High temperature superconducting (HTS) cables achieve large power capacity and low-loss power transmission in a compact package. In a new Japanese national project, Sumitomo Electric Industries, Ltd. is working to develop a 66 kV-5 kArms HTS cable with REBCO wires. One of the important technical targets is to reduce AC loss to less than 2 W/m/ph at 5 kArms. To investigate the effect of wire width on the AC losses in multi-layer cable conductors, 30-mm-wide REBCO tapes were divided into 4-mm-wide or 2-mm-wide strips, and two 4-layer cable conductors were manufactured with these strips. The measured AC loss characteristics of the two cable conductors were comparable. The measured AC loss in the cable conductor with 4-mm-wide wire was in good agreement with numerical calculations. However, the AC loss in the cable conductor with 2-mm-wide wires was larger than the numerical prediction. The difference may be due to the wires' non-uniform Jc distribution in the width direction, because the AC losses in cable conductors with narrow wires are strongly influenced by the Jc profiles of the wires. AC loss simulations assuming that the wire's Ic will be higher show that a 14000 A-Ic class cable with 4-mm-wide wires is expected to achieve the AC loss target. For cables with 2-mm-wide wires, the improvement of Jc distribution in the width direction will reduce the AC loss level, and the goal will be achieved with lower Ic wires.