On Thursday last week, two generating units at Tutuka power station in Mpumalanga tripped. There was, at the time, no mention of sabotage in the power system updates the utility put out.
But on Wednesday, when president Cyril Ramaphosa addressed media at Eskom's headquarters after cutting short an official trip to Egypt, he said that sabotage had caused the loss of 2 000MW of power for 10 hours, without specifying where and when the incident took place.
"Someone in the Eskom system disconnected one of the instruments that finally led to one of the boilers tripping," said Ramaphosa, saying the beleaguered power utility must work with the police and intelligence services to find out what happened.
Here is what we know about the alleged incident:
Bheki Nxumalo, Eskom's head of generation, said on Wednesday that the utility was alerted to the alleged sabotage when it picked up that an instrument monitoring the status of boilers – where coal is burned to produced steam – had been tampered with.
According to Nxumalo, a safety monitoring instrument was disconnected. He said the instrument monitors whether a flame is active in the boiler, so that you "don’t introduce coal when there is no fire". This, in turn, helps prevent damage to the boiler and a possible explosion.
Without the monitor working properly, the boiler tripped as a safety precaution, says Eskom. The problem was fixed by the weekend.
The power utility says it has been in contact with police.
Did the alleged sabotage cause stage 6 load shedding?
The alleged incident of sabotage took place on Thursday last week. While it did not directly cause stage 6 load shedding, implemented on Monday, Eskom says it contributed to capacity constraints.
Eskom's decision to implement stage 6 load shedding was caused by a "perfect storm" of unusually heavy rains causing floods in Mpumalanga, and the breakdown of two conveyor belts feeding coal into boilers at Medupi.
This, according to Eskom Chief Operating Officer Jan Oberholzer, exacerbated an already-tight electricity system that was suffering from constraints due to other generating units being down because of boiler leaks.
The load shedding status has since been downgraded to stage 2, which Eskom expects to end at 11pm on Thursday.
Who is responsible?
Speaking to Kieno Kammies on CapeTalk on Thursday, Oberholzer said that he "honestly has no idea" who is responsible, and could not say what the motive may be.
The Eskom COO said that while he could not reveal specific details about the incident due to the police probe, it was "obviously" carried out by an "individual or individuals" with full knowledge of the power station's inner workings.
"It's learning experience," he said. "You wouldn’t expect your own people to be up to mischief."
But Paris Mashego, the energy sector coordinator at the National Union of Mineworkers, told Fin24 on Thursday that Eskom leadership often resorts to accusations of sabotage, and the union wants to see proof.
"We have heard this. We are not surprised by the statement of the president. Every time there is an issue like this, they talk about sabotage. We knew he would mention it when there is nothing like that," he said.
"It's not truthful. Every time something goes wrong, workers are blamed. The last time workers went on strike there were accusations of sabotage. We have challenged Minister Gordhan to provide us with evidence of this and we are still waiting."
Is this the only incident of alleged sabotage?
On Thursday Oberholzer said the incident at Tutuka was not the only time that Eskom's power plants had been sabotaged.
He said the power utility had previously installed cameras in two power stations because of alleged acts of sabotage, adding that it did not, however, expect sabotage to take place at Tutuka.
He said that cameras were being added to more power stations and other critical infrastructure.