The real trick is distinguishing short term fluctuations that are caused by a flaky connection from some short term fluctuations caused by other big applicance turning on and off (you know, like an electric range/oven/water-heater/air-conditioner/pool-pump/etc)...

Arc-Fault-Detection may pick up some of the failure modes that lead to these issues, but when you are pulling 240V/40A to charge the car (9600W) It wouldn't take much of an issue to melt down a receptacle. And it won't pick up a high resistance connection in an outlet. A 3V drop in a small area (120W) probably more than enough to burn up a receptacle in the time it takes to charge the car but would otherwise be completely normal in most charging situations.

The proper fix here is to install a thermoswitch in the plug that triggers either a significant reduction in charge current, or shuts down charging completely.

You never see 208V measured from hot-hot in homes unless you have severe voltage sag - only 240V single phase with 120V measured from each hot to ground.

208V is commonly seen in commercial 3-phase situations, though, where you tap 2 out of 3 hots and each hot is 120V measured to ground.

Your typical house runs on 240V single phase power fed by two hots and a neutral.

Each hot is 120V, but shifted 180* out of phase, so you get 240V measured across both hots. The neutral handles any imbalance in power draw across the two hots.

Your typical household appliance runs on a single hot split phase at 120V and current is returned on the neutral line.

There's really no reason why we couldn't start using 240V directly these days and eliminate the neutral as long as all your appliances are able to run on 240V instead of 120V. Most modern electronics will run on both without issue.

NEC defines a continuous load as one that can run for 3+ hours.

The reason you are supposed to derate continuous loads is because the circuit breaker is likely to trip under those conditions. Not necessarily that it would be likely to cause a fire.

This is key and it is important to determine exactly where this fire occurred.

The Tesla supplied UMC is designed to adapt to multiple plug types with an adapter so one can plug into a NEMA 14-50 (typical stove outlet), 5-15 (standard 120V outlet) or others.

It is well documented that these adapters can melt - it appears that in some conditions the adapter's PINs do not establish a good connection leading to overheating. Here are three examples:

http://www.teslamotorsclub.com/showthread.php/15304-Plug-Adapter-on-my-Universal-Mobile-Connector-has-melted
http://www.teslamotorsclub.com/showthread.php/18092-Schmelted-UMC-NEMA-14-50
http://www.teslamotorsclub.com/showthread.php/23212-Scary-issue-with-Nema-14-50-adapter-melting

Now that doesn't mean that's what happened here. Faulty 14-50 outlets (no fault of Tesla) have also caused similar issues. There are two examples in this thread:

http://www.teslamotorsclub.com/showthread.php/19576-Burned-220V-Adapter

If it were me, I would not be using the Tesla UMC (Universal Mobile Connector) for daily charging - these plugs/outlets are not designed for daily plugging/unplugging. I would use the Tesla HPWC (High Power Wall Connector) instead and save the UMC for actual mobile use.

I am also not crazy about the design of the adapter plugs on the UMC. Not only do the pins appear not to necessarily mate very well (compare these pins to the connector that actually plugs into the car!), but the extra length of the adapter exerts extra leverage on the outlet/adapter which makes it easier to end up with a poor connection unless you support the UMC well.

NEC says that for continuous loads, you can pull up to 80% of the circuit's rating. Charging an EV qualifies as a continuous load. Below is a list of common copper wire sizes found in your typical home and it's 100% / 80% ampacity (assuming 60C rated insulation which is most common):

14AWG: 15/12A
12AWG: 20/16A
10AWG: 30/24A
8AWG: 40/32A
6AWG: 55/44A
1AWG: 110/88A

Note that for the last two, you typically would be using that wire on a 50A or 100A circuit, the max continuous loads on those would be 40A or 80A respectively.

Your typical plug for charging a Tesla Model S would be a NEMA 14-50 outlet rated at 50A. You might be able to find 75C rated outlets/wire, in which case one can use 8AWG wire for a 50A circuit instead of 6AWG.

If you want to be pedantic, your typical outlet will supply 120V.

Not 110V.

If a 15-20A outlet can't handle 12A current - then it's defective and should be repaired. You're generally only going to trip the breaker if something else is also plugged in to the same circuit and is drawing a significant amount of current.

Definitely, more EVSEs should be installed.

Actually, a 15A breaker may or may not trip at 15.1A. There is quite a bit of fudge room in the spec. You can pull quite a bit more than 15A on a 15A breaker for a short period of time.

Google for "Circuit Breaker Characteristic Trip Curves" for what may or may not trip a breaker.

Some interesting facts:

It is possible to pull between 95-115% of the rated current of a breaker basically indefinitely without it ever tripping.
It is possible to pull 150-240% of the rated current of a breaker for 60 seconds before it trips.
It is possible to pull 300-600% of the rated current of a breaker for 10 seconds before it trips.
It is possible to pull 900-2000% of the rated current of a breaker for 1 second before it trips.

If you're going to be an condescending asshole, you might as well get your facts correct. :-P

Peak production for solar in the summer generally occurs at 1 PM, not 12 PM (during non-daylight savings time the peak is at 12 PM).

Peak demand for the year is generally between 3-5 PM, not 6 PM and typically around 4:30 PM.

At 4:30 PM solar output is starting to drop, but is still producing significant power since many utility scale plants use tracking systems which allow production to remain very flat for a few hours around solar noon. Fixed pitch solar can easily be biased towards mid-late afternoon peaks by aiming farther west rather than south which most systems aim for in order to maximize energy production instead of aiming to match production to demand.

It would not take much storage for your typical home PV system to shift load to the utility peak - probably no more than 5-10 kWh of storage for your typical house.

References:
California ISO Today's Outlook
California ISO Renewables Watch
California ISO Peak Load History
Are Solar Panels Facing the Wrong Direction?

People say lots of things on the internet, does not mean it's true.

Inside the Tesla battery pack
The engineer who disassembed the pack (Ingineer) did not find any evidence of intumescent goo.

And if you want to see what the pack looks like after a less severe incident with a trailer hitch, look here:

As a point of interest, here's the result of a tow hook impact on a MS that resulted in significant battery damage, but no fire. The battery had to be replaced.

Easy to see that the bottom of the pack is aluminum, not steel from that picture (look at the size of the welds and how the aluminum shredded around the impact point) While steel would be stronger than aluminum, the weight of steel is just way too high to justify using it over aluminum.

Just a couple corrections:

1. The battery is protected by 1/4" aluminum, not steel.
2. There is no "intumescent goo" around the cells that people have found, even though Tesla has a patent on it. The cells themselves sure don't release anything non-flammable when they overheat.

Luckily all the big manufacturers have been building battery plants - the problem is that automobile manufacturers haven't been building good enough cars around those proposed battery packs to fully utilize those factories.

A few examples:

Nissan / AESC: Finished a large battery plant earlier this year in Tennessee thanks to DOE loan. Currently only supplies batteries for the Nissan LEAF (24 kWh battery pack), which sells about 1,600 / month or 20,000 / year in the USA. Maximum capacity of the plant when fully ramped up is claimed to be around 150,000 / year or over 12,000 / month.

LG Chem: Finished a large battery plant last year in Michigan thanks to DOE loan. Unfortunately, has been sitting idle for some time, though is finally starting to produce batteries for the Chevrolet Volt (16.5 kWh battery pack). Maximum capacity of the plant is claimed to be around 60,000 / year, currently the Volt is selling about 1,600 / month or 20,000 / year in the USA.

A123: Finished a large battery plant in 2010 in Michigan thanks to DOE loan. Capable of 30,000 battery packs/year. Unfortunately a very large bad bad of batteries delivered to Fisker and Fisker's demise also lead to A123's demise whose assets were bought out. Still operating, and delivering batteries for the Chevrolet Spark EV (20 kWh battery pack). Unfortunately the Spark EV is a low volume vehicle so far only available in a few markets. Launched late June, only sold 130 through July (August sales numbers should be out soon).

Anyway - my point is that there is plenty of supply out there for lithium batteries right now - there are more plants than just the ones mentioned here - both in the USA and abroad. The competition is tough (see A123's bankruptcy and others, too) so despite low interest loans manufacturers are going under. What's needed is a few more plug-ins with a bit more appear - either more utility or lower price.

Both Nissan / GM / Tesla have shown that the public will buy electric cars if they are good products and priced right.

Nissan says they are actually selling all the LEAFs they can make and are currently capacity constrained after a big price drop for the '13 model - they are apparently being conservative in ramping up production capability. Inventory levels support their claims. If Nissan could get at least 25% more range into the car (and perhaps a more neutral package) without increasing the price, I think they could easily sell quite a few more EVs.

GM needed to drop the price of the Volt - they finally did so for the '14 model and they are saying as a result August will be their best sales result yet. Inventory levels support their claims. If GM could get the Volt drivetrain into a slightly roomier vehicle without sacrificing much efficiency and keeping the price down, I think they could easily sell quite a few more PHEVs.

Tesla has finally worked through most of the backlog of their USA orders (there's only so many people who can afford $70k+ cars) and are starting to ship product to Europe. They are expecting to stay at maximum capacity for the foreseeable future (over 2,000 Model Ss / month).

While large format NiMH batteries are patent encumbered, large format Lithium batteries (the kind used in all EVs today except for Tesla) are not.

I believe that Toyota is the only manufacturer who currently uses large format NiMH batteries, but only in their hybrids. The referenced wikipedia article suggests Panasonic/Cobasys worked out an agreement as long as Toyota only used those NiMH batteries in hybrids and not in a plug-in vehicle.

Note that the large format NiMH battery patents are due to expire in 2014.

Not sure how much of this matters - Lithium batteries are superior to NiMH batteries now in just about every way.

Great comment. Also, the water intake issue affects more than just San Onofre - it affects all of the state's power plants sucking water from the ocean.

I hate linking to UT San Diego, but it's the only good article I could fine on the subject. Note the date of the article (May 4, 2010):

San Onofre gets another three years without cooling towers - New regulations approved for all state's coastal power plants