2023 NEC Articles 215 and 220
A feeder or service has to be big enough for what the building will actually draw, and Article 220 is how the code says to count that. The method is short: list the loads, apply the unit loads and demand factors the code gives, add them up, convert to amperes, and then size the conductors and the protection. This lesson runs a small office through the whole method. The circuit-level rules are Lesson 3, conductor ampacity is Lesson 8, and motor and air-conditioning loads are Lesson 11. Local adoption governs which NEC edition applies (see Lesson 1).
The load of a feeder or service may not be less than the sum of the loads on the branch circuits it supplies, after any demand factors the code allows (2023 NEC 220.40). "Demand" is the fact that not every outlet runs at full power at the same moment, so the code lets you count a smaller number for large groups of the same kind of load. Article 220 gives you the minimum. A designer may always use more, and should where the real equipment is known.
Use the nominal voltages listed in 220.5(A) for these calculations: 120, 120/240, 208Y/120, 240, 480Y/277, and so on. Floor area for each floor comes from the outside dimensions of the building (220.5(C)), not the inside measurement of the rooms. Calculations may be rounded to the nearest whole ampere, dropping fractions below 0.5 (220.5(B)).
For a building that is not a dwelling, the minimum lighting load is the floor area times the unit load for the occupancy in Table 220.42(A), in the 2023 edition (older reference sheets may show Table 220.12, so check which edition a sheet describes). The unit loads are minimums based on an 80 percent power factor, and the code warns they might not give enough capacity for the installation planned. Motors rated less than 1/8 hp connected to a lighting circuit count as general lighting. Some rows, in VA per square foot:
| Occupancy | VA per sq ft |
|---|---|
| Office (banks count as office) | 1.3 |
| Retail (stores, barber shops, beauty parlors) | 1.9 |
| Restaurant (clubs count as restaurant) | 1.5 |
| School or university | 1.5 |
| Religious facility | 2.2 |
| Warehouse | 1.2 |
| Hotel or motel | 1.7 |
| Parking garage | 0.3 |
The table carries a note that matters more than any single row: the 125 percent multiplier for continuous loads is already included, so no additional multiplier is used with these unit loads. Lighting is normally a continuous load, and the table has already done that arithmetic for you. Multiplying by 1.25 a second time is one of the most common errors on a submitted calculation. Where the lighting is LED or uses ballasts or transformers, the load is based on the ampere rating of the unit, not the watts of the lamps (220.11(B)). A project designed to a local energy code may use the energy code values only with a power monitoring system and the other conditions in 220.42(B).
Outside dwellings, each receptacle outlet counts at least 180 VA per single or multiple receptacle on one yoke, so a duplex counts 180 VA, not 360 (220.14(I)). A single piece of equipment made up of four or more receptacles counts at 90 VA per receptacle. Fixed multioutlet assemblies count 180 VA per 5 feet where appliances are unlikely to run together, or 180 VA per foot where they are likely to (220.14(H)). Other outlets not covered elsewhere count 180 VA each (220.14(K)).
For the feeder, receptacle loads may take the demand in Table 220.47: the first 10 kVA at 100 percent and the remainder at 50 percent (220.47). Office buildings have a floor: the receptacle load is the larger of the outlet count after demand or 1 VA per square foot (220.43 for feeders, 220.14(J) for the branch-circuit count). That floor protects an open-plan office wired sparsely today and furnished densely later.
Each sign or outline lighting outlet counts at least 1,200 VA for each required sign branch circuit (220.14(F)). Section 600.5(A) requires an outlet at each entrance to each tenant space that is accessible to pedestrians, on a circuit of at least 20 amperes that serves nothing else. Show windows count either by the outlets in them or at 200 VA per linear foot of window (220.14(G)). A heavy-duty lampholder outlet counts at least 600 VA (220.14(E)), and a luminaire outlet counts at the maximum VA rating of the luminaire and its lamps (220.14(D)). Motor outlets are sized by the motor rules covered in Lesson 11 (220.14(C)).
A continuous load is one where the maximum current is expected to continue for 3 hours or more (Article 100). A feeder that supplies continuous loads, or a mix, must have conductor ampacity of at least the noncontinuous load plus 125 percent of the continuous load (215.2(A)(1)). The overcurrent device rating follows the same arithmetic (215.3). If the whole assembly, including the overcurrent devices, is listed for operation at 100 percent of its rating, the 125 percent step is not required. Separately, the conductor ampacity must still hold up after the ambient and bundling adjustments of 310.14 (215.2(A)(2), Lesson 8). Signs, parking lot lighting, and store lighting are the usual continuous loads. A receptacle circuit in an office is normally treated as noncontinuous.
An office of 3,000 square feet, measured on the outside, is served at 208Y/120 V three-phase. Lighting: 3,000 x 1.3 = 3,900 VA, with the 125 percent already inside. Receptacles: 60 yokes x 180 VA = 10,800 VA. Demand takes the first 10,000 VA at 100 percent and the remaining 800 VA at 50 percent, so 10,000 + 400 = 10,400 VA. The office floor is 1 VA x 3,000 = 3,000 VA, which is smaller, so 10,400 VA governs. One sign outlet is 1,200 VA, and because the sign runs 3 hours or more it is multiplied by 1.25 to get 1,500 VA. The total is 3,900 + 10,400 + 1,500 = 15,800 VA. At 208 V three-phase, the current is 15,800 / (1.732 x 208) = 43.9, which rounds to 44 A. This example counts only these three loads, so the feeder needs at least 44 A of conductor ampacity and an overcurrent device of at least 44 A, which is a 45 A breaker. Had the designer multiplied the lighting by 1.25 again, the total would have been 16,775 VA and 47 A, and the owner would have paid for the next size up for nothing.
Table 220.45 gives lighting demand only for a few occupancies. Warehouses take the first 12,500 VA at 100 percent and the rest at 50 percent. Hotels and motels take 60 percent of the first 20,000 VA, 50 percent up to 100,000 VA, and 35 percent beyond. Every other occupancy, offices and stores included, takes 100 percent. In hotel and motel guest rooms, the general-use receptacles and required lighting are inside the unit load and need no separate count (220.44). Loads that will not run together, such as heating and cooling, may be counted as the larger one only (220.60). Separate optional methods exist for multifamily, schools, and new restaurants (220.84, 220.86, 220.88). The authority having jurisdiction may require a feeder diagram showing the area served, the load before and after demand, the demand factors, and the conductor size (215.5).
In the field
A GCHS estimator reviews the panel schedule for a converted church annex that is becoming a small health clinic. The calculation lists 2,800 square feet and the office row, but the plans show two floors of 1,550 square feet each measured on the outside, which is 3,100 square feet, and the occupancy is a health care clinic at 1.6 VA per square foot. The reviewer checks the floor area against the outside dimensions on every floor, confirms the occupancy row, looks for a second 125 percent on the lighting, and counts receptacle yokes on the plans against the count in the calculation. A panel sized from the light count alone comes up short once the real receptacles and the exterior sign are added.
1. A new one-story Group B office building has 8,000 square feet measured on the outside. What is the minimum general lighting load under 2023 NEC Table 220.42(A)?
2. A 4,500 square foot retail store is being fit out on a strip center service. What is its minimum general lighting load under 2023 NEC Table 220.42(A)?
3. A 20,000 square foot storage warehouse at 1.2 VA per square foot has 24,000 VA of general lighting load. What lighting load may the feeder calculation use after Table 220.45 demand for warehouses?
4. An open-plan Group B office has 6,000 square feet and 120 duplex receptacle yokes. What receptacle load does the feeder calculation use, after Table 220.47 demand and the office floor in 220.43?
5. A plan reviewer checks a 9,000 square foot office building that shows only 30 duplex receptacle yokes in the calculation. What receptacle load must the feeder calculation carry under 220.43?
6. A college computer lab has 22 feet of continuous fixed multioutlet assembly along its benches, where the appliances are likely to be used at the same time. What load does 220.14(H) assign to it?
7. A pedestrian entrance to a retail tenant space has a required sign outlet on its own 20 A circuit. What is the minimum load 220.14(F) assigns to that sign circuit, before any continuous-load multiplier?
8. A jewelry store has 12 feet of show window and the designer uses the linear foot option of 220.14(G). What load does the calculation include for the window?
9. A feeder to a lighting and equipment panel in a Group B building carries 40 A of noncontinuous load and 60 A of continuous load. The feeder assembly is not listed for 100 percent operation. What is the minimum conductor ampacity under 215.2(A)(1)?
10. The same feeder with 40 A noncontinuous and 60 A continuous load is protected by a breaker and enclosure assembly listed for operation at 100 percent of its rating. What is the minimum overcurrent device rating and conductor ampacity permitted by 215.3 and 215.2(A)(1)?
11. A calculation for a small office comes to 21,600 VA. What is the load current on a 208Y/120 V three-phase service, rounded to the nearest whole ampere under 220.5(B)?
12. GCHS is renovating a 3,200 square foot fellowship hall in a small church, measured on the outside. What minimum general lighting load applies under 2023 NEC Table 220.42(A)?
13. A designer submits a calculation for a 2,000 square foot bank branch using the office row of Table 220.42(A). Does the row match the occupancy, and what lighting load results?
14. A plan reviewer sees a lighting load of 3,000 sq ft x 1.3 VA x 1.25 = 4,875 VA for an office. What is wrong with the calculation under Table 220.42(A)?