The PVC outer sheath was damaged and the armouring distorted, exposing the internal lead sheath.
It was discovered hanging from the roof about 1m from the rib.
The NSW Resources Regulator said a duckbill carrying an air track was sitting underneath the cable.
"When developing control measures to manage the risks associated with roads or other vehicle operating areas, the placement of services that may be exposed to risk of damage such as cables and pipelines must be considered," it said.
"Factors for consideration should include roadway height and width; height and width of loads that are required to be transported in the roadways, including the effect of bumps and dips with overhanging loads; positioning of cables and other services suspended from the roof and effect of roadworks that may alter the effective roadway dimensions over time."
