the power line runs from the songo converter station, which is near the hydroelectric station and normally operates as a rectifier, to the apollo converter station near johannesburg, which normally operates as an inverter. each of the self-supporting steel towers along the route carries two bundles of four 565 square millimetre (1120 kcmil) cables, one per pole, and a single 117 square millimetre (231 kcmil) grounding conductor. there are approximately 7,000 towers with an average span of .