NEC 100-110 — General Requirements (Washington)

NEC 100-110 — General Requirements (Washington Journeyman)

Learning Objectives

1.1 Article 100 Definitions the Exam Tests

Accessible (as applied to equipment) means capable of being reached for operation, renewal, and inspection. Accessible (as applied to wiring methods) means capable of being removed or exposed without damaging the building structure or finish, or not permanently closed in or blocked by it. Accessible, Readily means capable of being reached quickly for operation, renewal, or inspection without tools other than keys, climbing, removing obstacles, or portable ladders.

Approved means acceptable to the authority having jurisdiction. Listed means included in a list published by an organization acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production and states that the item meets designated standards or has been tested and found suitable for a specified purpose. Labeled means the same items bearing a label or other identifying mark of that organization; the label is evidence of listing.

Ampacity is the maximum current, in amperes, a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Appliance is utilization equipment, generally other than industrial, built in a standardized size or type and connected as a unit to perform one or more functions; the Informational Note lists clothes washers and deep fryers. Ambulatory Health Care Occupancy provides services or treatment simultaneously to four or more patients on an outpatient basis. Adjustable Speed Drive System combines an adjustable speed drive, its associated motor(s), and auxiliary equipment. Aircraft Painting Hangar is built expressly for spraying, coating, and/or dipping applications and provided with dedicated ventilation supply and exhaust.

An article number in parentheses limits a definition to that article: Amplifier (Audio Amplifier) (Pre-Amplifier) carries (640), Applicator carries (665), and Ambulatory Health Care Occupancy carries (517).

1.2 Approval, Listing, and Equipment Suitability (110.2 and 110.3)

110.2 requires conductors and equipment to be acceptable only if approved, and approved means acceptable to the authority having jurisdiction. Unlisted equipment is not automatically permitted because the manufacturer publishes specifications or because the installer accepts liability; acceptability is the authority having jurisdiction's decision.

110.3(A) requires evaluating suitability for installation and use in conformity with the code, mechanical strength and durability, wire-bending and connection space, electrical insulation, heating effects, arcing effects, and classification by type, size, voltage, current capacity, and specific use.

110.3(B) requires equipment that is listed, labeled, or both, or identified for a use, to be installed and used in accordance with any instructions included in the listing, labeling, or identification, and those instructions must produce an installation that complies with the code. Equipment listed for dry locations cannot be installed in a wet location, and sealant does not change that; equipment listed for one application cannot be used in another. The installer's judgment, the equipment ratings, and matching occupancy classifications do not override the listing.

110.3(C) requires product testing, evaluation, and listing (product certification) by recognized qualified electrical testing laboratories, in accordance with product standards recognized as achieving equivalent and effective safety; the listing mark signifies compliance with one or more appropriate product safety test standards — not a guarantee against failures and not approval for every installation.

110.4 requires the equipment voltage rating to be not less than the nominal voltage of the circuit it is connected to.

1.3 Interrupting Rating, Coordination, and Fault-Current Marking (110.9, 110.10, 110.24)

110.9 requires equipment intended to interrupt current at fault levels to have an interrupting rating at nominal circuit voltage at least equal to the available fault current at the line terminals of the equipment. Where the available fault current is 25,000 amperes, a 25,000-ampere interrupting rating complies and a 10,000-ampere rating does not — system voltage never excuses the deficiency.

110.10 requires the overcurrent protective devices, equipment short-circuit current ratings, and other characteristics of the circuit to be protected to be selected and coordinated with the available fault current so the devices clear a fault without extensive damage to the circuit's equipment.

110.24(A) requires service equipment at other than dwelling units to be legibly marked in the field with the available fault current and the date the fault-current calculation was performed, complying with 110.21(B), with the calculation documented and available to those authorized to design, install, inspect, maintain, or operate the system. The marking goes on the service equipment. 110.24(B) requires that when modifications to the installation affect the available fault current at the service, the available fault current be verified or recalculated as necessary to confirm the service equipment ratings are sufficient, and the field markings be adjusted to reflect the new level; adding a large motor that raises the fault current triggers this rule.

1.4 Mechanical Execution and Electrical Connections (110.12 and 110.14)

110.12 requires electrical equipment to be installed in a professional and skillful manner; older material and exam options call this a neat and workmanlike manner. Under 110.12(A), unused openings must be closed to afford protection substantially equivalent to the wall of the equipment, and metallic plugs or plates used with nonmetallic enclosures must be recessed at least 6 mm (1/4 in.) from the outer surface; tape, paper, and open holes fail that test.

110.14 requires termination devices such as pressure terminal or pressure splicing connectors and soldering lugs to be identified, installed, and used for the material of the conductor. Conductors must not be intermixed where physical contact occurs between dissimilar conductors unless the device is identified for the purpose and conditions of use, and connectors for conductors more finely stranded than Class B and Class C stranding must be identified for that class. Splicing aluminum to copper therefore requires a connector identified for the purpose and suitable for both materials — not a standard wire nut and not a plain split-bolt.

110.14(A) permits connection to terminal parts by pressure connectors (including set-screw type), solder lugs, or splices to flexible leads, permits wire-binding screws or upturned lugs for 10 AWG or smaller conductors only, and requires terminals for more than one conductor, or used to connect aluminum, to be identified.

110.14(D) requires tightening torque values as indicated on the equipment or in the manufacturer's instructions, achieved by an approved means such as a torque tool, shear bolts, or breakaway-style devices with visual indicators.

Two further rules follow from "identified for the purpose and conditions of use": connections subject to vibration must use a locking device, and damp or wet location connections must use materials suitable for that environment.

1.5 Marking, Identification, and Servicing (110.16, 110.17, 110.21, 110.22)

110.21(A) requires the manufacturer's name, trademark, or other descriptive marking identifying the responsible organization to be affixed to all electrical equipment, of sufficient durability for the environment. 110.21(B) governs field-applied hazard markings: durable for the environment, warning by effective words, colors, symbols, or any combination, permanently affixed, and not handwritten except for variable portions, which must be legible.

110.16 requires a permanent arc-flash marking, field or factory applied, on service equipment and feeder-supplied equipment likely to require examination, adjustment, servicing, or maintenance while energized in other than dwelling units; the marking must comply with 110.21(B), be visible to qualified persons, and contain the nominal system voltage, the arc-flash boundary, the available incident energy or minimum required personal protective equipment level, and the date the assessment was completed.

110.22 requires each disconnecting means to be legibly marked with its purpose unless arranged so the purpose is evident. 110.17 requires servicing by qualified persons trained in servicing the equipment, in accordance with the original equipment manufacturer's instructions and information included in the listing information, applicable industry standards, or as approved by the authority having jurisdiction, using identified replacement parts verified under applicable product standards and provided by the original equipment manufacturer or an engineer experienced in such parts.

1.6 Working Space About Equipment Not Over 1000 Volts (110.26)

110.26 requires working space, and access to and egress from it, about all electrical equipment to permit ready and safe operation and maintenance. Open equipment doors must not impede access: access or egress is impeded if simultaneously opened doors restrict working space access to less than 610 mm (24 in.) wide and 2.0 m (6 ft 6 in.) high when such doors can be opened 90 degrees.

(A) Working Space. Working space is required for equipment likely to require examination, adjustment, servicing, or maintenance while energized; depth is measured from the enclosure front or opening where live parts are enclosed. Condition 1 — live parts on one side and no live or grounded parts on the other, or live parts on both sides effectively guarded by insulating materials; Condition 2 — live parts on one side and grounded parts on the other; Condition 3 — live parts on both sides.

(2) Width. The width of the working space must be the width of the equipment or 762 mm (30 in.), whichever is greater, and must permit at least a 90-degree opening of equipment doors or hinged panels. (3) Height. The working space must be clear and extend from the grade, floor, or platform to a height of 2.0 m (6 ft 6 in.) or the height of the equipment, whichever is greater; equipment or support structures associated with the installation may extend not more than 150 mm (6 in.) beyond the front of the equipment.

(B) Clear Spaces. Working space must not be used for storage. (C) Entrance to and Egress from Working Space. At least one entrance must be provided, and for large equipment rated 1200 amperes or more and over 1.8 m (6 ft) wide there must be one at each end of the working space, not less than 610 mm (24 in.) wide and 2.0 m (6 ft 6 in.) high. A single entrance is permitted where the location provides a continuous and unobstructed way of egress travel, or where the depth of the working space is twice that required by 110.26(A)(1) — in which case the distance from the equipment to the nearest edge of the entrance must be not less than the minimum clear distance in Table 110.26(A)(1) for that voltage and condition.

(E) Dedicated Equipment Space. Service equipment, switchboards, switchgear, enclosed panelboards, and motor control centers must be located in dedicated spaces and protected from damage. Indoors, the space equal to the width and depth of the equipment, from the floor to a height of 1.8 m (6 ft) above the equipment or the structural ceiling, whichever is lower, is dedicated to the electrical installation; no piping, ducts, or other foreign equipment may occupy that zone.

1.7 Entrances, Egress, and Working Space Over 1000 Volts (110.33 and 110.34)

Part III of Article 110 governs equipment operating over 1000 volts ac, 1500 volts dc, nominal.

110.33 Entrance to Enclosures and Access to Working Space. Under 110.33(A), at least one entrance to enclosures for electrical installations described in 110.31, not less than 610 mm (24 in.) wide and 2.0 m (6 ft 6 in.) high, must give access to the working space about electrical equipment. On switchgear and control panels exceeding 1.8 m (6 ft) in width there must be one entrance at each end; a single entrance is permitted where the location permits a continuous and unobstructed way of exit travel, or where the working space depth is twice that required by 110.34(A) — in which case the distance from the equipment to the nearest edge of the entrance must be not less than the minimum clear distance in Table 110.34(A) for that voltage and condition. Where bare energized parts at any voltage or insulated energized parts are adjacent to such an entrance, they must be suitably guarded. Where personnel doors intended for entrance and egress are less than 7.6 m (25 ft) from the nearest edge of the working space, the doors must open at least 90 degrees in the direction of egress and be equipped with listed panic hardware or listed fire exit hardware.

Under 110.33(C), the entrance to buildings, vaults, rooms, or enclosures containing exposed live parts or exposed conductors must be kept locked unless under the observation of a qualified person at all times, and permanent, conspicuous danger signs meeting 110.21(B) must read DANGER — HIGH VOLTAGE — KEEP OUT. Under 110.33(D), illumination must be provided for all working spaces about electrical equipment, control by automatic means only shall not be permitted, and lighting outlets must be arranged so persons changing lamps or repairing the lighting are not endangered by live parts.

110.34 Work Space and Guarding. Under 110.34(A), equipment likely to require examination, adjustment, servicing, or maintenance while energized must have clear working space to live parts not less than specified in Table 110.34(A).

Every row of Table 110.34(A) starts at 1001 volts and above; this is not the table used for 480-volt or 600-volt equipment, where Table 110.26(A)(1) applies.

110.34(B) Separation from High-Voltage Equipment. Where switches, cutouts, or other equipment operating at not over 1000 volts ac, 1500 volts dc, nominal, are installed in a vault, room, or enclosure with exposed live parts or wiring operating at over 1000 volts ac, 1500 volts dc, nominal, the high-voltage equipment must be effectively separated from the lower-voltage space by a suitable partition, fence, or screen. The exception permits such equipment serving only equipment within the high-voltage vault, room, or enclosure to be installed without a partition, fence, or screen if accessible to qualified persons only — it fails the moment the lower-voltage equipment serves loads outside that space.

Code Navigation

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Practical Field Points

Summary

Article 110 is the general-requirements gate, tested as precise thresholds and permissions. Approval under 110.2 belongs to the authority having jurisdiction; listing and labeling under 110.3(C) are third-party product certification, and 110.3(B) makes the instructions attached to that evaluation binding on the installer. 110.9 sets interrupting ratings against the available fault current at the line terminals; 110.10 coordinates devices and short-circuit current ratings with that current; and 110.24 requires service equipment marked with the available fault current and the date of calculation, updated when modifications change the fault level. Workmanship falls to 110.12, which requires professional and skillful work and closes every unused opening, and connections to 110.14, which requires terminals and splicing devices identified for the conductor material, bars intermixing dissimilar conductors unless the device is identified for the purpose and conditions of use, Markings follow 110.21, 110.16, and 110.17. The largest block is 110.26: depth from Table 110.26(A)(1) matched to the voltage-to-ground row and the condition on each side, width of the equipment or 762 mm (30 in.), height of 2.0 m (6 ft 6 in.), no storage in the working space, one entrance at each end of large equipment unless unobstructed egress or double working space applies, personnel doors with panic hardware within 7.6 m (25 ft), and a dedicated equipment space extending 1.8 m (6 ft) above the equipment and free of foreign piping. Read the table in your own code book.