A security officer who was contracted to Eskom was shot dead while patrolling in Soweto - the third officer to be attacked this month.
"An Eskom-contracted security officer sustained gunshot injuries on Thursday evening while on patrol along the Chris Hani Road in Soweto," the power utility said in a statement.
The incident on Thursday comes after two security officers, also contracted to Eskom, died after they were shot in Lenasia South on 10 November.
"The preliminary findings indicate that the officers were ambushed from behind. Both incidents were reported to the South African Police Service (SAPS) for further investigation and no one has been arrested for these crimes at this stage."
Police spokesperson Captain Mavela Masondo confirmed the first shooting but was unable to confirm Thursday's incident at the time of publication.
Eskom has condemned the shootings, saying the security guards are part of its strategy to "combat the escalating theft of its network infrastructure" which has caused prolonged outages in Gauteng.
"The power utility is deeply concerned about the escalating acts of theft and vandalism of its network equipment and infrastructure which are aimed at derailing its efforts to provide electricity," the statement reads.
In July, two security guards were shot dead in Philippi East, Cape Town, while escorting Eskom technicians out of the area.
The technicians were in the area attending to an electricity supply fault.
Anyone who has information about the shootings can contact the police on 08600 10111 or the Eskom Crime Line number 0800 11 22 27.