Reviewing, analyzing NEC 2014 changes

Changes in and additions to the NFPA 70: National Electrical Code (NEC) have a significant impact on commercial and industrial facilities.

12/11/2015


This article is peer-reviewed.Learning objectives:


Every 3 yr, NFPA 70-2014: National Electrical Code (NEC) is updated and released. However, not all states immediately adopt the new code changes. The adoption by many states doesn't typically occur until the year after the latest version is released.

According to NFPA, there were 3,745 proposals submitted recommending changes to the 2014 edition of the NEC. In addition, there were 1,625 comments concerning the NEC Code-Making Panels' responses to these proposals.

Overall impact of code changes

There are several new articles as well as some noteworthy changes included in the 2014 edition of the NEC. Some changes have had a significant impact on the electrical trade. An example is a codewide change to raise the maximum voltage level from 600 V to more than 1,000 V, primarily driven by the higher voltages in wind turbine and photovoltaic (PV) systems. The voltage increase affects numerous articles including 240, 250, 300, 430, 490, 690, 692, and 694.

While many of these changes are purely editorial in nature, the change in the transformer protection table, Table 450.3(A), compels system designers to use smaller overcurrent-protective devices (OCPDs) for protecting transformer primaries when within the 600 V-to-1,000 V range. Although there are no standard operating voltages within this range, this predominantly affects renewable energy sources, which can connect at voltages not commonly seen in standard distribution. It should also be noted that this reduction in OCPD sizing facilitates in the mitigation of arc flash hazards, which have been in the spotlight for safety awareness and recent code changes. Transformers are typically a location of elevated incident-energy levels, and faster OCPD tripping can reduce incident-energy levels.

Impact on commercial and industrial facilities

Some of the code additions and modifications have substantial impact on commercial and industrial facilities. The following list describes, in sequence, seven changes in NEC 2014 that have a high impact on commercial and industrial systems:

  1. Dedicated equipment space
  2. Ground-fault protection (GFP)
  3. Conductor sizing
  4. Arc energy reduction
  5. Surge protection
  6. Selective coordination requirements and health care
  7. Solar system rapid-shutdown systems.

Figure 1: This diagram illustrates outdoor dedicated-equipment space extending 6 ft above the width and depth of the equipment. Courtesy: Triad Consulting Engineers Inc.

The remainder of this article describes the changes in these areas.

Dedicated equipment space

NEC 2014 changeArticle 110: Requirements for Electrical Installations; Section 110.26(E) Dedicated Equipment Space, (2). Outdoor:

Outdoor installations shall comply with 110.26(E)(2)(a) and (b).

Subsection (b), Dedicated Equipment Space: The space equal to the width and depth of the equipment and extending from grade to a height of 1.8 m (6 ft) above the equipment shall be dedicated to the electrical installation. No piping or other equipment foreign to the electrical installation shall be located in this zone.

Analysis of changeAs with indoor equipment, dedicated space is now required for installation of outdoor equipment (see Figure 1). This is clarified in the code to pertain to all switchboards, switchgear, panelboards, and motor control centers. This removes the gray area of interpretation and clarifies the issue for design engineers, contractors, and the authorities having jurisdiction.

Ground-fault protection

NEC 2014 changeArticle 210: Branch Circuits; Section 210.13 Ground-Fault Protection of Equipment:

Each branch-circuit disconnect rated at 1,000 A or more and installed on solidly grounded wye electrical systems of more than 150 V to ground, but not exceeding 600 V phase-to-phase, shall be provided with ground-fault protection of equipment in accordance with the provisions of 230.95.

Informational note—For buildings that contain health care occupancies, see the requirements of Article 517.17.

Exception No. 1—The provisions of this section shall not apply to a disconnecting means for a continuous industrial process where an unorderly shutdown will introduce additional or increased hazards.

Figure 2: This single-line diagram shows the ground-fault protection now required on feeders. Courtesy: Triad Consulting Engineers Inc.Exception No. 2—The provisions of this section shall not apply if ground-fault protection of equipment is provided on the supply side of the branch circuit and on the load side of any transformer supplying the branch circuit.

Prior to this addition to the NEC, GFP was only required on each service disconnect rated 1,000 A or more. Now, GFP is required on each branch circuit with disconnects rated 1,000 A or more (see Figure 2). As before, this applies to solidly grounded wye electrical systems of more than 150 V to ground. Therefore, 208 Y/120 V systems are still exempt from GFP. Because the maximum setting of the ground-fault protective device on the main is still limited to 1,200-A pickup with a 1-sec delay (for ground faults exceeding 3,000 A only) per Article 230.95, this will require coordination between the settings of the GFP on the feeders or branch circuits with the ground-fault protective device on the main disconnect.

Analysis of changeThe intent of this code addition is to mitigate fires commonly associated with ground faults. This is because they have a tendency to burn until the event propagates into a more severe incident, eventually causing an open circuit—whether by tripping of upstream protective devices or equipment burn-down.

Conductor sizing

NEC 2014 changeArticle 210: Branch Circuits; Part II, Branch Circuit Ratings; Section 210.19 Conductors—Minimum Ampacity and Size:

Subsection (A), Branch Circuits Not More Than 600 V, (1) General: Branch-circuit conductors must have an ampacity of not less than the maximum load to be served. Conductors shall be sized to carry not less than the larger of Article 210.19(A)(1)(a) or (b).

(a) Where the branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size shall have allowable ampacity not less than the noncontinuous load plus 125% of the continuous load.

(b) Minimum branch-circuit conductor size shall have an allowable ampacity not less than the maximum load to be served after the application of any adjustment or correction factors.

Exception—If the assembly, including the overcurrent devices protecting the branch circuits, is listed for operation at 100% of its rating, the allowable ampacity of the branch-circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

NEC 2014 changeARTICLE 215: Feeders; Section 215.2 Minimum Rating and Size, (A) Feeders Not More than 600 V, (1) General:

Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. Conductors shall be sized to carry not less than the larger of 215.2(A)(1)(a) or (b).

(a) Where a feeder supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum feeder conductor size shall have an allowable ampacity not less than the noncontinuous load plus 125% of the continuous load.

(b) The minimum feeder conductor size shall have an allowable ampacity not less than the maximum load to be served after the application of any adjustment or correction factors.

Analysis of changeThe intent of this code change is to simplify the sizing of conductors. The changes clarify that the calculation procedure for continuous versus noncontinuous loads are separate from calculations in which ampacity or correction factors (e.g., number of current-carrying conductors in a raceway and/or ambient temperature above 86 F) are applied. After each method is calculated, the larger conductor size shall be used. A similar change can be found in Section 230.42 for the minimum size and rating of service-entrance conductors.

ExampleThe following is an example for a 200-A continuous load with three current-carrying conductors in a single conduit, located in a boiler room with a temperature of 100 F:

Based on the Article 215.2(A)(1)(a) requirement:

  • 200 A x 1.25 = 250 A
  • Conductor size = 250-kcmil THWN copper, rated 255 A at 75 C, based on Table 310.15(B)(16).

Based on the Article 215.2(A)(1)(b) requirement:

  • 250-kcmil THWN copper, rated 255 A at 75 C
  • 100 F correction factor = 0.88 for 75 C insulation, based on Table 310.15(B)(2)(a)
  • 200 A/0.88 = 227.3 A, which would require a 4/0 THWN copper conductor, rated 230 A at 75 C, based on Table 310.15(B)(16).

The larger of the two calculations is selected, requiring a 250-kcmil conductor.


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