Example D5(a) Multifamily Dwelling Served

at 208Y/120 Volts, Three Phase

All conditions and calculations are the same as for the multifamily dwelling

[Example D4(a)] served at 120/240 V, single phase except as follows:

Service to each dwelling unit would be two phase legs and neutral.

Minimum Number of Branch Circuits Required for Each Dwelling

Unit (see 210.11)

Range Circuit: 8000 VA ÷ 208 V = 38 A or a circuit of two 8 AWG

conductors and one 10 AWG conductor in accordance with 210.19(A)(3)

Minimum Size Feeder Required for Each Dwelling Unit (see 215.2)

For 120/208-V, 3-wire system (without ranges),

Net calculated load of 3882 VA ÷ 2 legs ÷ 120 V/leg = 16 A

For 120/208-V, 3-wire system (with ranges),

Net calculated load (range) of 8000 VA ÷ 208 V = 39 A

Total load (range + lighting) = 38.5 A + 16.2 A = 54.7 A

Feeder neutral: (range) of 8000 VA × 70% = 5600 VA ÷ 208 V = 27 A

Total load: (range + lighting) = 27 A + 16 A = 43 A

Minimum Size Feeders Required from Service Equipment to Meter

Bank (For 20 Dwelling Units — 10 with Ranges)

For 208Y/120-V, 3-phase, 4-wire system,

Ranges: Maximum number between any two phase legs = 4

2 × 4 = 8.

Table 220.55 demand = 23,000 VA

Per phase demand = 23,000 VA ÷ 2 = 11,500 VA

Equivalent 3-phase load = 34,500 VA

Net Calculated Load (total):

40,590 VA + 34,500 VA = 75,090 VA

75,090 VA ÷ (208 V)(1.732) = 208 A

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