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Tesla to Upgrade Wall Adapters After Reports of Garage Fires - Bloomberg News
- Thread starter DJ Frustration
- Start date
Merrill
Merrill
Thank you Bonnie, I think sometime people lose perspective on certain subjects. This forum should be for decemination of information, everyone has a point of view and it may not be shared by everyone. Keep it civil. You may want to look at the "Older Tesla's limited to 90kw" thread also.
It may bear repeating that voltage drop in longer runs may also require larger wire size. Here are a couple of comments regarding automatic charging current reductions that seem to be the result of the software upgrade that detects fluctuations in the input power to the vehicle. (see also Tesla Motors Press Release Jan 10, 2014) Might want to make sure your voltage drop is less than 5% (if this is how the MS senses problems).
(From False Positives With FW 5.8.4 Charge Current Reduction?
ToddRLockwood
Active Member
I suggest lowering your charge rate to 60A until you get a ranger over to check this out. This is not normal HPWC behavior.
I am going to repeat it one more time – your statement is incorrect. I do not want to beat the dead horse, but proper installation is important, because Tesla potentially can be undeservedly done much harm. There is a lot of confusion and few issues that need to be addressed here. I am going to do it step by step.
- Code requirements.
- Equipment ratings
- How improper wiring can cause overheating of Tesla NEMA 14-50 adapter.
- Tesla Motors recommendation for installation of Nema 14-50 outlet
Code Requirements
Per my original post NEC requires to consider temperature rating of terminations and possible derating of the circuit if temperature for continuous operation is going to exceed 30ºC (86ºF). Your general recommendation that #8 AWG in conduit is just fine for 50A feeding a 14-50 outlet is wrong and misleading because you are ignoring these two NEC requirements. The #8 AWG might work for some circuits, but certainly not for all of them, in fact not even for the majority.
You argument for ignoring the temperature rating of the terminations (NEC 110.14(C)) is that most equipment built after the 1980's has 75 degree termination rating. Certainly all new stuff does. This requirement is still need to be considered if the installation happens to have equipment with terminations rated at 60 ºC. In fact the wording in the Code by default requires assuming 60 ºC rated terminations unless the equipment is listed and marked otherwise (NEC 110.14(C)(1)).
Once it is established that all equipment has 75 ºC rated terminations (by observing that each piece of equipment stamped for use with 75 ºC conductors), sizing of the conductors for installation of NEMA 14-50 outlet requires considering the ambient temperature. You seem to suggest that this requirement is irrelevant because “I have never seen an in-wall or garage installation require derating.” This does not constitute good reason to dismiss this requirement. The NEMA 14-50 installation for charging is different than any other installation because this circuit will be used continuously at 100% rating of the circuit and typical temperature in garage WILL be above 30º (86ºF) during summer for at least half of the US, especially considering that two car garage might have ICE car parked in it, releasing massive amount of heat after it is driven and a Tesla which during charging on NEMA 14-50 will be equivalent to continuously operating 1500W heater (assuming 85% efficiency of the charger and ignoring the efficiency of the battery).
The problem with using #8 AWG even when all of the terminations are rated for 75 ºC is that at 75ºC allowable ampacity for #8 AWG is exactly 50A (NEC Table 310.15(B)(16) and will not allow for any derating for ambient temperature that for a lot of locations will most likely be higher than 30 ºC (86 ºF).
To conclude, between these two NEC requirements, the majority of installations in US will require using #6 for the NEMA 14-50 outlet.
That is why the default recommendation for the NEMA 14-50 circuit should be #6AWG, and that what is now recommended by Tesla Motors (more on this later)/
Equipment ratings
I agree that majority of terminations for circuits 100A and less are currently rated at 75 ºC. But it is certainly not true for older equipment. It is also not true for all equipment manufactured since 1980-ies.
While Leviton NEMA 14-50 outlet which I linked in my previous post indeed is rated for use with 75 ºC conductors, this is not true for all equipment.
As an example, main panel in my house (built in 1986) is rated only for 60 ºC conductors #14 to #2 AWG.
How improper wiring can cause overheating of Tesla NEMA 14-50 adapter.
The undersized conductors used for NEMA 14-50 outlet will lead to all parts of the circuit operating at the temperature which is higher than the temperature they are designed for, creating a fire hazard. When coupled with improperly tightened connections at the NEMA 14-50 outlet, or incompletely seated NEMA 14-50 adapter, the situation becomes even more onerous.
Tesla Motors recommendation for installation of Nema 14-50 outlet
Originally, when looking through the Tesla NEMA 14-50 installation requirements sheet, I was surprised that they did not include any requirements for conductor sizing. As mentioned before it is now my belief that improperly sizing NEMA 14-50 circuit conductors is quite common and contribute to the NEMA 14-50 adapter overheating problems, so I thought about writing to Tesla Motors suggesting that they should include more detailed requirements on conductor sizing in their NEMA 14-50 installation sheet. It turns out that this will not be required: The recommendation on using #6AWG for NEMA 14-50 installation was apparently added to the installation sheet, which now states:
Circuit installation should meet National Electric Code (NEC) wire and breaker ratings. In general, this means 6 AWG wire for installations under 100 feet
http://www.teslamotors.com/sites/default/files/downloads/US/universalmobileconnector_nema_14-50.pdf
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In order to eliminate confusion I would suggest that you either remove or modify all your posts that include blanket statement that it is ok to use #8AWG for NEMA 14-50 installation
How is this true when we are talking about 50A breakers and circuit sizing and the Mobile Connector (or other EVSE) only draws up to 40A? This is the standard 20% de-rating for continuous draw applications, right?
I'm interested because I just had a house built in 2012 and the electrical contractor put "E123775 8/3 W/G TYPE NM-B 600V (UL)" in the wall without conduit for my two 14-50's. This is Red/White/Black insulated 7 strand copper with a solid bare ground wire with the 4 wires sheathed in black plastic. I have since changed one of the 14-50's to a 6-50 for use with my Leviton EVB40 40A EVSE.
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Think of it this way: A continuous load must be used on a circuit rated to at least 125% of the continuous load.
Your electrician installed wire insufficient for the application and not to code.
All NM-B wire (aka romex) must be used under the 60C temperature rating. In other words, 8/3 NM-B is only good for a 40A circuit, or 32A when charging an electric vehicle. You should have 6/3 NM-B installed.
I do not recommend charging above 32A until that is corrected.
From what I understand for most residential installs, temperature derating based on "ambient" temperature is generally overlooked. However, if you were to follow the NEC guidelines you would look up the ASHRAE 2% design temperature and use that as your ambient temperature.
Mountain View is next door to Los Altos and has a temperature of 84F. This is not hot enough to require any additional temperature derating (need to exceed 86F).
Correction table can be found here: Wire Current Ampacities NEC Table 310-16
Ambient temperature can be found here: Building Wire - Outdoor and Rooftop Temperatures for Selected U.S and Canadian Locations
That's dangerous advice. A plug that is so hot that it burns a person, should not be used. It could still be dangerous at 60 amps. It is dangerous to use electrical equipment with known safety faults.
Another mentioned practice that can be very dangerous, is unplugging a charger during a charge. This can damage connectors, charging system and injure the user. It can burn the connectors, it could send thousands of volts through the charging system, and could cause molten metal to be ejected. The arc also could cause a fire or explosion.
I certainly would hope that Tesla would have been proactive on delivery of the vehicles by providing instructions advising against unsafe usage. IE Advising against using Chargers after connections have get excessively hot and/or connections that are burned. Advising against unplugging charge connections, while the charger is still charging.
I think it would be safer to hard wire HPWCs.
I appreciate your enthusiasm, but as I mentioned I do have quite a bit of experience and will not be doing so. I never include a blanket statement that it's ok, I mention that #8 is good up to 50A for conductors-in-conduit, the big common exception being when NM cable is present. I have talked to hundreds of AHJ's, who are the local authorities who are required to know the code, apply the code, and pass appropriate local judgment. You are the only person in my 20 years of experience with the electric code, residential and commercial wiring who has disputed what the code says (that #8 is fine up to 50A). You make a very big deal out of ambient derating, as if the temperature sensitivity is tenths of a degree; however, it is not, and again I state that in my experience never has an AHJ determined that a garage will need special derating for ambient temperatures. I've even seen several installations in Phoenix where the AHJ did not require ambient temperature derating. There is plenty of headroom in the code for this.
To those of you reading this, there is one lesson to be taken away from this -- there are a lot of people who have a lot of opinions (mine included); the authoritative source here is NOT an internet poster (including me), the NEC or some other book or academic material, but rather your appropriate zoning/building authority (the Authority Having Jurisdiction, or AHJ). They are the ones who interpret and apply the code, apply local amendments, and most importantly they are the ones who pass inspections... they are the ones your insurance company will want records from should anything happen. Even if you don't have inspections in your jurisdiction, they will provide guidance to you -- it may be that they simply tell you to trust a licensed electrician you hire. You have to listen to the AHJ; you can escalate to his superiors, then the town council or county board, but if they uphold it, you're required to support his demands unless you feel like using the courts.
The one place I have seen electricians and AHJ's use the ambient derating is when wiring is present in the attic of a home, up away from the insulated ceiling. In that case, drees' reference to the ASHRAE table is used to determine the derating factor, and in that case, #8 in conduit would not be acceptable for 50A.
In my uncooled/unheated garage, even when it is 40 degrees C outside, the internal temperature does not justify ambient temperature correction. I live roughly at the midpoint of the US population.
I think it's important to note that you did quite insist that the Leviton outlet was 60 deg C rated, and that was the reason you insisted #6 had to be used. Again, I appreciate your enthusiasm, but such a blatantly wrong answer is only harmful to people who read this.
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I find this discussion both educational and fascinating. One takeaway I have is that given the disagreements amongst experts, the reality of thousands of installs is that someone is bound to get it wrong. Maybe a TMC handbook on what to ask the electrician, how to verify that the electrician did proper work, and basic safety tips. Like not putting newspaper near the outlet. I'm sure quite a few installs are not inspected, especially 14-50's.
Please note, that as I've posted in #106 above Tesla did add requirement on sizing conductors for NEMA 14-50 install to their installation sheet, it is now explicitly states that the recommended conductor size is #6 AWG. The Falsher's opinion is not just different than mine, at this point it is direct contradiction to the recommendation put out by Tesla.
Circuit installation should meet National Electric Code (NEC) wire and breaker ratings. In general, this means 6 AWG wire for installations under 100 feet
http://www.teslamotors.com/sites/default/files/downloads/US/universalmobileconnector_nema_14-50.pdf
Indeed, which is why the FAQ exists.
Even in the liquid fuel world, we see plenty of people getting it wrong, both accidental and purposely. I've seen quite a few rigged installations to deliver flammable fuels in a way that they shouldn't be delivered -- farmers are especially good at this.
The FAQ can't address everything, though - and I don't want it to be a collection of warning stickers that are obvious to most individuals. In almost every case, the installation of any charging equipment, whether a 14-50 or an HPWC, requires adherence to the NEC (in the US) with any local amendments approved by the local authority (e.g., wire-in-conduit only in Chicago, outdoor outlets above 48" in areas with heavy snow, etc.) In most cases, it requires an inspection unless you're simply replacing an existing outlet. If you know what you're doing, the AHJ is your reference point; if you don't, hopefully an electrician is your reference point (and will manage the relationship with the AHJ for you).
Because the AHJ is the official authority, I can't tell you what is black-and-white right or wrong, I can just use my experience to tell you what most AHJ's have done. You may find an AHJ that has an extreme view on the technicality of the code... the difference is that you MUST listen to him/her.
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vgrinshpun, you have a rather interesting way of interpreting the English language.
I can appreciate that you really, really want to be right. Tesla says specifically that circuit installation should meet NEC wire and breaker ratings. The NEC says that #8 wire in conduit does conform to the code for a 40A continuous load. Bottom line, Tesla defers to the NEC. Tesla notes in addition that generally, it means 6 AWG wire -- but we don't know their assumptions for "generally". In my experience, this is because the average installation uses NM cable, which would require 6 AWG. It is not "direct contradiction".
To avoid this from being taken off track any further, I won't respond any more to this argument.
The summary is this:
1. It is perfectly legal by NEC standards to connect a 14-50 intended for a 40A continuous load with #8 AWG wire in conduit (subject to conduit fill requirements, current-carrying conductor requirements, et al); it is not legal to use #8 NM-B cable.
2. The super-technical interpretation of the NEC suggesting derating for ambient temperatures in a typical garage does not square with experience in the field.
3. Most electricians will run #6 anyway, to give some headroom and to keep the number of cable spools on the truck to a minimum. I recommend the same and my own installation uses #6 in conduit, but I would never force someone to rip out #8 if installed properly in conduit.
4. The AHJ serving your jurisdiction is the authority -- ask him or have your electrician do so.
The last point is the most important. A good Internet forum rule is that you don't have to trust me and you shouldn't solely rely upon my recommendations, because you and the AHJ are the two most important people in this installation.
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Ah, yes, I do remember going over that FAQ now. Thanks.
My local inspector insisted that, as part of my install, the it wasn't sufficient to have just a sub panel in the garage. I had to get a service disconnect near my other panels so that there was one place in the house to turn off all the circuits. Prudent, but it cost me about another $300.
I did manage to get 200A dedicated service installed with a separate meter and Schedule EV billing for the future that I might have more than 1 Tesla charging in the garage.
I suspect this is because you would have had unfused conductors from the base of your EV meter to the main lugs of the garage's subpanel. That's considered a big no-no around here, not only for the building disconnect rules, but from a safety standpoint -- you want to limit unfused service conductors running in/near the building as much as possible.
My service was upgraded from 200A on 2/0 conductors (yikes!) to 400A on 350 kcmil by the PoCo, and I put a subpanel in the garage designed for 1 HPWC, 1 14-50.
My garage routinely goes to 55 C in summer during the afternoon, so I did calculate the derating when installing the wiring (some 3 years ago now). However, at 4 am in the morning (when charging), the temperature is always below 30 C.
I went with 6 AWG, mostly for wanting 48 A continuous, and, as I recall, 2 pair of 6 AWG is the max you can put inside 3/4 " EMT.
Guys, this is a moot argument, as no competent electrician is going to recommend, and install #8 wire for a 50A outlet that will be used for continuously charging an EV. The difference in copper cost is so little, that you will make up for it in less than a years resistance loss on your electric bill. Using #8 for a 50A EV outlet is just stupid. It's tripping over dollars to pick up pennies.
I agree that most electricians are going to use #6. I recommend the same. What I said is that a #8 installation is perfectly legal (for example, if you had an RV outlet already in that location) and that I wouldn't rip out an installation done with #8 if your goal is to minimize cost to install. I have seen a number of RV outlets fed with #8, and I want to be clear that there's nothing wrong with them.
But I can't pass up a good math problem, either. Let's assume 100 ft. run, so 200 ft. of conductor length in the circuit. Let's assume kWh cost is national average of $0.13ish.
8 AWG is .06282 ohms / 100 ft, 6 AWG is .03951 ohms / 100 ft. Difference is .02331 ohms one-way, or .04662 ohms for the (200 ft) circuit.
P=(I^2)*R, so @ 40A, loss difference across 8 AWG vs. 6 AWG in this circuit is 74.59W. This means you'd waste 1 kWh every 13.41 hours of charging.
I used 2 suppliers on eBay as my price comparison point. mwscable has #8 THHN @ 1000 ft. for $298, cableall has #8 THHN @ 1000 ft. for $366; mwscable has #6 THHN @ 1000 ft. for $450, cableall has #6 THHN @ 1000 ft. for $561. We'll use the less expensive of the two suppliers (mwscable), and the price difference ratio for both suppliers checks out at ~2:3 for #8 to #6. This means that 200 ft. (circuit length) of #8 will cost $59.60, #6 will cost $90. The difference is $30.40 with the cable bought in bulk. Of course, if you use an electrician, he might charge a mark-up, but I'll be extra conservative and give us the benefit of the doubt.
$30.40 will pay for 233.8 kWh of electricity, or 3,135 hours of #8 vs. #6 loss while charging. You'd have to charge 8.59 hours a day @ 40A, every day, to recover it in a year, which would mean roughly a daily drive of 266.3 miles @ 31 rated miles/hour of charging, or ~97,200 miles a year.
So it's probably more like 6 years at 16k mi/yr, or 8 years at 12k mi/yr... but you will get a return at some point.
Definitely longer if you include the mark-up by an electrician or the opportunity cost of $30.- - - Updated - - -
Just curious - what's the outside ambient air temp when your garage goes to 55 deg C (130 deg F)? Our max tends to be 105 degree days outside, and my attic makes it to 120 degrees or so on the hottest days (fan-ventilated). What's the factor that drives it up -- do you have heavy use of glass? My garage -- 3 bays, 2 standard double-hung windows -- doesn't even make it to the outside ambient temp.
In your case, I would say that you should adjust for those factors, although I suspect the AHJ wouldn't even consider it during the inspection.
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Yes, it's legal per the NEC, and most RV parks use #8, especially the older installations. I ran the calculations when I had my outlet installed, and the cost difference came out to less than $20 difference in materials to run #6 in 1 inch conduit. Since I will be using this outlet for many years, it was a no brainer.
Don't recall exact numbers, but in the 30 to 33 deg C range. I have some glass in the doors (less than 1/8 of the surface area), but they do face SW. Main culprits are zero ventilation and heat generated by 6 kW PV inverter running full tilt.
He did not. But then, I had to brief him on the requirements of article 625.
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