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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