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The current trend in modern electrical power systems for terrestrial and aerospace applications is to utilize dc at voltages well above the traditional levels of 12 to 42 Vdc. New airborne systems contain numerous uses of 270 Vdc, and bipolar systems with a 540 V differential are likely to appear in the near future. The use of high dc potentials create flash-over and arcing risks that are much more problematic than the traditional ac or low-voltage dc. Low-pressures experienced in aerospace environments exacerbate the dangers. Traditional overcurrent protective devices may be too slow to mitigate damage caused by high current arcing. Likewise, the extinction of a low current, impedance-limited dc arc may require active power removal since there is no natural zero-crossing. Achieving robustness in high-voltage dc power systems, then, requires adequate insulation design criteria and reliable failure mitigation. Some design specifications and guidelines will be reviewed and shortcomings identified. Even with technically sound designs, absolute elimination of flashover and arcing cannot be assured in realistic environments as systems age. Hence, critical systems will require detection and mitigation strategies to prevent catastrophic consequences.