Spot the Violation

ElectricalTerminations, splices & conductorsLevel 32023 NEC

Garage subpanel with SER feeder

Taped fire-rated drywall wall of an attached garage beside the overhead door, whose vertical track and rollers show at the right edge, with a garage-door opener push button mounted on the wall between the panel and the door. A main-lug subpanel has its dead front removed. A gray SER cable printed 4-4-4-6 AL enters the top through a cable connector; two insulated black aluminum conductors land in the main lugs, which are stamped AL9CU, the white aluminum neutral lands on a neutral bar mounted on insulating standoffs, and the bare aluminum grounding conductor lands on a separate ground bar screwed to the enclosure; both bar lugs are stamped AL9CU. Copper branch-circuit conductors from yellow and white NM cables land on single-pole breakers, with whites on the neutral bar and bare copper on the ground bar. The stripped aluminum ends show bright metal with no visible compound. 5/8 in. TYPE X FIRE-RATED GYPSUM BOARD SER4-4-4-6AL AL9CU AL9CU AL9CU 201520201520
Attached-garage subpanel, fed from a 50 A two-pole breaker in the house panel

What's wrong here?

  1. Nothing. This installation is compliant
  2. The aluminum conductors must get antioxidant compound before landing in the lugs
  3. The neutral and equipment grounding conductors must be landed on the same bar
  4. 4 AWG aluminum is too small for a 50 A feeder
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Show the answer and the code reference

The answer

Nothing is wrong: the 4 AWG aluminum SER feeder is adequately sized for its 50 A breaker and lands on lugs identified for aluminum, with the neutral isolated from the separate ground bar.

Correct choice: 1. Nothing. This installation is compliant

Aluminum feeders are permitted, and 110.14 requires only that each terminal be identified for the conductor material; every aluminum termination here (main lugs, neutral lug, ground-bar lug) is stamped AL9CU, meaning it is identified for aluminum or copper. Table 310.16 gives 4 AWG aluminum 55 A even in the 60°C column, so a 50 A feeder works where the cable or terminals are held to 60°C (338.10(B)(4)(a) for SE cable in thermal insulation, 110.14(C)(1)(a) for terminations of circuits rated 100 A or less), and the 6 AWG aluminum ground beats the 8 AWG aluminum minimum in Table 250.122 for a 60 A device. Because this is a feeder panel, not the service, the neutral bar is isolated on standoffs and the grounds land on a separate bar bonded to the can, as 250.142(B) and 250.24(A)(5) require. The branch circuits match too (12 AWG on 20 A, 14 AWG on 15 A); GFCI protection for the garage receptacles (210.8(A)(2)) is not visible here and is assumed to be at the receptacles.

How to fix it

No correction needed. Confirm the lug and breaker terminals were tightened to the manufacturer's marked torque with a calibrated torque tool (110.14(D)) and keep the panel label and circuit directory complete.

Code references

  • NEC 2023 110.14 — Electrical Connections

    Pressure terminals and pressure splicing connectors must be identified for the material of the conductor (copper, aluminum, or copper-clad aluminum) and properly installed and used; dissimilar metals may not be mixed in one terminal unless it is identified for that.

    Drills citing 110.14

  • NEC 2023 Table 310.16 — Ampacities of Insulated Conductors in Raceway, Cable, or Earth

    For aluminum or copper-clad aluminum, 4 AWG is listed at 55 A (60°C), 65 A (75°C), and 75 A (90°C).

    Drills citing Table 310.16

  • NEC 2023 110.14(C)(1)(a) — Temperature Limitations — Equipment Provisions

    Termination provisions of equipment for circuits rated 100 A or less, or marked for 14 AWG through 1 AWG conductors, are used with 60°C conductors, or with higher-rated conductors whose ampacity is based on the 60°C column, unless the equipment is listed and identified for higher-temperature conductors.

    Drills citing 110.14(C)(1)(a)

  • NEC 2023 250.142(B) — Load-Side Equipment

    Except as specifically permitted, the grounded (neutral) conductor may not be used to ground non-current-carrying metal parts of equipment on the load side of the service disconnecting means.

    Drills citing 250.142(B)

2026 NEC:not yet checked Confidence: low

Minnesota

MN adopts the NEC rule as writtenConfidence: high

Minnesota adopted the 2023 NEC without amendment as the Minnesota Electrical Code (Minn. Rules 1315.0200; Minn. Stat. 326B.35), effective July 1, 2023, so 110.14, Table 310.16, and 250.142 apply as published. That edition governs permits filed through Aug. 16, 2026; permits filed on or after Aug. 17, 2026 fall under the 2026 NEC; see the 2026 NEC note on this drill for how the cited section fares there.

How Minnesota adopts the NEC

Why the other choices are wrong

  • The aluminum conductors must get antioxidant compound before landing in the lugs. The NEC does not require antioxidant compound. It is needed only where the terminal or conductor manufacturer's instructions call for it (110.3(B)), and AL9CU lugs are identified for aluminum as installed.
  • The neutral and equipment grounding conductors must be landed on the same bar. Neutrals and grounds share a bar only where the main bonding jumper is, at the service disconnect. Downstream of the service, the grounded conductor may not be connected to equipment grounding conductors or the enclosure (250.24(A)(5), 250.142(B)), so separate, isolated bars are correct here.
  • 4 AWG aluminum is too small for a 50 A feeder. Table 310.16 gives 4 AWG aluminum 55 A at 60°C and 65 A at 75°C, so it is adequate for a 50 A feeder even under the 60°C column.
Code complianceLevel 3 · Master#aluminum#feeder#subpanel#ampacity#garage#calibration

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