Gwent Police is appealing for information after 1.2km of copper cable was stolen in the Risca area.
The cable was taken from an electrical post with the theft reported to police on the morning of Wednesday August 25.
Anyone with any information about the incident is asked to call Gwent Police on 01633 838111 or Crimestoppers on 0800 555 111.
A Gwent Police spokeswoman said: “We are reiterating advice to people about the dangers involved in metal theft. Not only is it a serious crime but we know lives have been lost before by people embarking on this type of criminality.
“Anyone with information about anyone involved in such activity is asked to call the police.”