NEC 220.84 · 220.102 · 220.103 · 2023 NEC

How to use the NEC 220.84 multifamily optional calculation

Whether the building qualifies, what goes into each unit’s connected load, how the demand factor is picked, where house loads go — plus farm load demand under 220.103. Worked examples and a free link to the official tables.

Need the actual tables? Look up Tables 220.84 and 220.103 in the free NFPA viewer →

Does the building qualify for 220.84? (our checklist)

Check	What to confirm	If it fails
Unit count	Three or more dwelling units on the feeder or service being calculated	Use the standard method (Part III), or 220.82 for a single unit
One feeder per unit	No dwelling unit is supplied by more than one feeder	Use the standard method
Electric cooking	Each unit has electric cooking equipment	Check the exception in 220.84(A) — it compares against a calculated cooking allowance
Electric heat or A/C	Each unit has electric space heating, air conditioning, or both	Use the standard method

Our own summary of the 2023 NEC, not the code text. Look up 220.84, Table 220.84, 220.102, and Table 220.103 in the free NFPA viewer (nfpa.org/freeaccess) and verify against the NEC edition adopted by your AHJ. Not engineering advice — service sizing is the designer of record’s call.

How to run the 220.84 calculation, step by step

Step	What you do	Watch out for
1	For one unit, list the connected load: general lighting at the dwelling VA per sq ft, small-appliance and laundry circuits, nameplate of fastened-in-place appliances, ranges, dryers, water heaters	Everything goes in at nameplate — no Table 220.55 or 220.53 demand here
2	Add the larger of the heating or air-conditioning load	Do not add both — only the larger
3	Multiply by the number of units (or total each unit type separately if they differ)	Sum every unit on the feeder or service
4	Find the demand factor in Table 220.84 by the number of units	The factor keeps dropping as the unit count grows
5	Multiply the total connected load by that factor	This is the dwelling-unit portion only
6	Add house loads (hall lighting, elevators, pumps, site lighting) calculated by the standard Part III method	House loads do not get the Table 220.84 factor
7	Calculate the neutral separately under 220.61	The optional method sizes the ungrounded conductors

Worked example 1 — three-unit building, 1,000 sq ft per unit, 120/240 V

Input / step	Value	Source
Lighting: 1,000 sq ft × 3 VA	3,000 VA	220.84(C)
Two small-appliance + one laundry circuit	4,500 VA	220.84(C)
Range 12,000 + dryer 5,000 + water heater 4,500 VA (nameplate)	21,500 VA	220.84(C)
Larger of heat (10,000 VA) or A/C (5,000 VA)	10,000 VA	220.84(C)
Connected load per unit	39,000 VA	Sum
Three units	117,000 VA	× 3
Demand factor for three units	45%	Table 220.84
Dwelling-unit demand load	52,650 VA ÷ 240 V ≈ 219 A	Before house loads

Worked example values only. Add the house loads at the standard method, then size the service. Look up the other unit-count rows in the free NFPA viewer.

How farm load demand works (220.102 and 220.103)

Level	Rule	What it does
Each farm building or load group (not the dwelling)	220.102 / Table 220.102	Sizes the feeder to each building: loads that run together at full value, the balance reduced in steps
The whole farm service	220.103 / Table 220.103	Ranks the building loads largest to smallest and applies a falling demand percentage to each
Loads with the same function in different buildings	220.103	May be combined and treated as a single load in the ranking
Farm dwelling	Dwelling methods (Part III or IV)	Calculated on its own — check how your edition combines it at a shared service

Worked example 2 — farm service, two equipment buildings, 240 V

Input / step	Value	Source
Barn feeder load, after its own demand	100 A	220.102
Shop/shed feeder load, after its own demand	60 A	220.102
Largest load at 100%	100 A	Table 220.103
Second largest at 75%	45 A	Table 220.103
Farm equipment load at the service	145 A	Sum
Farm dwelling	Calculated separately by the dwelling method	220.102(A), 220.103

Worked example values only. The third-largest and remaining loads step down further — look up Table 220.103 in the free NFPA viewer.

Common mistakes

Mistake	What to do instead
Applying Table 220.55 range demand inside a 220.84 calc	The optional method takes ranges at nameplate — the table factor covers the diversity
Adding both heat and A/C	Only the larger of the two
Applying the Table 220.84 factor to house loads	House loads are calculated separately by the standard method and added
Using 220.84 on a gas-cooking building without checking the exception	Read 220.84(A) — it compares against a calculated cooking allowance
Counting the farm dwelling in the Table 220.103 ranking	Calculate the dwelling with the dwelling methods

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A smaller, defensible apartment service

Look up 220.84 and Table 220.84 in the free NFPA viewer. NFPA offers read-only access to current NEC editions at no cost. This page explains how the method works; it does not reproduce the tables. Written to the 2023 NEC — verify against the edition your AHJ has adopted.

Why use it. The standard method stacks separate demand factors for lighting, ranges, dryers, and appliances. The optional method in 220.84 takes almost everything in each unit at nameplate, adds it up, and applies one demand factor based on the number of units. On all-electric apartment buildings it usually produces a smaller — and still code-compliant — service than the standard method.

The qualifying conditions are strict. Three or more units, no unit fed by more than one feeder, electric cooking in every unit (with an exception for buildings that don’t have it), and electric heat or air conditioning in every unit. Miss one and you are back to the standard method. House loads — corridors, elevators, fire pump, parking lot lights — are calculated with the standard method and added on top.

Farms work in two layers. 220.102 sizes the feeder to each barn, shop, or pump load group, taking the loads that run together at full value and reducing the balance. 220.103 then ranks those building loads at the service and takes each one at a falling percentage — full value for the largest, less for the second, and so on. The farm dwelling is calculated separately with the dwelling methods.

Build the per-unit load from the general lighting load guide and the cooking appliance demand guide. Then size service conductors with the NEC 310.16 ampacity chart, the OCPD from the standard breaker sizes guide, check long feeders with the voltage drop calculator, and lay out each unit on the panel schedule template.

FAQ

When can I use the NEC 220.84 optional method?+

When the building has three or more dwelling units, no unit is supplied by more than one feeder, and each unit has electric cooking and electric space heating, air conditioning, or both. There is an exception in 220.84(A) for buildings without electric cooking. Look up 220.84 in the free NFPA viewer at nfpa.org/freeaccess.

How is the Table 220.84 demand factor chosen?+

By the number of dwelling units on the feeder or service. The factor gets smaller as the count goes up — a three-unit building is taken at 45% of connected load. Look up the other rows in the free NFPA viewer.

Where do house loads go in a multifamily optional calculation?+

Common-area loads such as hall lighting, elevators, pumps, and site lighting are calculated with the standard method in Part III and added to the demand-factored dwelling load. They do not get the Table 220.84 factor.

How do farm load demand factors work?+

Each farm building is first calculated under 220.102. At the service, 220.103 ranks those loads from largest to smallest, takes the largest at 100% and the second largest at 75%, and reduces the rest further. The farm dwelling is calculated separately with the dwelling methods.

Did the 2023 NEC change these sections?+

220.84, 220.102, and 220.103 kept their numbers through the 2023 reorganization of Article 220, and the methods are the same in principle. Check the edition your AHJ enforces for wording changes in the qualifying conditions and exceptions.

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