Basic Calculation of Neutral Loads
The basic calculation for the feeder or service neutral load according to the Philippine Electrical Code Section 2.20.3.22(A) is the maximum unbalance net load calculated between the neutral and any one ungrounded conductor.
Section 2.20.3.22 describes the basis for calculating the neutral load of feeders or services as the maximum unbalanced load that can occur between the neutral and any other ungrounded conductor. For a household electric range or clothes dryer, the maximum unbalanced load for a single-phase feeder or service may be assumed to be 70 percent, so the neutral can be sized on that basis. If the unbalanced load exceeds 200 amperes, Section 2.20.3.22(B)) permits the reduction of the feeder neutral conductor size under specific conditions of use. However, Section 2.20.3.22(C)(1) and (C)(2) cite a circuit arrangement and a load characteristic as applications where the capacity of a neutral or grounded conductor of a feeder or service is not permitted to be reduced.
The neutral is considered to be a current-carrying conductor if the loads may have harmonic currents in the neutral that may exceed the load current in the ungrounded conductors in accordance with 3.10.1.15 (B)(5)(c).
Neutral Conductor Size Reduction
The neutral conductor for a service or feeder shall be permitted to have a demand factor of 70 percent applied to the value determined by the basic calculation except when that portion consisting of nonlinear loads is supplied from a 4- wire, wye-connected, 3-phase system