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14-50 Wire Size

Discussion in 'North America' started by JWinter, Apr 23, 2018.

  1. JWinter

    JWinter Member

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    We have existing conduit that would be very hard to pull new wire through. There is already unused #12 copper run in it. What would happen if we tried to use that?
     
  2. brkaus

    brkaus Well-Known Member

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    The smoke manufactured into the wire at the factory would escape.
     
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  3. brkaus

    brkaus Well-Known Member

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    I ***THINK*** you could put a 6-20 outlet on it. 20A / 240V. But there are lots of factors involved.
     
  4. boaterva

    boaterva Supporting Member

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    Well, crap, you can’t ssy anything without knowing the distance. Resistance depends on distance. :D

    Having said that, 20 Amp is pretty innocuous but not too useful for charging.
     
  5. Lasttoy

    Lasttoy Active Member

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    02 gauge. 240 v, 100 amp, 4 wire, red, black, white, green, at home depot. You don't need in conduit if in garage. Buy 14.50 box and receptical at HD . Depending on house service? 100 or 200 amp on what CB you buy.
    You need double empty to install CB . Took me about an hour to istall. Only 6 feet to my plug from box.
     
  6. GHammer

    GHammer What a long strange trip its been.

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    fire.jpg
     
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  7. mongo

    mongo Well-Known Member

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    You can fit three 8 awg wires in 1/2 EMT. Assuming the conduit is not flex and was properly routed, it should be possible to set up a HPWC set to 40 Amp charge/ 50A breaker, it doesn't use the neutral. 7.6kW

    10 gauge would be earlier to run (can fit 4 wires (6 max)) and provide 5.8 kW.

    If it is individual wires, you technically can't recolor the neutral to be a 240v no neutral setup, if it is nm-b you can... 3.8kW output

    Wire needs to be protected regardless of gauge, but larger cables don't need a backing board when attached to the bottom of joists.
     
  8. brkaus

    brkaus Well-Known Member

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    And if it’s shoved in a conduit with lots of other stuff...

    20a / 240v would charge most folks overnight. It should at least be considered as the low cost alternative.
     
  9. boaterva

    boaterva Supporting Member

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    Yep, but OP asked about 14-50. :D Really not too useful for that.

    A lot of the questions for charging are for worst case and what do you want to spend your $$ on for convenience. I have two HPWCs and a 100 Amp circuit so that both cars (when we get the 3) will be fully charged when we need them. A simpler answer would be one UMC and one 14-50 or even a smaller socket/circuit. But that’s a lot of hassle and back and forth. It’s all a trade-off.
     
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  10. JWinter

    JWinter Member

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    We already have
    2 #3 THHN CU
    1 #8 THHN CU
    5 #12 copper
    inside of 1.5" Conduit that has 1 Radius out of panel > 10' straight shot > Radius up into a stub at location.
     
  11. brkaus

    brkaus Well-Known Member

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    Remove all that, pull something much bigger, put in a sub-panel? Disclaimer: I did not sleep at a holiday inn last night.
     
  12. boaterva

    boaterva Supporting Member

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    Seriously, if you want real numbers, see the FAQ in my sig. There are hundreds of posts here and lots of places to get what size wire should be used (code-wise) for x amps at y feet. It's an NEC code requirement, not a Tesla question and we've been talking about it for years and years.... :D
     
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  13. brkaus

    brkaus Well-Known Member

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    And many years in the future!
     
  14. boaterva

    boaterva Supporting Member

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    Sigh... I guess so... :D Seriously, though, it's too bad many electricians seem to have varying answers to installing a simple socket (14-50) or circuit for an HPWC.
     
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  15. Labman

    Labman New Member

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    By code, particularly if the outlet is outside, the circuit is required to be protected. Has anyone experienced or heard of issues with gfci breakers tripping on the 240 volt chargers?
     
  16. mongo

    mongo Well-Known Member

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    Yes, Standard GFCI has a 5mA trip limit, EVSE have a 20mA limit.
    I searched previously and did not find any code requirements for outside 240V outlets (that aren't for a hot tub/ pool pump) (only 15A and 20A 120V).
     
  17. eprosenx

    eprosenx Active Member

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    Well, this could be workable, though as others have pointed out there are a lot of factors. Are you suggesting that it has a pair of #12 wires (one for hot and one that is a dedicated neutral for that same circuit)? Then presumably there is a grounding conductor in the conduit with sufficient ampacity to cover all the circuits fed from that conduit? (or maybe the conduit itself is the ground -I am fuzzy on what situations in which it is allowed if any these days?)

    As others have pointed out, I am not sure what the rules around remarking a conductor to turn it from a neutral to a hot is at this point, but from a practical standpoint wire is wire and it is fairly common practice at least in romex to convert a white neutral wire to a hot (though they also make it with the "correct" colors if a new install).

    Yeah, the main factors to deal with are making sure there are two dedicated wires available (i.e. like there is not a shared neutral on the existing circuit), but then the bigger concern is going to be around derating due to the number of current carrying conductors in that circuit.

    I don't think the resistance of the wire is even remotely the top of the list of factors to consider here. The first consideration is if there are sufficient conductors unused, the next is derating issues due to # of current carrying conductors. Eventually we might get to concerns about voltage drop due to distance, though nobody has mentioned it being a really long way. While the NEC suggests target max numbers for voltage drop, they don't actually have rules around it as far as I am aware. With a Tesla, I don't think voltage drop is a particular safety concern - the Tesla will draw a max of 16 amps on a 20 amp circuit if used with the correct UMC adapter (or even a wall connector I think). If the voltage drops it will still draw the same number of amps, but just charge slower. It won't over stress the wiring like a motor might. If the voltage drop is too great, the Tesla might get concerned and back off its charge rate or refuse to charge, but I don't see it as a safety issue.

    There is so much wrong here. Using #2 AWG for a NEMA 14-50 plug is a silly idea. It is a huge gauge and would not fit under the terminals of a NEMA 14-50 receptacle. It would be a massive waste of wire and hard to deal with. For a NEMA 14-50 receptacle you would typically wire that with a 40 or 50 amp circuit (a 40 amp circuit is actually allowed if your load fit the parameters of a 40 amp circuit). I generally would think long and hard before putting a NEMA 14-50 receptacle on a 40 amp circuit for a car charger since even though a UMC Gen 2 can only draw 32 amps (which is the 80% derate of a 40 amp circuit), in the future, someone may try to use a higher ampacity charger.

    Yes you need conduit in a garage if it is exposed (MC cable or Flex is acceptable). You can run ROMEX not in conduit as long as it is protected inside the wall. If you run wire in conduit you can get away with #8 gauge for a 50 amp circuit as long as the breaker, wire, and terminals on the receptacle are all rated for 75C. If you use any NM (Romex) cable it is by default limited to 60c and so then you need #6 AWG for both hots and neutral. In either case, you can use just a #10 for ground.

    If we are talking about installing a Tesla "Wall Connector" it can handle a bunch of breaker sizes up to 100amps if you have sufficient ampacity wire installed. The trick with that (or even a NEMA 14-50) or really anything you add is that you need to do a load calculation to figure out how heavily loaded your current panel and service are. It is more complex than just whether your main service is 100a or 200a...

    Technically by my reading of the NEC, if you only put a single receptacle on a branch circuit you can put any size receptacle on a circuit as long as the rating of the receptacle is equal to or greater than the rating of the circuit breaker. I don't see anything that would stop you from putting a 14-50 on a 20a circuit, though it would be stupid. Also, if you were planning to put a UMC on it with the 14-50 adapter then that would be non-compliant since its nameplate says 32 amps and you have to rate it as a continuous load, which means you need a 40 amp circuit.

    But just putting a 14-50 receptacle on a 20 amp circuit is I think technically allowed, but very dumb. (I read up on this as I wanted to answer the debate of if a 40a circuit is fine for a 14-50 - and I believe the answer to that is a resounding YES - but I still would not generally do it)

    Ok, now we get into the meat of it! If you have more than three current carrying conductors in a raceway longer than 24 inches you have to derate their ampacity. So a #12 copper THHN is good to 25 amps at 75c rating. 80% of that is 20 amps so even if you have to derate at the first step (4-6 current carrying conductors requires derating to 80%) you are good (as long as no other adjustments like ambient temp are necessary).

    The trick here is that you have not provided enough details to determine how many current carrying conductors you currently have. Ground does not count. Neutral does count unless it is part of a multi-wire branch circuit where both (or all three in 3 phase) of the hot wires run in the same raceway. Then you count the hots and not the neutral since under full load the neutral carries no current.

    I am concerned here about the two #3 THHN wires and the one #8. Is that for a subpanel or something? My concern is that if it is for a subpanel that it does not have a separate ground (subpanel needs two hots, a neutral, and a ground). I guess it could be some really big 240v load with no neutral (#8 is the ground?), but not many loads are that big other than like a HPWC. Do you already have a HPWC? If so, you could install a second on the same circuit and have them share...

    Can you break down what all the existing wires are used for?

    Well, to be fair, it is pretty complex depending on the situation... A ton of factors go into it so other than some very simple use cases (like a NEMA 14-50 plug right next to the panel), there are a lot of different solutions that will work and be code compliant. It also depends a lot on jurisdiction...

    As others have mentioned, I don't think there is a GFCI requirement for 240v receptacles outside. They need to be in water tight boxes, but I don't think the GFCI code has snuck its way there yet (which is kind of surprising). I think the issue is that 240v loads are still pretty rare in residential. A lot of the loads that need 240v might not get along great with GFCI. The most common is RV's. Previously, the technology I don't think was even available for large GFCI's (though it has been required for Spa's for some time now). But it is very expensive still. Think like $100 for a breaker instead of $10. Can you imagine the cost delta to RV parks to do all GFCI units? While a good idea from a safety standpoint, the costs would be massive and you would have all sorts of nuisance trips due to folks crappy trailers.

    I don't think we have a lot of experiences collectively with the UMC units on GFCI 240v circuits since hardly anyone has GFCI breakers on them is my supposition.

    Do understand that GFCI is one of the key features that the UMC or wall connector (or any EVSE) provides. So I would say that there is no reason to do a GFCI breaker on a branch circuit feeding a Wall Connector and even very little reason to have one on a circuit feeding a UMC (indoors). I could make an argument for having one on an outlet feeding an outdoor UMC (since plugging in the UMC outdoors could be dangerous in the rain) but I would argue folks should install a hard wire wall connector outdoors in that case.

    Yeah, so I am curious if anyone has had GFCI issues on 15a and 20a 120v circuits with the UMC. The UMC tests for voltage from hot to ground to make sure it is connected to ground before it will supply power to the car, but I am sure they have carefully designed it to not leak too much current that it would trip a GFCI. I have to imagine that pretty much any 15a or 20a 120v outlet you would think to plug a UMC into should already be GFCI protected. If it blew GFCI's that would be a pretty massive product fail...
     
  18. eprosenx

    eprosenx Active Member

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    Hrm, actually, I need to go read up more on derating of wire due to conduit fill. If you have 90c rated THHN in conduit you may be able to do the derate off that rating since the issue is not the temp rating of the terminals at the ends but instead it is of the wire insulation inside the conduit. So given that #12 is rated to 30 amps at 90c you could derate it to 70% (which is required for having 7-9 current carrying conductors in a conduit) and still have 21 amps of usable capacity.

    I am curious what you are using the #3 THHN for since that could be closer to its limits already?
     
  19. Rocky_H

    Rocky_H Well-Known Member

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    Yes, I've seen that reported several times. There's how things are "designed" and then there's how they "are". That UMC grounding test is supposed to be small enough current that it's below the threshold of a GFCI to trip, but there is very little margin in between, and apparently old GFCI outlets or breakers can degrade a bit from what their original specifications were supposed to be, and can have those tripping problems from a UMC. Replacing the old GFCI outlet with a new one usually fixes it.
     
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  20. FlatSix911

    FlatSix911 Porsche 918 Hybrid

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