I found it strange that the breaker was tripping without the outlet hooked up until it stopped tripping the last time I put it together :(

    I shut it off and wiggled the wire in the wall around and turned it back on and it would not trip, so it must have been something in the box. The thing is, what would you suggest I do short of running a while new run? I mean I can take it apart and look again, but I already did this and couldn't find anything....
     
  6. mongo

    mongo Well-Known Member

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    Ah, I didn't follow that the tripping went away immediately after fixing the exposed wire. Assuming several wraps of tape and a well attached cover/ outlet (minimal wiggle) you should be good.
     
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  7. Glamisduner

    Glamisduner Member

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    It wasn't immediate which is why I am also uneasy about it. It still tripped AFTER i fixed that wire. But I suspect something similar was happening somewhere in the box that I could not find. Messing with 10AWG wirenuts is a real pain! Still I feel like I should be better off than before the upgrade, at least everything is grounded now, and I have clamps on the entrances to the box (there were none before)! I don't see the wires moving around much in the future... I'll be keeping a close eye on any strange occurrences though...

    Using this chart, it looks to me like 10awg SHOULD be ok?
    https://www.cerrowire.com/files/file/voltagedrop.pdf
    I mean I'm likely somewhere between 50 and 100ft... So I might be getting slight voltage drop, however nothing will actually pull 30 amps either. I believe even the tesla EVSE will only pull 24 amps, which would side the chart closer to 10awg being acceptable.
     
  8. eprosenx

    eprosenx Member

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    Yes, 10 AWG should be fine for a 30 amp circuit (you are correct that a Tesla on a UMC with the proper adapter won't draw more than 24 amps). The NEC has recommendations about voltage drop, but it does not have hard and fast rules that you have to comply with. The way the Tesla charger works it won't pull more current if the voltage drops, it will still draw the same current but since the voltage reduces it will not charge quite as fast. If the voltage drops too much from what it first sensed before charging it will assume there is an issue and it will reduce the charge speed or stop charging. I doubt your distance will be an issue.

    I would recommend making sure your electrical connections are nice and tight in those wire nuts. Having loose connections in wire nuts can create hotspots.

    Was the breaker blowing as soon as you turned it on? If so, you likely had a direct short and it sounds like you have rectified it (but yeah, you always want to run those issues down if possible).

    How many times did you blow and reset the breaker? I have heard that most breakers are not really good for too many reset cycles. If you blow them more than a handful of times they should be replaced to ensure they still function properly.
     
  9. trm2

    trm2 Member

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    If you are home 6 hours a day, you don't need any more than the 30 amp circuit. You will get 100 miles of range back in less than 6 hours.
     
  10. Rocky_H

    Rocky_H Active Member

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    By the way, if you're going to reference wire ampacity tables, you should probably realize how to use them. You don't use the 24A number. There is a rating difference between constant loads and intermittent loads. Constant loads build up much more heat than higher current levels that are on and off and have some chances to cool down, which is why the constant load of 24A has to use a 125% overrated circuit size of 30A. But it is that 30A number of the rating of the circuit that you have to use with the table for finding the right wire gauge.
     
  11. Glamisduner

    Glamisduner Member

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    Right, if I was running new wire I would use 8awg.
    But if I have a 75 or 80 foot run of 10awg will I be in trouble if I have just over 3% loss?
    Most sources seem to indicate I should be ok, even though ideal would be 8awg, but it depends where I look...
     
  12. Rocky_H

    Rocky_H Active Member

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    That mainly just comes down to whether the equipment on the end that's trying to use it is OK with the voltage level. And since the chargers in the car are OK with pretty wide voltage levels, the lower voltage itself won't be a problem with it. And over a really long wiring run, normal voltage loss would not be a heat concern since that would be spread out evenly, so there is plenty of physical area to dissipate that.

    So the main thing is just that protection circuit in the car that tries to identify wiring problems. If the voltage loss is really bad from no load to loaded, then it identifies that as likely a bad wiring situation and will cut to a lower amperage level to see if it will stay steady. So 3% or 5% or probably most single digit percentages should be fine for some normal voltage drop without tripping that and reducing the amps. If you can keep it from tripping that artificial lowering then that should be fine.

    And I have seen a few people's threads here where their 40A kept getting cut to 30A because the utility supply to their house was a little flaky and the circuit was being too sensitive to very short term voltage drops. Reducing to something like 35 or 38A was usually enough to not pull on the voltage as hard and would keep it clear of that overprotectiveness.
     
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  13. eprosenx

    eprosenx Member

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    I am not sure I would use 8 awg even if I was running a new circuit. 10 awg is rated just fine for it - my calculations put that well within the recommended 3% loss amount even at 100' of wire even assuming a full 30 amp draw (which won't be the case - only 24 amps will ever be actually drawn). I can't figure out why that document you linked to above recommended #8, but perhaps the explanation is that they are a company that sells wire and so they would rather you use more than less. ;-) Also, they were calculating at 220v I think, but nominal voltage here in the US should be 240v, so I would think you would use that? (I need to read more about the formulas)

    Yeah, exactly. I don't think there is any chance of the voltage dropping enough for the Tesla to back off unless there are other issues with your electrical feed. In this thread below another Model 3 owner says Tesla told them the current backoff happens at 8% voltage drop (from nominal voltage before charging starts compared to after charging is underway).

    Home Charging

    I would also call out that if my car was tripping due to "short term voltage drops" from the utility I would be bugging my utility. They may have your house on too long a feeder line from the transformer, or not a thick enough gauge from the transformer, or not a large enough transformer. If all the in-house wiring is correct then I would beat on the utility to make it right. (or maybe Tesla is overly sensitive and should de-sensitize the control software for charging).
     
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  14. Rocky_H

    Rocky_H Active Member

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    Uh huh. Well, there's what should happen, and then there's what you can actually force a utility to do. Someone had a big thread on here where their utility had this problem, and he kept on them for well over a year, and finally gave up on it I think. The utility would send someone with a meter, read the voltage and say, "Huh, it looks fine right now--no problem." and do nothing.
     
  15. Glamisduner

    Glamisduner Member

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    Lucky for me I have a new panel and the company ran new wire to my house just a few years ago (They used aluminum off the pole :(, but I guess it doesn't matter). So getting bad power from the company shouldn't be an issue (although I guess it could be somewhere else in the chain.

    I think I'm going to get a 14-50 installed for the model 3 anyways, but may use the dryer plug when I first get it for a while. The volt has been charging great off it so far at 15 amps (bought a cheap clipper based evse off amazon for it because I was tired of charging off 110) There has been several occasions I don't get a full charge and need to drive the car (even just getting home late) While is likely not economic to have bought the EVSE, in energy savings over buying gas its well worth it in saving frustration with not being charged. Plus it forced me to do this 10/30 to 14/30 upgrade and ground the metal boxes.
    IMG_20180707_212630.jpg
     
  16. mongo

    mongo Well-Known Member

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    That's normal, nothing to worry about. I used aluminum for a 250' run to my barn.

    Are you on a shared transformer?
     
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  17. Glamisduner

    Glamisduner Member

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    How do I tell? The pole is practically in my front yard.
     
  18. mongo

    mongo Well-Known Member

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    Each house would have a separate set of wires running to it from the transformer.
     
  19. eprosenx

    eprosenx Member

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    If you are going to run new wire and you have stated you have like a 90 mile round trip commute, I probably would spend the $$$ to put in a Wall Connector. It is what I did. I just wanted to be able to max out my 48 amp charger in the car vs. being limited to the 32 amps that the UMC Gen 2 would limit you to.

    Moving from a 14-30 to a 14-50 will only move you up from 24 amps of charging to 32 amps of charging. A decent bump, but putting in a HPWC would take you from 24 to 48 (assuming your electrical service has the capacity to support that, etc...).
     
  20. Glamisduner

    Glamisduner Member

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    Getting a second run of wire allows me to leave the dryer plugged in without worrying about someone trying to use it while charging too.

    Getting to 32 amps will cost me about $650 getting to 48 would be around $1300 (for 60 amp, not sure what it would cost to get a 100 amp, but I only have a 200 amp panel too) Also, a 14-50 can be used for other things like the welder I may never buy :) Probably overkill for an electric homebrewing system too but another possible use for it. Hmmmm gotta make a decision eventually.
     

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