CAPE TOWN (Reuters) - South Africa slashed its 2014 growth expectations for the second time this year on Wednesday, with the Treasury forecasting expansion of just 1.4 percent as strikes, an electricity crunch and weak private investment take their toll. Africa's most advanced economy, which was recently overtaken by Nigeria as the largest, has been battered by waves of labour unrest that has hobbled output in the platinum mining and manufacturing sectors. "A number of factors that were perceived as temporary have become embedded into expectations," the Treasury said, singling out an electricity supply squeeze and labour tension. In February the Treasury cut its 2014 growth forecast to 2.7 percent, from an earlier estimate of 3 percent. Expansion is expected to edge up steadily to 3 percent by 2017, supported by investments in energy and transport, rising exports and improving global growth, the Treasury said. But this was still far below the level of growth required to cut employment from 25 percent. The economy expanded by an annual 5 percent in the five years before a 2009 recession, but has struggled to reach 2 percent growth since. Growth would improve as new energy came on stream while the weaker rand exchange rate would boost exports if not eroded by wage settlements that outpaced productivity.