What is the lettering for examples of hard or extra hard usage type electrical cords?

• A. S, ST, SO, STO and SJ, SJO, SJT, SJTO
• B. NEMA designations A-D
• C. H, HH, HHH
• D. Cords rated I, II, III

Answer: (A)

The labeling for hard or extra hard usage electrical cords is the S-series family with various suffixes, such as S, SJ, STO, SJO, SJT, SJTO, and so on. These designations come from standard cord classifications and are used to indicate rugged service and environmental resistance. The base S (and SJ) indicates a hard/service type cord, while the added letters denote specific properties like oil resistance, temperature rating, or weather resistance. That’s why the set that lists S, ST, SO, STO and SJ, SJO, SJT, SJTO is the correct way to refer to examples of hard or extra hard usage cords. Other options point to different, unrelated designations and don’t describe this hard-use cord family.