Change List for this Rule

 

General Order 128


Section III

 

Requirements for Supply Systems

36.3     Neutral Conductors

 

A.    Material

Neutral conductors shall be of suitable corrosion–resisting material.

 

B.    Size

Neutral conductors shall be of the size required to carry the estimated current to which they may be subjected. As a minimum they shall have an ampacity of not less than one–quarter (25%) that of the largest related phase conductor, provided that the short time ampacity of the neutral conductor is maintained. The short time ampacity of a neutral conductor is either: the current that a non–insulated conductor can carry for the time which the current flows without annealing, melting, or separating; or the current that an insulated conductor can carry for the time that the current flows without damaging the insulation. In no case shall neutral conductors be smaller than the equivalent of #6 AWG copper.

No neutral conductor need have a greater ampacity than either the phase conductor which would supply the ground current, or the maximum current which can flow through the neutral conductor to the ground or electrode of the neutral grid system. The neutral conductor shall have a short time ampacity adequate for the fault current which can flow in the neutral conductor for the operating time of the system protective device. If this value cannot be readily determined, the continuous ampacity of the neutral conductor shall not be less than the full load continuous current of the system supply transformers or other source of supply. In no case shall the neutral conductor have less ampacity than #6 AWG copper.

Note:    Revised January 19, 1994 by Resolution SU–25.