> Boston Edison used to provide 600 volt DC service for the operation of >> elevators and cranes. I don't know if they still do. > Chicken-and-egg question: 600V is one of the breakpoints in the > standards process (specifically in NFPA 70, the National Electric > Code, in which article 710 is dedicated to special requirements for > circuits at "over 600 volts, nominal", and in which several other > articles have their own special cases for >600V. It also appears to > be the highest voltage for which a standard plug-and-recptacle pair > (e.g., L9-30) is defined in the NEC. > Was the decision to use 600V for hoist installations driven by the > standards, or were the standards written to have the requirement for > speical protection begin one volt above the highest nominal voltage > for hoists? > Joe Morris
As someone who's worked on standards bodies (insurance industry computer file exchange issues) it's likely both. The dominant players (I was one) want to protect their investment, the minor players want the field re-leveled (break the the installed base) to allow them entry, and the body as a whole has some mission statement about being fair, technically advanced, a boon to world peace, a chicken in every pot, etc ... :)600V seems high to me from a safety point of view. But I bet it was chosen to allow existing things to stay in place and was at the limit of technology for making flexible conductors with jacketing that did wear out quickly.