I've been living for a few weeks with the equivalent of a very long thin extension cord: a 5 amp current draw will cause a 10V voltage drop, so 2 ohms line resistance. I'm only using a short extension cord so most of that is within the walls (as it were; actually an outlet at the far end of a parking lot with a long run of wire). If you are set for the default 12A draw, the 24V drop will take the line voltage well below the 105-125VAC operating range. Charging stops. If I use 5 to 7A draws, it will stay stable overnight--all consistent with my 119VAC no-load supply staying above 105 at the car with the load. It doesn't kick out immediately at 104, but often does during the night. I am getting 1.5 m/h charging (at 20 hours per day, about 30 miles range). I offer the following as a procedure for those inclined toward extension cords. But the whole thing could be implemented in Tesla's firmware when a 120VAC charging session was about to begin: Start charging at 5A setting (that's the minimum for some reason). Note the very first voltage display, when current still reads 0A, then note the V when current jumps to 5A. That's your voltage drop; divide by 5 to get the line resistance R. Increment load by 1A and note the reduced voltage. Repeat until V nears 105V. A little mental arithmetic with Ohm's Law will get you there faster.