Methodology
Follow the following steps in the electrical calculation of multifamily dwelling.
- Calculate each dwelling unit like a single family dwelling. Service equipment and conductors will be selected like sngle family dwelling.
- The result of the single family dwelling will be multiplied with the number of units
- The resulting total load will be applied with a demand factor. The net calculated load will be used to select the service equipment and service conductor for the multifamily dwelling.
Note: This sample calculation is Example D7 in the Philippine Electrical Code 2017 Edition.
Description and Loads
Multifamily dwelling having 12 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.
Multifamily Dwelling Unit, 230 Volts Single Phase Service
| Description | Value |
|---|---|
| Multifamily dwelling having 12 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 12 Dwelling Units: [See Section 2.20.4.5(A)] | |
| General lighting and convenience receptacle load, 2160 VA x 12 = | 25,920 VA |
| Small appliance load, 1500 VA x 12 = | 18,000 VA |
| Laundry circuit load, 1500 VA x 12 = | 18,000 VA |
| One 8-kW electric range, 8000 VA x 12 = | 96,000 VA |
| One 1-Hp room acu, 1840 VA x 12 = | 22,080 VA |
| Total Computed Load | 180000 VA |
| Application of Demand Factors: (See Table 2.20.4.5) 180,000 volt-amperes x 0.41 = | 73,800 VA |
| 6. Main Service Entrance Conductors: | |
| Total Full Load Current: 73800 volt-amperes / 230 V = |
321 Amperes |
| Use two 325 mm² or two sets of two 100 mm² THW wires. Note:See Section 3.10.1.4 for conductors in parallel |
|
| 7. Main Service Equipment: | |
| (A) Maximum Current Rating. 73800 volt-amperes / 230 V = |
321 Amperes |
| (B) Service Equipment Rating. (1)Use one 600-ampere, 1PST, 250-volt safety switch with one 500-ampere fuse; or (2) Use one 500-ampere trip, enclosed molded case circuit breaker (see Section 2.40.2.3). |
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