General (Minnesota Class A Journeyworker)

Learning Objectives

Apply the interrupting-rating rules to equipment that interrupts fault current and to equipment that interrupts current at other than fault levels.

Apply the temperature limitation rules of 110.14 and the markings required on disconnecting means.

Apply the working space and dedicated equipment space rules of 110.26 and the Part III rules above 1000 volts.

2.1 Article 100 Definitions That Drive Article 110

Approved — acceptable to the authority having jurisdiction.

Listed — equipment, materials, or services included in a list published by an organization acceptable to the authority having jurisdiction, concerned with evaluation of products or services and maintaining periodic inspection of production, whose listing states that the item meets appropriate designated standards or has been tested and found suitable for a specified purpose.

Labeled — equipment or materials bearing a label, symbol, or other identifying mark of an organization acceptable to the authority having jurisdiction and concerned with product evaluation, by whose labeling the manufacturer indicates compliance with appropriate standards.

Identified (as applied to equipment) — recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular code requirement.

Grounded Conductor — a system or circuit conductor that is intentionally grounded. The informational note states that although an equipment grounding conductor is grounded, it is not considered a grounded conductor.

Identification of these conductors is a separate matter: 200.7 gives the means of identifying grounded conductors, 200.8 governs the use of white or gray insulation or three continuous white or gray stripes, and 250.119 governs equipment grounding conductors.

2.2 Approval, Examination, and Installation of Equipment (110.2 and 110.3)

Section 110.2 states the general rule: the conductors and equipment required or permitted by the code shall be acceptable only if approved.

Section 110.3(A), Examination, lists the considerations evaluated in judging equipment: suitability for installation and use in conformity with the code; mechanical strength and durability; wire-bending and connection space; electrical insulation; heating effects under normal and abnormal conditions; arcing effects; and other factors affecting practical safeguarding.

Section 110.3(B), Installation and Use, 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, with those instructions resulting in an installation and use that complies with the code. Section 110.3(C) requires testing, evaluation, and listing to be done by recognized qualified electrical testing laboratories. Section 90.7 states the intent of the code that factory-installed internal wiring, or the construction of equipment, need not be inspected at the time of installation except to detect alterations or damage, if the equipment has been listed by a qualified electrical testing laboratory in accordance with 110.3(C).

2.3 Interrupting Rating and Available Fault Current (110.9 and 110.24)

Section 110.9 contains two sentences that must not be interchanged. Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the available fault current at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that must be interrupted.

Section 110.10 requires the overcurrent protective devices, equipment short-circuit current ratings, and other circuit characteristics to be selected and coordinated with the available fault current so that a fault is cleared without extensive damage. Section 110.24(A) requires service equipment at other than dwelling units to be legibly marked in the field with the available fault current, including the date the calculation was performed.

2.4 Mechanical Execution of Work and Connections (110.12 and 110.14)

Section 110.12 states that electrical equipment shall be installed in a professional and skillful manner. Section 110.12(A) requires unused openings, other than those intended for the operation of equipment or for mounting purposes, to be closed to afford protection substantially equivalent to the wall of the equipment; metallic plugs or plates used with nonmetallic enclosures must be recessed at least 6 mm (1/4 in.) from the outer surface.

Section 110.11 prohibits conductors and equipment from being installed in damp or wet locations, or where exposed to deteriorating agents or excessive temperatures, unless identified for that environment. Section 110.14(A) requires terminal connections to be made by pressure connectors, solder lugs, or splices to flexible leads without damaging the conductors. Wire-binding screws, or studs and nuts with upturned lugs or the equivalent, are permitted for 10 AWG or smaller conductors. Section 110.14(C) limits the temperature rating associated with a conductor's ampacity to the lowest rating of any connected termination, conductor, or device:

Termination Provisions	Governing Temperature Basis
Circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors — 110.14(C)(1)(a)	Conductors rated 60 degrees C (140 degrees F), or higher-rated conductors whose ampacity is determined from the 60 degrees C ampacity of the size used
Circuits rated over 100 amperes, or marked for conductors larger than 1 AWG — 110.14(C)(1)(b)	Conductors rated 75 degrees C (167 degrees F), or higher-rated conductors whose ampacity does not exceed the 75 degrees C ampacity of the size used

2.5 Marking and Identification of Disconnecting Means (110.21 and 110.22)

Section 110.21(A)(1) requires the manufacturer's name, trademark, or other descriptive marking on all equipment, and 110.21(B) governs field-applied hazard markings: they must warn using effective words, colors, or symbols, be permanently affixed, and shall not be handwritten.

Section 110.22(A) requires each disconnecting means to be legibly marked to indicate its purpose unless its location makes the purpose evident, and adds that in other than one- or two-family dwellings the marking shall include the identification and location of the circuit source that supplies it unless that identification and location is evident.

Under 110.22(B), enclosures for series combination ratings selected under engineering supervision under 240.86(A) shall be legibly marked in the field and state:

> CAUTION — ENGINEERED SERIES COMBINATION SYSTEM RATED _______ AMPERES. IDENTIFIED REPLACEMENT COMPONENTS REQUIRED.

Under 110.22(C), enclosures for series combination ratings marked on the equipment by the manufacturer under 240.86(B) shall be legibly marked in the field and state:

> CAUTION — SERIES COMBINATION SYSTEM RATED ____ AMPERES. IDENTIFIED REPLACEMENT COMPONENTS REQUIRED.

The word ENGINEERED appears only in the 110.22(B) marking, and both markings must meet 110.21(B) and be readily visible.

2.6 Working Space and Dedicated Equipment Space (110.26)

Section 110.26 requires working space, and access to and egress from it, about all electrical equipment; access or egress is impeded if simultaneously opened doors restrict access to less than 610 mm (24 in.) wide and 2.0 m (6 1/2 ft) high when the doors are or can be opened 90 degrees. The depth of working space in the direction of live parts must be not less than Table 110.26(A)(1) requires.

Nominal Voltage to Ground	Condition 1	Condition 2	Condition 3
0–150 ac or dc	900 mm (3 ft)	900 mm (3 ft)	900 mm (3 ft)
151–600 ac or dc	900 mm (3 ft)	1.0 m (3 ft 6 in.)	1.2 m (4 ft)
601–1000 ac or 601–1500 dc	900 mm (3 ft)	1.2 m (4 ft)	1.5 m (5 ft)

Condition 1 means live parts on one side and no exposed or enclosed live or grounded parts on the other side, or live parts on both sides effectively guarded by insulating materials; Condition 2 means exposed or enclosed live parts on one side and grounded parts on the other side, with concrete, brick, or tile walls considered grounded; Condition 3 means exposed or enclosed live parts on both sides.

The width of the working space must be the width of the equipment or 762 mm (30 in.), whichever is greater, and the space shall extend to 2.0 m (6 1/2 ft) or the height of the equipment, whichever is greater, and shall not be used for storage. Section 110.26(E)(1)(a) defines the dedicated electrical space for indoor installations as the space equal to the width and depth of the equipment extending from the floor to 1.8 m (6 ft) above the equipment or to the structural ceiling, whichever is lower, with no piping, ducts, or other equipment foreign to the electrical installation.

2.7 Work Space and Guarding Over 1000 Volts ac or 1500 Volts dc

Part III of Article 110 supplements Part I and does not apply on the supply side of the service point. Section 110.31 requires such installations to be accessible only to qualified persons, in a vault, room, or closet, or in a fenced area not less than 2.1 m (7 ft) high. Section 110.32, Work Space About Equipment, requires the clear work space about equipment to be not less than 2.0 m (6 1/2 ft) high measured vertically from the floor or platform and the width of the equipment or 914 mm (3 ft) wide measured parallel to the equipment, whichever is greater, with the depth as required in 110.34(A). Section 110.33(A) requires at least one entrance to the working space not less than 610 mm (24 in.) wide and 2.0 m (6 1/2 ft) high.

Table 110.34(A) sets the depth of the work space. For 1001–2500 volts to ground the depths are 900 mm (3 ft), 1.2 m (4 ft), and 1.5 m (5 ft); for 2501–9000 volts they are 1.2 m (4 ft), 1.5 m (5 ft), and 1.8 m (6 ft); Section 110.34(C) requires locked rooms, vaults, and enclosures containing exposed live parts to be marked DANGER — HIGH VOLTAGE — KEEP OUT.

Code Navigation

Topic	NEC Section	What It Contains
Definitions and approval	Article 100, 110.2, 110.3	Approved, Listed, Labeled, Identified, Grounded Conductor; approval and installation per instructions
Connections and terminals	110.14(A), (C)	Pressure connectors; wire-binding screws for 10 AWG or smaller; 60/75 degrees C bases
Marking and disconnecting means	110.21, 110.22	Manufacturer markings; purpose, circuit source, series combination wording
Over 1000 volts	110.32, 110.34	2.0 m (6 1/2 ft) height; 914 mm (3 ft) width; Table 110.34(A) depths

Common Exam Traps

Confusing Approved with Listed. Article 100 defines Approved as acceptable to the authority having jurisdiction, while Listed describes equipment included in a list published by an organization acceptable to that authority. A testing laboratory lists equipment; it does not approve it.

Assuming the 60 degrees C (140 degrees F) basis applies everywhere. Section 110.14(C)(1)(a) covers circuits rated 100 amperes or less or marked for 14 AWG through 1 AWG; larger equipment takes the 75 degrees C (167 degrees F) basis.

Choosing the wrong Condition in Table 110.26(A)(1). Concrete, brick, or tile walls are grounded parts, so a wall opposite the equipment selects Condition 2; live parts on both sides selects Condition 3.

Confusing the dedicated equipment space height with the working space height. Section 110.26(E)(1)(a) uses 1.8 m (6 ft) above the equipment; 110.26(A)(3) uses 2.0 m (6 1/2 ft) for the working space.

Practical Field Points

Record the available fault current and its calculation date on service equipment as 110.24(A) requires, and update the marking after a service change.

Recess metallic plugs and plates at least 6 mm (1/4 in.) when closing unused openings in nonmetallic enclosures; loose covers over knockouts do not meet 110.12(A).

Keep the working space clear of storage and the 1.8 m (6 ft) dedicated equipment space free of piping and ducts.

Summary

Article 110 is the code's general requirements article. Section 110.2 makes approval the condition of acceptability, and 110.3 obligates listed, labeled, or identified equipment to be installed and used per its instructions. Section 110.9 rates equipment that interrupts current at fault levels against the available fault current at its line terminals, and equipment that interrupts at other than fault levels against the current that must be interrupted. Section 110.12 requires a professional and skillful installation and closes unused openings to protection substantially equivalent to the wall of the equipment, with metallic plugs and plates recessed at least 6 mm (1/4 in.) in nonmetallic enclosures. Section 110.14 permits wire-binding screws only for 10 AWG or smaller conductors and sets termination temperature bases of 60 degrees C (140 degrees F) for circuits rated 100 amperes or less or marked for 14 AWG through 1 AWG and 75 degrees C (167 degrees F) for larger equipment. Section 110.22 requires the purpose of each disconnecting means, the circuit source outside one- and two-family dwellings, and the exact CAUTION wording for engineered and tested series combination systems. Section 110.26 sets working space depths, a 762 mm (30 in.) minimum width, and a dedicated equipment space to 1.8 m (6 ft) above the equipment or the structural ceiling. Part III of Article 110 applies over 1000 volts ac or 1500 volts dc, where 110.32 requires a 2.0 m (6 1/2 ft) height and a 914 mm (3 ft) width with depths from Table 110.34(A).

General