Home Inspect Cert · Free practical tool

Measured voltage drop calculator

Document the difference between source and loaded receiving measurements. Keep the numerical observation distinct from diagnosing the underlying electrical condition.

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Example values loaded. Replace them with your own measurements.

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Enter your values, choose the units, and calculate. You’ll see the result and the working here.

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The method

Measured difference = source − loaded receiving voltage; percentage = difference/source × 100.

Before using the result

  • Use comparable measurements under documented load conditions. Results do not diagnose a fault or determine an installation-compliance threshold.

Worked examples

These original training examples illustrate the method for InterNACHI Certified Professional Inspector (CPI). Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.

1. Worked example

Document the difference between source and loaded receiving measurements. Keep the numerical observation distinct from diagnosing the underlying electrical condition.

Measured source voltage (V)
230
Loaded receiving voltage (V)
223
  1. Difference = 230 − 223 = 7 V.
  2. Percentage = 7 / 230 × 100%.
  • Measured voltage difference: 7 V
  • Measured percentage difference: 3.043478 %

2. Comparison example

Compare a different supplied condition using the same method. For Home Inspect Cert, the important check is that the input meaning, units and method assumptions still match the problem.

Measured source voltage (V)
230
Loaded receiving voltage (V)
220
  1. Difference = 230 − 220 = 10 V.
  2. Percentage = 10 / 230 × 100%.
  • Measured voltage difference: 10 V
  • Measured percentage difference: 4.347826 %

Check your understanding

1. Which relationship is used?

Measured difference = source − loaded receiving voltage; percentage = difference/source × 100.

2. Which assumption should you check first?

Use comparable measurements under documented load conditions. Results do not diagnose a fault or determine an installation-compliance threshold.

3. How should you verify a different unit system?

Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.

Continue with the matching exam topic

This tool connects to InterNACHI Certified Professional Inspector (CPI) free practice. Work through a question independently, then use the calculation steps to identify where your method differs. The tool stays free whether or not you choose paid preparation.

Tool terms and notices

Measured voltage drop calculator — free with working | Home Inspect Cert