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The 2012 edition of NFPA 70E®: Standard for Electrical Safety in the Workplace® is now available in necplus.

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Bulk storage plants are considered hazardous locations because of the presence of flammable liquids. A facility like the one shown here might include hazardous areas classified as Class I or Class II, according to the criteria in Table 515.3.

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Section 500.7 identifies 11 protection techniques that can be used to mitigate ignition hazards associated with electrical equipment installed in hazardous (classified) locations.  Explosionproof apparatus such as the motor controller shown in the photograph on the right is the most widely used and recognized protection technique. However other methods, such as purged and pressurized electrical equipment enclosures as shown in the photograph on the left , are available that facilitate the safe operation of electrical equipment in volatile environments. The NEC® does not prohibit using more than one protection technique in a single hazardous (classified) location and in some cases, the use of a combination of techniques is required. Motor fuel dispensing facilities are a good example of where two protection techniques - explosionproof apparatus and intrinsic safety - are used to provide for safe electrical equipment operation.

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Section 250.122(F) specifies that when conductors are run in parallel, the equipment grounding conductors must be installed in parallel and that the EGC should be sized according to Table 250.122.

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For the purposes of terminating in a circuit breaker or fusible switch, a parallel conductor arrangement (3-separate raceways or cables) of 3-750 kcmil aluminum XHHW conductors per phase has an allowable ampacity of 1155 amperes. Based on the general rules for conductor overcurrent protection, this parallel arrangement is not permitted to be connected to a 1200-ampere circuit breaker like the one shown here. This month’s article explains the limitations of the “rounding-up” provision specified in 240.4(C).

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Articles 342 through 390 of the NEC cover installation and protection of various types of raceways and conduit. Listed and labeled wiring methods, such as metal-clad cable, armored cable, flexible metal conduit, and electrical metallic tubing, provide an inherent degree of physical protection.

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The conductor connection terminal shown could be within the service disconnecting means for a service supplied system, or at the source, first system disconnecting means, or first system overcurrent protective device of a separately derived system. This common connection point is “ground zero” for the conductors associated with the grounding and bonding of a premises electrical system and equipment. The prescriptive provisions of Article 250 covering the installation, connection, and interconnection of grounded conductors, grounding electrode conductors, equipment grounding conductors, main and system bonding jumpers, and equipment bonding jumpers provide the methodology to meet the overall performance requirements  for the grounding and bonding of electrical systems specified in Sections 250.4(A) and (B).

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A label providing a general warning of the potential for an arc flash hazard is an installation requirement in the NEC for equipment such as but not limited to switchboards, industrial control panels, panelboards, motor control centers and meter socket enclosures.  More detailed incident energy and personal protective equipment information is outside the scope of the NEC, but is specified in NFPA 70E.  When that information is to be provided is a function of implementing an electrical  safety program at a facility or site.

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Utilization equipment such as this chiller and the luminaires in the mechanical room are loads supplied by branch circuits originating in some type of electrical distribution equipment. The distribution equipment is supplied by a set of service or feeder conductors, and there may be multiple levels of electrical distribution between the service equipment and the utilization equipment. Throughout the electrical system the conductors, distribution equipment, and other components associated with delivery of power to utilization equipment have to be sized to carry the “load.” From an NEC® standpoint, the “load” is the minimum load current or kVA rating calculated in accordance with the requirements of Article 220. Load calculations are the essential first step in ensuring conductors and distribution equipment are adequately sized.

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Since 1999 the NEC® has contained requirements focused on electrical safety in portable structures at fairs, carnivals, circuses, and similar events. Article 525 covers the installation of portable wiring and equipment, including wiring in or on all of these portable structures.

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Article 440 contains requirements unique to air-conditioning and refrigeration equipment with hermetic motor-compressors. The topics covered by these requirements parallel those in Article 430 for similar elements of a motor branch circuit.

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The NEC contains requirements standardizing the identification of various conductors that are components of the grounding and bonding system. Requirements on grounded conductor identification are located in Article 200, and requirements for equipment grounding conductor identification are found in Article 250. Adherence to these rules provides for safe initial connection of these conductors as well as safety for personnel who service the equipment after it has been installed.

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Modern health care facilities rely heavily on electrically powered medical equipment to provide numerous patient care related activities. The lifeblood for this equipment is a safe and reliable electrical distribution system. Two significant objectives addressed by the requirements in Article 517 are reducing the patient exposure to electric shock and providing a reliable system that helps ensure continuity of power to important patient care related equipment.

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Since the 1984 edition, the NEC® has contained requirements on interactive and stand-alone photovoltaic (PV) systems. Because of its location in the NEC (Chapter 6), the requirements in Article 690 amend or modify the general requirements of Chapters 1 through 4. Most PV systems involve ac and dc voltages, and many of the Article 690 requirements cover the installation of equipment unique to this type of power supply system. Article 690 requirements on disconnecting means, grounding, and overcurrent protection have their basis in the fundamental requirements of Chapters 1 through 4 but have been adapted, modified, or amended to ensure that the fire and shock protection purpose of the NEC is met while at the same time accommodating the technology needed to produce electrical power using a renewable energy source.

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A clear, well maintained working space about electrical equipment is an important element in providing ready access to disconnecting means and overcurrent protective devices, as well as helping to ensure that qualified personnel can safely work on energized electrical equipment.

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Article 210 contains requirements covering branch circuits, including a number of prescriptive provisions for branch circuits installed in dwelling units. Topics covered by these provisions include: required outlet location, outlet spacing, types of branch circuits,  ground-fault circuit-interrupter protection for receptacles, and arc-fault circuit-interrupter protection for branch circuit conductors. The prescriptive requirements for branch-circuit installations in dwelling units is reflective of how the American household uses electricity.

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The uninsulated aluminum bonding strip on this Type AC cable is required by 320.100 to help ensure the grounding ability of the armor. Since that strip is not required to be connected to an equipment grounding terminal, it can be cut off or bent back over the metal jacket.