Example No. D3 Store Building
A store 50 ft. by 60 ft., or 3000 sq. ft., has 30 ft. of show window. There are a total of 80 duplex receptacles. The service is 120/240-volt, single-phase 3-wire service. Actual connected lighting load, 8500 volt-amperes.
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Calculated Load (See 220.40) |
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Noncontinuous Loads |
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Receptacle Load (see 220.44) |
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80 receptacles at 180 VA |
14,400 volt-amperes |
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10,000 VA at 100% |
10,000 volt-amperes |
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14,400 VA - 10,000 VA = 4400 VA at 50% |
2200 volt-amperes |
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Subtotal |
12,200 volt-amperes |
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Continuous Loads |
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General Lighting[*] |
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3000 sq. ft. at 3 volt-amperes per sq. ft. |
9000 volt-amperes |
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Show Window Lighting Load |
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30 ft. at 200 volt-amperes per foot |
6000 volt-amperes |
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Outside sign circuit 1200 volt- amperes [see 220.14(F)] |
1200 volt-amperes |
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Subtotal |
16,200 volt-amperes |
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Subtotal from noncontinuous |
12,200 volt-amperes |
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Subtotal noncontinuous loads plus continuous loads |
28,400 volt-amperes |
[*] In the example, 125 percent of the actual connected lighting load (8500 VA x 1.25 = 10,625 VA) is less than 125 percent of the load from Table 220.12, so the minimum lighting load from Table 220.12 is used in the calculation. Had the actual lighting load been greater than the value calculated from Table 220.12, 125 percent of the actual connected lighting load would have been used.
Minimum Number of Branch Circuits Required
General Lighting: Branch circuits need only be installed to supply the actual connected load [see 221.11(B)].
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8500 VA x 1.25 = 10,625 volt-amperes |
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10,625 volt-amperes ÷ 240 volts |
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= 44 amperes for 3-wire, 120/240 V |
The lighting load would be permitted to be served by 2-wire or 3-wire, 15- or 20-ampere circuits with combined capacity equal to 44 amperes or greater for 3-wire circuits or 88 amperes or greater for 2-wire circuits. The feeder capacity as well as the number of branch-circuit positions available for lighting circuits in the panelboard must reflect the full calculated load of 9000 VA x 1.25 = 11,250 volt-amperes.
Show Window
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6,000 VA x 1.25 = 7500 VA |
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7500 volt-amperes ÷ 240 volts |
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= 31 amperes for 3-wire, 120/240V |
The show window lighting is permitted to be served by 2-wire or 3-wire circuits with a capacity equal to 31 amperes or greater for 3-wire circuits or 62 amperes or greater for 2-wire circuits.
Receptacles required by 210.62 are assumed to be included in the receptacle load above if these receptacles do not supply the show window lighting load.
Receptacles
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Receptacle Load: |
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14,400 volt-amperes ÷ 240 volts |
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= 60 amperes for 3-wire, 120/240 V |
The receptacle load would be permitted to be served by 2-wire or 3-wire circuits with a capacity equal to 60 amperes or greater for 3-wire circuits or 120 amperes or greater for 2-wire circuits.
Minimum Size Feeder (or Service) Overcurrent Protection [See 215.3 or Section 230.90]
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Subtotal noncontinuous loads |
12,200 volt-amperes |
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Subtotal continuous load @ 125% |
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16,200 VA x 1.25 |
20,250 volt-amperes |
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Total |
32,450 volt-amperes |
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32,450 VA ÷ 240 volts = 135 amperes |
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The next higher standard size is 150 amperes (See 240.6).
Minimum Size Feeder (or Service Conductors) Required [See 215.2, 230.42(A)]
For 120/240-volt, 3-wire system: 32,450 volt-amperes ÷ 240 volts = 135 amperes.
Service or feeder conductor is 1/0 Cu per 215.3 and Table 310.16 (with 75°C terminations).