Seven to twelve kV are typical limits of voltage buildup. When the humidity is high, moist skin becomes conductive, continually draining off charges and minimizing ESD effects. Transient Entry Transients gain entry to wiring and circuit traces by conduction or radiation. Examples of conduction include a direct hit by lightning or a resulting side-flash, inductive load switching across a power source, and contact by en ESD spark. Radiated energy, transferred by electromagnetic coupling and magnetic induction is picked up by conductive material in close proximity to a discharge channel of lightning or ESD, or from nearby wiring carrying a hefty transient of any origin.
Power lines are prime targets for direct lightning hits.
Although surge suppression is provided by the power company to protect transformers, up to 10kV can still get through to the service entry of a building. Any other load in close proximity to an inductive load being switched feels the sting of the transients produced. The energy of an inductive source transient is often consumed by other parallel loads. The greater the number of parallel loads, the lesser the effects of the transient. Conducted ESD normally enters a system through the touch of a fingertip or hand held metal tool.