Appliance load calculation is a crucial skill for electricians working on residential projects. It ensures that the electrical service can safely handle the power demands of various fixed appliances in a dwelling. This calculation is essential for proper sizing of service-entrance conductors and equipment, preventing overloads and potential fire hazards. Mastering this topic is vital for passing NEC electrical exams and for real-world application in residential electrical work.
Using the standard method of calculation for a one-family dwelling, determine the minimum demand load, in VA, on the ungrounded service-entrance conductors when the residence has the following fixed appliances installed: water heater – 4,800 VA, dishwasher – 1,200 VA, garbage disposal – 1,150 VA, trash compactor – 800 VA.
Calculate the demand load for a dwelling unit with the following appliances: electric range – 12,000 VA, water heater – 4,500 VA, dishwasher – 1,200 VA, and an ice maker – 1,000 VA.
Calculate the minimum demand load, in VA, for the fixed appliances in a one-family dwelling. The residence has the following fixed appliances installed: water heater – 4,500 VA, dishwasher – 1,200 VA, garbage disposal (1/2 HP single-phase 115V motor), and a 1,200 W microwave.
Key phrases to look out for in the Appliance Load Calculation question:
When you spot these elements: Confirm it's an appliance load calculation question, not a general load calculation or service sizing question. Refer to NEC section 220.53 (NEC 2017, 2020, 2023)
To correctly apply NEC Article 220.53, focus on these main elements:
To summarize how to use the codebook:
Calculate the minimum demand load, in VA, for the fixed appliances in a one-family dwelling. The residence has the following fixed appliances installed: water heater – 4,500 VA, dishwasher – 1,200 VA, garbage disposal (1/2 HP single-phase 115V motor), and a 1,200 W microwave.
Step 1: Identify and List Appliances
Step 2: Calculate VA for the Single-Phase Motor (Garbage Disposal)
For the garbage disposal, we need to convert the horsepower to VA:
Step 3: Calculate Total VA
Total VA = 4,500 + 1,200 + 1,127 + 1,200 = 8,027 VA
Step 4: Determine Number of Appliances
There are 4 appliances listed.
Step 5: Apply Demand Factor
Since there are 4 appliances, we apply the 75% demand factor as per NEC 220.53.
Demand Load = Total VA × 75% Demand Load = 8,027 VA × 0.75 = 6,020.25 VA
Step 6:
Round down to the next whole number per Section 220.5(B);
Final Demand Load = 6,020 VA
Therefore, the minimum demand load for these fixed appliances is 6020 VA.
Note: This calculation method applies to general-purpose household appliances. For specific appliances like ranges, ovens, or dryers, there may be separate calculation methods outlined in other NEC sections (e.g., 220.55 for cooking equipment).
Download now to access 3,000+ practice questions and master the NEC Code!