South African markets are on edge about an impending ratings review by Moody's, with some economists fearful that a power crisis will cost the country its last investment-grade rating and lead to outflows of billions of dollars. Moody's is indicatively scheduled to review the Baa3 rating and stable outlook it assigns South Africa later on Friday. The other two big rating agencies, S&P and Fitch, have already downgraded the sovereign to "junk". This year South Africa has experienced its worst power cuts in several years, known locally as load-shedding, as cash-strapped utility Eskom struggles with capacity constraints. Eskom has not implemented rolling blackouts this week, but has warned the power system remains vulnerable.