No, it's neither... just like any other product, they couldn't possibly anticipate every single electrical installation or grid attachment out there. The Roadster MC / UMC / HPWC has nothing to do with it. There were only 2,500 of the Roadsters manufactured (compared to 16x that in Model S today), and the customer base was less diverse. They didn't run into some of the same issues that they are running into with a much larger, more diverse customer base today. They are also more prominent -- being under the microscope means having to be more careful, hence the titanium plates or the charging back-off algorithm.
The continuous load aspect really can't be changed without increasing charge time, and that's a trade-off Tesla must make. Rather than forcing everyone to have an average of 37.5A as you suggested, they chose to address the risk by allowing those installations that "look good" in terms of the ohm's law profile to work at continuous, and for those that look marginal, they back off the charging current.
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Sorry, I'm boggled by the response. It's not like Tesla is just deciding to screw with you and backing off the current arbitrarily. It sees a significant fluctuation that points to a problem in the electrical system where you're charging. Just because you don't believe that, or just because the segment from your meter to your receptacle is good, doesn't make it untrue. Do you really consider it a bad thing that the manufacturer of the largest kWh load your home will ever see is protecting you?
I've said it several times, I'll say it again - just because something works doesn't mean it's safe. Placing an override there will cause the average person to hit it every single time, regardless of whether he understands the risks or the physics of the situation -- "my electrician said my side was safe, so why not?" Just the fact that someone would ask for an override without being able to explain precisely why the Tesla detects that profile and backs off is proof why it is needed.
It has been established that a manufacturer *CAN* take away features that have been paid for, when they're unsafe. This happens in child toy recalls all the time. There were several examples cited in the "low" suspension thread. Charging works at the full rate when the infrastructure is there to support it. Fix your infrastructure, and the product works as designed.
The FAQ (below) has the appropriate troubleshooting steps. Call in your power company, explain what you're seeing. Have them talk to Tesla about the voltage fluctuations that are seen. My power company was happy to hear that I was going to give them more business and upgraded, no questions asked. If, however, the answer is not satisfactory, file a complaint with the PUC -- some PoCo's are living in the 1960's where we only used power for incandescent light bulbs, refrigerator and sawmill motors, and resistance heating, and they have to be sync'ed up with the reality of the world. That 10 kVA transformer serving 3 houses isn't going to cut it anymore, and they need to be held accountable, not Tesla.
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Finally found the post I was looking for:
Smokin' transformers
In this case, I'm sure Adelman's home wiring was just fine... the transformer was horribly undersized. I think that protection is a good thing.