A method for performing a power scaling is discussed. The method performed by a user equipment (UE) includes determining, by the UE configured with dual connectivity to a first cell group and a second cell group, a first power for transmitting a first uplink channel on a first subframe toward the first cell group; determining a second power for transmitting a second uplink channel on a second subframe toward the second cell group; and scaling down the second power for transmitting the second uplink channel if a maximum power is exceeded, wherein the first uplink channel includes a first physical random access channel (PRACH), wherein the second uplink channel includes a second PRACH, and wherein the scaling down is performed if the first subframe is overlapped with the second subframe.