rhumbliner
Member
Electricians are expensive. Wire is not. You’re trying to save $7?
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NEMA 14-50 8 gauge wire
- Thread starter psyrob
- Start date
Electricians are expensive. Wire is not. You’re trying to save $7?
eprosenx
Active Member
Because that is NM wire (Romex), NEC says you must use the 60c rating instead of 75c or 90c even if that is what is labeled on the cable. So that wire is only good for up to 40 amps.
Electric Vehicle Chargers are considered "Continuous Loads" under the NEC and so you must size the wire and circuit breaker 25% larger. So for a 32a charger you need a 40a capable wire and breaker. For a 40a charger you need 50a capable wire and breaker.
So please do not just switch the breaker to 50a! That would be dangerous and not code compliant. Note that the new UMC Gen 2 that ships with all new Tesla's now is only 32a so it would be fine on a 40a circuit.
So I appreciate the doc that was linked to from Tesla, but I disagree with it. #8 AWG copper wire is ok for a 50a circuit if run in conduit (though I might still use #6 myself). I think Tesla just dumbs it down to 6awg since that is safe in virtually all conditions. From a code standpoint, I don't think that doc has any applicability. I went and looked at the actual UMC Gen 2 manual and it does not specify how to wire up the NEMA 14-50 receptacle. So even if the "you must follow the manufacturers instructions" would apply for wiring a NEMA 14-50 receptacle, the manual says nothing (and I don't know that the following manufacturers instructions thing even applies to non-hard wired devices). The fact that an extra document exists on Tesla's web site I am not sure gives it any standing.
Just to those asking why am I trying to save money on the wire, that is not the issue. my electrician recommended #8, not #6 wire, and I don't know anything about electricity so I was asking for advice. This is not a money issue, especially if it is just 30 bucks, just looking for why he would say that and what it means
ucmndd
Well-Known Member
He probably recommended #8 because it’s easier to pull through conduit than thicker wire. Laziness is a powerful motivator.
eprosenx
Active Member
Yeah, I do tend to agree here. I probably would ask what the cost delta would be to use #6 AWG and I might just go with that... Hopefully it would not require upsizing the conduit and so the only difference would be conductor cost. I ran my NEMA 14-50 with #6 AWG since it was only a few feet of wire and it was in flex conduit. I also ran my Wall Connector with #6 in EMT and put it on a 60a breaker.
An EV is likely the highest current draw device in the house and it is on for many hours a day potentially, so the worst case is you spend a big more and have some cooler running wires and lower line losses...
(I encourage anyone to double check my calcs here. Split-phase circuits can trip me up sometimes.)
A quick check of an online voltage drop calculator shows that upgrading from 8AWG to 6AWG on a 35 foot run will reduce line losses on a 240V circuit drawing 32A from 0.59% down to 0.37%. So a you'd get a 0.22% reduction/improvement in line losses.
If you drive 10,000 miles per year and get the EPA efficiency of 0.26 kWh/mile, then you'd save (10,000 x 0.26 x 0.0022 =) 5.7 kWh/year. Multiply that by your $/kWh rate to get $/year, then multiply by years you expect to use this circuit for charging an EV to get total cost savings.
For example, if you pay $0.20/kWh, you'd save $1.14/year. If you expect to use the circuit/outlet for 15 years, then you'd save $17 over that period.
Or maybe it's just because the smallest wire that meets code is what is used the vast majority of the time. No need to impugn his character.
A quick check of an online voltage drop calculator shows that upgrading from 8AWG to 6AWG on a 35 foot run will reduce line losses on a 240V circuit drawing 32A from 0.59% down to 0.37%. So a you'd get a 0.22% reduction/improvement in line losses.
If you drive 10,000 miles per year and get the EPA efficiency of 0.26 kWh/mile, then you'd save (10,000 x 0.26 x 0.0022 =) 5.7 kWh/year. Multiply that by your $/kWh rate to get $/year, then multiply by years you expect to use this circuit for charging an EV to get total cost savings.
For example, if you pay $0.20/kWh, you'd save $1.14/year. If you expect to use the circuit/outlet for 15 years, then you'd save $17 over that period.
Or maybe it's just because the smallest wire that meets code is what is used the vast majority of the time. No need to impugn his character.
So people who buy Bolts (or other non-Teslas) skimp on electrical work? Dafuq? Seriously?
I just had an electrician install a 14-50 outlet. 6 gauge wire, 50A breaker, no skimping . Sorry for not living up to your stereotype.
This is an old thread but one thing I read here really concerns me is that ppl are putting a 40 Amp breaker on a Nema 14-50 outlet. Even though the Gen 2 mobile connector only pulls 32A in theory necessitating a 40A breaker, the expectation of a Nema 14-50 outlet is that it is 50 A amp capable. The next owner of the house may plug in a dryer, welder, or compressor expecting a 50A circuit with a 50 A outlet for 40 Amp continuous service (there is a 20% derating between peak and continuous). It is dangerous to undersize the breaker as a future device may pull 40A continuous, tripping (best case) or worse overheating the the undersized 40 A peak breaker. An overheating breaker can lead to a fire caused by the resistance heating.
If installing a HPWC set to 40A for a 32 Amp continuous draw, then the 40 Amp breaker is permissable as the device is permanently wired to the 40 Amp device and will not be disconnected to operate a device of higher and lower current.
If installing a HPWC set to 40A for a 32 Amp continuous draw, then the 40 Amp breaker is permissable as the device is permanently wired to the 40 Amp device and will not be disconnected to operate a device of higher and lower current.
davewill
Active Member
I get your concern, but the fact is that it's to code, and it's even the recommended install for a number of 30-32a J1772 EVSEs out there (like the one I own). My take is that people should install a 50a circuit if they can, but if their service or existing wiring can only handle 40a, then go ahead and do that.
My electrician installed a NEMA 14-50 with a 50 amp breaker next to the panel which is about 1 foot and used an 8 gauge wire. I asked him and he said it is ok since it is very close to the panel. I noticed later that he hasn't used the separate ground, instead, he connected the ground and neutral (white wire). Is it safe? Please advice. Thank you
This isn't enough information to answer by just telling the wire gauge. Different types of wire or cable have different amp ratings, so you haven't given enough of a description of exactly what it is to tell. Is this separate wires run though conduit? Or is it that a whole cable that has several wires bundled together inside a tight rubber sheath? 8 gauge would be acceptable if it's separate wires in conduit, but not acceptable if it's NM-B cable.
Connected them where? If they are just tied together in the outlet box, then that is definitely wrong. They need to stay separate all the way back to the main panel in the house. If that main panel, then yes, ground and neutral can be interchanged and tied together there (and ONLY there).
Thank You so much for the quick reply. Yes, there are 3 separate cables. Black, Red, and White. The wires running from the electric panel to NEMA14-50 is just 1 ft. long and all wires are separate but the gauge is 8. Is that enough to charge my Tesla Model Y(which is delivering next month).? My main concern is neutral and Ground wire since it is connected with a small 2-inch wire in the NEMA receptacle. Is that safe?
You didn't mention a conduit, but there should be some if they are individual wires. But yes, if those are separate wires, 8 gauge is acceptable for a 50A rated circuit. If you look up in the table here, the wires in conduit would be THWN or THHN, those both have a rating of at least 50A. So the thickness of the wire would be OK, but only 3 wires is definitely a problem.
Cerrowire Resources - Ampacity Charts
Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.
www.cerrowire.com
But this is still a problem. A 14-50 outlet MUST have 4 wires to connect it properly. Do you mean that the white wire goes to it, and then it uses a small 2 inch wire to basically "jumper" the neutral and ground pins together on the outlet itself? That is definitely wrong. Neutral and ground each need to have their own separate wires running all the way back to the panel. The ground wire is allowed to be much smaller and can be a bare copper wire that's not insulated, but it does need to be there.
I'm getting really concerned about who the person is who did this. An actual electrician would know that a 14-XX type of outlet can't be installed with just 3 wires.
*EDIT* Oh, I did just remember something. In some places, the metal conduit the wires are in can be used as the ground wire that goes back to the panel if it is connected on both ends. Is this in metal conduit that is being used as the ground?
⚡️ELECTROMAN⚡️
Village Idiot
I think it just needs a ground and the two 120V wires to be able to charge at 240V. I find it strange that he didn't run a green ground wire. Is this in a conduit? Is the box that the receptacle is installed in, metal? You should definitely have a green ground wire attached to the receptacles ground terminal.
AC Traction
Member
Yes, an EVSE only needs the two hots and a ground. But it's a 14-50 receptacle, which is required to have a neutral. The car won't care if there isn't a neutral connected to the neutral lug in the receptacle, in fact I don't believe the neutral pin is connected to anything in the mobile connector. But something else like an RV or electric range would DEFINITELY care if the neutral isn't there. A floating neutral will burn up all sorts of things in something expecting it to be there. If you don't want to run a neutral, install a NEMA 6-50 receptacle instead.
If it's solid conduit all the way back to the panel (NO flex in the run at all), a separate equipment grounding conductor is not necessary as the conduit serves that purpose. That could possibly explain the conduit only containing two hots and a neutral.
Why? A 120V device is the only thing looking for a neutral. If the neutral leg isn't there, the device simply wouldn't get power.
As for this installation, with such a small run, it seems there wouldn't be much reason not to run the 6 ga wires and have a proper ground. Even replacing the wires at this point would be trivial.
davewill
Active Member
Most appliances use a 14-50 because they need both 120v and 240v. Unfortunately, leaving the neutral out does not necessarily mean the 120v parts simply get no power. Instead the return voltage can find it's way through other parts of the circuit to the other leg or to ground.
It's even worse in the case of something like an RV which will have appliances connected to both 120v legs. The return voltage will find it's way through the wiring to another appliance and through it to the other leg. Since the neutral is floating one appliance may see a low voltage and the other may see a very high one. Finally, you can end up with a hot chassis if one of those appliances only has a two prong plug, creating a shock hazard.
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