OK, as stated before, I am the electrician that installed the charger. Grab yourself a cup a coffee, this is going to be a long one.
First off, I'd like to stated that my trade isn't rocket science. Like any other job, it's knowing the correct procedures to accomplish a task laid out by the higher-ups to provide a product in line with safety for you and me. The installation isn't any different than an installation that I would provide for someone else. In line with NEC code, the Tesla charger gives different settings for the homeowner to charge with. ie.small house with small service - the charger can be set to charge at a lower ampacity. Large house with a large service or even a second service - you can charge at high ampacity as long as you follow the rules.
This installation, after double checking, follows the rules. It has a 60 amp breaker installed. Check. (I believe I said 50 in my last post, my error) EMT conduit installation. Check. Proper mounting of unit. Check. Proper size wiring, #6. Check. Length/distance of installed charger (for voltage drop) only 40 feet. Check. Proper termination of wires. Check. Proper dial and dip switch settings on charger. Check. Tugged wires to make sure proper seating. Check.Proper voltage on both phases and phase to phase. Check.
What happened? Honestly...I don't know.
Theories:
1) Consistently high or low voltages beyond nominal acceptable tolerances. I don't think that happened here. Although low voltage would cause higher ampacity. But a higher ampacity would still be under the maximum ampacity of the cable. Not really going with this theory.
2) The cable itself. I used a typical #6 awg THHN wire. this insulation is rated at 90 degC. (almost boiling conditions) it has fine stranded wires. Generally speaking a better product than a course stranded wire. Education: wire comes in 2 different types:solid and stranded. solid wire goes from teeny tiny 26ish to 8 gauge. (smaller number is bigger wire) after #8, we move into stranded. you can buy stranded smaller wire, but for this application, the charger, stranded is the only way to/can go. but you have 2 options: fine stranded or course stranded. fine stranded is better than course. However this is the theory of error that I'm going with. Let me explain why:
When striping wire to remove the insulation and expose the conductor, we use wire strippers. Anything bigger than a #6 however we use a knife. I have a set of strippers that are designed to strip stranded wire and up to #6. What can happen and does happen, is that sometimes the strippers leave a cut line into the copper itself. Hence a cut line can occur on a few or all the way around the conductor. If a FINE stranded conductor (all the strands are called conductors as well) is broken or damaged and its on more than one, this could be the cause of the heat. Even if the fine conductor wasn't broken, what can happen is the corona effect. The corona effect is when electricity jumps over a divot on the face of the conductor itself. think of it as a pothole in the road. At the beginning the pot hole is really small. Your tire skips over top of it. But do that enough times, the hole begins to get bigger because the edges around the hole start to weaken and fall away. (I know a bit about this as well, i have a bachelor in civil engineering) same as the corona effect, around the divot becomes burnt and it gets bigger until failure. It also causes heat build up. If there are many divots then there is a conductor failure. This could have been the case in this installation. However upon opening the unit and investigating it, I did not find any broken or missing fine conductors. usually they burn and break at the divot. Additionally, the heat was so extensive that the wire was brittle. Notice though in the pictures, it was only one conductor.
How to fix this. As stated in my first post, I would looked to see if the wire is salvageable. It wasn't. The heat crept down and weakened the conductor further down beyond saving. So I pulled it. I then replaced all the wires with course stranded wire and a solid ground. I made sure to not nick the copper conductor when reinstalling it. Made sure it was tight and seated properly in its lug.
Right now, this heat issue still should not have happened. What I installed there first time should not have done that. Its not any different from the thousand other system installations that I've done. I'll chock this up to human error. Theory 2 is the best I can think of. It shouldn't happen again. If it does, then there has to be something more to it than the installation. Remember, an electrician's job is to bring electricity to the device in a proper manner. If the device is at fault, then it becomes a technicians job, or appliance repairman (just yesterday a client asked me to fix her stove, said it wasn't getting power and wasn't turning on, outlet worked, voltage fine, nothing more i can do, call an appliance guy).
I hope this has helped anyone with the same issue. Its good to share knowledge. good to hear educated experience. everyone can learn from mistakes. including myself.
