Terms of the private transaction were not disclosed, but two people close to the matter said on Monday said that the company was valued at just below 700 million euros (585.52 million pounds)including debt.

SGB-SMIT posted earnings before interest, tax, depreciation and amortization of 80 million euros on sales of 730 million euros in 2016.

BC Partners had launched the sale of SGB-SMIT in 2016, four years after a sale to China's State Grid was halted by political intervention and OEP entered the auction only fairly recently, one of the sources said.

(Reporting by Alexander Hübner; Writing by Arno Schuetze; Editing Harro ten Wolde)