Free NEC 220.84 Multifamily Load Calculator — Step-by-Step Feeder/Service Workflow

This article explains NEC 220 and Article 84 interpretation for multifamily load calculations and feeders. Step-by-step methodology, free calculator workflow, feeder and service sizing, demand factors, and documentation NFPA guidance

NEC 220.84 Multifamily Feeder/Service Load Calculator (kVA and A)

Number of dwelling units (qty)

Average dwelling unit floor area (ft²)

System line-to-line voltage (V)

System phase configuration Single-phase 3-wire Three-phase 4-wire

Advanced options

General lighting load density (VA/ft²)

General load demand factor above 10 kVA (%)

Small-appliance branch circuits per dwelling (qty)

Laundry branch circuits per dwelling (qty)

Load per small-appliance circuit (VA)

Load per laundry circuit (VA)

Total diversified cooking range load (kVA)

Total diversified dryer load (kVA)

Total cooling (A/C and heat pump) load (kVA)

Total electric space-heating load (kVA)

HVAC demand factor on larger of cooling or heating (%)

You can upload a data plate or single-line diagram photo to suggest typical values for the inputs.

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Enter the basic dwelling, area, and system data to compute the NEC 220.84 multifamily feeder/service load.

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Formulas and NEC 220.84 workflow used by this calculator

• Total floor area: Total_area (ft²) = Number_of_units × Average_unit_area (ft²)
• General lighting and receptacle load: General_lighting_VA = Total_area × VA_per_ft²
• Small-appliance load: SA_total_VA = Number_of_units × SA_circuits_per_unit × SA_VA_per_circuit
• Laundry load: Laundry_total_VA = Number_of_units × Laundry_circuits_per_unit × Laundry_VA_per_circuit
• Total general dwelling load before demand: General_total_VA = General_lighting_VA + SA_total_VA + Laundry_total_VA
• Demand per NEC 220.84 (first 10 kVA at 100%, remainder at demand factor): General_total_kVA = General_total_VA / 1000
  First_10_kVA = min(10, General_total_kVA)
  Remainder_kVA = max(0, General_total_kVA − 10)
  General_demand_kVA = First_10_kVA × 1.0 + Remainder_kVA × (General_remainder_demand_factor_percent / 100)
• Other loads (user already diversified per applicable NEC tables):
  Ranges_kVA = Total_diversified_range_kVA
  Dryers_kVA = Total_diversified_dryer_kVA
  HVAC_larger_kVA = max(Total_cooling_kVA, Total_space_heating_kVA)
  HVAC_demand_kVA = HVAC_larger_kVA × (HVAC_demand_factor_percent / 100)
• Total feeder/service apparent power: Total_kVA = General_demand_kVA + Ranges_kVA + Dryers_kVA + HVAC_demand_kVA
  Total_VA = Total_kVA × 1000
• Feeder/service current:
  For single-phase 3-wire: I (A) = Total_VA / V_LL
  For three-phase 4-wire: I (A) = Total_VA / (√3 × V_LL)

Parameter	Typical value	Comment
General load density	3 VA/ft²	NEC standard value for dwelling unit general lighting and receptacles.
Small-appliance circuits per unit	2 circuits	Minimum two per NEC; both included at 1,500 VA each.
Laundry circuits per unit	1 circuit	1,500 VA per laundry circuit where laundry is provided.
General load demand factor above 10 kVA	40%	Per NEC 220.84 for multifamily dwelling units (optional method).
HVAC inclusion	Larger of heat or cool at 100%	Only the larger of cooling or electric space heating is added to the load.

How does this calculator implement the NEC 220.84 optional method?

This tool combines the area-based general dwelling load (3 VA/ft² by default), small-appliance and laundry loads, and then applies the NEC 220.84 demand factors: 100% of the first 10 kVA plus the specified percentage on the remainder. It then adds user-supplied diversified cooking, dryer, and HVAC loads and converts the result to feeder/service current based on the selected system voltage and phase.

What information do I need before using this multifamily load calculator?

You should know the number of dwelling units, a reasonable average unit floor area, the system line-to-line voltage and phase, and whether electric cooking, dryers, and electric space heating or cooling are present. For precise results, you should also have separate diversified kVA values for ranges, dryers, and HVAC calculated from the applicable NEC tables.

Can I override the default 3 VA/ft² and 40% demand factor used by NEC 220.84?

Yes. In the Advanced options panel you can change the VA per square foot, small-appliance and laundry assumptions, and the demand factor applied to the portion of the general load above 10 kVA. This is useful for what-if analysis or when local amendments or engineering judgment justify different values.

Does this calculator size conductors and overcurrent protection devices?

No. The calculator provides the calculated multifamily feeder/service load in kVA and amperes. Conductor sizing, overcurrent protective device selection, and equipment ratings must be determined separately using the calculated load together with the applicable NEC articles, temperature ratings, correction factors, and local code requirements.

NEC 220 and Article 84 framework for multifamily load calculations

NEC Article 220 defines methods to determine electrical load for services, feeders, and branch circuits. Article 84 provides definitions referenced by Article 220 that affect terminology such as "connected load," "general lighting load," and "appliance." For multifamily buildings the NEC provides several calculation methods, including unit-based and general-area methods, and specific demand factors and tables for ranges, dryers, HVAC, and other fixed appliances. Always confirm the jurisdictional edition of the NEC before final design. This article provides a step-by-step feeder and service workflow that an engineer or designer can use with a free calculator or spreadsheet. It includes precise formulas, variable explanations with typical values, extensive tables of common appliance ratings and demand assumptions, and two fully developed real-world examples with detailed solutions. Links to authoritative sources and NEC references are included for verification.

Workflow overview: Feeder and service sizing process

Follow this ordered workflow to derive a compliant service/feeder size for multifamily dwellings:

1. Collect load data per unit and common areas (nameplate ratings, areas, HVAC types).
2. Classify loads: general lighting/receptacles, small appliance and laundry circuits, fixed appliances, heating/cooling, motors, elevators, common loads (corridors, mechanical rooms), and renewable systems or EV loads.
3. Tabulate connected loads and assign NEC-required minimum values (e.g., 1500 VA small appliance circuits).
4. Apply NEC demand factors and optional methods where permitted (per Article 220 tables and paragraphs).
5. Calculate feeder/service load using formulae, including diversity, largest motor contributions, and continuous loads 125% multiplier where applicable.
6. Select conductor ampacity and overcurrent protection based on load current and correction/ambient factors; check voltage drop and short-circuit coordination.
7. Document all assumptions, table references, and applied NEC sections for inspection and permitting.

Key formulas and variable definitions

Below are the primary calculation formulas used in the workflow. Each formula is presented with variable definitions and typical values:

Total Connected Load (sum of nameplate)

Total_Connected_Load = Σ P_i Where:

• P_i = nameplate power of load i in volt-amperes (VA) or watts (W). Typical values: small appliance circuit = 1500 VA, range = 8000–12000 W, dryer = 4800–6000 W, water heater = 4500 W.

General Service Load after demand factors

Service_Load = (Σ GL) + (Σ SA+LD × DF_SA) + (Σ FAP × DF_FA) + Σ HVAC + Σ Motors_effective Where:

• Σ GL = sum of general lighting loads (VA), typically GL_area × area_ft2.
• GL_area = lighting density, typical residential value = 3 VA/ft².
• Σ SA+LD = summed small appliance and laundry circuits (VA); usually 1500 VA per circuit × number of circuits.
• DF_SA = demand factor applied to combined small appliance/laundry circuits per NEC or optional method (example values shown in tables below).
• Σ FAP = sum of fixed appliance nameplate ratings (oven, dryer, water heater, etc.).
• DF_FA = appliance demand factor per NEC tables or manufacturer data.
• Σ HVAC = sum of HVAC loads (use nameplate or ASHRAE estimated heating/cooling wattage).
• Σ Motors_effective = effective motor loads: apply locked-rotor or starting contributions as required for sizing switches and feeder short-time ratings; for continuous load sizing use running current.

Conversion to current (amperes)

I = Service_Load / V_phase_to_phase Where:

• I = design current in amperes (A).
• Service_Load = total VA load (see formula above).
• V_phase_to_phase = system voltage; typical values: 120/240 V single-phase = use 240 V for two-hot calculations; 208Y/120 V three-phase = use 208 V.

Continuous load adjustment (NEC requirement)

If any portion of the load is continuous (operating ≥ 3 hours), apply 125%: Adjusted_Continuous_Load = 1.25 × Continuous_Component Then include in Service_Load sum.

Feeder ampacity selection

Required_Ampacity = max(I_noncontinuous, 1.25 × I_continuous) Where:

• I_noncontinuous = current from non-continuous loads.
• I_continuous = current from continuous loads (before 1.25 adjustment).

Voltage drop check (recommended limit)

VD% = (2 × L × I × R_conductor) / (V_service) × 100 Where:

• VD% = percent voltage drop.
• L = one-way conductor length in feet.
• I = load current in amperes.
• R_conductor = DC resistance per foot of conductor at 75°C (ohms/ft), selected from conductor tables.
• V_service = nominal voltage (e.g., 120 V for single-phase branch, 240 V for feeder phase-to-phase).

Acceptable targets: design for VD% ≤ 3% for feeders to branch circuits, ≤ 5% total for feeder + branch.

Extensive tables of common values and demand assumptions

Note: The second table provides illustrative demand-factor categories. For mandatory design values use the specific NEC edition tables (Article 220 and referenced tables) adopted by the authority having jurisdiction.

Step-by-step calculation procedure for a free calculator or spreadsheet

Use this algorithm in a calculator:

1. Input building data: number of units, floor area per unit, common-area floor area, appliance counts per unit, HVAC type, water heater type.
2. Compute general lighting: GL_unit = area_unit × GL_area; GL_common = area_common × GL_area.
3. Compute small appliance and laundry circuits: SA_total = 1500 VA × #SA_circuits_total; LD_total = 1500 VA × #laundry_circuits_total.
4. Sum fixed appliances per unit and common appliances; list nameplate rating for each.
5. Apply NEC demand factors: apply DF_SA, DF_FA, and any optional multifamily methods permitted. For appliances subject to specific NEC tables, consult table and apply values.
6. Sum all loads into Service_Load. Identify continuous components and sum separately for 125% multiplier.
7. Convert Service_Load to current with appropriate system voltage and phase configuration.
8. Apply conductor sizing rules: choose conductor with ampacity ≥ Required_Ampacity, apply correction factors for temperature/ambient, and check overcurrent device sizing rules (NEC 240.4 and 240.6 for standard OCPD increments).
9. Voltage drop analysis: calculate VD% and increase conductor size if VD% exceeds design target.
10. Document results, including NE C references for each applied factor and table.

Worked example 1: Four-unit multifamily building, single-phase 240 V service (detailed)

Project data (assumptions listed and used for calculation):

• Number of dwelling units: 4 identical units.
• Unit area: 900 ft² each.
• Common area (corridor, mechanical room): 400 ft².
• Per unit fixed appliances: range 8.4 kW nameplate, electric dryer 5.0 kW, water heater 4500 W.
• Per unit small appliance circuits: 2 circuits at 1500 VA each; laundry: 1 circuit 1500 VA.
• Lighting density: 3 VA/ft² (residential typical).
• Voltage: 240 V single-phase (two hot legs), service neutral and grounds not used for load VA conversion.
• Assumed demand factor usage for this example: apply 35% demand on combined small appliance + laundry total for aggregate after first unit (illustrative; check NEC for adopted method).

Step 1 — General lighting:

• Per unit GL = 900 ft² × 3 VA/ft² = 2700 VA
• Total GL for units = 2700 × 4 = 10,800 VA
• Common GL = 400 ft² × 3 = 1200 VA
• Σ GL = 10,800 + 1200 = 12,000 VA

Step 2 — Small appliance and laundry:

• Per unit SA + LD = (2 × 1500) + 1500 = 4500 VA
• For 4 units, connected SA+LD = 4 × 4500 = 18,000 VA
• Apply illustrative demand: for multifamily the first unit 100% then 35% for remainder: DF example = 1.00 + 0.35 × (n_unit − 1)
• Effective SA+LD = 4500 × [1 + 0.35 × 3] = 4500 × (1 + 1.05) = 4500 × 2.05 = 9225 VA per equivalent unit
• For all units effective SA+LD_total = 9225 × 1 (since the multiplier already accounts for units) = 9225 VA (this technique collapses units into effective single-unit equivalent for illustration)
• Alternatively, many designers compute: Effective_SA_total = 4500 + 3 × (4500 × 0.35) = 4500 + 3 × 1575 = 4500 + 4725 = 9225 VA — same result.

Step 3 — Fixed appliances (ranges, dryers, water heaters):

• Per unit: range = 8400 W, dryer = 5000 W, water heater = 4500 W → total per unit = 17,900 W
• Total connected for 4 units = 4 × 17,900 = 71,600 W
• Apply appliance demand factor: if NEC table allows demand reduction for multiple ranges/dryers, apply accordingly. For this illustration, apply conservative DF_FA = 65% for combined fixed appliances (example assumption).
• Effective fixed appliance load = 71,600 × 0.65 = 46,540 VA

Step 4 — Total service load before continuous multiplier:

• Σ = Σ GL (12,000) + SA+LD effective (9,225) + FAP effective (46,540) = 67,765 VA

Step 5 — Continuous loads and 125% multiplier:

• Assume water heaters and some lighting components are continuous for design purposes? For this example treat none as continuous except maybe corridors continuous lighting (1,200 VA). Only corridor lighting considered continuous.
• Continuous_component = common GL = 1,200 VA
• Continuous_adjustment = 1.25 × 1,200 = 1,500 VA; replace continuous part in total with adjusted value: 67,765 − 1,200 + 1,500 = 68,065 VA

Step 6 — Convert to current:

• I_service = 68,065 VA / 240 V = 283.6 A

Step 7 — Feeder ampacity and OCPD selection:

• Required ampacity = 283.6 A; choose next standard conductor and OCPD per NEC 240.6(A).
• Typical selection: 350 A main with three 350 A fuses or circuit breaker (check conductor thermal ratings); or use parallel feeders if permitted.

Step 8 — Voltage drop check:

• Assume feeder one-way length = 150 ft to the farthest unit distribution point, I = 284 A. Using an example conductor copper 600 kcmil R ≈ 0.000032 ohm/ft at 75°C (example value for demonstration), VD% = (2 × 150 × 284 × 0.000032) / 240 × 100 ≈ 1.14% (acceptable).

Documentation: Record all assumptions, applied DF values, NEC table references used (Article 220 and applicable tables for appliances), and verify with AHJ.

Worked example 2: Ten-unit multifamily building, three-phase 208Y/120 V service (detailed)

Project assumptions:

• Number of units: 10
• Unit area: 650 ft²
• Common area: 1200 ft² corridors and mechanical spaces
• Per unit appliances: refrigerator 800 W, dishwasher 1500 W, electric range 10 kW (assumed nameplate for some units), dryer 5 kW in 4 of the units only.
• Small appliance circuits: 2 per unit × 1500 VA; laundry circuit provided in all units (1 × 1500 VA).
• HVAC: packaged heat pump for each unit with electric supplemental heat (design heating load per unit 3000 W supplemental).
• Service voltage: 208Y/120 V three-phase.

Step 1 — General lighting:

• Per unit GL = 650 × 3 = 1950 VA; units total = 1950 × 10 = 19,500 VA
• Common GL = 1200 × 3 = 3,600 VA
• Σ GL = 23,100 VA

Step 2 — Small appliance and laundry:

• Per unit SA+LD = (2 × 1500) + 1500 = 4500 VA
• Connected SA+LD = 4500 × 10 = 45,000 VA
• Apply illustrative multifamily demand: first unit 100% then 35% for each additional: Effective_SA_total = 4500 + 9 × (0.35 × 4500) = 4500 + 9 × 1575 = 4500 + 14,175 = 18,675 VA

Step 3 — Fixed appliances and selective dryers:

• Ranges: assume 6 units have electric range 10,000 W = 60,000 W connected
• Dryers: 4 units have dryer 5,000 W = 20,000 W connected
• Dishwashers: 10 × 1500 = 15,000 W connected
• Refrigerators: 10 × 800 = 8,000 W connected
• Water heaters: assume centralized gas water heater (electrical minimal) — ignore electric heater load for this example.
• Total fixed connected = 60,000 + 20,000 + 15,000 + 8,000 = 103,000 W
• Apply appliance demand factor assumptions: for ranges, use NEC table values where multiple ranges reduce sum; for this example apply DF_range = 0.75 (illustrative). For dryers DF_dryer = 0.50 (illustrative). For dishwashers/refrigerators, no reduction assumed beyond small motor diversity.
• Effective fixed = (60,000 × 0.75) + (20,000 × 0.50) + 15,000 + 8,000 = 45,000 + 10,000 + 23,000 = 78,000 VA

Step 4 — HVAC supplemental heating:

• Per unit supplemental electric heat = 3,000 W × 10 = 30,000 W connected
• Assume diversity for electric heating may be reduced if not all operate simultaneously; for conservative sizing treat as 100% unless diversity info available.

Step 5 — Total load and continuous adjustments:

• Σ preliminary = GL (23,100) + SA_eff (18,675) + FAP_eff (78,000) + HVAC_heat (30,000) = 149,775 VA
• Continuous loads: assume HVAC supplemental heating is potentially continuous during cold weather — treat as continuous for 125% factor: Continuous_component = 30,000 VA
• Adjust continuous = 1.25 × 30,000 = 37,500 VA
• Total adjusted = 149,775 − 30,000 + 37,500 = 157,275 VA

Step 6 — Convert to three-phase current (line-to-line voltage 208 V):

• I_line = Service_Load / (√3 × V_line_to_line) = 157,275 / (1.732 × 208) = 157,275 / 360.256 ≈ 436.7 A per phase

Step 7 — Feeder selection and parallel conductors:

• Required ampacity ≈ 437 A; common choices: use 600 kcmil copper or 750 kcmil aluminum per phase depending on derating; or use parallel feeders if allowed by NEC 310.10(G) and AHJ.
• Consider temperature and ambient correction factors and conductor bundling which may increase required conductor size.

Step 8 — Voltage drop check:

• Assume one-way length 200 ft, I = 437 A, conductor example 600 kcmil copper R ≈ 0.000020 ohm/ft (approx); VD% = (√3 × I × L × R) / V_line_to_line × 100 (for three-phase, single-run formula) ≈ (1.732 × 437 × 200 × 0.000020) / 208 × 100 ≈ 1.45% (acceptable).

Document all steps, applied NEC table numbers, and manufacturer data for the ranges, dryers, and HVAC units. Use this documented calculation for permit submission.

Regulatory references and authoritative links

• NFPA 70, National Electrical Code (NEC), Article 220: Load Calculations — primary regulatory source for load and demand-factor methodology. For code queries consult the edition adopted by the authority having jurisdiction: https://www.nfpa.org/NEC
• NEC Article 84 — Definitions, provides definitions for terms used in load calculations: https://www.nfpa.org/ (search Article 84 in the applicable NEC edition)
• IAEI (International Association of Electrical Inspectors) technical articles and training on calculating dwelling-unit loads and multifamily services: https://www.iaei.org/
• IEEE and NEMA provide guidance on conductor ampacity, motor starting, and power system coordination: https://www.ieee.org/ and https://www.nema.org/
• US Department of Energy: guidance on residential electrification and appliance typical loads: https://www.energy.gov/

When preparing final drawings and calculations, always cite the exact NEC edition and table numbers used, and upload manufacturer nameplate data as supporting documentation.

Practical considerations, common pitfalls, and QA checklist

• Confirm jurisdictional NEC edition and any local amendments; demand factors may differ between editions or local amendments.
• Always use actual nameplate ratings for appliances and HVAC equipment; do not substitute estimated values unless noted and approved.
• Account for continuous loads with the 125% requirement in feeder and OCPD sizing.
• Include motor starting currents and potential inrush when selecting overcurrent devices and evaluating voltage drop or feeder voltage regulation impact on HVAC and sensitive electronics.
• Document every applied demand factor: reference the NEC paragraph/table and the reason for choosing optional methods.
• Verify conductor ampacity adjustments for ambient temperature, raceway fill, and bundling per the NEC ampacity correction factors.
• Plan for load growth, EV charging infrastructure, and potential future conversions; provide spare capacity or design for parallel feeders with space for future conductors.

How to implement this workflow in a free calculator or spreadsheet

Key features to include in a free load-calculator UI or spreadsheet:

• Input form for unit counts, areas, and per-unit equipment counts with nameplate fields.
• Auto-populate typical VA values from an internal library with editable fields for conservative or manufacturer-specific values.
• Selection dropdown for NEC edition to toggle applicable demand factor tables (user must supply tables or reference manual updates).
• Separate summation fields for continuous vs non-continuous loads and an automatic 125% multiplier for continuous parts.
• Phase selection (single-phase or three-phase) and automatic conversion to line currents.
• Conductor ampacity lookup and derating tables, including ambient and grouping factors.
• Voltage drop calculator with recommended conductor minimums to meet specified VD% limits.
• Exportable calculation report that cites NEC sections, tables, and lists input assumptions and nameplate attachments.

Record-keeping and submission documentation

Provide the AHJ and project stakeholders a calculation package including:

1. Single-line riser diagram with feeder conductor sizes, OCPD ratings, and grounding details.
2. Load calculation spreadsheet printout with itemized connected loads, applied demand factors, and all formula steps.
3. Nameplate copies for all significant appliances, HVAC units, and variable-speed drives.
4. Voltage drop calculations and conductor ampacity tables used.
5. References to NEC Article 220, Article 84 definitions, and any other applied NEC articles (motors, feeders, overcurrent protection).

Final engineering notes and compliance reminders

- The exact demand-factor application and permissible optional methods are edition-dependent; verify the NEC tables and paragraph numbers in the code edition governing the project. - Where manufacturer data differs materially from assumed values, use the manufacturer data and document the change. - For large multifamily projects consider diversity based on measured usage data from similar buildings or utility load profiles, and coordinate with the utility on service transformer sizing and service-point protections. References (authoritative):

• NFPA 70, National Electrical Code (NEC). NFPA. https://www.nfpa.org/NEC
• International Association of Electrical Inspectors: technical resources for load calculation and inspection practices. https://www.iaei.org/
• U.S. Department of Energy — Residential Building Electrification Guidance and appliance loads. https://www.energy.gov/
• NEMA — conductor and equipment standards. https://www.nema.org/

If you want, I can produce a ready-to-use spreadsheet template implementing this exact workflow, pre-populated with the example data and formulas so you can run alternative scenarios rapidly.