Reading the letters
North American flexible cord types are described by a letter code. S is a hard service cord, SJ is junior hard service with thinner insulation, SV is vacuum cleaner cord for light portable use, and SPT is a parallel cord with no overall jacket. T added means a thermoplastic jacket, O means oil resistant, OO means oil resistant on both insulation and jacket, W means suitable for wet locations and E means a thermoplastic elastomer.
So what does SJTOW mean?
Junior hard service, thermoplastic jacket, oil resistant, wet location rated. That is a general purpose outdoor site cord. SOOW is the heavier version: hard service, oil resistant inside and out, wet rated.
Gauge and current
Conductor size is given in AWG, and the number goes down as the conductor gets bigger. 18 AWG suits light appliance cords, 16 and 14 AWG cover general extension cord use, 12 and 10 AWG carry higher loads or longer runs, and 8 and 6 AWG are used on 30 A and 50 A dryer, range and RV cords. Length matters as much as load, because voltage drop grows with distance.
European cable types
European flexible cable uses the H code. H05VV-F is a 300/500 V PVC insulated and PVC sheathed flexible cable used on most appliance cords. H03VVH2-F is a lighter flat twin cord. H05RN-F is a rubber sheathed cable used where the cord is handled or used at low temperature. LSZH versions replace the PVC compound with one that gives off little smoke and no halogen gas.
