The cables in question will be exposed to temperature extremes (0-100 F in ambient swing alone). The insulation of these cables will have to stand up to that, as well as engine heat, and do so for a design life of a decade or more. No cracking or degradation of the insulation will be acceptable.
Your imagination is correct, Rob. Even in non-accident situations, the use of higher voltages adds an additional layer of engineering, as Chuck points out, in the form of isolators. Supposedly, a high-voltage isolator fault was at issue in the recent Fisker Karma car which "died" when it was brought out to Consumer Reports's test track.
Fifty-six-year-old Pasquale Russo has been doing metalwork for more than 30 years in a tiny southern Italy village. Many craftsmen like him brought with them fabrication skills when they came from the Old World to America.
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