GO95, Rule 20.6

20.6 Circuit means a conductor or system of conductors located outside of buildings and through which an electric current flows or light is transmitted.

A. Class C Communication Public and Private Circuits mean circuits used for public or private communication service and are divided as follows:

(1) Current carrying circuits operating at potentials not exceeding 400 volts to ground or 750 volts between any two points of the circuit and the transmitted power of which does not exceed 150 watts. When operated at less than 150 volts, no limit is placed on the capacity of the system. Any circuit which exceeds the above values used for information transport shall be treated as a supply circuit and must meet the supply requirements for the voltage involved.

(2) Fiber optic circuits transmitting light for communication purposes (see definition, Rule 20.4 ).

Note: Information systems including, but not limited to, telephone, railroad–signal, data, clock, fire or police alarms, cable television and other systems conforming with the above are included in this classification.

C. Railway Signal Circuits mean 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.

(1) Circuits which operate at less than 400 volts to ground are considered as communication (Class C) circuits and shall be so classified and treated provided that, if the voltage exceeds 150 volts between conductors the power transmitted shall not exceed 150 watts. Where all circuits of a line are owned and operated by one utility, the voltage between conductors carrying in excess of 150 watts may be increased to not more than 250 volts and the signal circuits may be considered as communication (Class C) circuits.

(2) All railway signal circuits which do not meet the requirements above shall be treated as supply circuits of corresponding voltage.

D. Supply Circuits mean those circuits which are used for transmitting a supply of electrical energy.

(1) Class E circuits include constant potential alternating or direct current circuits of 300,000 volts or more between any two conductors.

(2) Class H circuits include the following:

Constant potential alternating current circuits of 5,000 volts or more but less than 300,000 volts between any two conductors.

Constant potential alternating current circuits of 2,900 volts or more but less than 174,000 volts between any conductor and ground.

Constant potential direct current circuits exceeding 750 volts but less than 150,000 volts between any conductor and ground.

Constant current circuits of 7.5 amperes or less supplied from transformers or devices having a normal full–load output voltage of 5,000 volts or more.

Constant current circuits of more than 7.5 amperes supplied from transformers or devices having an open–circuit voltage of 2,900 volts or more.

(3) Class L circuits include the following:

Constant potential alternating or direct current supply circuits of lower voltage than Class H.

Constant current circuits of 7.5 amperes or less supplied from transformers or devices having a normal full–load output
voltage less than 5,000 volts.

Constant current circuits of more than 7.5 amperes supplied from transformers or devices having an open–circuit output voltage less than 2,900 volts.

E. Class T Circuits mean trolley contact conductors, feeder wires and other conductors metallically connected to such contact conductors, used in electric railway or trolley operation. These Class T circuits are supply circuits, further classified as Class L or Class H depending upon the voltage and nature of current used (See Rule 20.6–D ).