3.1 Approval, Listing, Interrupting Rating & Terminations
Key Takeaways
- NEC 110.3(B) requires listed or labeled equipment to be installed and used in accordance with any instructions included in the listing or labeling, which makes the manufacturer's instructions enforceable Code text.
- NEC 110.9 requires equipment intended to interrupt fault current to have an interrupting rating at nominal circuit voltage sufficient for the available fault current; 110.10 requires the circuit components to withstand that fault.
- NEC 110.14(A) prohibits connecting conductors of dissimilar metals in the same terminal or splicing device unless the device is identified for the purpose.
- NEC 110.14(D) requires terminations to be torqued to the manufacturer's specification using a calibrated torque tool where the equipment is marked with a torque value.
- NEC 110.16(A) requires a field-applied arc-flash warning label on switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers in other than dwelling units.
Approval, Listing and Identification
110.2 Approval. Conductors and equipment required or permitted by the Code shall be acceptable only if approved. "Approved" is defined in Article 100 as acceptable to the authority having jurisdiction. Note what that means: listing is not the Code's approval mechanism — the AHJ is. Listing is the usual evidence the AHJ relies on.
110.3(A) Examination. In judging equipment, considerations include 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, classification by type and size, and other factors contributing to the practical safeguarding of persons using or in contact with the equipment. An Informational Note points out that suitability may be evidenced by listing or labeling.
110.3(B) Installation and Use. "Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling."
This one sentence converts every manufacturer's installation instruction into an enforceable Code requirement. Recessed luminaire spacing from insulation, breaker torque values, conduit-body volume limits, the specific lugs a panel is listed for — all become mandatory through 110.3(B). It is one of the most-cited sections in the entire Code and appears constantly in exam stems.
110.3(C) Listing. New in the 2020 edition: for specified equipment — including switchboards, panelboards, industrial control panels, motor control centers, and elevator control panels — the equipment shall be listed, where the product is available listed.
Interrupting Rating and Short-Circuit Current Rating
These two are constantly confused. Learn them as a pair.
| Section | Applies to | Requirement |
|---|---|---|
| 110.9 Interrupting Rating | Equipment intended to interrupt current at fault levels (breakers, fuses) | Interrupting rating at nominal circuit voltage sufficient for the current available at the line terminals |
| 110.10 Circuit Impedance, SCCR and Other Characteristics | The rest of the circuit — conductors, busbars, panels, controllers | Components must be selected and coordinated to permit the circuit-protective devices to clear the fault without extensive damage to the components |
110.9 also states that equipment intended to interrupt current at other than fault levels — a snap switch, a contactor — shall have an interrupting rating sufficient for the nominal circuit voltage and the current that must be interrupted. 110.10 requires that listed equipment applied within its listing be considered to meet the requirement.
110.24 Available Fault Current. Service equipment in other than dwelling units must be field marked with the maximum available fault current, including the date the calculation was performed, and the marking must be sufficiently durable to withstand the environment. When modifications increase the available fault current, the calculation must be verified or recalculated and the marking updated.
Conductor Terminations and Splices — 110.14
110.14 opening text. Connection of conductors to terminal parts shall ensure a thoroughly good connection without damaging the conductors, and shall be made by pressure connectors (including set-screw type), solder lugs, or splices to flexible leads. Terminals for more than one conductor and terminals used to connect aluminum shall be so identified.
110.14(A) Terminals. Connection by means of wire-binding screws or studs and nuts with upturned lugs is permitted for 10 AWG or smaller conductors. Terminals for more than one conductor must be identified for that use. Conductors of dissimilar metals shall not be intermixed in a terminal or splicing connector where physical contact occurs, unless the device is identified for the purpose and conditions of use.
110.14(B) Splices. Conductors shall be spliced or joined with splicing devices identified for the use, or by brazing, welding, or soldering with a fusible metal or alloy. Soldered splices shall first be spliced or joined so as to be mechanically and electrically secure without solder and then be soldered. All splices and joints and the free ends of conductors shall be covered with an insulation equivalent to that of the conductors, or with an identified insulating device.
110.14(D) Terminal Connection Torque. New emphasis in 2020: "Where a tightening torque is indicated as a numeric value on equipment or in installation instructions provided by the manufacturer, a calibrated torque tool shall be used to achieve the indicated torque value, unless the equipment manufacturer has provided installation instructions for an alternative method." Feeling the connection "tight enough" is no longer defensible where a torque value is marked.
Working with Aluminum
Aluminum termination failures are a persistent source of fires and inspection failures. The Code hooks are 110.14 (dissimilar metals, identified terminals) and 110.3(B) (the connector's listing). Practical requirements that flow from listings: use AL/CU or AL9CU rated lugs, apply the antioxidant compound where the connector's instructions call for it, wire-brush the conductor where instructed, and torque to the marked value.
Also remember 110.5: conductors shall be of copper, aluminum, or copper-clad aluminum unless otherwise provided in the Code; where the conductor material is not specified, the sizes given in the Code are based on copper. That default matters when a question gives a table value without naming the metal.
Other General Rules in Article 110 Part I
- 110.7 Wiring Integrity. Completed wiring installations shall be free from short circuits, ground faults, or any connections to ground other than as required or permitted elsewhere in the Code.
- 110.11 Deteriorating Agents. Equipment must be identified for the operating environment — moisture, corrosive vapors, chemicals, excessive temperatures. An Informational Note reminds that some cleaning and lubricating compounds cause deterioration of many plastics. Equipment not identified for outdoor use and equipment identified only for indoor use must be protected against damage from the weather during construction, a rule that matters on any Alaska site where gear sits on a pad through a snowfall.
- 110.12 Mechanical Execution of Work. Electrical equipment shall be installed in a neat and workmanlike manner. (A) Unused openings other than those intended for the operation of equipment, for mounting purposes, or those permitted as part of the design shall be effectively closed to afford protection substantially equivalent to the wall of the equipment. (B) Integrity of Electrical Equipment and Connections — internal parts shall not be damaged or contaminated by foreign material such as paint, plaster, cleaners, abrasives, or corrosive residues, and there shall be no damaged parts that may adversely affect safe operation or mechanical strength. (C) Cables and Conductors installed exposed on the surfaces of ceilings and sidewalls shall be supported by the building structure so the cable or raceway will not be damaged by normal building use.
- 110.13 Mounting and Cooling. Equipment shall be firmly secured to the surface on which it is mounted; wooden plugs driven into holes in masonry, concrete, plaster, or similar materials shall not be used. Equipment that depends on natural air circulation must be installed so that room airflow over and through the equipment is not prevented.
Arc-Flash Labeling — 110.16
110.16(A) General. Electrical equipment such as switchboards, switchgear, panelboards, industrial control panels, meter socket enclosures, and motor control centers in other than dwelling units, that are likely to require examination, adjustment, servicing, or maintenance while energized, shall be field or factory marked to warn qualified persons of potential electric arc-flash hazards. The marking must be located to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance.
110.16(B) Service Equipment. In other than dwelling units, service equipment rated 1200 A or more shall have a permanent label giving the nominal system voltage, the available fault current at the service overcurrent devices, the clearing time of those devices based on that fault current, and the date the label was applied.
A recessed luminaire's installation instructions require a minimum 3-inch clearance from thermal insulation. An electrician packs insulation against the housing. Which Code section does this violate?
What does NEC 110.9 require of a circuit breaker installed at a service where 42,000 amperes of fault current is available?
A panelboard lug is marked with a torque value of 275 lb-in. Under NEC 110.14(D), how must the connection be made?
Under NEC 110.16(B), service equipment in other than dwelling units of what minimum rating requires a permanent label showing nominal system voltage, available fault current, clearing time, and the date the label was applied?