Abstract: An electrical penetration apparatus is described for mounting within a containment wall of a nuclear reactor installation to pass electrical currents while avoiding the outward leakage of radioactive gasses, which can be constructed at relatively low cost. The apparatus includes a pair of cup-shaped casings that face away from one another and have slightly separated base walls, a group of rod-shaped conductors extending through aligned holes in the base walls of the casings and through the separation space between them, and a quantity of potting material disposed in each of the casings and sealed to the conductors and to the inside surfaces of the casings.