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SESK: Stuff Everyone Should Know · sesk.info/elec-ocpd-small-conductor

For conductors 18 AWG to 10 AWG, what two things limit the size of the overcurrent device?

Size and material of the small conductor set the limit.

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  1. Voltage and wire color
  2. Conductor size and material ✔
  3. Conduit length and breaker brand

Why: Section 240.4(D) caps the breaker size for small conductors by AWG size and by whether the wire is copper or aluminum. It overrides what the ampacity table alone would allow.

Huh, didn't know that: The article points readers to 240.4(D)(1) through (7) for the individual limits.

The dad joke
Why did the copper wire win the 20A race? It had better material.
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References

Answer: Conductor size and material. Section 240.4(D) caps the breaker size for small conductors by AWG size and by whether the wire is copper or aluminum. It overrides what the ampacity table alone would allow.

  1. EC&M: Protecting Conductors Part 3 www.ecmweb.com/maintenance-repair-operations/article/20901392/protecting-conductors-part-3
    For small conductors (18AWG to 10AWG), the size and material of the conductor limit the size of the OCPD.
    Checked 2026-10-10.

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Trades & ShopUnder 240.4(D), the maximum overcurrent device for 14 AWG copper is how many amps?Trades & ShopThe 240.4(B) 'next size up' rule allows rounding up the overcurrent device only up to what rating?Trades & ShopBranch-circuit conductors serving a single motor must have an ampacity of at least what percent of the motor's FLC?

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