The Vulcan Science Directorate has determined that the primary cause of death during electric shock is not voltage, but amperage. As long as you keep amperage minimal you can increase voltage to great heights without causing death. It works by overiding signals from the brain and sending the muscles into a constant spasm, like a body wide cramps, causing instant and complete loss of body control and a lot of pain. The voltage uses is large enough to make mass of the target irrelevant.