Wiring Design Examples

Note: This is work in progress.

This part contains wiring design examples to illustrate the application of some of the provisions of this Code. The examples illustrated herein, although not exhaustive, cover several scenarios which are typically encountered by the practitioners. The examples illustrates how to determine the size of branch circuits, feeders and services.

Typical single-family and multi-family dwelling units of different demand load are presented considering the single phase and three-phase service systems. Single and multiple motor examples illustrate how to size the branch circuit conductors and overload protection. Several overload protection schemes are presented. Examples on system with fire pump to illustrate its special requirement and a system with voltage regulator are also included.

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]. For the minimum number of branch circuit required, see Section 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 that pertains to such tables. (Tables through and the Notes that pertain to such tables.) For the minimum size of service entrance conductor, see Section 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 Maximum rating or setting of motor branch circuit short-circuit and ground-fault protective device are given in Table


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.


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 and 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.

Single Family Dwelling Unit, Up to 50 square meters Floor Area with Load not Exceeding 3,680 VA. See Example…

Single Family Dwelling Unit, Up to 150 Square Meters Floor Area. (Not more than six circuits.)

Single Family Dwelling Unit, Up to 150 Square Meters Floor Area. (More than six circuits.)

Single Family Dwelling Unit, Up to 150 Square Meters Floor Area. (Optional Calculation)

Single Family Dwelling Unit, More than 150 Square Meters Floor Area, 230V Single Phase service.

Single Family Dwelling Unit, More than 150 Square Meters Floor Area, 400/230V Three-Phase 4-Wire Service.

MultiFamily Dwelling Unit, 230V Single Phase ServiceĀ 

MultiFamily Dwelling Unit, 400/230V Three-Phase 4-Wire ServiceĀ 

Motors, Motor Circuits and Controller, Single Motor

Motors, Motor Circuits and Controller, Multiple Motors

Voltage Regulators, Single Phase, 60 Hz, 165-280V Input, 230V output VR

Voltage Regulators, Three Phase, 60 Hz, 350-530V Input, 230V output VR

Feeder Ampacity Determination for Generator Field Control

Feeder Ampacity Determination for Adjustable Speed Drive Control

Mobile Home, Single Phase, 2-wire Service

Park Trailer, Single Phase 2-Wire Service

Store Building

Industrial Feeders in a Common Raceway

Industrial Feeders in a Common Raceway

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