But the supervisor then used a piece of timber and his hands to dig the area to confirm the rod had connected with a cable.
"While no one was injured, there was a risk of injury or death," the WorkSafe report said.
The company involved had identified the location of the cable, and had a "permit-to-dig" system.
"However, the permit system only considered excavation below ground and not the penetration of the ground without digging," the report said.
"Therefore because the workers were not digging below the ground, they did not use the permit system which would have identified the location of the buried cable."
Making matters worse, the job plan and paperwork had been left at home by the supervisor, and the workers were not briefed about the known buried cable.
"The supervisor put their life at risk by attempting to remove the rod or dig around the cable," the report said.
CRL's Rob Mair said it was a "serious incident" that resulted in a thorough investigation.
"Following the incident, works in the immediate area stopped and the area made safe and secure.
"The welfare of those involved was checked, Worksafe NZ was notified of the incident, and the critical incident investigation commissioned."
After the investigation, CRL had taken action including improving the identification and markings of underground services, expanding the scope of the "permit-to-dig" system, and the management of critical hazard information to those undertaking this work.
"This was a serious incident and was treated as such," Mair said.
"The project is committed to ensuring workers get home safely at the end of their shifts."
A spokesman said there had been three serious workplace injuries in the past year.
CRL refused to release the report into the incident, nor other reports into injuries that had occurred during the project.
The $4.4 billion CRL is New Zealand's biggest infrastructure project.
When completed in 2024, the CRL's tunnels from Britomart to Mt Eden will be able to carry up to 54,000 commuters an hour to and from the CBD - twice the current capacity of the rail network.