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Wisconsin Journeyman Electrician

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4.1 Dwelling Unit Load Calculations: Standard Method

Key Takeaways

  • Under NEC Article 220 Part III, dwelling unit general lighting is calculated at 3 VA per square foot of living area (measured by outside dimensions, excluding open porches, garages, and unfinished/unused spaces not adaptable for future use) per Table 220.12 and Table 220.42.
  • A minimum of two 20-ampere small appliance branch circuits (1,500 VA each = 3,000 VA) and one 20-ampere laundry branch circuit (1,500 VA) must be added to the general lighting load before applying Table 220.42 demand factors (first 3,000 VA at 100%, 3,001 to 120,000 VA at 35%, and remainder over 120,000 VA at 25%).
  • Fastened-in-place appliances (excluding ranges, clothes dryers, space heating, and air conditioning) qualify for a 75% demand factor under NEC 220.53 ONLY when there are four or more such appliances served by the same feeder or service.
  • Electric clothes dryers must be calculated at a minimum of 5,000 VA (or nameplate rating if higher) per NEC 220.54, with single-dryer installations evaluated at 100% demand factor.
  • Under NEC Table 220.55 Column C, a single household electric range rated up to 12 kW has a standard demand of 8 kW (8,000 VA); for ranges exceeding 12 kW, demand increases by 5% per kW or major fraction (0.5 kW or more) over 12 kW; non-coincident HVAC loads are evaluated per NEC 220.60 by omitting the smaller load; and 25% of the largest motor load is added per NEC 220.14(C) / 430.24.
Last updated: September 2026

4.1 Dwelling Unit Load Calculations: Standard Method

Edition control: This worked method uses the demand factors common to the assigned Wisconsin exam references, but Article 220 numbering moved between editions. A candidate testing through September 30, 2026 must use the 2017 table and section numbers; a candidate testing beginning October 1 must locate the corresponding provisions in the 2023 NEC. Wisconsin SPS 316.220 supplies the controlling floor-area definition.

Calculating the electrical service and feeder load for a single-family dwelling unit is one of the most critical and heavily tested core competencies on the Wisconsin Journeyman Electrician examination. The National Electrical Code (NEC / NFPA 70) establishes two distinct methodologies for residential load calculations:

  1. The Standard (General) Method codified in NEC Article 220, Part III (Sections 220.40 through 220.61).
  2. The Optional Method codified in NEC Article 220, Part IV (Section 220.82).

The Standard Method is the universal baseline applicable to any dwelling unit, subpanel, feeder, or service upgrade, regardless of service size. It applies systematic demand factors based on national statistical diversity curves reflecting how electrical equipment is actually operated in residences.

1. Step-by-Step Architecture of the Standard Method

Performing a compliant service calculation under Article 220 Part III requires following an exact, sequential six-step procedure:

Total Service Demand (VA)=Net Lighting+Fastened Appliances+Dryer+Cooking+HVAC+Largest Motor Addition\text{Total Service Demand (VA)} = \text{Net Lighting} + \text{Fastened Appliances} + \text{Dryer} + \text{Cooking} + \text{HVAC} + \text{Largest Motor Addition}

+-------------------------------------------------------------------------+
|                 NEC ARTICLE 220 PART III CALCULATION FLOW               |
+------------------------------------+------------------------------------+
                                     |
     +-------------------------------+-------------------------------+
     |                                                               |
     v                                                               v
+---------------------------------+  +------------------------------------+
| STEP 1: GENERAL LIGHTING & SA   |  | STEP 2: FASTENED APPLIANCES        |
| - Floor Area x 3 VA/sq ft       |  | - Water heater, disposal, etc.     |
| - Small Appliance: 2 x 1,500 VA |  | - Sum nameplate ratings            |
| - Laundry Circuit: 1 x 1,500 VA |  | - 4 or more units? Multiply x 75%  |
| - Apply Table 220.42 Demands:   |  | - 3 or fewer units? Take at 100%   |
|   * First 3,000 VA @ 100%       |  +------------------------------------+
|   * 3,001 - 120,000 VA @ 35%    |                                  |
|   * Excess > 120,000 VA @ 25%   |                                  |
+----------------+----------------+                                  |
                 |                                                   |
                 +-------------------+-------------------------------+
                                     |
     +-------------------------------+-------------------------------+
     |                               |                               |
     v                               v                               v
+-----------------------+ +-----------------------+ +---------------------+
| STEP 3: CLOTHES DRYER | | STEP 4: ELECTRIC RANGE| | STEP 5: HVAC LOADS  |
| - Min 5,000 VA or     | | - Table 220.55 Col C  | | - Compare 100% AC   |
|   nameplate rating    | | - Single range <=12 kW| |   vs. 100% Heat     |
|   (whichever greater) | |   = 8,000 VA          | | - Omit the smaller  |
| - 1 unit @ 100% demand| | - Over 12 kW: +5% / kW| |   non-coincident    |
+-----------+-----------+ +-----------+-----------+ +----------+----------+
            |                         |                        |
            +-------------------------+------------------------+
                                      |
                                      v
+-------------------------------------------------------------------------+
| STEP 6: LARGEST MOTOR ADDITION & SERVICE SIZING                         |
| - Add 25% of largest motor full-load VA (NEC 220.14(C) / 430.24)        |
| - Total Amperes = Total Calculated VA / 240 Volts                       |
| - Select standard service disconnect & OCPD rating per NEC 240.6        |
+-------------------------------------------------------------------------+

2. Step 1: General Lighting, Small Appliance & Laundry Loads

Floor Area Calculation (NEC 220.11 & 220.14(J))

Under the NEC, the general lighting load for a dwelling unit is based on outside building dimensions, calculated per floor level:

  • Include: Finished living areas, basements (finished or unfinished), and habitable spaces.
  • Exclude: Open porches, exterior patios, garages, or unused or unfinished spaces not adaptable for future use.
  • Unit Load: Under NEC Table 220.12 and Table 220.42, dwelling units require 3 VA per square foot of living space.

General Lighting Load (VA)=Total Square Feet×3 VA/sq ft\text{General Lighting Load (VA)} = \text{Total Square Feet} \times 3\text{ VA/sq ft}

Small Appliance & Laundry Branch Circuits (NEC 220.52)

The NEC mandates dedicated 20-ampere, 120-volt circuits for kitchens and laundry areas to serve portable countertop and washing appliances:

  • Small Appliance Branch Circuits (NEC 210.11(C)(1) & 220.52(A)): At least two 20-ampere circuits serving kitchen countertops, pantry, and dining area receptacles. Each circuit is assessed at 1,500 VA, for a statutory minimum of: 2×1,500 VA=3,000 VA2 \times 1,500\text{ VA} = 3,000\text{ VA}
  • Laundry Branch Circuit (NEC 210.11(C)(2) & 220.52(B)): At least one 20-ampere circuit dedicated to laundry receptacle outlets. Assessed at 1,500 VA.

Applying Table 220.42 Demand Factors

A common exam error is applying demand factors to lighting and small appliance circuits separately. The NEC strictly requires adding the general lighting load, small appliance circuits, and laundry circuit together into a single General Subtotal before applying the demand factors from Table 220.42:

General Subtotal (VA)=Lighting VA+Small Appliance VA+Laundry VA\text{General Subtotal (VA)} = \text{Lighting VA} + \text{Small Appliance VA} + \text{Laundry VA}

Portion of General Subtotal (VA)Demand FactorNet Calculated Load Formula
First 3,000 VA100% (1.00)$\min(\text{Subtotal}, 3,000) \times 1.00$
From 3,001 to 120,000 VA35% (0.35)$(\min(\text{Subtotal}, 120,000) - 3,000) \times 0.35$
Remainder over 120,000 VA25% (0.25)$(\text{Subtotal} - 120,000) \times 0.25$

Exam Tip: In virtually all residential single-family exam problems, the general subtotal falls between 3,001 VA and 120,000 VA. Thus, the net general lighting demand is simply: $3,000\text{ VA} + [(\text{General Subtotal} - 3,000) \times 0.35]$.

3. Step 2: Fastened-in-Place Appliances & The 75% Rule (NEC 220.53)

NEC 220.53 permits a demand factor to be applied to fastened-in-place appliances in dwelling units, reflecting operational diversity:

Qualifying Appliances

Fastened-in-place or fixed appliances include:

  • Electric storage water heater
  • Under-counter dishwasher
  • In-sink garbage disposal
  • Built-in microwave oven
  • Trash compactor
  • Attic ventilation or whole-house exhaust fan
  • Well water pump / sump pump

Strict Code Exclusions

[!WARNING] Never include these loads in the NEC 220.53 calculation:

  1. Household electric cooking equipment (ranges, cooktops, ovens) — governed separately under NEC 220.55.
  2. Electric clothes dryers — governed separately under NEC 220.54.
  3. Electric space heating equipment — governed separately under NEC 220.51 / 220.60.
  4. Air-conditioning equipment — governed separately under NEC 220.50 / 220.60.

The Four-or-More Appliance Rule

  • If four (4) or more qualifying fastened-in-place appliances are served by the same feeder or service, a demand factor of 75% (0.75) may be applied to the sum of their nameplate ratings.
  • If fewer than four (1, 2, or 3) appliances are installed, they must be included at 100% of their total nameplate ratings.
\begin{cases} \sum \text{Nameplates} \times 0.75, & \text{if count} \ge 4 \\[6pt] \sum \text{Nameplates} \times 1.00, & \text{if count} < 4 \end{cases}$$ --- ## 4. Step 3: Electric Clothes Dryers (NEC 220.54) The feeder and service calculation for electric clothes dryers in dwelling units is governed by **NEC 220.54** and **Table 220.54**: 1. **Statutory Floor (Minimum Rating):** The load must be calculated at a minimum of **5,000 VA (watts)** or the **nameplate rating**, whichever is greater. 2. **Demand Factors (Table 220.54):** - For **1 to 4 dryers**, the demand factor is **100% (1.00)**. - (For multi-family installations with 5 or more dryers, deratings progressively decrease from 85% down to 25%). $$\text{Dryer Demand (VA)} = \max(5,000\text{ VA}, \text{Nameplate VA}) \times 1.00$$ > **Exam Trap:** If a question states an electric dryer has a nameplate rating of **4,500 VA**, you must calculate it at **5,000 VA**. If the dryer has a nameplate of **5,500 VA**, you calculate it at **5,500 VA**. --- ## 5. Step 4: Household Electric Ranges & Cooking Appliances (NEC 220.55) Household electric ranges, wall-mounted ovens, and counter-mounted cooking units are calculated using **NEC Table 220.55**: ### Column C: Standard Demand for Ranges up to 12 kW For a single household range rated up to **12 kW (12,000 watts)**, **Column C** specifies a standard maximum demand of: $$\text{Demand for 1 Range } (\le 12\text{ kW}) = 8\text{ kW} = 8,000\text{ VA}$$ ### Ranges Exceeding 12 kW (Table 220.55, Note 1) When a single household range exceeds 12 kW, Note 1 dictates: 1. The maximum demand in Column C (8 kW) must be increased by **5% for each additional kilowatt of rating (or major fraction thereof)** by which the rating exceeds 12 kW. 2. A "major fraction" is **0.5 kW (500 watts) or more**. A fraction below 0.5 kW is dropped. $$\text{Excess kW} = \text{Nameplate kW} - 12\text{ kW}$$ $$\text{Percentage Increase} = \text{Round}(\text{Excess kW}) \times 5\%$$ $$\text{Calculated Demand (kW)} = 8\text{ kW} \times (1 + \text{Percentage Increase})$$ | Range Nameplate Rating | Excess over 12 kW | Major Fraction? | Integer kW Excess | Percentage Increase | Calculated Feeder Demand | | :--- | :--- | :--- | :--- | :--- | :--- | | **12.0 kW** | 0.0 kW | None | 0 kW | 0% | **8,000 VA (8.0 kW)** | | **13.0 kW** | 1.0 kW | None | 1 kW | $1 \times 5\% = 5\%$ | $8 \times 1.05 = \mathbf{8,400\text{ VA}}$ | | **13.5 kW** | 1.5 kW | Yes ($0.5$ is a major fraction) | 2 kW | $2 \times 5\% = 10\%$ | $8 \times 1.10 = \mathbf{8,800\text{ VA}}$ | | **13.6 kW** | 1.6 kW | Yes ($> 0.5$) | 2 kW | $2 \times 5\% = 10\%$ | $8 \times 1.10 = \mathbf{8,800\text{ VA}}$ | | **14.6 kW** | 2.6 kW | Yes ($> 0.5$) | 3 kW | $3 \times 5\% = 15\%$ | $8 \times 1.15 = \mathbf{9,200\text{ VA}}$ | | **16.4 kW** | 4.4 kW | No ($\le 0.5$) | 4 kW | $4 \times 5\% = 20\%$ | $8 \times 1.20 = \mathbf{9,600\text{ VA}}$ | ### Branch Circuit Sizing vs. Feeder Demand (NEC 210.19(A)(3)) - The branch circuit supplying a single household range rated 8-3/4 kW or more must have a minimum rating of **40 amperes**. - For a standard 12 kW range, 8,000 VA / 240V = 33.3 amperes, which is legally supplied by a 40A branch circuit (typically 8 AWG copper or 6 AWG aluminum). --- ## 6. Step 5: Heating vs. Air Conditioning (NEC 220.60) Under **NEC 220.60** (*Non-Coincident Loads*): > *"Where it is unlikely that two or more non-coincident loads will be in use simultaneously, it shall be permissible to use only the largest load that will be used at one time for calculating the feeder or service load."* In standard residential design, central space heating and central air conditioning do not run at the same time. The calculation procedure is: 1. Determine total cooling load at **100%** (compressor + outdoor condenser fan + indoor air handler blower). 2. Determine total heating load at **100%** (electric central furnace or resistance baseboard heaters). 3. Compare the two totals and **select the larger load**. 4. **Completely drop (omit) the smaller load** from the feeder/service calculation. --- ## 7. Step 6: Motor Load Multiplier (NEC 220.14(C) / 430.24) Under **NEC 220.14(C)**, **220.18(A)**, and **NEC 430.24**, conductors supplying multiple motors or motor-operated appliances must have an ampacity based on: $$\text{Motor Feeder Demand} = 100\% \text{ of all motors} + 25\% \text{ of the largest motor}$$ In a standard dwelling calculation, motors already included in previous steps (such as the AC compressor or garbage disposal) are already counted at 100% (or 75%). Therefore, you must add an **additional 25% of the largest motor's full-load VA (or current)** to the grand total. --- ## 8. Comprehensive Worked Dwelling Calculation Example To see how all code sections interlock, consider a realistic licensing examination scenario: ### Given Dwelling Specifications - **Dwelling Size:** Single-family home, outside dimensions: 2,600 sq. ft. living area. - **Required Circuits:** 2 Small Appliance circuits (120V 20A), 1 Laundry circuit (120V 20A). - **Fastened-in-Place Appliances:** - Water heater: 4,500 VA (240V) - Dishwasher: 1,300 VA (120V) - Garbage disposal: 900 VA (120V motor load) - Built-in microwave: 1,200 VA (120V) - Trash compactor: 1,000 VA (120V) - **Clothes Dryer:** 5,500 VA nameplate rating (240V). - **Cooking Equipment:** Electric range rated 14.0 kW (240V). - **HVAC Loads (Non-coincident):** - Central air conditioner: 5,800 VA (240V; compressor is largest motor: 4,200 VA). - Electric central space heating: 10,000 VA (240V). ### Step-by-Step Mathematical Solution #### Step 1: General Lighting, Small Appliance & Laundry - General Lighting: $2,600\text{ sq ft} \times 3\text{ VA/sq ft} = 7,800\text{ VA}$ - Small Appliance: $2 \times 1,500\text{ VA} = 3,000\text{ VA}$ - Laundry Circuit: $1 \times 1,500\text{ VA} = 1,500\text{ VA}$ - **General Subtotal:** $7,800 + 3,000 + 1,500 = 12,300\text{ VA}$ *Apply Table 220.42 Demand Factors:* - First 3,000 VA @ 100% = $3,000\text{ VA}$ - Remainder: $(12,300 - 3,000) = 9,300\text{ VA} \times 35\% (0.35) = 3,255\text{ VA}$ - **Net General Lighting Demand:** $3,000 + 3,255 = \mathbf{6,255\text{ VA}}$ #### Step 2: Fastened-in-Place Appliances (NEC 220.53) - Count of qualifying appliances: 5 units (Water heater, dishwasher, disposal, microwave, compactor). - Since $5 \ge 4$, the **75% demand factor** applies. - Sum of nameplates: $4,500 + 1,300 + 900 + 1,200 + 1,000 = 8,900\text{ VA}$ - **Calculated Fastened Appliance Demand:** $8,900\text{ VA} \times 0.75 = \mathbf{6,675\text{ VA}}$ #### Step 3: Clothes Dryer (NEC 220.54) - Nameplate = 5,500 VA. Since $5,500\text{ VA} > 5,000\text{ VA}$, use nameplate rating. - Demand factor for 1 dryer = 100%. - **Calculated Dryer Demand:** $5,500\text{ VA} \times 1.00 = \mathbf{5,500\text{ VA}}$ #### Step 4: Household Electric Range (NEC 220.55) - Nameplate = 14.0 kW. - Excess over 12 kW: $14.0 - 12.0 = 2.0\text{ kW}$. - Percentage increase: $2 \times 5\% = 10\%$. - Column C base = 8,000 VA. - **Calculated Range Demand:** $8,000\text{ VA} \times 1.10 = \mathbf{8,800\text{ VA}}$ #### Step 5: Heating vs. Air Conditioning (NEC 220.60) - Air conditioning = 5,800 VA. - Electric space heating = 10,000 VA. - Comparison: $10,000\text{ VA (Heat)} > 5,800\text{ VA (AC)}$. - **Selected HVAC Demand:** $\mathbf{10,000\text{ VA}}$ (Omit the 5,800 VA AC entirely). #### Step 6: Largest Motor Addition (NEC 220.14(C)) - The AC compressor was omitted under non-coincident rules. Among remaining active loads, the garbage disposal motor is 900 VA. - Motor addition: $900\text{ VA} \times 25\% (0.25) = \mathbf{225\text{ VA}}$. #### Step 7: Grand Total & Service Sizing | Calculation Category | Applicable NEC Section | Connected VA | Demand Factor | Calculated Demand (VA) | | :--- | :--- | :--- | :--- | :--- | | **General Lighting & Receptacles** | NEC 220.12 / 220.42 | 7,800 VA | Table 220.42 | 4,680 VA | | **Small Appliance Circuits (2)** | NEC 220.52(A) | 3,000 VA | Table 220.42 | Combined | | **Laundry Circuit (1)** | NEC 220.52(B) | 1,500 VA | Table 220.42 | Combined: **6,255 VA** | | **Fastened-in-Place Appliances (5)** | NEC 220.53 | 8,900 VA | 75% | **6,675 VA** | | **Clothes Dryer** | NEC 220.54 | 5,500 VA | 100% | **5,500 VA** | | **Electric Range (14 kW)** | NEC 220.55 | 14,000 VA | Col. C + 10% | **8,800 VA** | | **Electric Space Heating** | NEC 220.60 | 10,000 VA | 100% (Omit AC) | **10,000 VA** | | **Largest Motor Addition** | NEC 220.14(C) / 430.24 | 900 VA | 25% | **225 VA** | | **TOTAL CALCULATED LOAD** | — | — | — | **37,455 VA** | $$\text{Total Service Current} = \frac{\text{Total Calculated Load}}{\text{System Voltage}} = \frac{37,455\text{ VA}}{240\text{ Volts}} = \mathbf{156.06\text{ Amperes}}$$ - **Service Disconnect Sizing (NEC 230.79(C) & 240.6):** The calculated load of 156.06A exceeds 150A. NEC 240.6(A) includes **175 amperes** as a standard rating, so the next standard rating is 175A, subject to selecting service conductors and equipment with adequate ampacity and ratings. - Therefore, the calculation establishes a minimum standard service rating of **175 amperes**, not 200 amperes. A 200A design may be selected, but it is not the next standard rating produced by this calculation. --- ## 9. Common Exam Traps & Practical Review > [!CAUTION] > **Five Pitfalls That Cost Points on the Wisconsin Journeyman Exam:** > 1. **Applying Table 220.42 to Small Appliances Separately:** Never derate the 3,000 VA small appliance load by 35% on its own. It must be added to lighting *first*, taking the first 3,000 VA of the combined total at 100%. > 2. **Derating Ranges with the 75% Rule:** The 75% fastened-appliance demand factor under NEC 220.53 *never* applies to electric ranges, wall ovens, cooktops, or clothes dryers. > 3. **The 5,000 VA Dryer Floor:** An electric dryer with a 4,500 VA nameplate must be calculated at 5,000 VA. Do not use 4,500 VA. > 4. **Improper Range kW Rounding:** For ranges over 12 kW, a fraction of 0.5 kW or less is dropped (e.g., 13.5 kW = 1 kW excess). A fraction greater than 0.5 kW rounds up (e.g., 13.6 kW = 2 kW excess). > 5. **Counting Heating AND Cooling:** Never add both space heating and air conditioning together in a dwelling calculation unless the system is designed to operate simultaneously (such as reheat coils).
Test Your Knowledge

When calculating the general lighting and receptacle load for a 2,400 sq. ft. single-family dwelling using the assigned 2017 NEC Article 220 Part III standard method, what is the net demand load after including the minimum required small appliance and laundry branch circuits and applying Table 220.42 demand factors?

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Test Your Knowledge

Under NEC 220.53, an electrical service calculation includes five fastened-in-place appliances: a 4,500 VA electric water heater, a 1,200 VA dishwasher, an 800 VA garbage disposal, a 1,500 VA built-in microwave, and a 600 VA exhaust fan. What is the calculated demand load for these appliances under the Standard Method?

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Test Your Knowledge

What is the minimum feeder/service demand load required by NEC Table 220.55 for a single household electric range with a nameplate rating of 14.6 kW?

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Test Your Knowledge

An electrician is performing a standard service calculation for a home with a 4,200 VA electric clothes dryer and two non-coincident loads: a 7,200 VA central air conditioning system and a 10,500 VA electric space heating system. How should these loads be entered into the service calculation under NEC 220.54 and NEC 220.60?

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4.2 Dwelling Unit Load Calculations: Optional Method

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