Sealing current and regeneration of copper junctions

In selected situations, the operating telephone companies apply a sealing (wetting) current of ≈20 mA to lines containing copper junctions to prevent the contact resistance of the junctions from increasing and/or fluctuating, or to reduce the resistance of an already degraded junction. The effect of a variety of sealing current treatments on the contact resistance of a set of junctions that were aged in an accelerated atmospheric corrosion chamber is examined. A junction configuration in which the wires are only light twisted together was used. Measurements made during and after exposure show that application of 20-mA sealing current approximately limits the contact resistance to less than 21 Ω. Smaller currents allow correspondingly higher contact resistances and fluctuations. Sealing current is shown to be ineffective in preventing the degradation of a junction predisposed to degrade and in regenerating an already degraded junction