Building Electrical Capacity Screener

How it’s calculated. The stack below is rebuilt on every change; each line names the section it comes from (2023 NEC).

What the model assumes, and where each number comes from.

• General lighting — floor area × the Table 220.12 unit load for the occupancy you choose (2023 NEC; office 1.3, retail 1.9, restaurant 1.5, warehouse 1.2, manufacturing 2.2, health care 1.6, hotel 1.7, school 1.5, religious 2.2, parking garage 0.3 VA/ft² — the full non-dwelling table is in the drop-down). The 220.42 demand factors apply to hospitals (first 50 kVA at 40%, rest 20%), hotels/motels (first 20 kVA at 60%, next 80 kVA at 50%, rest 35%) and storage warehouses (first 12.5 kVA at 100%, rest 50%); 220.42 excludes areas where all lighting is on at once, which the screener cannot see. Lighting is carried at 125% as a continuous load (230.42(A)(1)).
• Receptacles — 180 VA per yoke (220.14(I)) when you enter a count, with Table 220.44 on that yoke load (the first 10 kVA at 100%, the remainder at 50%). Banks and office buildings take the larger of the yoke load after demand factors and 1 VA/ft² (220.14(K)), so the 1 VA/ft² figure is never reduced; with no count an office is screened at 1 VA/ft² at 100%. For other occupancies with no count, 1 VA/ft² stands in for the unknown yoke load as a disclosed screening floor and Table 220.44 applies to it.
• Sign outlet — 1,200 VA minimum at a grade-level public entrance (220.14(F), 600.5(A)), continuous (600.5(B)), so 1,500 VA. Untick it for a building with no public entrance.
• Existing HVAC — your nameplate tonnage × 1,400 VA per ton. The 1,400 VA/ton is an AES screening figure adopted 5 September 2026: ASHRAE 90.1-2019 Table 6.8.1-1 sets roughly 11 EER as the minimum for 135–240 kBtu/h air-cooled units (12 ÷ 11 = 1.09 kW/ton for compressor and condenser fans), plus a 0.13 kW/ton supply-fan allowance, at 0.87 power factor. With no tonnage entered the screener estimates it from floor area at an occupancy-specific square-feet-per-ton figure (office 350, retail 300, restaurant 150, clinic 275, hotel 400 — the hot-dry-climate end of the ASHRAE cooling-load check-figure ranges, AES screening figures adopted 5 September 2026); warehouses and parking are treated as unconditioned until you enter a tonnage. Enter the real tonnage — it replaces both figures.
• Kitchen equipment — Table 220.56 demand: 1–2 units 100%, 3 units 90%, 4 units 80%, 5 units 70%, 6 or more 65%, and never less than the two largest units (assumed equal when you do not enter them). Power factor 1.0.
• EV charging — each charger at the larger of 7,200 W and its nameplate (220.57), carried at 125% because EVSE is a continuous load (625.41). With an energy management system, the EVEMS setpoint is the load (625.42), still at 125%. Level 2 default 7.2 kW, DC fast charger default 150 kW — both replaceable.
• Largest motor — 25% of the single largest motor or compressor load, once (430.24, 440.33): the proposed load when you flag it as a motor or enter it in tons, otherwise the largest existing HVAC unit you enter (default: the smaller of the total tonnage and 10 tons, a screening default).
• Amps and sizes — VA ÷ (V × √3) for three-phase, VA ÷ V for single-phase. The next standard service is the panel-schedule ratings list (60–600 A) continued with the common switchboard ratings 800–4,000 A; 120/240 V single-phase stops at 600 A and larger loads are re-screened three-phase. The transformer is the next standard kVA (the Transformer Sizing calculator’s lists). Above 4,000 A at 480 V — about 3,300 kVA, the same ceiling in kVA — no secondary service is plausible.
• The permit record — read from our saved copy of the public record for the parcel (never a live city or county request). Only a permit whose recorded status is a final (“Complete”, “Final”, “C of O” and the rest of the shared vocabulary) can show a service size; an issued permit is “permitted, completion not confirmed”. The amperage is read out of the permit’s own wording (“upgrade to 1200 amp”, “new 800A 480/277V service”) and compared at the voltage the permit states, or at yours if it states none. A permit shows what was permitted, never what exists.
• Floor area and year — the Pima County Assessor’s current building cards, summed per parcel (the figure the parcel’s own report prints), from a snapshot the page names. No area on the card and none typed = no screening.

Not modelled: show-window and track lighting adders (220.14(G), 220.43), noncoincident heating vs cooling (220.60 — enter the larger), power factor below 1.0 on kW entries, harmonic neutral loading, and feeder-level detail. All of that is what the paid review is for.

Section numbers follow the 2023 NEC; the edition adopted by your jurisdiction governs. Screening figures dated 5 September 2026.