Arc-Energy Reduction, Defining ‘Qualified’ and More

Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Send questions to Answers are based on the 2017 NEC.

240.6(C) and arc-energy reduction

I understand that Section 240.87 requires a means of arc energy reduction for circuit breakers rated at 1,200 amperes (A) or more. Does 240.87 still apply if we install a 1,200A circuit breaker with the long-time pickup setting set at 1,000A, with the circuit breaker behind locked doors making it accessible only to qualified people, and we meet the requirements for restricted access to the circuit breaker adjusting means as seen in 240.6(C)? We think it would not because we now have a circuit breaker rated at 1,000A. If we did the same with a 1,200A fusible switch with 1,000A fuses installed and labels on the fused disconnect prohibiting fuses rated over 1,000A, would 240.67 still apply?

The requirements of 240.87 apply 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 1,200A or higher. The circuit breaker you describe is a 1,200A device, and it can be adjusted to 1,200A; therefore, 240.87 applies. This requires the application of one of the means to achieve arc energy reduction in 240.87(B).

An explanation of 240.6 is needed here. It exists to provide standard overcurrent device ratings. These standard ratings are necessary for use in the application of other requirements throughout the NEC. Section 240.6(A) provides standard ampere ratings for fuses and inverse time circuit breakers. Section 240.6(B) requires the maximum setting possible to be the standard overcurrent device rating for adjustable-trip circuit breakers with external means to adjust the long-time current pickup setting that are not installed with restricted access. Section 240.6(C) permits the adjusted long-time pickup setting as the standard overcurrent device setting where there is restricted access to the adjustable-trip circuit breakers.

An example of where these standard ratings are referenced is seen in 240.4(B). Arc energy reduction requirements impact the instantaneous trip function of the circuit breaker, not the long-time trip function. The 1,200A threshold in 240.87 was chosen only to limit the number of devices impacted by 240.87. Where the permissive rules of 240.6(C) are applied, they do not modify the requirements of 240.87. Where 1,000A fuses are installed in a 1,200A fusible switch, the arc energy reduction requirements do not apply. See 240.67 which addresses only fuses rated 1,200A or higher; this requirement does not reference the size of the fusible switch or enclosure.

Qualified person

As an electrical inspector, I am involved in many industrial installations. Where these installations exercise one of the many industrial exceptions, it is my responsibility to ask for documentation of “qualified persons” that will service the equipment. At a recent inspector meeting, the reference to NFPA 70E was discussed. Is that the documentation we should be asking for?

The reference to NFPA 70E that you are referring to is in the informational note following the Article 100 definition of “qualified person.” These notes are explanatory only and are not an enforceable part of the NEC—see 90.5(C). It is not the responsibility of the authority having jurisdiction to outline required training, required experience and continuing education for the qualified person that will service the equipment in question. It is your job to simply request that information from the installer and to document it. The installer must obtain that information directly from the owner or through a general contractor or construction manager.

There are many ways an owner can document their qualified people. An owner may simply provide documentation that all service on the equipment will be performed by licensed electrical contractors. As the electrical inspector enforcing the NEC requirements, you could, in writing, request documentation based on the Article 100 definition of qualified person. That would include documentation of: (1) the skills and knowledge related to the construction and operation of the electrical equipment and installations, along with (2) documentation of safety training to recognize and avoid the hazards involved.

The documented safety training should include but not be limited to all required training to implement the owners’ electrical safe work practices, create and verify a zero-energy state through the implementation of an electrical safe work condition, determine justification of energized work, perform shock and arc flash risk assessments and to choose required personal protective equipment. While NFPA 70E is the gold standard, it is not required by the NEC and cannot be enforced by the electrical inspector.

Grouping service disconnects

We have a question about installing a transfer switch rated as service equipment for optional standby systems supplying a large dwelling unit. In our area, we have multiple jurisdictions for electrical inspections, and we get differing opinions. The installations are typically optional standby systems on large dwelling units that have two service disconnects. There are typically two 200A main circuit breakers (service disconnects) in two panelboards grouped together in the same indoor location in the dwelling unit. We install transfer switches rated for use as service equipment with a 200A main circuit breaker outdoors between the utility meter housing and the standby generator. The load side of the transfer switch then supplies one of the 200A panelboards. In one jurisdiction, the inspector requires that we relocate the service disconnect for the other indoor panelboard with the transfer switch so they are grouped. Why? The service disconnects are still grouped. The other jurisdiction does not require that. What is required?

In general, Section 230.71(A) permits up to six disconnecting means for each service. Section 230.72(A) requires the two to six disconnecting means as permitted in 230.71 to be grouped, and each disconnect must be marked to indicate the load served. The initial installation of the service equipment described in your question complied with this requirement with two service disconnects supplying two panelboards in the same indoor location.

The installation you describe relocates one of the service disconnects outdoors into the service rated transfer equipment. This means the service disconnects are no longer grouped as required by 230.72(A). To comply with this requirement and group the service disconnects in the scenario you describe, you must either relocate the second service disconnect outdoors or install the transfer equipment indoors next to the existing service disconnect.

In the scenario you describe, the service disconnects are no longer grouped, and the conductors from the load side of the 200A circuit breaker (service disconnect) in the transfer equipment are a feeder. The 200A circuit breaker in the panelboard supplied from the transfer equipment is no longer a service disconnect. The installation would also require compliance with requirements for the grounding electrode system and 250.24(A)(5) in the panelboard supplied by the transfer equipment. This panelboard is no longer service equipment, and the grounded conductor is not permitted to be connected to normally non-current-carrying metal parts of equipment, to equipment grounding conductor(s), or be reconnected to ground on the load side of the service disconnecting means in this installation.

Grounded conductor to fire pump controller

I read your reply to the question asking if a neutral conductor is required to fire pump controller even though the load supplied is 3-phase at 208 with no neutral load. I am confused by your reply. Wasn’t the question, is the neutral required to the equipment? I read 250.20(A) but that is reference to a system ground. The neutral was not being used so why must it be added to the conduit? I have the same situation in my town. Can you clarify?

There were multiple issues with the fire pump installation that drove the response you reference. This response will focus on the NEC requirement to bring the grounded conductor to the service disconnect and the reasons behind the rule. Section 250.24 contains requirements for grounding service-supplied AC systems. Section 250.24(C) requires that where a utility supplied system (service) is grounded at any point, the grounded conductor must be routed with the ungrounded conductors to each service disconnecting means and must be connected to each disconnecting means grounded conductor terminal or bus. Additionally, a main bonding jumper must be installed to connect the grounded conductor(s) to each service disconnecting means enclosure.

It is important to note that where a fire pump enclosure is supplied by service conductors, it is service equipment and contains a service disconnecting means. The NEC requirement for bringing the service supplied grounded conductor to the service disconnecting means has nothing to do with whether or not the grounded conductor will be utilized as a current carrying conductor for supplied loads.

Your question is based on a fire pump load that does not require a grounded conductor to operate the fire pump or any associated equipment. The grounded conductor is required to be bonded to the service disconnect enclosure to provide an adequate ground fault return path to back to the source. Where the grounded conductor is not brought to the enclosure for the service disconnecting means (fire pump enclosure in this case) and bonded as required to the enclosure, very serious safety issues exist.

About the Author

Charles R. Miller

Code Contributor

Charles R. Miller, owner of Lighthouse Educational Services, teaches classes and seminars on the electrical industry. He is the author of “Illustrated Guide to the National Electrical Code” and NFPA’s “Electrical Reference.” He can be reached at 615...

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