12.1 General Disconnecting Means Principles

Why This Matters for the TX Journeyman Exam

Content Area 8 (Control Devices & Disconnecting Means) sits mostly in the NEC Knowledge part of the two-part Texas Journeyman exam (59 questions, 130 minutes). Examiners test whether you can identify the correct disconnect location, rating, and enclosure for a given installation — not just recite definitions. The 2023 NEC Articles 100, 404, and 225 supply the rule set for general disconnecting means; Articles 430, 440, and 424 supply the equipment-specific rules covered in Sections 12.2 and 12.3 and in Chapters 10 and 11.

Article 100 Definitions You Must Quote

Disconnecting means. A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.

In sight (within sight). Visible and not more than 15 m (50 ft) distant from each other. Two pieces of equipment are 'in sight' of each other only when both conditions are met: (1) a person standing at one can see the other, and (2) the separation is ≤ 50 ft. The 'line of sight' rule is the default basis for 430.102(A) motor disconnect location, 440.14 HVAC disconnect location, and 225.32 building-disconnect placement.

Article 404 Switch Installation — Beyond the Basics

Chapter 10 covers Article 404 switch basics (neutrals, ratings, grounding, dimmers, luminaire/appliance disconnects). This section owns the accessibility, grouping, and knife-switch rules that Ch10 does not cover.

Wet/damp enclosures are governed by 312.2 (damp or wet locations — enclosures shall prevent moisture entry) and 314.15 (boxes in wet locations shall be weatherproof and have drainage), not by 404.8 — do not confuse the articles.

Knife switches (404.13) are the oddity examiners love. Above 1200 A at ≤ 250 V (or above 1000 A at higher voltages) a knife switch is an isolating switch only — it shall not be opened under load. 404.13 also requires knife switches to be mounted so gravity cannot close the blades, and on single-throw types the blades shall be dead when the switch is open. There is no 600 A limit in 404.13; the real threshold is the 1200 A / 1000 A isolating-switch rule. Knife switches are rare in modern work but appear on the exam.

Article 225 — Outside Building/Structure Disconnects

Article 225 governs feeders and branch circuits that run outside to a separate building or structure. The disconnect rules mirror the service-equipment rules in Article 230 (covered in Chapter 4) but apply on the load side.

The 'One Building, One Disconnect' Concept (225.54)

225.54 restricts a building or structure to one feeder or branch-circuit supply. The permitted additional supplies (Exceptions No. 1–4) include: additional capacity where a single supply is impractical, multi-occupancy buildings with separate occupancy supplies, different characteristics (voltage, frequency, system), and standby/parallel systems. This rule pairs with 230.71 (the six-disconnect rule for service equipment, Chapter 4) — together they limit the number of disconnect handles an operator must throw to de-energize a building.

Tie to the Service Disconnect (Chapter 4)

225.51 is the feeder-side twin of 230.70 (service disconnect). For a service, 230.70 requires a readily accessible disconnect at or ahead of the service entrance (Chapter 4 covers 230.71's six-disconnect rule, 230.72 grouping, and 230.79 ratings). For an outside feeder to a second building, 225.51 requires the disconnect at the second building. The two rules together guarantee that every building on a property has a local means to cut power.

Worked Scenario: Feeder to a Detached Garage

A single-family residence has a 120/240 V feeder run underground to a detached garage. What disconnect is required, and where?

1. Apply 225.51 — the garage is a separate structure; an outside feeder to it requires a disconnecting means located at the garage, not at the house.
2. Apply 225.32 — the disconnect shall be at the point of entry of the feeder conductors into the garage, or at the nearest readily accessible location to that point. It cannot be in a bathroom or near combustible storage.
3. Apply 225.54 — only one feeder may supply the garage unless an exception applies (e.g., a separate 120 V lighting feeder plus a 240 V HVAC feeder is not permitted without meeting an exception).
4. Apply 225.52 / 225.53 — mark the disconnect ('Garage Main') and ensure its rating is suitable for the feeder load.
5. Cross-reference 230.70 (Chapter 4) — the garage disconnect is the load-side analog of the house service disconnect; both must be grouped where there are multiple disconnects (225.33 mirrors 230.72).

Result: Install a suitably rated disconnect (e.g., 60 A or 100 A main-breaker panel) on the exterior or interior wall of the garage at the point where the feeder conductors enter, marked, accessible, and not in a bathroom. If the feeder conductors enter through the back wall, the disconnect must be on that wall or the nearest readily accessible point — not across the garage.

Common Exam Traps

• 'In sight' = 50 ft, not 25 ft. The 15 m metric equivalent is the source of the number; do not confuse with the 6 ft (1.8 m) rule for receptacle spacing.
• 225.32 point-of-entry is the rule for building disconnects; 430.102(A) is the rule for motor disconnects — they are different articles.
• Knife switches are not banned; above 1200 A at ≤ 250 V (or above 1000 A at higher voltages) they are limited to isolating-switch duty and shall not be opened under load (404.13).
• 225.54 lets a building have more than one supply only via listed exceptions — the default is one supply, one disconnect.