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Article 90 — Purpose & Scope

90.1(A)The NEC's purpose is practical safeguarding of persons and property from electrical hazards. It is not a zero-risk guarantee; misuse or poor maintenance can still make an installation unsafe.
90.3Arrangement: Chapters 1-4 apply generally; 5, 6, 7 modify/supplement for special occupancies, equipment, or conditions; 8 is independent (communications); 9 contains tables.
90.5Shall = mandatory; May = permissive; Should = advisory. Informational Notes are *not enforceable*—exams love to bait you here.
90.7Listed/labeled products are presumed safe, but must still be installed and used per their listing and instructions.

EXAM TRAP

PRACTICAL SAFEGUARDING

If a choice hints the NEC guarantees absolute safety, it’s wrong. The phrase is practical safeguarding (90.1(A)). Also, Informational Notes are not enforceable—don’t let the exam turn a note into a rule.

NEC scope diagram showing chapter relationships

Scope of the NEC and which chapters modify others.

Graphic showing the words SHALL and MAY on tags

‘Shall’ = mandatory. ‘May’ = permissive. Notes aren’t enforceable.

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Article 100 — Definitions You’ll Fight On

Branch CircuitConductors between the final OCPD protecting the circuit and the outlets. If you're upstream of the last OCPD, you're not on a branch circuit.
FeederAll circuit conductors between the service equipment (or power source) and the final branch-circuit OCPDs. The last OCPD is the boundary.
Readily AccessibleReachable quickly without tools, ladders, or moving obstacles. If you need a screwdriver or must move a refrigerator, it isn't readily accessible.
Identified / Listed / LabeledIdentified = suitable for a specific purpose (often by listing/labeling). Listed = evaluated by an NRTL. Labeled = marked with the NRTL symbol and info.
Grounded vs Equipment Grounding ConductorThe grounded (neutral) conductor carries current in normal operation; the equipment grounding conductor (EGC) carries fault current and bonds metal parts.

RULE OF THUMB

BRANCH STARTS AFTER THE FINAL OCPD

Stuck on feeder vs branch? Default to this: the branch starts after the final OCPD. Everything upstream is feeder. That single line solves many layout and article-selection questions.

Terminal block mapping service, feeders, and branches

Service → feeders → branch circuits: know where you are.

UL and CSA listing marks on an equipment label

‘Identified’ usually means listed and used per labeling and instructions.

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110.3(B) — Listing, Labeling, and Instructions

Use Per ListingInstall and use equipment in accordance with instructions included in the listing/labeling: orientation, clearances, ambient limits, torque, accessories.
AHJThe Authority Having Jurisdiction enforces the Code and listing use. If the label says use kit X only, that's what passes.
Field LabelingWhen a product or arrangement isn't listed for the application, a field evaluation and field label may be required.
Label WinsWhen Code allows options, the manufacturer's instructions can be more restrictive. The label wins on the job and on the exam.

NEC REFERENCE

FOLLOW THE LABEL

110.3(B) is a top-5 exam anchor. If a label gives a torque, that’s your torque. If the manual requires a specific accessory or orientation, that’s the rule.

Product label with torque, ambient, and kit limitations

If the label lists a torque and kit pairing, follow both.

AHJ inspection sticker on an electrical panel

AHJ signs off when it’s installed per listing/labeling.

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110.14 — Terminations, Temperature Ratings, and Torque

Temp RatingConductor ampacity is limited by the lowest temperature rating of any termination in the circuit.
Cu vs AlUse terminals identified for AL/CU when landing aluminum. Anti-oxidant is often required by the manufacturer and AHJ expectations.
Torque ToolsTerminals must be tightened to the manufacturer's specified torque (110.14(D)). Use a calibrated torque tool.
Re-TorqueMany listings require re-torque after a short load cycle. Check the paperwork.

TABLE

EXAMPLES OF COMMON TERMINATION TORQUES (ALWAYS VERIFY LABEL)

Item	Conductor / Range	Typical Torque (in-lb)
Breaker terminal	15–20A Cu	25
Mechanical lug	#2–#6 Cu	45–50
Main lugs	2/0–4/0 Cu	180–250

Examples only. Inspectors expect the exact value from the product label or instructions.

Electrician using a torque screwdriver on a breaker

Torque to the printed value; inspectors check this.

Closeup of termination temperature stamps 60°C/75°C

Use the lowest temperature rating among connected terminations.

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110.26 — Working Space Around Electrical Equipment

Depth3 ft (Condition 1) up to 4 ft (Condition 3). Measured from live parts/enclosure to the opposing surface.
Width & HeightWidth: 30 in. or equipment width, whichever is greater. Height: floor to 6-1/2 ft. Doors must open at least 90°.
Dedicated SpaceAbove equipment to the structural ceiling must be kept clear of unrelated systems; suspended ceilings count as structural for this rule.
Egress≥1200A and >6 ft wide often requires two egress paths from the working space unless exception applies.

CHART

TABLE — 110.26(A)(1) WORKING SPACE DEPTHS

Voltage Range	Condition 1	Condition 2	Condition 3
0-150V to ground	36 in. (914 mm)	36 in. (914 mm)	36 in. (914 mm)
151-600V to ground	36 in. (914 mm)	42 in. (1067 mm)	48 in. (1219 mm)
601-1000V to ground	42 in. (1067 mm)	48 in. (1219 mm)	54 in. (1372 mm)
1001-2500V to ground	48 in. (1219 mm)	54 in. (1372 mm)	60 in. (1524 mm)
2501-9000V to ground	54 in. (1372 mm)	60 in. (1524 mm)	66 in. (1676 mm)
9001-25000V to ground	60 in. (1524 mm)	66 in. (1676 mm)	72 in. (1829 mm)

Official NEC Table 110.26(A)(1) — Working space depths vary by voltage and exposure conditions. Condition 1: exposed live parts on one side only. Condition 2: exposed live parts on one side, grounded surface on opposite side. Condition 3: exposed live parts on both sides.

Tape measure showing 36 inches clearance in front of panel

Minimum 3 ft depth for many indoor panels (Condition 1).

Overhead view of dedicated space kept clear above gear

Dedicated space above gear stays free of unrelated systems.

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110 — Guarding of Live Parts

Guarding ≥50VLive parts operating at 50V or more must be guarded by enclosures/covers, by location (height), or by placement in a locked room.
EntrancesRooms with exposed live parts: doors swing outward and require panic hardware when equipment is ≥1200A and more than 6 ft wide.
Work PracticesBarricade temporary exposures during maintenance; restore guards before leaving the work area.

EXAM TRAP

50V IS THE LINE

Guarding kicks in at 50V and up. Big-gear rooms (≥1200A and >6 ft wide) need outward-swing doors with panic hardware—common miss on exams.

Guarding prevents accidental contact with energized parts.

Large gear rooms require outward-swinging, panic-hardware doors.

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110 — Identification & Field Marking

110.21(B)Field-applied hazard markings must be durable and warn of the hazard (e.g., arc-flash). They must remain legible for the environment.
110.22(A)Each disconnecting means must be legibly marked to indicate its purpose unless the purpose is obvious by location/arrangement.
DurabilityUse UV/chemical-resistant labels in hot, wet, or oily spaces; paper labels won't last.

RULE OF THUMB

LABELS THAT SURVIVE

Place labels where techs can read them with doors closed. Use materials that survive the environment. If it peels or fades, expect a red tag.

Arc-flash and shock warning labels on gear

Field-applied labels must be durable and legible.

Disconnects must indicate their purpose.

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110 — Illumination & Egress

110.26(E)Working spaces must have fixed lighting; don't rely on portable lights for service/inspection.
110.26(C)For equipment rated ≥1200A and over 6 ft wide, provide two means of egress from the working space unless an exception applies.
AccessDoors used for egress must be usable when equipment doors are open; avoid blocking clear egress with equipment doors.

NEC REFERENCE

LIGHTING & EGRESS

Fixed lighting in working spaces is required. Know the two-egress triggers and exceptions so you can spot compliant layouts on drawings.

Fixed lighting is required for safe work.

Two separate egress paths from an electrical room

Large installations often require two exits.

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110 — Equipment Labeling & SCCR

Available Fault CurrentService equipment must be marked with available fault current where required, and equipment SCCR must be adequate for the system's available fault current.
UpdatesIf available fault current changes (utility upgrade), labels and studies must be updated.
CoordinationObtain fault current data from the utility or use an engineered study; don't guess from nameplate kVA alone.

TABLE

SCCR & Fault-Current Labels — What They Mean

Label	What it shows	Trigger / Notes
Available Fault Current	Calculated fault current at service or equipment location	Required where specified; update if utility/system changes
SCCR (Short-Circuit Current Rating)	Max fault current the equipment assembly can safely withstand	Must be ≥ available fault current at installation point
Date/Method	Basis of available fault-current calc or study	Good practice to include; some AHJs expect it
Contact for Updates	Who to call when service changes	Keeps labels current after utility work or renovations

SCCR of the equipment must be greater than or equal to the available fault current. If the utility increases capacity, re-check the calc and update labels.

Fault current labels keep maintenance safe and compliant.

Verify SCCR ≥ available fault current at the equipment.

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110.26 — Clearance Violations in the Wild

Common MissStorage, piping, or door swings often violate required working space. Plan the room so clearances exist on day one and remain usable.
Be ProactiveCoordinate early with mechanical, plumbing, and IT. Dedicated space and drip pans above gear are frequent friction points.
Protect the SpaceMark floors/walls early; add signage and barrier rails where traffic tends to encroach.

JOBSITE HORROR STORY

DEDICATED SPACE LOST

A copper line was routed across a new switchboard after rough-in. Result: drain, reroute, re-inspect, re-schedule—thousands burned. Lock in dedicated space on the drawings, tag ceilings early, and walk the room with mechanical before they hang pipe.

Stored materials blocking the panel working space

Storage in the working space = violation and fail.

Unrelated piping above gear violates dedicated space rules.

Chapter 1 — General

Article 90 — Purpose & Scope

Article 100 — Definitions You’ll Fight On

110.3(B) — Listing, Labeling, and Instructions

110.14 — Terminations, Temperature Ratings, and Torque

110.26 — Working Space Around Electrical Equipment

110 — Guarding of Live Parts

110 — Identification & Field Marking

110 — Illumination & Egress

110 — Equipment Labeling & SCCR

110.26 — Clearance Violations in the Wild

Knowledge Check

NEC 90.1(A) says the Code’s primary purpose is:

Per 90.1(B), the NEC is NOT intended to be:

90.3 explains Code arrangement. Which is correct?

Mandatory vs permissive language per 90.5:

Article 100 provides:

Informational Notes in the NEC are:

90.2 Scope mainly covers:

Which is typically outside NEC scope per 90.2(B)?

The AHJ is responsible for:

“Listed” equipment means:

Which statement best reflects NEC intent?

If Chapters 5–7 conflict with Chapters 1–4:

Chapter 8 (Communications) is:

Per 90.7, equipment examination/identification typically involves:

When the NEC is adopted by a jurisdiction, enforcement occurs through: