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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.

By Robert C. Corson, PE; and Philip M. Grenci, PE; Triad Consulting Engineers Inc., December 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.

Overcurrent protection—arc energy reduction

NEC 2014 changeArticle 240: Overcurrent Protection; Section 240.87 Arc Energy Reduction:

Where the highest continuous-current trip setting for which the actual overcurrent device installed in a circuit breaker is rated, or can be adjusted, is 1,200 A or higher, Article 240.87(A) and (B) shall apply.

(A) Documentation shall be available to those authorized to design, install, operate, or inspect the installation as to the location of the circuit breakers.
(B) Method to Reduce Clearing Time: One of the following or approved equivalent means shall be provided:
  • Zone-selective interlocking
  • Differential relaying
  • Energy-reducing maintenance switching with local status indicator
  • Energy-reducing active arc flash mitigation system
  • An approved equivalent means.

Informational note No. 1—An energy-reducing maintenance switch allows a worker to set a circuit breaker trip unit to "no intentional delay" to reduce the clearing time while the worker is working within an arc flash boundary as defined in NFPA 70E-2012: Standard for Electrical Safety in the Workplace, and then to set the trip unit back to a normal setting after the potentially hazardous work is complete.

Informational note No. 2—An energy-reducing active arc flash mitigation system helps in reducing arcing duration in the electrical distribution system. No change in the circuit breaker or the settings of other devices is required during maintenance when a worker is working within an arc flash boundary as defined in NFPA 70E.

Analysis of change—Arc flash safety has been one of the most rapidly evolving facets in the industry during recent years. This code update further stresses the importance of arc flash mitigation techniques.Figure 3: The time-current curve shows a circuit breaker with maintenance-mode settings. Courtesy: Triad Consulting Engineers Inc.

The arc energy reduction article was added to replace the previous Article 240.87: Noninstantaneous Trip, which was new to the 2011 NEC. To comply with the 2011 code, many system designers were simply implementing instantaneous-trip circuit breakers. While this facilitates mitigating arc flash hazards, other more complicated methods that have the potential to significantly reduce arc flash incident energy were being avoided. The intent is to reduce potential arcing time in larger equipment, which typically presents an elevated arc flash hazard. One method is to implement maintenance mode, in which the trip unit has a second group of settings that are configured to trip the breaker significantly faster, depending on the fault current. To increase personnel safety, coordination is typically sacrificed during the period in which the maintenance mode settings are engaged. Figure 3 illustrates the two groups of settings on a time-current curve in which the maintenance mode settings have significantly reduced pickup currents and time delays.

It is important to note that any circuit breaker in which the long-time pickup setting can be adjusted to 1,200 A is subjected to this code requirement. Simply dialing down breaker settings will result in noncompliance. In addition, fused distribution is exempt due to the inherent current limitation of fuses in high fault-current applications.

Surge protection

NEC 2014 changeException to 240.21(B)(1)(1)(b) and 240.21(C)(2)(1)(b):

Where listed equipment, such as a surge-protective device (SPD), is provided with specific instructions on minimum conductor sizing, the ampacity of the tap conductors supplying that equipment shall be permitted to be determined based on the manufacturer’s instructions.

Analysis of changeIn previous code editions, it was permissible to wire Type 1 SPDs before or after the service entrance. While Type 1 units are considered to be self-protected, many inspectors questioned whether the conductors serving the SPD were considered to be protected as well. The 2011 code clarified this in two exceptions located in Article 240, commonly referred to as the "Tap Rules." These new exceptions allow for a direct connection of SPDs without an OCPD for feeder taps and transformer secondary taps with distances not exceeding 10 ft that are wired in accordance with the manufacturer’s instructions.

NEC 2014 changeARTICLE 285: Surge-Protective Devices 1,000 V or Less; Part II, Installation; Section 285.13, Type 4 and Other Component-Type SPDs:

Type 4 component assemblies and other component-type SPDs shall only be installed by the equipment manufacturer.

Analysis of changeIn the previous code editions, the application of Types 1, 2, and 3 SPDs were included, but Type 4 was not. The result was misapplication of Type 4 SPDs. Article 285.13 was added to prevent Type 4 SPDs from being field-installed, as they do not comply with the same mandatory safety features of Types 1, 2, or 3 SPDs. They are intended to be selected by the equipment manufacturer and to be part of the equipment listing and the associated testing. Type 4 units have exposed terminals and are typically DIN-rail-mounted in an enclosure, which makes them unsuitable for an external installation.

NEC 2014 changeARTICLE 700: Emergency Systems; Part I. General; Section 700.8, Surge Protection:

A listed SPD shall be installed in all emergency-system switchboards and panelboards.

Analysis of changeThe new paragraph 700.8 in Article 700 requires surge protection for legally required emergency systems. These systems automatically supply power to designated emergency loads upon loss of utility (normal) power. SPDs prevent damage to emergency control and sensitive critical-load circuits.

Additional commentsPrevious code editions did not require SPDs. However, the industry applied them anyway over time, as the potential for damage to sensitive electrical circuits and subsequent downtime of critical systems was evident. It was determined that SPDs were effective in preventing damage to sensitive equipment from surges and spikes. In 2005, Article 285 introduced the new term "SPD" while also using the old term "transient-voltage surge suppressor (TVSS)." The name change emphasizes the safety differences between a TVSS and an SPD as specified in UL 1449-2014: Standard for Surge Protective Devices. Allowing sufficient time over the course of several update cycles for the industry to adjust, the term TVSS was removed from Article 285.

Figure 4: The time-current curve and corresponding single-line diagram show the coordination and selectivity requirements in NEC Articles 517, 700, 701, and 708. Courtesy: Triad Consulting Engineers Inc.

Selective coordination requirements

NEC 2014 changesArticle 100: Definitions:

Coordination (Selective)—Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the selection and installation of OCPDs and their ratings or settings for the full range of available overcurrents, from overload to the maximum available fault current, and for the full range of OCPD opening times associated with those overcurrents.

Analysis of changesFirst, the definition of selective coordination was clarified in the 2014 NEC, such that its application is for the full range of available overcurrents, from overload to the maximum available fault current. Many system designers and engineers interpreted that the selectivity requirement applied to a limited range of faults, instead of fully selective coordination.

This stipulation was made to address the inherent difficulties of coordinating OCPDs in the high fault current range, specifically with circuit breakers. The complication is a function of the operation and tolerances of the 3-cycle rating associated with UL 489 breakers, resulting in overlap (or noncoordination) of trip curves and creating difficulty in designing a fully selective system with circuit breakers.

NEC 2014 changesSelective coordination sections for:

  • Article 620: Elevators, Dumbwaiters, Escalators, Moving Walks, Platform Lifts, and Stairway Chairlifts
  • Article 700: Emergency Systems
  • Article 701: Legally Required Standby Systems
  • Article 708: Critical Operations Power Systems (COPS).

The following excerpt was added to each selective-coordination section for the aforementioned articles:

"Selective coordination shall be selected by a licensed professional engineer or other qualified person engaged primarily in the design, installation, or maintenance of electrical systems. The selection shall be documented and made available to those authorized to design, install, inspect, maintain, and operate the system."

Figure 5: Rapid-PV-shutdown configurations to de-energize controlled conductors at the point of common coupling (POCC) include UL 1741-compliant with rapid-shutdown requirements within 10 ft of the PV array (a); smart combiner box with switching capabilitAnalysis of changesThe primary reason for the addition of this excerpt to the various articles of the NEC that require selective coordination was to assign responsibility. By clarifying that a licensed professional engineer must perform this task, it limits unqualified personnel from performing the analysis, and it allows electrical inspectors to enforce the code by simply reviewing the documentation already prepared by the engineer.

Selective coordination in hospitals

NEC 2014 changeArticle 517.30: Essential Electrical Systems for Hospitals; (G) Coordination:

OCPDs serving the essential electrical system shall be coordinated for the period of time that a fault’s duration extends beyond 0.1 sec.

Exception No. 1—Between transformer primary and secondary OCPDs where only one OCPD or set of OCPDs exist on the transformer secondary.

Exception No. 2—Between OCPDs of the same size (ampere rating) in series.

Informational Note—The terms "coordination" and "coordinated" as used in this section do not cover the full range of overcurrent conditions. The device closest to the fault must open without opening the upstream protection-faulted circuit.

Analysis of changeThis article of the NEC was updated to require coordination, including the life safety branch, only up to 0.1 sec, to coincide with the requirements that were established in the latest NFPA 99: Health Care Facilities Code. Prior to this stipulation in the NEC, Article 517 classified hospital essential systems as "emergency system," which subjected it to the requirements of selective coordination for the full range of overcurrents defined therein. This code change is further clarified in Article 517.26, which states that these requirements include the life safety branch, in which it is stated that the life safety branch is subjected to the requirements of Article 700, except as amended by Article 517.

Figure 5: Rapid-PV-shutdown configurations to de-energize controlled conductors at the point of common coupling (POCC) include UL 1741-compliant with rapid-shutdown requirements within 10 ft of the PV array (a); smart combiner box with switching capabilitThis interesting development seems to indicate that the OCPD coordination of health care systems is not necessary as in other emergency or critical systems, which do require fully selective coordination. This update was likely endorsed by the committee to allow for circuit breakers in hospital distribution systems, which typically have issues being fully selective after the 0.1-sec range.

Figure 4 illustrates a time-current curve and its corresponding single-line diagram in which the coordination and selectivity requirements associated with Articles 517, 700, 701, and 708 are depicted.

PV rapid-shutdown systems

NEC 2014 changeArticle 690: Solar Photovoltaic (PV) systems; Part II, Circuit Requirements; Section 690.12, Rapid Shutdown of PV Systems on Buildings:

Figure 5: Rapid-PV-shutdown configurations to de-energize controlled conductors at the point of common coupling (POCC) include UL 1741-compliant with rapid-shutdown requirements within 10 ft of the PV array (a); smart combiner box with switching capabilitPV system circuits installed on or in buildings shall include a rapid-shutdown function that controls specific conductors in accordance with Article 690.12(1) through (5) as follows: 

  1. Requirements for controlled conductors shall apply only to PV system conductors of more than 1.5 m (5 ft) in length inside a building, or more than 3 m (10 ft) from a PV array.
  2. Controlled conductors shall be limited to not more than 30 V and 240 VA within 10 sec of rapid-shutdown initiation.
  3. Voltage and power shall be measured between any two conductors and between any conductor and ground.
  4. The rapid-shutdown initiation methods shall be labeled in accordance with Article 690.56(B).
  5. Equipment that perform the rapid shutdown shall be listed and identified.

There has been significant controversy and debate about the specific requirements in this new section, particularly because the methodology is addressed in the product standards, not in the NFPA documents. A key concern is often defining the location of the device to de-energize the controlled conductors of the PV system, and if more than one is required.

Analysis of changePrior to the NEC 2014 update, there were no requirements for a rapid power shutdown of rooftop PV systems. The intent of this change is to increase the safety of first responders by creating a protected zone in which shock hazards have been mitigated.

With the inverter anti-islanding requirements of UL 1741-2010: Standard for Inverters, Converters, Controllers, and Interconnection System Equipment for Use with Distributed Energy Resources, opening the main service disconnect will result in the de-energizing of the PV system. As long as any potential storage devices (e.g., capacitors) within the inverters discharge within this time frame, and the inverters are located within 10 ft of the PV array, the main service disconnect could satisfy this requirement. Alternate configurations involve implementing smart combiner boxes or dc-to-dc converters with switching capability. Schematics of different configurations are illustrated in Figure 5.

With the plethora of changes witnessed in the 2014 revision to the NEC, we focused on seven key changes affecting the electrical industry for commercial and industrial systems. We also expect to see continued code updates in the next revisions for renewable energy systems as well as selective coordination and arc flash hazard protection.

Robert C. Corson is a principal engineer at Triad Consulting Engineers. He has experience in the design and analysis of power systems for commercial, industrial, renewable energy, and mission critical facilities including 120/208 V through 230 kV, PV plants up to 20 MW, emergency microgrid generation, and UPS systems for critical applications.

Philip M. Grenci is the chief electrical engineer at Triad Consulting Engineers. He has 30 yr of experience in the industry and supervises the electrical engineers and designers at the company’s New Jersey office.