Forums » Electrical Engineering

Neutral conductor

    • 43 posts
    April 24, 2019 11:02 PM PDT
    I am looking to choose the neutral conductor size.
    Some colleague are asking that neutral conductor should be the same size as phase conductor.
    Since neutral conductor is only carrying unbalanced current, why it should be same size?
    What is regulation for this?
    This post was edited by Rajish Rakish at April 24, 2019 11:03 PM PDT
    • 157 posts
    April 25, 2019 2:36 AM PDT

    It depends on whether the neutral is part of a feeder or service conductors.  The neutral does not need to be the same size as the phase conductors if the calculated load is lower however, the service neutral cannot be smaller than than what Table 250.102(C)(1) requires.  

     

    If this neutral is part of a feeder then it cannot be smaller than the requirements of T. 250.122

     

    230.23(C) Grounded Conductors. The grounded conductor shall
    not be less than the minimum size as required by 250.24(C).

     

    250.24(C)(1) Sizing for a Single Raceway or Cable. The grounded
    conductor shall not be smaller than specified in Table
    250.102(C)(1).

     

    215(A)(2) Grounded Conductor. The size of the feeder circuit
    grounded conductor shall not be smaller than that required by
    250.122, except that 250.122(F) shall not apply where grounded
    conductors are run in parallel.

    • 72 posts
    April 25, 2019 6:52 AM PDT
    Dennis Alwon said:

    It depends on whether the neutral is part of a feeder or service conductors.  The neutral does not need to be the same size as the phase conductors if the calculated load is lower however, the service neutral cannot be smaller than than what Table 250.102(C)(1) requires.  

     

    If this neutral is part of a feeder then it cannot be smaller than the requirements of T. 250.122

     

    230.23(C) Grounded Conductors. The grounded conductor shall
    not be less than the minimum size as required by 250.24(C).

     

    250.24(C)(1) Sizing for a Single Raceway or Cable. The grounded
    conductor shall not be smaller than specified in Table
    250.102(C)(1).

     

    215(A)(2) Grounded Conductor. The size of the feeder circuit
    grounded conductor shall not be smaller than that required by
    250.122, except that 250.122(F) shall not apply where grounded
    conductors are run in parallel.

    The grounded neutral conductor of a 4-wire, 3-phase system supplying nonlinear loads must be the same size as the ungrounded phase conductors?

    • 157 posts
    April 25, 2019 9:29 AM PDT
    Reynaldo Danilo said:
    Dennis Alwon said:

    It depends on whether the neutral is part of a feeder or service conductors.  The neutral does not need to be the same size as the phase conductors if the calculated load is lower however, the service neutral cannot be smaller than than what Table 250.102(C)(1) requires.  

     

    If this neutral is part of a feeder then it cannot be smaller than the requirements of T. 250.122

     

    230.23(C) Grounded Conductors. The grounded conductor shall
    not be less than the minimum size as required by 250.24(C).

     

    250.24(C)(1) Sizing for a Single Raceway or Cable. The grounded
    conductor shall not be smaller than specified in Table
    250.102(C)(1).

     

    215(A)(2) Grounded Conductor. The size of the feeder circuit
    grounded conductor shall not be smaller than that required by
    250.122, except that 250.122(F) shall not apply where grounded
    conductors are run in parallel.

    The grounded neutral conductor of a 4-wire, 3-phase system supplying nonlinear loads must be the same size as the ungrounded phase conductors?

     

     

    Actually in some cases it may be larger than the phase conductors.  I only gave the smallest the conductor can be and that always depends on the calculated load.  But, of course, if you have lots of non linear then the neutral may be required to be larger.  I have seen specs by an engineer where the neutral was required to be twice as large as the phase conductors.

     

    • 103 posts
    May 17, 2019 7:33 AM PDT

    Besides the normal load current it must be large enough to survive any fault current, as it provides part of the path back to the source.

    • 157 posts
    May 17, 2019 8:51 AM PDT
    Steve Ward said:

    Besides the normal load current it must be large enough to survive any fault current, as it provides part of the path back to the source.

    And that is why it cannot be smaller than the equipment grounding conductor.