This calculation is a continuation of the previous example. The single family dwelling has the same area and household appliances. The number of dwelling units however is increased to 40 units.
Each dwelling unit has floor area of 90 square meters and with typical household appliances including one 8-kW electric range and one 1-Hp room air-conditioning unit.
Methodology
The methodology for this calculation is similar to this article. The only difference is that the supply voltage is now three (3) phase.
Note: This sample calculation is Example D8 in the Philippine Electrical Code 2017 Edition.
Calculation
| Description | Value |
|---|---|
| Multifamily dwelling having 40 dwelling units with individual feeder to each dwelling unit. Each dwelling unit has floor area of 90 square meters and with typical household appliances including one 8-kW electric range and one 1-Hp room air-conditioning unit. | |
| 1. Total Load for Each Dwelling Unit: | |
| (A) General Lighting and ConvenienceReceptacle-Load: [See Table 2.20.2.3] Note: Table 2.2. 1.3 includes the receptacle outlets of 20-ampere or less. |
|
| 90 m² x 24 VA/m² = Provide two 20-ampere lighting and convenience receptacle circuits. |
2160 VA |
| (B) Small Appliance Load: [See Sections 2.10.1.11(C)(1) and 2.20.3.13(A)] | |
| One 20-ampere @ 1500 volt-amperes = Provide one 20-ampere small appliance So circuit. |
1500 VA |
| (C) Laundry Circuit Load: [See Sections 2.10.1.1) (2) and 2.20.3.13(B)] | |
| One 20-ampere @ 1500 volt-amperes = Provide one 20-ampere laundry circuit. |
1500 VA |
| Subtotal | 5160 VA |
| Application of DemandFactors: (See Table 2.20.3.3) First 3000 volt-amperes @ 100% D.F, = |
3000 VA |
| Remainder @ 35% D.F. (2160 VA x 0.35) = | 756 VA |
| D) Other Loads: : | |
| One 8-kW electric range @ 80% D.F. (See Table 2.20.3.16) = Provide one 40-ampere electric range circuit |
6400 VA |
| One 1-Hp room acu, 8 A x 230 V @ 100% D.F. = Provide one 20-ampere room acu circuit. |
1840 VA |
| Total Net Computed Load (For Each Dwelling Unit) = | 11996 VA |
| 2. Circuit Requirement for Each Dwelling Unit: | |
| Use five 20-ampere 2-wire branch circuits and one 40-ampere 2-wire branch circuit | |
| 3. Service Feeder Conductors for Each Dwelling Unit: | |
| Total Full Load Current: (See Sections 4.30.2.4 and 4.40.1.7) | |
| [11996 VA + 25% (1840 VA) / 230 V] = | 54 Amperes |
|
Use two 22 mm² THW wires Note: See Section 2.20.2.3 for the conductor and overcurrent protection ampere rating. |
|
| 4. Service Equipment for Each Dwelling Unit: | |
| (A) Maximum Current Rating of Protective Device, with: (See Section 4.30.4.2 and Table 4.30.4.2) | |
| (1) Nontime Delay Fuse. | |
| [3000 VA +756 VA + 6 400 VA + VA) / 230V = | 68 Amperes |
| (2) Inverse Time Circuit Breaker. | |
| [3000 VA + 756 VA + 6400 VA + 2500; VA)] / 230 V = | 64 Amperes |
|
(B) Service Equipment Rating, Use one 100-ampere, 1PST, 250-volt safety switch with one 100-ampere fuse; or use one 100. trip, 1-pole, 240-volt molded case circuit bre. Section 2.40.1.6). |
|
| 5. Total Load for 40 Dwelling Units: [See Section 2.20.4.5(A)] | |
| General lighting and convenience receptacle load, 2160 VA x 40 = | 86,400 VA |
| Small appliance load, 1500 VA x 12 = | 60,000 VA |
| Laundry circuit load, 1500 VA x 12 = | 60,000 VA |
| One 8-kW electric range, 8000 VA x 12 = | 320,000 VA |
| One 1-Hp room acu, 1840 VA x 12 = | 73,600 VA |
| Total Computed Load | 600,000 VA |
| Application of Demand Factors: (See Table 2.20.4.5) 600,000 volt-amperes x 0.28 = | 73,800 VA |
| 6. Main Service Entrance Conductors: | |
| Total Full Load Current: 168,000 volt-amperes / (400 V)(1.732) = |
242 Amperes |
| Use three 200 mm² + one 200 mm² (neutral) THW Note:See Section 3.10.1.4 for conductors in parallel |
|
| 7. Main Service Equipment: | |
| (A) Maximum Current Rating. 168,000 volt-amperes / [(400 V)(1.732)] = |
242 Amperes |
| (B) Service Equipment Rating. (1) Use one 400-ampere, 3-pole, 415-volt safety switch with three 300-ampere fuses; or (2) Use one 250-ampere trip, 3-pole, 415-volt molded case circuit breaker (see Section 2.40.2.3). |
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