An electrical connector is used to mount to a circuit board. The electrical connector comprises a housing having a spacer, a cage and a terminal block. The cage is engaged with the housing, the cage and the housing together are provided on the circuit board and the spacer is spaced apart from the circuit board, so as to together define a first slot positioned above the spacer and a receiving space positioned under the spacer and is adjacent to the circuit board. The terminal block comprises an insulative plate positioned in the receiving space and the insulative plate is parallel to and spaced apart from the spacer so as to in turn form a second slot in the receiving space.