A downline wire (10) serves to connect a location on the ground surface to at least one detonator (52) in a blast hole. The downline wire includes at least two flexible electrical conductors (12, 14) encased by respective flexible layers of an insulating material (20, 22) and a flexible sheath (24) in which the insulated conductors are embedded. Each conductor (12, 14) is made of a copper-clad steel core and the insulating material is either a filled flexible polyvinylchloride (PVC) composition or a polyester elastomer. The sheath (24) is made from a medium or high density polyethylene compound which includes carbon black.