Prepare for your electrical licensing exam with this free NEC electrical exam question! Understanding how to calculate the minimum demand load for fixed appliances is a crucial skill for both journeymen and master electricians. This question provides a step-by-step walkthrough that mirrors what you’ll see on real practice tests.

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Question Breakdown

Question: 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)
  • Hood fan – 2,000 VA

This question will test your understanding of NEC 220.53 and appliance demand factors.

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Step-by-Step Solution

Step 1: Identify and List Appliances

Start by listing all appliances and their respective VA ratings:

  • Water heater: 4,500 VA
  • Dishwasher: 1,200 VA
  • Garbage disposal: 1/2 HP single-phase 115V motor (VA to be calculated)
  • Hood fan: 2,000 VA

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Step 2: Calculate VA for the Single-Phase Motor (Garbage Disposal)

For motors, always refer to NEC Table 430.248 to find the full-load current.

  • From the table, the full-load current for a 1/2 HP single-phase 115V motor is 9.8 A.
  • Calculate VA for the garbage disposal:

VA = Volts × Amperes
VA = 115 × 9.8
VA = 1,127 VA

The garbage disposal adds 1,127 VA to the total load.

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Step 3: Calculate Total VA

Now, sum up the VA for all fixed appliances:

Total VA = 4,500 + 1,200 + 1,127 + 2,000
Total VA = 8,827 VA

The total connected load is 8,827 VA.

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Step 4: Apply the Demand Factor

When a dwelling has four or more appliances, NEC 220.53 allows you to apply a 75% demand factor to the total VA.

Demand Load = Total VA × 75%
Demand Load = 8,827 × 0.75
Demand Load = 6,620.25 VA

The minimum demand load for these fixed appliances is 6,620 VA.

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Code Reference: Understanding Demand Factors

The NEC 220.53 demand factor ensures that electrical systems are sized efficiently without oversizing circuits for loads that don’t operate simultaneously. Memorizing this code section and applying demand factors is essential for success on journeyman and masters practice tests.

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Key Takeaways for Your NEC Practice Test

  1. Appliance VA Ratings: Always list appliance VA values clearly. Look up motor current in NEC Table 430.248 when needed.
  2. Demand Factors: Apply the 75% reduction when there are four or more appliances as per NEC 220.53.
  3. Practice Makes Perfect: Questions like this frequently appear in practice tests for journeymen and masters.
  4. Separate Rules for Specific Appliances: Keep in mind, ranges, ovens, and dryers often require calculations from NEC 220.55.

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Why This Question Matters

This type of calculation is a fundamental skill for electricians. It ensures compliance with the National Electrical Code while designing residential systems efficiently and safely. For those preparing for licensing exams, mastering questions like these is a must to excel on NEC practice tests.

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