Power utility Eskom on Wednesday called on consumers to switch off geysers, pool pumps and all non-e.
The strike by bus drivers from Piotrans, the company which operates the Rea Vaya service, related to salary progression and the status of drivers who were shareholders in the company, the city said in a statement.
"We understand from Piotrans that the workers' demands are not the same as those of the workers involved in the nationwide strike as a result of the dispute at the SA Road Passenger Bargaining Council," it said.
Piotrans had advised the city that the drivers would be on strike from 4am, and that it would seek an urgent Labour Court interdict to have the strike declare illegal.
The SA Transport and Allied Workers' Union (Satawu) announced a nationwide strike on Thursday, which it said was a result of a wage negotiations deadlock. Workers were demanding an 18 percent increase.
While Satawu said employers had offered 2.5 percent, the Commuter Bus Employers' Organisation (CBEO) said the offer on the table was 6.5 percent.
The CBEO said workers were demanding a minimum monthly wage of R6000 across the industry, a R1000 housing allowance, and an increase in medical aid contributions.
Gautrain buses were not operating on Friday, but municipal buses were operating in Johannesburg.