Conductive-rubber shielded low-voltage cables - An update

Recent efforts to fabricate and test a conductive-rubber shielded cable for shuttle-car applications has shown progress, especially in regards to lower-volume-resistivity shield materials. Earlier work had indicated a need for volume resistivities on the order of 100 Ω.cm or less. An experimental cable recently evaluated under Bureau of Mines contract J0338001 had volume resistivities less than 50Ω.cm. The cable was a flat three-conductor G-GC No. 6 AWG with an SHD configuration. Cross-sectional dimensions were 0.75 x 2 in (19 x 51 mm) compared to typical unshielded designs of 0.68 x 1.64 in (17.3 x 41.7 mm), but it appeared that the differences could be reduced with further developments. In addition to volume resistivity, key considerations in the cable evaluation were splicing and the adhesive bond between the shield material and the conductor insulations. At this time it appears that the choices of bonding are either tenacious or only slightly adhering. The experimental sample was the latter and proved to be spliceable; however, the weaker adhesive bond might not be sufficient to maintain cable integrity with excessive flexing. No in-mine evaluations were performed, although cable is available for this purpose and the cable is expected to be tested at a later date.