The water-cooled furnace power cables provide the only flexible connection in the secondary circuit. These cables must be flexible to permit movement of the electrode arms up and down and to allow swinging the electrode arms and roof when charging of the furnace. The connections from the delta closure, which are on the outside of the transformer vault, are silver plated to provide a clean contact for the power cables. The power cables consist of copper wire strandings forming a cylindrical construction, which is soldered to copper terminals at either end of the cable.
A rubber jacket around the outside of the cable permits cooling water for the cable. The rubber hose is attached at either end of the cable using stainless steel clamps, vulcanized bumpers or an anti-chaffing hose. The cooling water hose is covered with a protective sleeve which may be fabricated of fiberglass, vulcanized material, and silicon or aluminum glass fiber sleeves. As cable design advanced, it was noted that due to the "skin effect" typical of AC operations, the current was carried predominantly by the outer portion of the copper strands. Therefore the center strands were replaced with a hollow rubber tube which reduced the cable weight, the reactance and the cost of the cable. At a later date, some operations used this inner channel for water cooling as well.
In DC furnace operations, the inner rubber tube in the cable is used for cooling because DC operations do not experience the "skin effect" and the whole cross section of the copper cable carries the current uniformly. However, DC cables are cooled more effectively from the center and cooling from the outside is not always used.