HV cables are the highest tier conventional Cables. They can tolerate High Voltage (512 EU/s) and Extreme Voltage (2048 EU/s), but have an extremely high distance-related energy loss. HV cables can have 3 different levels of insulation. Considering that a shock from a poorly insulated HV cable will most likely prove fatal, it is recommended to insulate them well unless the cable is located in a completely unreachable area. Even then, insulation should be applied to reduce the massive energy losses. It's possible to reduce this by stepping down the voltage and using glassfibre cables till it arrives at it's destination and then stepping it back up.
Damage caused per EU packet from standing by HV cables
The mod currently lists the most insulated HV Cable as "4xInsulated." However, this is incorrect, as the player is merely adding layers and not doubling the amount of layers. This means that this level of HV Cable would actually be called "3xInsulated."
Quantum Armor will totally nullify the effects of uninsulated HV Cable. This then makes a unique and large scale defensive system.
Damage from uninsulated HV Cable will travel though occupied blocks, much like damage from a Tesla Coil.