NEC Articles 404 & 406 — Switches and Receptacles: The Complete Exam Guide

Articles 404 and 406 govern two of the most common devices electricians install: switches and receptacles. While neither article is as voluminous as Article 250 or 430, they contain highly specific rules that appear on virtually every residential and commercial exam — particularly around ratings, tamper resistance, weatherproofing, and grounding.

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NEC Article 404 — Switches

Article 404 covers the general requirements for all types of switches: snap switches, motor-circuit switches, and other disconnecting switches used in electrical installations.

404.2 — Switch Connections

The fundamental rule: every switch must open the ungrounded (hot) conductor, never the grounded (neutral).

Exam tip: A switch wired in series with the neutral is a code violation — the load remains energized with the switch "off." This is both a safety hazard and a violation of 404.2(A). Switches go in the hot leg, always.

Three-way switches: Where two three-way switches control the same load, the travelers connect the two switch boxes. The common terminal of each three-way switch connects to either the hot supply or the switched hot going to the load.

Grounded conductor (neutral) through a switch box: When a cable is run to a switch location and the neutral is needed to complete a circuit, the neutral passes through without interruption. The switch only opens the ungrounded conductor.

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404.4 — Damp or Wet Locations

Switches installed in damp or wet locations must be enclosed in weatherproof enclosures.

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404.6 — Position of Knife Switches

Knife switches must be mounted so the blades are de-energized when the switch is in the open position.

Single-throw knife switches must be mounted vertically such that gravity will not close the switch — blades up when closed, blades down when open.

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404.9 — Position and Connection of Snap Switches

404.9(A): Snap switches must clearly indicate whether they are in the open (off) or closed (on) position. For vertically operated switches, up = ON, down = OFF.

404.9(B) — Grounding: Snap switches, including dimmer switches, must be connected to an equipment grounding conductor to allow grounding of a metal faceplate.

Exception: In existing installations where no grounding means exists in the switch box, the switch may be installed without connecting to an EGC if a nonmetallic, nonconducting faceplate is used, or if the switch itself is GFCI protected.

Exam tip: The grounding exception only applies to existing installations where no ground wire is present. New construction must always have the switch yoke grounded.

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404.10 — Mounting of Snap Switches

Snap switches must be mounted with the yoke seated against the wall surface or box. The switch must be flush with the faceplate or recessed — not protruding.

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404.14 — Ratings Required

404.14(A) — AC General-Use Snap Switches

A general-use snap switch marked for AC only may be used to control:

• Resistive and inductive loads up to the ampere and voltage rating of the switch
• Motor loads not exceeding 80% of the switch's ampere rating

404.14(B) — AC-DC General-Use Snap Switches

An AC-DC rated switch may control resistive loads up to its full rating on AC or DC circuits. For inductive loads on DC, the switch must be derated.

404.14(C) — CO/ALR Switches

Switches used with aluminum conductors must be marked CO/ALR. Switches marked only for copper may not be used with aluminum wire.

Exam tip: CO/ALR marking is required for switches and receptacles used with aluminum wiring — a common exam question for service-upgrade or older home work.

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404.15 — Markings

Snap switches must be marked with:

• Current rating
• Voltage rating
• Whether AC-only or AC-DC

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Key Article 404 Numbers

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NEC Article 406 — Receptacles, Cord Connectors, and Attachment Plugs

Article 406 covers the selection, installation, and replacement of receptacles — one of the highest-volume topics on residential exams.

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406.3 — Receptacle Rating and Type

15A vs 20A receptacles on branch circuits — this is the most-tested provision in Article 406:

210.21(B) — Single receptacle: A single (individual) receptacle outlet installed on a branch circuit must have an ampere rating no less than that of the branch circuit.

210.21(B) — Multiple receptacle outlet: Where a circuit supplies multiple receptacles or outlets, the receptacle rating must conform to Table 210.21(B)(3):

Exam tip: The critical rule: a 15A receptacle is permitted on a 20A multi-outlet circuit. A 20A single outlet requires a 20A T-slot receptacle. This distinction appears on almost every residential journeyman exam.

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406.4 — General Installation Requirements

406.4(A) — Circuit Voltage: Receptacles must not be installed on circuits with a voltage exceeding the receptacle rating.

406.4(B) — Grounding Type: Receptacles installed on grounded systems (standard 120V/240V circuits) must be of the grounding type (three-prong).

406.4(D) — Replacements: When replacing a receptacle in a location that requires GFCI protection per 210.8, the replacement receptacle must be GFCI protected. This applies even in older homes where the original receptacle was two-prong and non-GFCI.

Replacement with a GFCI receptacle or a standard receptacle downstream of a GFCI breaker both satisfy this requirement. The replacement does not have to be a grounding-type if no grounding means is available — the GFCI protection is the safety element.

Exam tip: 406.4(D) is frequently tested in scenarios about replacing old two-prong outlets. In a kitchen or bathroom without a ground wire: replace with a GFCI receptacle (not required to be grounding-type, but must be GFCI protected) and mark it "No Equipment Ground."

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406.9 — Receptacles in Wet and Damp Locations

406.9(A) — Damp Locations:

Receptacles in damp locations must have a weatherproof cover. The cover must maintain weatherproofing with no attachment plug inserted. A standard in-use weatherproof cover (listed for damp locations) is acceptable.

406.9(B) — Wet Locations:

Receptacles installed in wet locations must be protected by an in-use cover listed as extra-duty, which maintains weatherproofing even with a cord plugged in (sometimes called a "bubble cover").

Exam tip: Damp vs wet — a covered porch is damp; an exposed outdoor wall is wet. The exam often describes a scenario and asks which cover is required. Extra-duty in-use = wet location. Standard weatherproof = damp location.

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406.11 — Tamper-Resistant Receptacles in Dwelling Units

All 15A and 20A, 125V receptacles in dwelling units must be tamper-resistant. This includes:

• Every room, hallway, and common area
• Garages and accessory structures
• Outdoors
• Crawl spaces and unfinished basements
• Kitchen and dining countertops

Exceptions: Receptacles located more than 5½ feet above the floor, receptacles that are part of a luminaire or appliance, locked receptacles accessible only to qualified persons, and non-grounding-type replacements where no grounding means is available.

Exam tip: In any new construction dwelling unit, ALL 15A/20A 125V receptacles must be tamper-resistant — not just those in children's rooms. This requirement applies building-wide.

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406.12 — Receptacles in Specific Locations

Face-up receptacles in countertops — a receptacle installed in a countertop face-up (horizontal) must be listed and identified for that use. Standard outlet boxes installed face-up in a countertop are not permitted unless specifically listed for countertop installation.

CO/ALR receptacles — receptacles used with aluminum conductors must be marked CO/ALR. Standard receptacles marked only for copper cannot be used with aluminum wiring.

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Key Article 406 Numbers

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Common Exam Mistakes on Articles 404 & 406

1. Wiring a switch in the neutral leg — always in the ungrounded conductor; the load stays hot with the switch off if wired wrong
2. Installing a 15A single-outlet receptacle on a 20A dedicated circuit — a single 20A circuit requires a 20A receptacle; 15A is only OK when there are multiple outlets
3. Using a standard weatherproof cover in a wet location — wet requires extra-duty in-use cover; standard covers don't protect when a cord is plugged in
4. Forgetting tamper-resistant applies to the whole dwelling — not just bedrooms; every 15/20A 125V outlet in the building
5. Replacing a two-prong outlet without GFCI in a required location — 406.4(D) requires GFCI protection on all replacements in locations covered by 210.8

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Ready to Practice Articles 404 & 406 Questions?

GetLicenseReady includes questions on switch ratings, receptacle rules, tamper-resistant requirements, and wet/damp location covers — the specific scenarios that appear on residential and commercial exams.

Related reading: NEC Article 210 — Branch Circuits | NEC Article 110 — Requirements for Electrical Installations | GFCI and AFCI Requirements