TELECOM Digest OnLine - Sorted: Re: 25 Hz Power

Re: 25 Hz Power

Joe Morris (jcmorris@mitre.org)
Sat, 11 Mar 2006 14:43:02 UTC

Thomas D. Horne, Electrician <hornetd@mindspring.com> writes:

> 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

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