General Order 128
Definitions of Terms as Used in These Rule
20.4     Communication System means an underground communications
system including all of the subsurface and associated above ground structures,
cables, ducts, manholes, equipment and appurtenances used for transmitting
information. Circuits of a communication system not contained in grounded
metallic sheathed or shielded cable shall not operate at more than 400 volts
to ground or 750 volts between any two points of such circuit, nor shall
the transmitted power exceed 150 watts except that when operated at less
than 150 volts, no limit is placed on the transmitted power.
Note:     As limited above, with respect to voltage, power and cable shield or sheath telephone, telegraph, messenger–call, clock, police, fire alarm, and traffic control circuits may be classified as circuits of a Communication System. Other circuits, not exceeding the above limitations, used for signal or control purposes may also be included.
A.     Public Communication System means a communication system used to provide communication service to the general public.
B.     Private Communication Circuit means a
circuit used for private communication, signal, or control purposes in the
operation of other facilities.
C.       Railway Signal Circuit means those supply and communication circuits used primarily for supplying energy for controlling the operation of railway block signals, highway crossing signals, interlocking apparatus and their appurtenances. Railway signal circuits which operate at less than 400 volts to ground may be considered as private communication circuits provided that if the potential exceeds 150 volts between conductors, the power transmitted shall not exceed 150 watts. Where all the circuits and underground system are owned and operated by one utility, the potential between conductors carrying in excess of 150 watts may be increased to not more than 250 volts. Railway signal circuits not meeting the foregoing requirements shall be treated as circuits of a supply system (Rule 23.5).
Note:     Revised November 6, 1992 by Resolution SU–15.