Optional calculation method applies to a single dwelling unit, whether it is a separate building or located in a multifamily dwelling.
Philippine Electrical Coode, Article 2.20.4 permits optional calculations for feeder and service load calculations for dwelling units.
Conditions for Optional Calculations
This section applies to a dwelling unit if the following conditions are complied with:
- The total connected load served by a single 115/230-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater.
- The general calculated load shall be not less than 100 percent of the first 10 kVA plus 40 percent of the remainder loads
- 24VA/sq.m. for general lighting and general-use receptacles.
- 1500 VA load for each 20-ampere small-appliance branch circuit and each laundry branch circuit.
- Nameplate rating of all appliances that are fastened in place, permanently connected, or located to be on a specific circuit
Sample Calculation
A sample calculation has been provided in the Philippine Electrical Code 2017 Appendix D, Example D1.
| The dwelling has a floor area of 145 sq. m. It has the typical household appliances including one 8-kW electric range, two 1-Hp room air-conditioning unit, one 1.5-Hp room air-conditioning unit, and one 1-Hp water pump. | |
| Air Conditioning Load: (See Section 2.20.4.3) | |
| Two 1-Hp room air-conditioning unit, 8A x 230 V x 2 = | 3680 VA |
| One 1.5-Hp room air-conditioning unit, 10A x 230 V x 1 = | 2300 VA |
| Other Loads: | |
| General lighting and convenience receptacle load, 145 m² x 24 VA/m² = | 3480 VA |
| One 20-ampere small appliance circuit @ 1500 volt-amperes = | 1500 VA |
| One 20-ampere laundry circuit @ 1500 volt-amperes = | 1500 VA |
| One 8-kW electric range = | 8000 VA |
| One 1-Hp water pump, 8A x 230V = | 1840 VA |
| Total Other Loads: | 16320 VA |
| Application of Demand Factors (Other Loads): [See Section 2.20.4.3(C)] | |
| First 10 000 volt-amperes @ 100% D.F. = | 10000 VA |
| Remainder @ 40% D.F. = (6 320 VA x 0.40) = | 2528 VA |
| Total Net Computed Load = (3680 + 2300 + 10000 + 2528) = | 18508 VA |
Circuit Requirement:
Use eight 20-ampere 2-wire branch circuits and one 40-ampere 2-wire branch circuit.
Service Entrance Conductors:
Total Full Load Current: 18508 volt-amperes / 230V = 80 amperes
Use 2 x 38mm² THW wires.
Note 1: See Section 2.40.1.4 for the conductor and overcurrent protection ampere rating.
Note 2: See Section 2.30.2.3 for minimum service entrance conductor.
Service Equipment:
(A) Maximum Current Rating of Protective Device with (See Section 4.30.4.2 and Table 4.30.4)
(1) Nontime Delay Fuse.
[3 680 VA + 300% (2300 VA) + 10000 VA + 2528 VA] +230 V = 100 Amperes
(2) Inverse Time Circuit Breaker.
[3 680 VA + 250% (2300 VA) + 10000 VA + 2528 VA] +230 V = 95 Amperes
(B) Service Equipment Rating.
Use one 200-ampere, 1PST, 250-volt safety switch with one 125-ampere fuse (renewable); or use one 125-ampere trip, 1-pole, 240-volt molded case circuit breaker (see Section 2.40.1. 6).
