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Electrician Journeyman Exam Study Guide

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Load & Demand – Electrician Journeyman Exam Study Guide


Overview

This study guide covers the essential load and demand concepts tested on the Electrician Journeyman Exam, including NEC code requirements, load calculation procedures, and special load considerations. Mastery of these topics requires understanding both the underlying electrical theory and the specific NEC tables and percentages used in real-world calculations. Expect calculation-based questions that require you to apply demand factors, VA values, and sizing rules quickly and accurately.


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Definitions & Core Concepts


Foundational Terms


  • • Connected Load – The total wattage (or VA) of all electrical equipment wired to a system, whether operating or not. This is your starting number before any demand factors are applied.
  • • Maximum Demand – The greatest demand that has occurred over a specified period of time, measured in kW or kVA.
  • • Demand Factor – The ratio of maximum demand to total connected load; always ≤ 1 (or ≤ 100%).
  • • Diversity Factor – The ratio of the sum of individual maximum demands to the maximum demand of the whole system; always ≥ 1.
  • • Continuous Load – A load where maximum current is expected to last for 3 hours or more.

    • Key Formula


    ```

    Demand Load = Connected Load × Demand Factor

    ```


    Demand Factor vs. Diversity Factor Compared


    | Feature | Demand Factor | Diversity Factor |

    |---|---|---|

    | Formula | Max Demand ÷ Connected Load | Sum of Individual Demands ÷ System Max Demand |

    | Value Range | ≤ 1 (≤ 100%) | ≥ 1 |

    | Purpose | Reduces connected load | Accounts for staggered peak demands |


    Key Terms

  • • VA (volt-amperes) – Unit of apparent power used in load calculations
  • • kVA – kilovolt-amperes (1,000 VA)
  • • kW – kilowatts (1,000 watts)
  • • Feeder – Conductors between the service equipment and the final branch circuit overcurrent device
  • • Service Entrance – The conductors and equipment that deliver electricity from the utility to the building

    • > Watch Out For: Students commonly confuse demand factor and diversity factor. Remember: demand factor goes DOWN (less than 1), diversity factor goes UP (greater than or equal to 1). They move in opposite directions.


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    NEC Code Requirements


    General Lighting Loads – Dwelling Units


    Unit Load: 3 VA per square foot for dwelling unit general lighting (NEC Table 220.12)


    #### NEC Table 220.42 – Demand Factors for General Lighting (Dwelling Units)


    | Portion of Lighting Load | Demand Factor |

    |---|---|

    | First 3,000 VA | 100% |

    | 3,001 VA to 120,000 VA | 35% |

    | Over 120,000 VA | 25% |


    Required Branch Circuit Loads (Dwelling Units)


    | Circuit Type | Required Quantity | VA Each |

    |---|---|---|

    | Small Appliance Branch Circuits | Minimum 2 | 1,500 VA |

    | Laundry Branch Circuit | Minimum 1 | 1,500 VA |


    > Watch Out For: Small appliance and laundry branch circuit VA allowances (1,500 VA each) are added to the general lighting load before demand factors are applied in the Standard Calculation Method. Don't forget these mandatory additions.


    Continuous Load Conductor Sizing


    Per NEC 210.19(A)(1):

  • • Conductors serving continuous loads must be sized at 125% of the continuous load
  • • Formula: `Conductor Ampacity = Continuous Load (A) × 1.25`

    • Minimum Service Size


  • • Single-family dwelling minimum service: 100 amperes (NEC 230.79(C))

    • Key Terms

  • • NEC Table 220.42 – Demand factor table for general lighting
  • • NEC Table 220.55 – Demand factors for household electric ranges
  • • NEC Table 220.54 – Demand factors for electric dryers
  • • NEC 220.51 – Fixed electric space heating
  • • NEC 210.19(A)(1) – Continuous load conductor sizing rule

    • > Watch Out For: The 35% demand factor for general lighting applies to a very wide range (3,001–120,000 VA). On most residential calculations, nearly all of your lighting load above 3,000 VA will fall into this bracket.


    ---


    Load Calculation Methods


    Two Permitted Methods for Dwelling Unit Services


    #### 1. Standard Calculation Method – NEC 220.82


  • • Apply unit load (VA/sq ft) to square footage
  • • Add mandatory branch circuit loads
  • • Apply Table 220.42 demand factors to lighting
  • • Apply Table 220.55 demand factors to ranges
  • • Add motor loads at 125%, heating/cooling loads per NEC rules

    • #### 2. Optional Calculation Method – NEC 220.83


    | Portion of "All Other Loads" | Demand Factor |

    |---|---|

    | First 10 kVA | 100% |

    | All loads exceeding 10 kVA | 40% |


    > The optional method is often simpler and may yield a smaller (more economical) calculated load for larger homes.


    Step-by-Step: Standard Dwelling Calculation (Summary)


    ```

    Step 1: Calculate general lighting load

    = Square Footage × 3 VA/sq ft


    Step 2: Add small appliance loads

    = 2 circuits × 1,500 VA = 3,000 VA


    Step 3: Add laundry circuit load

    = 1,500 VA


    Step 4: Apply Table 220.42 demand factors to Steps 1–3 total


    Step 5: Add range load (Table 220.55)

    1 range = 8,000 VA (8 kW) Column C


    Step 6: Add dryer load (Table 220.54, min. 5,000 W)


    Step 7: Add heating OR A/C (whichever is larger)


    Step 8: Add largest motor at 125%


    Step 9: Convert total VA to amperes

    I = VA ÷ Volts

    ```


    Worked Example: General Lighting


    Given: 2,000 sq ft dwelling unit

    ```

    Connected Lighting Load = 2,000 × 3 VA = 6,000 VA

    + Small appliance circuits = 3,000 VA

    + Laundry circuit = 1,500 VA

    Total before demand = 10,500 VA


    Apply Table 220.42:

    First 3,000 VA × 100% = 3,000 VA

    Remaining 7,500 VA × 35% = 2,625 VA

    Demand Load Total = 5,625 VA

    ```


    Worked Example: Service Ampere Rating


    Given: 240V single-phase, 24,000 VA calculated demand load

    ```

    I = VA ÷ V

    I = 24,000 ÷ 240

    I = 100 amperes → Minimum 100A service required

    ```


    Key Terms

  • • Standard Method – NEC 220.82; applies individual demand factors to each load type
  • • Optional Method – NEC 220.83; simplified two-tier demand factor approach
  • • Column C – The column in NEC Table 220.55 used for single household ranges

    • > Watch Out For: Don't use the "demand load" formula on ranges without checking Table 220.55. A single range defaults to 8 kW (8,000 VA) regardless of actual nameplate rating (for ranges rated 8¾ kW or less, use Column C values).


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    Motor & Special Loads


    Motor Load Rule


    Per NEC, when calculating feeder or service loads:

  • • Include the largest motor at 125% of its full-load current (FLC) rating
  • • All other motors are included at 100% of FLC

    • ```

    Largest Motor Contribution = FLC × 1.25

    ```


    Electric Ranges – NEC Table 220.55


    | Number of Ranges | Demand (Column C) |

    |---|---|

    | 1 range | 8,000 VA (8 kW) |

    | Multiple ranges | See Table 220.55 for further reductions |


    Electric Dryers – NEC Table 220.54


    | Number of Dryers | Demand Factor |

    |---|---|

    | 1 | 100% |

    | 2 | 100% |

    | 3 | 100% |

    | 4 | 100% |

    | 5+ | Reductions begin |


    Minimum dryer load: 5,000 W (5 kW) per dryer, or nameplate rating if higher.


    > Watch Out For: Many students expect a demand reduction for 2 dryers — there is none. The 100% demand factor holds through the first several units. Reductions only apply to larger multifamily scenarios with 5+ dryers.


    Fixed Electric Space Heating – NEC 220.51


  • • Fixed electric space heating loads are calculated at 100% of total connected load
  • • No demand factor reduction is permitted

    • Air Conditioning vs. Electric Heat – Omission Rule


  • • When both A/C and electric heat are present, include only the larger of the two loads
  • • The smaller load may be omitted because simultaneous operation is unlikely
  • • This is sometimes called the "non-coincident load" rule

    • Key Terms

  • • FLC (Full-Load Current) – The rated operating current of a motor at full load
  • • Non-coincident loads – Loads unlikely to operate at the same time (A/C vs. heat)
  • • Nameplate rating – The manufacturer's specified electrical rating on the equipment label
  • • NEC 220.51 – Code section governing fixed electric space heating load calculations

    • > Watch Out For: The 125% motor rule applies only to the single largest motor on the feeder/service. Do not multiply all motors by 125% — only the largest one.


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    Quick Review Checklist


    Use this checklist before your exam to confirm mastery of all key concepts:


  • • [ ] I can define demand factor, connected load, maximum demand, and diversity factor — and explain the difference between demand factor and diversity factor
  • • [ ] I know that a continuous load is defined as lasting 3 hours or more
  • • [ ] I can state the general lighting unit load for dwelling units: 3 VA/sq ft
  • • [ ] I have memorized the three tiers of NEC Table 220.42: 100% / 35% / 25%
  • • [ ] I know that dwelling units require a minimum of two small appliance circuits at 1,500 VA each and one laundry circuit at 1,500 VA
  • • [ ] I can apply the formula: Demand Load = Connected Load × Demand Factor
  • • [ ] I can convert VA to amperes using: I = VA ÷ Volts
  • • [ ] I know the minimum service size for a single-family dwelling is 100 amperes
  • • [ ] I understand both the Standard Method (220.82) and Optional Method (220.83) and the optional method's 100%/40% split at 10 kVA
  • • [ ] I know a single household electric range uses 8,000 VA (Column C, Table 220.55)
  • • [ ] I can apply the largest motor at 125% rule for feeder/service calculations
  • • [ ] I know the minimum dryer load is 5,000 W and that 2 dryers = 100% demand (no reduction)
  • • [ ] I know fixed electric space heating is calculated at 100% — no reduction allowed
  • • [ ] I can apply the A/C vs. heat omission rule (include only the larger load)
  • • [ ] I know conductors serving continuous loads must be sized at 125% of the continuous load

    • ---


    Tip: Practice at least five full dwelling unit load calculations — one using the Standard Method and one using the Optional Method — before exam day. Speed and accuracy with these procedures is essential.

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