Spot the Violation

ElectricalPanels, breakers & overcurrentLevel 12023 NEC

Main-breaker load center

Open residential load center with the dead front removed and a 100 A main breaker at the top. Two columns of 15 A and 20 A single-pole breakers sit on the bus; in the right column, two black 12 AWG conductors enter the terminal of the third breaker from the top. White and bare conductors run to the bars in the side gutters, and a manufacturer's rating label is fixed inside the can at lower right. 100 20 15 20 15 20 20 15 20 20 15 LOAD CENTER120/240V 1PH 3W100A MAX
Residential load center, dead front removed

What's wrong here?

  1. A breaker terminal listed for one conductor is holding two
  2. A 20 A breaker is not allowed on 12 AWG copper conductors
  3. A 100 A main is too small for this many branch circuits
  4. Nothing. This installation is compliant
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Show the answer and the code reference

The answer

Two circuit conductors are terminated under a single breaker lug that is listed for only one conductor.

Correct choice: 1. A breaker terminal listed for one conductor is holding two

A breaker terminal may hold more than one conductor only if the breaker is listed and marked for it (certain Square D QO and Homeline breakers are, for two conductors of the same size and material; many breakers are not). Landing two conductors under a single-conductor lug violates 110.14(A), which requires terminals for more than one conductor to be identified for that purpose, and 110.3(B), which requires equipment to be used per its listing instructions. The second conductor is usually clamped unevenly, so it loosens with thermal cycling, arcs, and overheats the breaker.

How to fix it

Move one conductor to its own breaker, or splice both conductors to a single pigtail in the panel gutter and land the pigtail on the breaker (312.8 permits splices in a cabinet that is not more than 75% full), as long as both loads belong on one 20 A circuit. A breaker listed and marked for two conductors is also acceptable.

Code references

  • NEC 2023 110.14(A) — Terminals

    Terminals for more than one conductor shall be so identified. Connection of conductors to terminal parts shall ensure a thoroughly good connection without damaging the conductors.

    Drills citing 110.14(A)

  • NEC 2023 110.3(B) — Installation and Use

    Equipment that is listed, labeled, or both shall be installed and used in accordance with any instructions included in the listing or labeling.

    Drills citing 110.3(B)

2026 NEC:same rule and number. The 2026 NEC rewrote the wire-binding-screw sentence of 110.14(A) (10 AWG and smaller solid or Class B stranding; Class C strands must be fully enclosed or made solid), but the requirement that terminals for more than one conductor be identified is retained, so this double-lug answer is unaffected. Confidence: medium

Minnesota

MN adopts the NEC rule as writtenConfidence: high

Minnesota adopts the NEC by reference without amendment (Minn. Rules 1315.0200; Minn. Stat. 326B.35), so 110.14(A) applies as published. The 2023 NEC governs permits filed July 1, 2023 through Aug. 16, 2026; the 2026 NEC governs permits filed on or after Aug. 17, 2026 (exams moved to the 2026 NEC on Sept. 8, 2026). See the 2026 NEC note on this drill.

How Minnesota adopts the NEC

Why the other choices are wrong

  • A 20 A breaker is not allowed on 12 AWG copper conductors. 12 AWG copper is protected at 20 A by 240.4(D)(5); that pairing is exactly right.
  • A 100 A main is too small for this many branch circuits. Service size comes from the Article 220 load calculation, not from counting breakers, and 230.79(C) sets 100 A as the minimum for a one-family dwelling.
  • Nothing. This installation is compliant. The double-landed terminal is a listing violation and a loose-connection fire risk.
Safety hazardLevel 1 · Apprentice#panel#breaker#double-tap#termination

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