3.2 Optional Dwelling & Multifamily Demand

Part IV Optional Methods — When They Appear on Prov

Article 220 Part IV provides optional feeder and service load calculations that can reduce the calculated load compared with the standard Part III method — but only when the Code’s eligibility rules are met. Arkansas JW candidates lose time by applying 220.82 percentages to a commercial building or to a dwelling that does not meet the ampere threshold. Read the stem for words like optional, 220.82, multifamily, or Table 220.84.

This section covers:

• 220.82 — optional calculation for a dwelling unit
• 220.84 — optional calculation for multifamily dwellings
• How to compare results mentally against the standard method so you can spot wrong distractors

Related sections you may see on the outline edge cases: 220.83 (existing dwelling unit), 220.85 (two dwelling units). Know they exist; focus drills on 220.82 and 220.84.

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Optional Calculation — One Dwelling Unit (220.82)

Eligibility

220.82(A) — This optional method is permitted for a dwelling unit served by a 120/240-volt or 208Y/120-volt three-wire service or feeder with an ampacity of 100 A or greater. If the problem states a 60 A or 100 A feeder, check eligibility carefully: the service/feeder must be 100 A or larger to use 220.82.

General Loads — 220.82(B)

Calculate the following at 100% and add them together (this is the “general load” pile before the 10 kVA / 40% step):

• 3 VA/ft² × floor area (same floor-area idea as the standard method)
• 1500 VA for each 20 A small-appliance branch circuit (220.52(A) quantities)
• 1500 VA for the laundry circuit (220.52(B))
• The nameplate VA of all other appliances that are fastened in place, permanently connected, or on a specific circuit — including ranges, wall-mounted ovens, cooktops, dryers, water heaters, etc., as listed in 220.82(B)
• The nameplate VA (or other permitted values) of motors and other low-duty-cycle loads as the section directs

Then apply 220.82(B) demand to that total:

Heating and Cooling — 220.82(C)

After the general-load demand, add the heating and air-conditioning load selected per 220.82(C) — which gives specific percentage options (for example, 100% of the nameplate rating of the air-conditioning load, 100% of heat-pump compressors, percentages of electric thermal storage, 65% of central electric space heating below certain thresholds, 40% of four or more separately controlled space-heating units, and “largest of” rules where listed). Do not memorize a single HVAC percentage — open 220.82(C) and pick the row that matches the equipment described.

Exam habit: Separate (B) math from (C) math. Many wrong answers mix a 40% factor into the HVAC adder or apply 220.60 thinking inside an optional-method question.

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Worked Example — 220.82 Optional Method

Dwelling: 2000 ft²; two small-appliance circuits + laundry; 12 kW range; 5 kW dryer; 4.5 kW water heater; 1.2 kW dishwasher; 5 kW A/C; 8 kW electric heat (noncoincident central heat — select per 220.82(C) as the problem states). Assume the service is 200 A (eligible).

Step A — Assemble 220.82(B) total at 100%:

• Lighting/area: 2000 × 3 = 6000 VA
• SA + laundry: 4500 VA
• Range: 12,000 VA
• Dryer: 5000 VA
• Water heater: 4500 VA
• Dishwasher: 1200 VA
• Sum = 33,200 VA

Step B — Apply 100%/40%:

• First 10,000 VA × 100% = 10,000 VA
• Remainder 23,200 × 40% = 9280 VA
• General demand = 19,280 VA

Step C — HVAC per 220.82(C): Suppose the stem says to use 100% of the A/C nameplate and that heat is not coincident under the selected 220.82(C) option — add 5000 VA for A/C (example path). Total calculated load ≈ 24,280 VA → 24,280 ÷ 240 ≈ 101 A.

If instead 220.82(C) required including a heating percentage larger than A/C, you would add that heating value instead. The point for Prov is: eligibility → sum (B) → 10 kVA/40% → add (C).

Compare mentally to standard method: optional often lands lower because appliances are folded into the 40% remainder instead of taking large Table 220.55 / 220.53 chunks at higher percentages. That does not mean optional is always allowed — eligibility first.

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Multifamily Optional Method (220.84)

Eligibility Snapshot

220.84 permits an optional calculation for a multifamily dwelling when all listed conditions are met (read the section): typically each dwelling unit has electric cooking equipment, electric space heating or air conditioning (or both) as specified, and no dwelling unit is supplied by more than one feeder, among other conditions. If a question describes gas ranges in half the units, stop — you may be forced back to the standard method or a hybrid approach as the Code requires.

Calculation Pattern

1. Compute the load in VA for each dwelling unit using the loads 220.84 points to (lighting/SA/laundry style loads, appliances, cooking, heating/A/C as detailed in the section).
2. Add house loads (laundry rooms, corridors, etc.) as required.
3. Multiply the total by the demand factor from Table 220.84 based on the number of dwelling units.

Table 220.84 (open the Code — values below illustrate how the table behaves; always verify the printed factor for the exact unit count):

Do not invent a factor for “12 units” from memory if you can open the table in three seconds. Prov is open book; table lookup is the skill.

Mini Multifamily Example

Assume each of 10 dwelling units calculates to 20,000 VA of connected/calculated unit load under 220.84’s instructions, and house loads add 15,000 VA. Gross = (10 × 20,000) + 15,000 = 215,000 VA. If Table 220.84 lists a demand factor of 43% for 10 units (confirm in your NEC), demand = 215,000 × 0.43 = 92,450 VA. Feeder amperes depend on system voltage (for example ÷ 208 × √3 for a three-phase feeder, or as the problem defines).

Exam traps:

• Using Table 220.45 dwelling lighting factors instead of Table 220.84
• Applying 220.82’s 10 kVA/40% rule to an entire apartment building
• Forgetting house loads
• Counting units wrong (include only dwelling units that meet 220.84)

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Standard vs Optional — Decision Tree for Timed Work

1. Commercial / non-dwelling? → Not 220.82/220.84 dwelling optional methods (use Part III commercial rules — next section).
2. One dwelling, stem says optional, ≥100 A? → 220.82.
3. One dwelling, stem silent or says standard? → Part III standard method (Section 3.1).
4. Multifamily with 220.84 conditions met and stem allows optional? → 220.84 + Table 220.84.
5. Multifamily that fails 220.84 conditions? → Calculate per Part III (and any other applicable sections), not Table 220.84.

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Neutral and Feeder Follow-Ons

Optional calculations size the ungrounded feeder/service load. Neutral load still follows 220.61 (including possible 70% reductions for certain dryer/range loads under 220.61(B) where applicable). A question can ask for calculated load under 220.82 and then ask a second question about neutral — treat them as separate lookups.

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Arkansas JW Timing Strategy

With 3 hours for 60 questions, spend no more than about 3–4 minutes on a full optional dwelling calc unless it is clearly a multi-step item. For many questions you only need:

• Eligibility (100 A),
• Whether 10 kVA/40% applies to the listed total, or
• Which Table 220.84 factor matches the unit count.

Practice writing the 220.82 skeleton on scratch paper: Sum (B) → 10k @100% + rest@40% → + (C).