Worked Example: Electrical Conductor Sizing

This worked example demonstrates how to find the required minimum ampacity ( $I_{req}$ ) of a wire carrying a combination of continuous and non-continuous loads.

1. Problem Statement

A commercial lighting circuit (which is considered a continuous load because lights typically stay on for more than 3 hours) draws $16 \text{ A}$ . On the same circuit, there is an intermittently used exhaust fan that draws $4 \text{ A}$ (noncontinuous load). Calculate the required minimum conductor ampacity.

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2. Given Data

Non-continuous Load (I_noncontinuous)

Continuous Load (I_continuous)

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3. Formula and Calculation

Calculate the required minimum ampacity ( $I_{req}$ ):

Error: Formula electrical-conductor-ampacity not found in the Formula Registry.

The required minimum ampacity for the conductor is $24 \text{ A}$ . From standard tables (at $75^\circ\text{C}$ ):

12 AWG is rated at $20 \text{ A}$ ( $20 < 24$ , inadequate)
10 AWG is rated at $30 \text{ A}$ ( $30 \ge 24$ , acceptable) Therefore, the 10 AWG wire must be selected.

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