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. Questions can be sent to firstname.lastname@example.org. Answers are based on the 2014 NEC.
Earlier this year, there was a question concerning arc-resistant switchgear. Can you provide more information? We recently did a plan review for a client, and a note for switchgear on the drawings required it to be “arc resistant.” The notes also called for the arc-resistant switchgear to be “type 2.” Are there many different types? What is the difference? In this case, the switchgear was rated at 13.2 kilovolts (kV). Is arc-resistant switchgear used for high voltage only? How does it work? What are the benefits?
The National Electrical Code (NEC) does not require the use of “arc-resistant switchgear” under any conditions. The only NEC reference to arc-resistant switchgear is in an informational note that follows the Article 100 definition of the term “switchgear.” The last sentence of the informational note explains that switchgear is available in both non-arc-resistant and arc-resistant construction. This type of switchgear is used to enhance safety for equipment operators and maintenance personnel.
Arc-resistant switchgear is designed to redirect arc energy up and out of the equipment through ducts/vents outdoors away from equipment operators. The system is designed with vent flaps that will open under the pressure of an arcing fault and redirect the super heated gases and arc flash energy up and out of the equipment, away from personnel. This is a significant increase in safety, and it helps prevent damage to adjacent equipment. Non-arc-resistant switchgear does not provide the same level of safety. For example, consider the racking in or out of large low-voltage power circuit breakers into switchgear. Arc-resistant designs allow for this task to be done with the doors completely closed in equipment designed to redirect energy if an arcing fault occurs. Non-arc-resistant designs do not provide the same protection, and, in this case, the worker is interacting with the equipment that increases the likelihood of exposure to an arc flash hazard.
Arc-resistant switchgear is available for low- and medium-voltage systems. Type 1 is arc-resistant from the front only, and type 2 is arc-resistant from the front, sides and rear. Use of this equipment is based on the system design considerations for safety.
Other methods that may be considered to reduce exposure to arc energy in switchgear include, but are not limited to, remote switching, remote racking and methods to reduce the clearing time of upstream overcurrent protective devices.
Working space above ceilings
At a recent seminar on NEC changes, I learned that there are now requirements for working space to access and work on electrical equipment related to duct heaters. This is long overdue. My company does a significant amount of maintenance on heating, ventilating and air conditioning systems. Safely accessing equipment that needs to be examined in an energized state for troubleshooting is a real challenge. Why does the NEC address only working space above ceilings for duct heaters? There are all types of systems installed above ceilings that may need to be worked on while energized for troubleshooting purposes.
The 2014 NEC included a new second level subdivision 424.66(B), Limited Access, and addressed only spaces above a ceiling. The arrangement of the NEC in 90.3 clearly states that chapters 1–4 are general and apply in all locations unless modified or supplemented in chapters 5, 6 or 7. This means that the general rules for working space clearances in Section 110.26 apply in all spaces. Working space in 110.26 is required for all equipment that is likely to require examination, adjustment, servicing or maintenance while energized. The technical committee with purview over duct heaters recognized that strict compliance with the general rules in Section 110.26 was not feasible and, in many cases, impossible. For those reasons, they developed new text to address spaces above a ceiling, which always have limited access.
The revision in Section 424.66(B) is intended to provide some relief from the general rule in Section 110.26. The new rule requires access through a lay-in type ceiling or access panel, minimum width of 30 inches or the width of the equipment, doors and hinged panels to open 90 degrees and permission to allow a horizontal T-bar in the working space.
During the public input stage for the 2017 NEC, the committee with purview over 110.26 recognized the need to specifically address working spaces with limited access. The first revision creates a new second-level subdivision 110.26(A)(4), Limited Access, that addresses spaces above ceilings and in crawl spaces. This first revision will certainly get some attention in the public comment stage, but it seems certain that the 2017 NEC will include a new general rule for working space in areas with limited access.
Conduits entering handholes
On a recent decorative-lighting project in 12 buildings, we installed many handholes. During the inspection, we were informed that there were several problems. We had run the conduits horizontally and ended them directly below the handhole enclosures. The inspector told us that we had to turn a 90-degree piece of conduit on each conduit to get it to turn up into the handhole. In addition, we were told that all of the covers must be marked with the word “electric” and that all of the wire nuts had to be listed for use in wet locations. We have done this type of installation in the past and never had an issue. Are these new requirements?
No, these are not new requirements. Section 314.30 contains the requirements for handhole-enclosure installation. Wiring entries into handholes are covered in Section 314.30(B) and are required to extend into, but not be mechanically connected to, the handhole enclosure. Section 314.30(C) requires all enclosed wiring, splices and terminations inside a handhole enclosure to be listed for wet locations. This includes any wire nuts used for splices.
All handhole covers used for electrical wiring are required to be clearly marked as electrical equipment. The NEC does not mandate a specific term for the cover and requires a marking such as “electric.” There are other marking options (e.g., “lighting”).
Emergency system power sources
Why is the use of a completely separate utility connection for use as an emergency power supply based on the approval of the electrical inspector? A recent plan review we submitted to the city was rejected for our use of a completely separate electrical service as an emergency power source. The service came from a different utility substation. We met all of the requirements for a separate service as an emergency source. Their rejection was based on their opinion that, in the event of a fire, the utility company may disconnect all electric service to the building. If that is the case, why does the NEC include a separate service as an option?
Section 700.12 provides general requirements for emergency power sources and the types of sources permitted. Six first-level subdivisions address specific types of power sources that include storage batteries, generators, uninterruptible power supplies, separate services, fuel cell systems and unit equipment. The requirements for the use of a separate service as an emergency source of power in 700.12(D) are permitted only “where approved by the authority having jurisdiction (AHJ) as suitable for use as an emergency source of power.” This text is written intentionally to provide the AHJ with the final determination of suitability.
In some cases, electric utilities will not provide a separate service for use as emergency power and some go on record to inform an AHJ that the service is not considered to be reliable. This situation also occurs where an installer chooses not to install an alternate source of power for a fire pump and claims that the electric utility connection meets the general requirement in Section 695.3, which mandates a “reliable source of power.” Electric utilities cannot control the weather, vehicle accidents or other unforeseen occurrences that may affect distribution to a given building or structure and have no choice but to go on record stating that their electric service should not be considered as a continuously reliable source of supply for fire pumps and emergency systems. The reality is that the electrical utility-supplied service is indeed the most reliable source of power in most areas.