Seven Mozambican nationals were arrested on Saturday after they were caught cutting copper cables at the City Power station in Kew, northern Johannesburg, police said.
Spokesperson Moses Maphakela said the men had pretended to be City Power employees.
"This is the biggest bust we have ever made. There have been a number of copper cable theft cases but this is the biggest," he said.
Maphakela said the copper was worth R12000.
He said police received a tip-off that there were suspicious-looking men stealing cables at the station.
"When the police got there, the men were busy cutting cables and some of it was already loaded in their bakkie."
The suspects will appear in the Wynberg magistrate's court today.