WASHINGTON, June 30 : The Federal Communications Commission, the U.S. telecoms watchdog, said on Tuesday it plans to vote next month on a measure that would bar sales of devices in the United States that contain components from blacklisted companies. The FCC maintains a list of firms - including Chinese telecoms giant Huawei - whose equipment is barred for sale in the United States over national security concerns. But no regulations currently prohibit American sales of electronics such as