Low voltage
600 V and below covers building wire, tray cable, portable cord, control and instrumentation. Insulation is thin, shielding is usually absent, and handling is straightforward.
Medium voltage
2 kV to 35 kV introduces semi-conducting screens and a metallic shield. Cable is thicker, heavier, and requires care at terminations; a damaged shield can make an otherwise good reel unusable.
High voltage
Above 35 kV, cable is engineered as a system with accessories, and testing requirements are formal. Reviews are case by case because handling and proof testing dominate the decision.
Why the class changes value
Higher classes serve fewer buyers but carry more value per foot. The narrowing market means identification and documentation matter more, not less.