A.TN—S B.TN—C C.TT D.IT
A.TN—S B.TN—C C.TT D.TN—C—S
A.单孔 B.双孔 C.三孔 D.四孔
A.接头处 B.拐弯点 C.预留长度处 D.中间处 E.四孔