Wiring Design Examples

Branch Circuit Required

For small single-family dwelling unit having a floor area of not more than 50 square meters with load not exceeding 3,680 VA, the code permits the use of only 1-circuit as illustrated in Example D1 [See section 2.10.1.11(d)]. For the minimum number of branch circuit required, see Section 2.10.1.11(a) to (c).

Feeder of Service Load Calculation

Feeder or service load calculation in the example follows the method provided in the Part 2.20.2. The optional calculations method of Part 2.20.3 is also illustrated [See Example D4].

Selection of Conductors

For conductor types and sizes, refer to 0V through 2000V ampacity tables of Article 3.10 and Section 3.10.1.15 that pertains to such tables. (Tables 3.10.1.16 through 3.10.1.21 and the Notes that pertain to such tables.) For the minimum size of service entrance conductor, see Section 2.30.4.3. Conductor ampacities given in these examples for copper wires are based on ambient air temperature of 30 degrees Celcius except specified otherwise. In the examples given, conductors are selected such that their ampacities are atleast 125% of the continuous current through the conductor. Voltage drops, however, have not been considered on the selection.

Selection of Overcurrent Protection

Standard ratings fuses and inverse time circuit breakers are listed in Section 2.40.1.6. Maximum rating or setting of motor branch circuit short-circuit and ground-fault protective device are given in Table 4.30.14.6.

Voltage

For uniform application of the provisions of Articles 2.10, 2.15 and 2.20, a nominal voltage of 230 V is used in computing the ampere load on the conductor.

Grounding

In conformance to the provisions of the code on grounding, illustrations herein show partial grounding requirements. Feeder and circuit wires indicated in the examples are for phase wires only. For sizes of grounding conductors and electrodes, see Tables 2.50.3.17 and 2.50.6.13 respectively.

Allowance for Future Expansion

It is advisable to use larger service conductors and the corresponding overcurrent protective devices to accommodate future loads depending on the anticipated expansion.