In portable cord terminology, each letter of the cable type indicates the construction of the cable. For example: S = service, O = oil-resistant jacket, J = junior service (300 volts), W = weather resistant, T = thermoplastic, and OO = oil-resistant insulation and jacket. We've outlined nearly three dozen acronyms to explain what the letters used to describe them mean and where they. Flexible cords come in a number of UL and CSA types including SO, SOW, SOOW, SJ, SJO, SJOW, STO and SJTO. The manufacturer's name, trademark, or other distinctive marking—some way to identify the organization that made that conductor. This. This guide is intended to assist code authorities, installers and contractors in determining the suitability of UL Certified, Listed, Classified and Verified wire and cable for use in a specific installation.