Aug 4 (Reuters) - Canada’s main stock index inched lower at open on Wednesday, weighed down by a 2% fall in energy stocks, while official data showed the value of domestic building permits rose in June from May. * At 9:30 a.m. ET (13:30 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 17.59 points, or 0.09%, at 20,348.26. (Reporting by Amal S in Bengaluru; Editing by Subhranshu Sahu) Our Standards: The Thomson Reuters Trust Principles.