MikeHolt_Section07_Commercial Calcs

Unit 11: Commercial Calculations

NEC Article 220, 430, 440, 550, 551, 555, 630, Tables 220.12, 220.42

  • With individual branch circuits & feeders for continuous loads, use a 125% multiplier for ungrounded conductors
  • Neutral conductor sized to 100% of continuous/non-continuous loads for branch circuits & feeders when not connected to over-current protection device
  • General Lighting
    • Table 220.12
    • Table 220.42
    • General lighting unit load VA per sq ft (table 220.12) is reduced according to demand factors listed in table 220.42.
    • Hospitals
      • 1st 50,000 VA at 40%
      • Remaining VA at 20%
    • Hotel/Motel Guest Rooms
      • 1st 20,000 VA at 50%
      • Next 80,000 VA at 40%
      • Remaining VA at 30%
    • Warehouses
      • 1st 12,500 VA at 100%
      • Remaining VA at 50%
    • Feeder/Service General Lighting Loads without a demand factor is calculated with a 100% demand factor
      • Lighting loads listed in Table 220.12 are minimums.  If actual lighting load is known & larger, use this instead
    • Commercial Building Sign
      • 220.14(F)
      • 600.5
      • Each commercial property must have one 20A branch circuit for a sign
        • Must be a minimum of 1200 VA
    • Show-Window Lighting
      • 220.14(G)
      • Feeder/Service demand load must be 200 VA per linear ft
      • assume continuous load
  • Multi-Outlet Receptacles
    •  220.14(H)
    • Must be calculated according to one of the following:
    • Each 5 ft, or fraction of, is equal to 180 VA
    • If simultaneous use, each 1 ft, or fraction of, equals 180 VA
  • General-use Receptacles
    •  220.14(I)
    • 220.44
    • 180 VA per yoke
      • 1 yoke is 1 mounted standard outlet bracket with any number of receptacles
    • Receptacle number permitted per circuit
      •  depends on circuit rating
      • Calculated by circuit VA rating ÷ 180 VA for each yoke
  •  Receptacle Demand Load
    • 220.44, pg 70-72
    • Not considered continuous loads
    • 1st 10 kVA at 100%
    • Remaining kVA at 50%
    • Some confusing text here, see MH-pg 498, 220.14(I)&(H), 220.42, 220.44
  • Banks and offices_Receptacle Demand Load
    • 220.14(I)
    • Table 220.44
    • 220.14(K)(2)
    • Larger calculation of the following:
      • Determine the receptacle demand load at 180 VA per yoke (when receptacle count is known), than apply demand factor from table 220.44, or
      • Determine the receptacle demand load at 1 VA per sq ft (when receptacle count is unknown)
  • Manufactured Home Parks
    • Table 550.31
      • Sizing park service demand load to larger of 16000 VA for each lot, or
    • 550.18
      • size the demand load for each lot
    • 550.33(B) and 310.15(B)(7)
      • Also permitted to size service/feeder conductors to individual home
    • Demand Load = VA * Number of Sites * Demand Factor
    • I = VA ÷ E
  • Recreational Vehicle Parks
    • 551.71
    • Table 551.73(A)
    • 12000 VA for 50A, 120/240V receptacle, sites
    • 3600 VA for 20A & 30A, 120V receptacle, sites
    • 2400 VA for 20A, 120V receptacle, sites
    • 600 VA for 20A, 120V receptacle, tent sites
    • I = VA / E
  • Marinas
    • Table 555.12
    • Demand factor based on number of receptacle on feeder
    • Receptacles must be balanced between phases
    • Demand Load per Line = Connected Load per Line * Demand Factor
  • New Restaurant Feeder/Service Load Optional Method Calculation
    • Table 220.88 + Notes
    • Must have electric heating &/or air-conditioning
    • Step 01: Determine the Total Connected Load
      • Add all loads nameplate ratings at 100%
        • Include both heating and air-conditioning
    • Step 02: Apply demand factors from table 220.88 to Step 01-total connected load
    • I = VA ÷ (E * 1.732)
  • Welders

    • Arc Welders
      • Supply Conductors ampacity
        • Single welder
          • Table 630.11(A)
          • Must have ampacity not less than welder nameplate rating
          • If nameplate unavailable
            • must have ampacity not less than rated primary current adjusted by table 630.11(A) multiplier, based on welder duty cycle
          • Demand Load = Primary Rating * Multiplier (Table 630.11(A))
        • Group of Welders
          • 630.11(B)
          • Must have feeder conductor minimum ampacity not less than the sum of currents determined in 630.00(A), based on:
            • 100% of 2 largest welders
            • 85% of the 3rd largest
            • 70% for the 4th largest
            • 60% for remaining welders
          • Demand Load = Primary Rating * Multiplier (Table 630.11(A)) * Welder % (630.11(B)
      • Over-current Protection
        • 630.12(A)
        • 630.12(B)
        • 240.4(G)
        • Each welder must be protected to not more than 200% of maximum rated supply current
        • Conductors must be protected to not more than 200% of conductor rating
        • If the calculated over-current protection value doesn’t correspond to the standard in 240.6(A), the next higher standard is permitted.
        • Sec. 240.4(D) does not apply to electric welders, they’re specified in 240.4(G)
      • Disconnecting Means
        • 630.13
        • Required for each welder not equipped with an integral disconnect
    • Resistance, Varied-Duty Cycle, Welders
      • Supply Conductors ampacity
        • Single welder
          • Table 630.31(A)(1)
          • Table 630.31(A)(2)
          • Must not be less than 70% of the rated primary current for Seam & Auto-fed welders
          • Must not be less than 50% of the rated primary current for manually-operated welders
          • Supply conductor ampacity for welders with a specific duty cycle & non-varying current levels must have ampacity not less than rated primary current adjusted by table 630.31(A)(2) multiplier, based on welder duty cycle
          • Demand Load = Primary Rating * Multiplier (Table 630.31(A)(2))
        • Group of Welders
          • 630.31(B)
          • Must have feeder conductor ampacity not less than the sum of value determined in 630.31(A)(2) for the largest welder in the group.
            • plus 60% for remaining welders
          • Demand Load = Primary Rating * Multiplier (Table 630.31(A)(2)) * Welder % (630.31(B)
        • Over-current Protection
          • 630.32(A)
          • 630.32(B)
          • 240.6(A)
          • Each welder must be protected to not more than 300% of maximum rated supply current
          • Branch-circuit conductors must be rated not more than 300% of conductor rating
          • If the calculated over-current protection value doesn’t correspond to the standard in 240.6(A), the next higher standard is permitted.
        • Disconnecting Means
          • 630.33
          • Switch or CB is required to disconnect each welder from the supply circuit
    • DO EXAMPLES PG 511-513
  • Schools
    • Optional Method Load Calculations
      • Table 220.86
      • Calculate service load in accordance with this table