Jan 13, 2014
jerry33 When you press the button on either the UMC or HWPC the charging stops before the connector unlock happens (LEDs turn light blue/white). No danger.�
Jan 13, 2014
scaesare However, if one unplugs the UMC head plug from the 14-50 (or similar) while a charge is in progress, the issue remains. Not that this is a Tesla issue, but the dangers the OP referred to still exist.�
Jan 13, 2014
jerry33 That's certainly true. You always unplug the car first.�
Jan 13, 2014
qwk About the only way I can see this happening, is when someone that knows nothing about your car, tries to steal your UMC.�
Jan 13, 2014
scaesare With 10's (and soon to be 100's) of thousands of Teslas out there, it's a statistical certainty that even owners will try every combination of inadvisable actions.�
Jan 13, 2014
qwk Unfortunately, you are probably right.�
Jan 13, 2014
xhawk101 Rainbow is a troll�
Jan 13, 2014
roblab How in the world have RVs been able to plug into 14-50 outlets for YEARS and not figured out how to kill themselves??
Of course it's a danger. Has the danger been calculated as to the risk of fire if you fill your car at a gas station? But who cares?�
Jan 13, 2014
NigelM Nonsense. And certainly no more dangerous than unplugging your dryer while it's running.�
Jan 13, 2014
bonnie You should probably learn a little more about how the Tesla charging system works (and disengages) before posting slanderous things like this.�
Jan 13, 2014
Doug_G He is referring to arc flash, which is basically an electrical explosion producing 5000 degrees temperature and spraying molten metal. This does exist, and it's the reason why higher power circuits are permanently wired instead of having plugs.
You are NOT going to get anywhere that level of arc flash by interrupting an operating 240V, 40A circuit. Heck even SHORTING the circuit to ground isn't going to create an arc large enough to cause personal injury. That is total nonsense. If there was such a danger the electrical code wouldn't permit NEMA 14-50 plugs to exist.
Here's some basic reading on the topic: Arc flash - Wikipedia, the free encyclopedia�
Jan 13, 2014
dsm363 I think you may be onto something. I unplugged my car while charging and saw this
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Jan 13, 2014
FlasherZ True that an arc flash from a circuit supplied by a #6 or #8 conductor is highly unlikely to spray molten metal; however, it is indeed capable of personal injury under a short. I saw an electrician once short a #6 120V leg to ground when manipulating a spliced conductor within a metal junction box, and the box cut through the insulation. The resulting UV light from the arc blinded him for a few moments (and the flash was seen by a bystander 2 doors away). However, the biggest risk in those types of arc flashes are the human's reaction to them. He jerked his hand away at high speed and smacked it hard against the edge of a ceiling joist, severely bruising it.
However, a 14-50 receptacle is well designed. The receptacle's clasping prongs are deep within the receptacle, and unless you are purposely trying to arc the receptacle, it is not possible to sustain an arc that would become visible outside the 14-50 receptacle; you would break the arc distance-wise long before that arc flash would affect you. There is no truth to the argument that unplugging a 14-50 will create any damage to either the Tesla or the person doing so.�
Jan 13, 2014
Doug_G Okay, yes, the flash certainly might dazzle you, but as you say his injury was from an instinctive reaction to it, not the flash itself.
Agreed that it would be nearly impossible to be injured pulling a NEMA 14-50 out of the socket.�
Jan 13, 2014
brianstorms As long as you are not wearing a red shirt when you pull a live NEMA 14-50 adapter out of a wall plug while the car is charging, you should be okay. Otherwise, this happens, as the crew of the Enterprise found out:
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Jan 13, 2014
Rainbow I was across the room when a florescent ballast shorted out. Was quite surprised how powerful it was. It blew through the sheet metal case of the ballast. Then blasted through another layer of sheet metal that covered the ballast. It sounded like a gunshot and an arc. Molten metal went several directions. The largest piece I found, was the size of a pea.
I know a guy that was checking wire size with a vernier caliper, but he forgot to shut off the power. It was only one leg of a 220 circuit so it was only 120 when he touched the caliper to ground. He got slag burns on his face and shirt. He might have been blinded by slag if it wasn't for his glasses.
I know a guy that was starting up an air compressor, but the compressor was frozen. He didn't want to throw the off switch because the belt was smoking and slinging molten rubber near the switch, so he pulled the plug. He got some minor burns from splattering metal about the size of grains of sand.
Don't be so sure that a hot disconnect couldn't hurt the electronics in the Tesla charger. Switching circuits around the electronics typically have a capacitor to dampen the collapsing fields in magnetic coils. Hot disconnects, typically don't have the protection of a capacitor. So an extremely high voltage can occur for a fraction of a second.
Take an audio transformer. Hold the output with your bare fingers, and scratch input leads on the terminals of a 9 V battery. Hold the leads of a solenoid with your bare fingers as you scratch the leads on the terminals of a 9 V battery. You should feel a higher voltage than 9 V.Scale that up a bit and you could have something that could do serious damage to electronics and people. A hot disconnect and bad connections that arc can do serious damage to electronics
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Jan 14, 2014
scaesare I'll let the other posts that speak to the significance of the dangers address that. I'm merely pointing out that it is possible to unplug the outlet-side of the UMC while under full load, the protection offered by the car discontinuing charging before unlocking the charge-port previously mentioned only applies to one end of the UMC.
While the dangers are likely slight, I certainly wouldn't recommend unplugging any 240V/80A connections under full load if you can avoid it.�
Jan 14, 2014
NigelM And the relevance in comparison with a UMC would be?
Darwin award #1. Checking live wires with a metal caliper and not shutting off the power.....
Darwin award #2. Everyone knows that air expands when warmed so filling a frozen air compressor is asking for all sorts of problems...
P.S. Remind me never to stand anywhere near you and electrical equipment. ;-)�
Jan 14, 2014
Doug_G Ballast is a large inductor - that has energy storage. Different situation.
I shorted 110V directly to ground once. During a visit friend asked me to fix a minor home wiring problem for him, but he switched off the wrong breaker. I didn't have a meter so, being cautious I deliberately bridged the circuit with a screw driver. There was a modest flash and bang, a snap as the breaker flipped, and my screwdriver had a black mark on it. Okay, now we've got the right breaker. End of story. No flying slag, no blinding flash. But again, that is a short circuit, not breaking an active circuit.
In this case we are interrupting a 9.6 kW circuit, and the break is occurring inside a NEMA 14-50 socket. Significantly less power is involved than shorting the circuit. You'll get a little "pop" sound and that's about it.�
Jan 14, 2014
Chris TX I love reading threads like this. They make me feel glad that I did the THREE 14-50 outlets in two of my properties and one at my parents' house. The one at my parents' house had a ~20' run of 6-3 copper to a surface mount outlet. Pulling all 40A for an hour or so yielded a cold 6-3 wire, a slightly warm 50A breaker, and a warm UMC cable. If anyone is concerned about their 14-50 outlet, just shut the breaker off, pull out the 14-50 outlet, and inspect the connections. Torque them down! Those are huge lugs that can take quite a large amount of torque. 6GA Wire needs a lot of love�
Jan 14, 2014
FlasherZ I hope it's obvious, but I'll say it anyway, deliberately inducing a short-circuit to test that power has been disconnected is a horribly bad practice. In US FPE panels (which should be eliminated but are unfortunately still out there), it can jam the breaker's overload mechanism so that the breaker will never trip again. Better than being killed, of course, but it's a good idea to find a different way. I've used a pigtail light socket, even a cellphone charger to determine the power is off when my meter was still on my truck.
Concur.
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Careful - don't torque too much, you'll break things. Manufacturers almost always specify torque, but if they don't, (I)NETA publishes default torque recommendations.
Torque Specs
Most people don't carry a torque screwdriver with them, though - so how do you know it's tight? Tighten 'til it breaks, then back off 1/4 turn? No!
The point of torquing a #6 in a connection is to get the stranded cable to flatten out in the connector to generate the largest surface area for current conduction, in addition to holding the cable tight. I will agree that it does take a good amount of torque. I find that (with a screwdriver) if I tighten until my continuous tightening motion stops due to resistance, then get a good grip and turn it about 1/4 turn more, that I'm usually right near the torque numbers.
And use the right tools. I can recall 2 different cases where I was asked to troubleshoot a problem with a circuit and found loose connections. In both cases, I asked for a screwdriver and was handed a #1 Phillips, to torque connections on #12 or #10 wire - the same one that the person used. No wonder it wasn't torqued, the bit slipped in the screw head or couldn't get enough torque.
EDIT: One other point I'll make here: those "strip gauges" that you see on electrical devices are there for a reason, use them to make sure you've stripped the right length. Losing surface-area conductivity because a wire or cable wasn't stripped enough will also get it hot; sometimes because there's not enough conductivity, but also because the connector may have been torqued onto the wire insulation, which will make the connection to the fastener loose as well.�
Jan 14, 2014
Cottonwood This last suggestion to retorque the lugs is even more important on old installs. Where I had my hot 14-50 was an old install. I don't know whether it was not torqued well when installed, or years of hot cold cycles loosened it up (my guess is the latter), but torquing the lugs down again made a world of difference in the temperature of the 14-50.
As I said before, if this is a charge connection that you have not used before, wait 5-15 minutes and check for hot spots. If find any, figure out why they are hot, or find somebody to do the figuring, and correct the problem. Warm is OK, hot is not.�
Jan 14, 2014
Doug_G Right, this wasn't something I would normally recommend. It was a nonfunctional light fixture, so I had no way to plug something in to test the circuit. I didn't have any tools with me - I was using what he had. I wasn't expecting the circuit to be energized, because we had both followed the wiring and I thought he had found the right circuit. I "tested" it with the screwdriver because I'm paranoid. Fortunately.
Lesson learned - if this ever happens again I'll just tell my friend I'll fix it next time I visit, and bring a meter.�
Jan 14, 2014
FlasherZ You are conflating so much here it's hard to determine where to start. Suffice it to say that these are not the reasons you might damage electronics by disconnecting AC input power.
In all the cases you're citing, you're talking about a DC power source (9V battery), not AC. In all of your examples, you're using an inductive coil without any filtering. In some cases, the use of an audio transformer can be used in a step-up fashion, where your flicking it will indeed generate above 9v due to your "contact scratching" emulating AC, inducing a higher-voltage current through the transformer. This possibility just isn't present in AC power supplies, because the power supply is already designed to work with alternating current at a specific voltage. In addition, in-rush voltage (and in some cases, collapsing field voltage) can be dangerous in only certain designs, generally involving the DC side of the supply when unprotected or unconsidered.
The AC world is considerably different. First, the power is expected to be dirty, with some random surges and spikes. As a result, any sensitive electronics connected to AC power supplies will have a filter built into them. The Tesla indeed has a pretty beefy supply built into it. Second, by the very nature of AC, the double-voltage issues you see in an inductance-capacitance reaction in a DC circuit are simply not an issue.
If they weren't protected as you say they are, we'd be blowing up computer PC supplies just by unplugging them or plugging them in.
The arc flash danger you mention is only related to persisting the high current through the blades as they lose contact, and as I mentioned, it's nearly impossible to create an issue on a 14-50 unless you're purposely trying to.�
Jan 14, 2014
TexasEV Rainbow is a troll. Let's all stop feeding the troll.�
Jan 14, 2014
xhawk101 Agree mods please mute or ban the rainbow troll�
Jan 14, 2014
Nathan Smith Ok,
Let's see if I can be called a troll to...
1st off I've had zero problems with power going from my home to my tesla -- none, nada, zip, etc, etc. And I have over 20K on my car.
2nd Rainbow & others are identifying that Telsa failed on this safety issue (not the media reporting on it) - which I agree with them on. However, I take a slightly different way of getting to my issue with Tesla on it. The cause of the over heating, fires, melted adapters may indeed be due to poor/improper installs. In fact, I would say that in all likelyhood the Tesla equipment isn't the ultimate cause of the issues at all... However, what this suggest is that Tesla failed to do FMEA, because if they had we wouldn't be having this discussion. I can't imagine missing improper/poor installations as a failure mode for both the car and the adapter (both part of the system). And if you identify them as failure modes, you should plan for them -- if nothing less than a very descriptive warning about issues arising from improper/poor installations.
Lastly -- people shouldn't assume someone is being nefarious because they are disagreeing with your position or pointing out thier perceived shortcomings with Telsa (even if they maybe wrong). Since I don't know anyone on here who is omniscient, we should be a little less judgemental.�
Jan 14, 2014
TexasEV Nathan, no one would consider you or anyone else to be a troll for disagreeing with someone or writing about a perceived shortcoming of the car. There are countless posts like that, and much stronger than what you wrote above. A troll posts an outrageous, extreme statement in order to get a reaction. Usually from someone who doesn't own a Tesla and has an agenda. Trolls post to get attention, not to provide useful information or to make a meaningful contribution to a discussion.�
Jan 14, 2014
J in MN In their letter to NHTSA Tesla states that 2.7% of returned UMC's has thermal damage at the interface between the UMC and 14-50 adapter. An unspecified "several" cases of damage at the interface between the 14-50 and wall plug occurred.
So, I agree that they botched their FMEA. And it irks me that they think software updates are the solution to all problems, when in fact this is a hardware problem (undersized connector pins between the 14-50 and UMC that can become misaligned when the UMC is hung from the adapter, and no thermal monitoring in the adapter).
But, to be fair, GM had a very similar problem with the Volt. There were several forum reports of melted and distorted 5-15 plugs on the portable EVSE. Eventually GM recalled the EVSE's, and replaced them with a revised design.
Which reminds me of another reason why I think the software update is just stupid. If 12A was enough to almost cause fires on the Volt EVSE, what on earth gives Tesla the idea that reducing current from 40A to 30A "fully addresses this issue"?�
Jan 14, 2014
Lyon I don't want to start something here but this argument only works if everything else is the same between the two systems, right? I mean, 12A caused problems with the Volt EVSE but that's a totally different system than the Tesla UMC. I know that they're both EV charging systems and all but the the Volt EVSE doesn't have anything like the plug adaptor on the UMC. Hell, the Volt EVSE really wouldn't like 240v, 40amp!
Basically it seems like Tesla's UMC is sufficiently engineered for most installations but is almost good enough for some. Frankly, the software update reduces the power draw by 25%. Seems like it was a good, immediate, safety measure until they could engineer something better.�
Jan 14, 2014
drees The problem with the Volt EVSE was the same problem that faces all 120V EVSEs (including the Tesla UMC + 120V adapter).
You're often plugging into receptacles that are rarely used under the kind of load that charging a car puts on it. You try to pull 12A through a worn 120V outlet, or an outlet with those crappy stab-lock wire holes, or an outlet with loose wires, and you're going to get significant heating in the outlet leading to overheated plugs and outlets.
This has happened to the Volts, Teslas, LEAFs, and Prius Plug-Ins. I'm not aware of any significant fires as a result, but I'm sure it's happened.
As JinMN noted, the Volt portable EVSE was redesigned, and now the Volt will only charge at 8A by default no 120V unless you explicitly override it to 12A - every singe time. The iMiEV portable EVSE only lets you charge at 8A.
On a high quality, properly installed outlet - it's not a problem. But obviously it can be and hench JinMN's argument that _all_ adapters should have the thermal overheating detection - not just the 14-50 adapter.�
Jan 15, 2014
Cottonwood The power to the car is reduced by 25%, but the heat in problem connections is I^2*R. The reduced current (I) is 3/4 of the original, so the new power in the connectors is now, (3/4)^2 of the original or 9/16 of the original; the parasitic power in connections is therefore almost cut in half (reduced by 7/16).�
Jan 15, 2014
FlasherZ ...because a 5-15 plug is engineered for a certain standard of quality (not to mention what drees points out), and a 14-50 plug a different standard of quality. I've charged my Model S through a 12/3 SOOW extension cord at an outdoor car show and the plug was hot to the touch, because of its construction. If GM's EVSE construction used standard, off-the-shelf power cords that come with everything from computers to blenders to whatever, it's possible that they weren't designed for continuous, high-current operation. It's likely that Tesla's early field tests of the 14-50 showed that everything seemed okay until heavier-duty users got out in the field with them.
As for why 30A, Cottonwood explained it - power/heat dissipated isn't linear with current, it's a square of the current times the resistance. Heat dissipated through resistance at 30A is only 56% of that dissipated at 40A. That's a pretty significant reduction and one they likely felt safe with.�
Jan 17, 2014
digitaltim I think Nigel said it, but I am glad I don't know you...�
Jan 18, 2014
J in MN I fully understand that, but the point I failed to make (being too upset), is this:
At 40 A the failure rate is 2.7%. So what is the failure rate at 30 A? Is it 1.3%? 0.1%? Only time will tell. But I cannot accept that it will be 0% as Tesla claims ("software update fully addresses the issue", "adapter replacement not needed").
The tungsten filament in a 0.74 W flashlight bulb reaches 2500 ?C. At 30 A there is enough current to reach some spectacular temperatures. It is all a matter of ambient temperature and the ability of the components surrounding the fault to shed that heat through radiation, conduction and convection.�
Jan 18, 2014
Doug_G IIRC the 2.7% refers to returned adapters. It is not the failure rate for ALL adapters. So it exaggerates the problem.�
Jan 18, 2014
J in MN Doug, not sure I understand what you mean. Tesla said that 2.7% of the distributed UMCs were returned with damage. If we consider that only a fraction of the distributed UMCs are actually being used (many people have HPWCs, or use J1772), then the potential failure rate could be even higher.�
Jan 18, 2014
neroden The software update needs to be reverted ASAP. In addition to at least six cases of the software tripping on perfectly good public chargers, we now have witnesses of the software "update" INCREASING the amperage draw above the draw programmed by the user, which is actually dangerous and requires a recall.
Yuck.�
Jan 18, 2014
ToddRLockwood That's the only way you can install a HPWC. And it requires a dedicated 240V/100A circuit, although the standard load while charging is 80A.�
Jan 18, 2014
Cottonwood The HPWC is a nice permanent install. It has dip switches for 100A down to 40A circuits in 10A increments; the pilot sent to the car is then set to 80% of the breaker. See page 12 of http://download.waidy.com/EV/HWPCinstallation.pdf. The default dip switch setting is for a 50A breaker and 40A charging.�
Jan 22, 2014
yobigd20 Did anyone catch this article regarding that garage fire? Exclusive: No permit for electrical work where Tesla charging fire occurred - Torque News
In short, there was no permit or inspection done.
But here's the other thing that I noticed when reading that article and reading about the report: 1) it was a NEMA 14-50 receptional with the owner using the UMC 2) the homeowner states that the electrician used 100amp breaker for this. Nobody seemed to pick up on that in the article. What happens if you use a 100amp breaker, lets assume 6AWD wiring, and a NEMA 14-50 with the UMC? Would this cause the adapter to melt or the home wiring to get too hot and catch fire? Obviously a 50 amp breaker should have been used. I'm just curious what would happen if I went down to my panel and started swapping breakers for ones twice their size...(ok CLEARLY I am just looking for a technical answer for this, lol, not that I would do that or anything, I'm just wondering from an engineering perspective what actually would happen... what would cause the heat to generate and resulting fire? ).�
Jan 22, 2014
Kalud I read in the report that there were two 50A breakers in the subpanel being fed by one 100A in the main panel. So there were presumably two 40A outlets (on 50A breakers) which would be correct.
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Jan 22, 2014
yobigd20 ah. I skimmed it too fast then, missed that. makes sense. I bet he used 8 gauge wire instead of 6 LOL�
Jan 22, 2014
Kalud Or very simply a bad (so high resistance) connection in either the socket (wire not torqued to spec) or loose wall socket to UMC connection. Then 40A for 3h -> high heat then we know the result...�
Jan 22, 2014
FlasherZ Neither a permit nor an inspection would change the outcome of this, in my opinion. An inspector will typically not check lug torque - he will look to see that the conductors are the proper size, the conduit is the proper size, the proper bushings and connectors are used, the boxes are grounded properly, etc. And if the homeowner relied upon a licensed electrician, certainly there would be an expectation that lugs were torqued properly.
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Ha, ha. I realize you're speaking in jest. However, even 10 ga. would get warm but it's unlikely it would catch fire. Loose connections are what typically cause extremely high, melting heat.�
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