The branch connection cable is used to connect a PV microinverter string to the solar array junction box. One branch connection cable is needed for each string of YC500A microinverters.
From the manufacturer:
Provides connection from junction box to first microinverter in string. Connector at one end, bare wire at other. 6 foot 3 conductor connector, 12AWG, 600V. Type TC-ER 90C, -40C. Insulation color: red-black-white. UL certified.