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Why does my 50 amp breaker (fuse) trip with NEMA 14-50?

Discussion in 'Model S: Battery & Charging' started by jsaccio, Apr 10, 2015.

  1. jsaccio

    jsaccio Member

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    I have a HPWC connected to 100 amp circuit and it works great. I decided to install (myself) a NEMA 14-50 plug into my panel through a 50 amp breaker-fuse just for a backup in case my HPWC goes down. My install went fine, plugged car in using charger that came with car and all looked good (green lights). Of course the HPWC is not being used at the same time. I noticed after about 30 min of charging the 50 amp breaker tripped. I reset it and it did it again after another short period. I then lowered the charge down from 40 amps inside the car to 30 amps and it did not trip after that. Any ideas what might cause this? Should I replace the breaker with a 60 amp? thank you.
     
  2. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    #2 Cottonwood, Apr 10, 2015
    Last edited: Apr 10, 2015
    It sounds like you have a faulty breaker or a faulty install of the breaker.

    Make sure the breaker is well seated in the panel and that the wire is cleanly installed in the breaker with the lug nuts torqued correctly. A bad install can create extra heat leading to a false trip of the breaker. If all checks out on the breaker install, it's time to ask for a replacement breaker from your supplier.

    Do not put in a 60 Amp breaker for a 14-50! That is against code and unsafe.

    Good Luck!
     
  3. green1

    green1 Active Member

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    Do not replace the breaker with a higher rating unless you know that all components can handle it, if you have a 14-50 plug, it's not rated for 60A, and unless you over spec'd the wiring, it won't be rated for it either.

    seems most likely a defective breaker (tripping too low) but it could be some other form of defective wiring, etc.
     
  4. FlasherZ

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

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    Breakers are defective more commonly than you think. If you're sure you didn't puncture the cable or have a fault in there somewhere, try a new breaker.

    Like the other posters say, nothing more than 50A.
     
  5. jsaccio

    jsaccio Member

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    It's a very short cable run maybe 18". There is a sharp bend to route the wire so not sure if that would cause this. I guess I could plug in the charger and se if the wires run hot?
     
  6. OConnorStP

    OConnorStP Member

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    I had a similar problem where the main (100 amp) breaker in the box tripped. 17356 iterations of flipping that breaker on and off cleared off the crud and corrosion that had probably accumulated over the years and it's been smooth sailing since then. Seriously... exercise the breaker a little and see if it works better.
     
  7. mrElbe

    mrElbe Member

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    With a 50A breaker you should only draw 40A charging. Never draw the limit. That is why the HPWC with a 100A breaker for safety reasons only draws 80A.
     
  8. benfrank3

    benfrank3 Member

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    Are you sure your connections are solid and tight in the outlet and at the panel? Are you sure the wire is the right size? I think it should be 6 gauge. Mine is an 80' run and I haven't had any problems charging at 40 amps. I was very careful when I terminated the screws.
     
  9. Cosmacelf

    Cosmacelf Active Member

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    How hot does the breaker get before tripping? How old is the breaker? Normally, breakers get too hot to comfortably keep touching before tripping. Assuming the wire size is big enough (what gauge did you use?), then I would suspect the breaker. They are relatively cheap and easy to replace.
     
  10. brucet999

    brucet999 Active Member

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    HeHe! 17356 times cycling the breaker on/off? At one second per cycle, 5 hours 48 minutes of switching your main breaker on/off should not only have knocked the crud off the contacts, it should have worn out the springs and contacts and pretty much all of the skin of your fingers!

    If it quit doing nuisance trips after 17,356 cycles, it might just have failed in the "on" position. :)
     
  11. FlasherZ

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

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    This is actually a really good point - I was on a plane last night and unable to be any more verbose... Breakers can use two different mechanisms to trip - one is by using a bi-metallic strip, which creates a spring action that trips the breaker after heating; the other is to use an electromagnetic trip mechanism. Most home breakers use the former.

    If your wires are not terminated well, the breaker will trip early. Look for signs of the insulation getting hot on the wire (burned, browned, etc.) Check the tightness of your breaker connections and torque them well. I have seen cases where homeowners were afraid to place torque on the breaker screw because the breaker flexed slightly on the bus bar of the panel. hold the breaker in place while you tighten that screw with a square-drive (if you have it) or a proper wide flat-blade screwdriver (it makes a BIG difference the specific type of screwdriver you use).
     
  12. jsaccio

    jsaccio Member

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    Thanks everyone for the input. I took the panel off and plugged in the charger to feel the heat from the wires. After no heat I checked the breaker again for fit and noticed it said "30 amps" not the 50 amp I thought I purchased. Dumb mistake on my part. Good news is I replaced it with 50 amp and it works great. Now I have a back up to HPWC if I ever need it.
     
  13. FlasherZ

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

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    I'm glad you found the problem.

    And this is a good example of how breakers work. The 30A breaker didn't trip at 30.1A - it let you run at 40A (33% overcurrent) for nearly half an hour before tripping...
     
  14. green1

    green1 Active Member

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    Which makes me wonder how important it is to derate to 80%? (why charge at 40A on a 50A breaker when it seems it would likely be fine at 45, or even 50A for a long time (If it can handle 130% for half an hour, why not 100% for the full charge duration?)
     
  15. brianman

    brianman Burrito Founder

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    Just because some instances of a manufactured product can withstand higher load / speed / etc. than required, doesn't mean that all instances do.

    Think about overclocked CPUs where sometimes you get a "rockstar" (with high tolerance for sustained crazy) and sometimes you get an "accountant" (who might flip out at the first slightly under-tipped restaurant bill). (Yah, I'm mixing unusual metaphors a bit today it seems.)
     
  16. FlasherZ

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

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    Technicality: It's not "derating", which has a specific meaning within the NEC. It's requiring a circuit rating to be 125% of the continuous load. It makes a difference when you get into multiple derating calculations.

    The 125% of continuous load rule is primarily intended to manage heat build-up of conductors and termination points in enclosed spaces. The NEC does build in tolerance, as brianman mentions, and tends to be on the conservative side. This is to address a wide range of operating environments: NM-B cable performance in open air is going to be different than when enclosed in a wall cavity, surrounded by insulation.

    There are certain types of equipment that are rated at 100% operation and can legally be used for same, but most homeowners won't be able to afford them. Your NEMA 14-50 isn't. :)

    A reason to follow it? It's the law in most jurisdictions, and can carry liability and insurance implications. In some jurisdictions, violation is not just an infraction but rather a misdemeanor and can be carried on a criminal record (Olympia, WA is one example).
     
  17. Cosmacelf

    Cosmacelf Active Member

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    And the practical reason to follow the 80% rule is that there are all sorts of situations where not following it can result in a fire. As Flasher alluded to, the rules allow for 110 degree days where it is 140 degrees in an attic, and where the wire is buried in insulation.
     

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