Article 110: Requirements for Electrical Installations – Based on the 2011 NEC
By Mike Holt for EC&M Magazine
Taken from Mike Holt’s Illustrated Guide to Understanding the National Electrical Code, Volume 1, 2011 Edition
The title of Article 110 might seem misleading, because every Article in the NEC provides requirements for electrical installations. The first four Chapters of the NEC apply generally to all installations (the last five apply to specific installations or situations).
Chapter One has only two Articles. We covered Article 100 in the previous issue. Article 110 provides general requirements not covered by Chapters 2, 3, and 4 (Wiring and Protection, Wiring Methods, and Equipment for General Use).
Approval and listing
You must:
- Use equipment that’s Listed and Labeled for the intended use.
- Follow instructions included in the Listing or Labeling.
Analysis: Some pieces of electrical equipment have special requirements (e.g., limitations on elevation, ambient temperature correction, power quality, specific types of overcurrent devices). This information may be in the product literature, in the listing and labeling information, or marked on equipment. This rule helps users know about these special conditions.
Electrical equipment must have a short-circuit current rating that permits the circuit protective device to open from a short circuit or ground fault without extensive damage [110.10]. Listed equipment applied per its listing meets the requirements of this section.
Analysis: The short-circuit current rating of equipment is a vital part of determining whether a system or circuit can withstand the effects of a short circuit or ground fault.
With the 2011 revision, “other characteristics” was replaced with specific examples in 110.10. This revision also replaces the term “grounding conductors” with “equipment grounding conductors.” The second term has a more specific meaning.
Deteriorating agents
No, this has nothing to do with aging characters in your favorite spy thriller series. Installers must give consideration to the presence of corrosive gases, fumes, vapors, liquids, or other substances that can have a deteriorating effect on the conductors or equipment [110.11].
You can’t use conductors in an area where there’s exposure to sunlight (ultraviolet) unless they are identified for use in such an area [310.10(D)]. Raceways, cable trays, cablebus, cable armor, boxes, cable sheathing, cabinets, elbows, couplings, fittings, supports, and support hardware must be of materials that are suitable for the environment of installation, per 300.6.
Another issue is that some cleaning and lubricating compounds contain chemicals that can cause deterioration of the plastic used for insulation and structural applications. Check the MSDS and usage information of any solvent or lubricant before using it.
Fine-stranded cables
Use only conductor terminal devices and splicing devices specifically identified for the conductor material [110.14], and follow the recommended installation procedures.
Fine-stranded cables and conductors are a fairly new option in the NEC (2008 Article 690). Usage of these cables has increased, but awareness of the special termination provisions for them has not. Consequently, the 2011 NEC stresses the need to use specific terminations for fine stranded conductors and cables. Table 10 in Chapter 9 makes its first appearance with the 2011 revision. The new language in this section refers to that table, making its provisions enforceable by the Authority Having Jurisdiction (AHJ).
Connectors and terminals for conductors more finely stranded than Class B and Class C (as shown in Table 10 of Chapter 9) must be identified for the conductor class (see Sidebar).
Per UL Standard 486 A-B, a terminal/lug/connector must be listed and marked for use with conductors stranded in other than Class B. With no marking or factory instructions to the contrary, terminals may be used only with Class B stranded conductors.
Arc flash
The requirements for arc flash warning markings have been increased (again), and the title of this section has been revised.
Electrical equipment (in other than dwelling units) must be field-marked to warn qualified persons of the danger associated with an arc flash from short circuits or ground faults [110.16]. The field-marking must be clearly visible to qualified persons before they inspect or work on the equipment.
NFPA 70E, Standard for Electrical Safety in the Workplace, provides assistance in determining the severity of potential exposure, planning safe work practices, and selecting personal protective equipment.
Analysis: The 2008 NEC used the term “other than dwelling occupancies” in this section. Consequently, the warnings required by this section didn’t apply to multifamily dwellings, even though such dwellings might have remarkably larger services than some nondwelling occupancies. To address that issue, the Code now requires the marking on multifamily dwellings (but not the individual dwellings of a multifamily dwelling unit building).
The title of this section was revised in the 2011 cycle. This section doesn’t provide any “protection” as the previous title (flash protection) implied. Rather, it provides for a warning against the hazards associated with an arc flash.
Available fault current
A new section requires some equipment to be marked with the available fault current and requires updating of that marking if modifications of the electrical system occur [110.24].
(A) Field Marking. Service equipment in other than dwelling units must be legibly field-marked with the maximum available fault current, including the date the fault current calculation was performed and be of sufficient durability to withstand the environment involved.
(B) Modifications. When modifications to the electrical installation affect the maximum available fault current at the service, the maximum available fault current must be recalculated to ensure the service equipment ratings are sufficient for the maximum available fault current at the line terminals of the equipment. The required field marking(s) in 110.24(A) must be adjusted to reflect the new level of maximum available fault current.
Exception: Field markings aren’t required for industrial installations where conditions of maintenance and supervision ensure that only qualified persons service the equipment.
Analysis: All equipment must have an interrupting rating or short-circuit current rating that’s at least equal to the available fault current [110.9 and 110.10]. As wiring systems age, utilities may change transformers in an effort to become more efficient or to increase capacity. This can easily cause an increase in the available fault current, often with a noncompliant (and dangerous) wiring system.
The intention of this new provision is that owners reevaluate the ratings of equipment when they install onsite generation or when anyone changes the supply transformers.
Opponents of this change argue that often the ratings of equipment are based on “worst case.” While this is suitable for designing a system, it isn’t suitable for performing the calculations required to establish the proper personal protective equipment (PPE) for working on the equipment. Using artificially high values of fault current for equipment ratings often produces a lower PPE rating.
Working space height
The 2011 NEC revises 110.26(A)(3) to include all of the height requirements found in 110.26, and adds a new exception for meters in meter sockets.
The height of the working space in front of equipment can’t be less than 6½ ft, measured from the grade, floor, platform, or the equipment height (whichever is greater).
You can install raceways, cables, or similar equipment above or below electrical equipment, but it can’t more than 6 in. into the working space of that equipment.
Two exceptions:
- The minimum headroom requirement doesn’t apply to service equipment or panelboards rated 200A or less in an existing dwelling unit.
- Ex 2: Meters can extend beyond the other equipment.
Analysis: In previous Code editions, height requirements were in 110.26(A)(3) and 110.26(E). Because there’s no reason to have two subsections giving similar provisions, 110.26(E) was deleted, and the text was incorporated into 110.26(A)(3).
Meters are obviously installed inside the working space discussed in this section. Previously, the NEC allowed meters to protrude up to 6 in. into the work space. Now meters can extend more than 6 in. into the work space.
Illumination
The illumination for indoor service equipment, switchboards, panelboards, and motor control centers must not be controlled only by automatic means [110.26(D)].
Analysis: Previously, this requirement applied only to electrical rooms. But equipment addressed by this rule is often installed in spaces that aren’t “electrical rooms.” If you install panels, provide a manual means of controlling the lighting for them.
Now that we’ve shed some light on important aspects of Article 110, you can probably see why it’s beneficial to periodically read through Article 110. Because Article 110 applies to all installations, time spent understanding it pays off with every installation job you do.
Sidebar. What are conductor classes?
- Class B stranding (Standard) has 7 strands of wire per conductor in sizes 18-2 AWG, 19 strands in sizes 1-4/0 AWG, and 37 strands in sizes 250-500 kcmil.
- Class C stranding has 19 strands of wire per conductor in sizes 18-2 AWG, 37 strands in sizes 1-4/0 AWG, and 61 strands in sizes 250-500 kcmil.
- Class D stranding has 37 strands of wire per conductor in sizes 18-2 AWG, 61 strands in sizes 1-4/0 AWG, and 91 strands in sizes 250-500 kcmil.
Taken from Mike Holt’s Illustrated Guide to Understanding the NEC 2011, Volume 1 textbook. To order, please click here, or call 888-632-2633 for more information.
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