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Smallest stranded wire that can be used with 20 Amp breakers

3 Answers 3

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Generally what you're asking is NEC 240.4(D)(6) limits the maximum overcuurent protection of #12 AWG of solid or stranded to 20A. The next size smaller #14 is limited to 15A.

But that's just "Mostly True", the NEC is full of details. Here's what is says:

(D) Small Conductors. Unless specifically permitted in 240.4(E) or (G), the overcurrent protection shall not exceed that required by 240.4(D)(1) through (D)(8) after any correction factors for ambient temperature and number of conductors have been applied.

(4) 14 AWG Copper, 15 amperes

(6) 12 AWG Copper, 20 amperes

Ah, but what do (E) and (G) say?

(E) covers tap conductors that almost never apply to DIY, and (G) gives a table of applications where 240.4(D) doesn't apply.

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For those listed applications if your terminals and wire meet 75°C requirements then table 310.16 says you could use wire as small as #14 copper for the listed applications. (For examples THWN wire meets the requirement, NM "romex" doesn't because type NM is limited to 60°C column of 310.16.)

So #14 copper is the smallest allowed for some circuits, but for most circuits the answer is #12 on a 20A.

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12 gauge for the house circuits. The wires from the panel to the receptacle/light box.

Bought devices(lights, stuff that is plugged in) that has UL/CSA listing/label can have smaller gauge wires if the manufacturer supplies them, the cord that came with the light.

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A 20A breaker requires 12Ga copper or 10Ga aluminum (or larger).

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