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