This article focuses on revisions in Chapter 5 of the 2020 NEC, “Special Occupancies,” and it includes the requirements for equipment, systems, and wiring in hazardous (classified) locations, healthcare facilities, temporary wiring installations and so forth. This part of the series provides a look at some of the significant changes in articles 500 through 590.
(Editor's note: to read part 6 of this series, click here.)
Section 500.5(C)(1)(3) Class II Locations
The words “in normal or abnormal operating conditions” were added to 500.5(C)(1)(3). The revision clarifies that the classification of the area applies regardless of operation condition. Equipment and wiring within such locations must meet the applicable rules in Article 502 for Class II, Division 1 locations in both abnormal and normal operating conditions.
Section 500.7(L), (M) and (N) Protection Techniques
Three new protection techniques have been incorporated into Section 500.7, which provides the protection techniques under the Division system. Each new protection technique is directly related to optical radiation, which, in some instances, is a source of ignition for explosive atmospheres. A reference to ANSI/UL 60079-28 has been added where additional information about protection from optical radiation can be obtained.
Section 500.10(B)(1)(3)(4)(5) and (6) Wiring Methods
The phrase “include an equipment grounding conductor in addition to a drain wire” has been added in items (3), (4) and (5). Equipment grounding conductors are required to be connected at both ends, and some drain wires are not. List item (6) now includes PVC-coated rigid and IMC as an acceptable wiring method for use in areas where corrosion is a concern.
Section 502.10(A)(2)(7) and (8) Wiring Methods
Two new list items and wiring methods have been incorporated into Section 502.10(A)(2). List item (7) addresses Type TC-ER-HL and (8) addresses Type P Cable. Both are limited to use in industrial establishments with other specific restrictions that must be met.
Sections 511.12 and 513.12 GFCI Protection
Sections 511.12 and 513.12 have been revised and simplified to reference Section 210.8(B). The general requirements for GFCI protection in other than dwelling units are already covered in 210.8(B). There is no longer a need to list the types of equipment connected to circuits and receptacles that are required to provide GFCI protection.
Section 514.11 Emergency Electrical Disconnects
A new last sentence has been added covering emergency electrical disconnects. The requirements for emergency controls require disconnection of the grounded conductor as in 2014 NEC. The revision also clarifies that equipment grounding conductors must remain connected.
Section 517.2 Dental Office
A new definition of the term “Dental Office” has been added. The definition is derived and extracted from NFPA 99, and it includes care limited to outpatient services, no overnight stays for patients or 24-hour operations. The new definition provides the needed differentiation between the term “Medical Office” and “Dental Office.”
Section 517.10(B)(3) Not Covered
A new second-level subdivision item (3) has been added to Section 517.10(B). This clarifies types of patient care and procedures that do not have to comply with the wiring requirements in Part II of Article 517. Designers, installers and inspectors benefit from this practical relief that conveys what was intended in practice.
Section 517.16 Use of Isolated Ground Receptacles
This section has been revised to clarify the isolated equipment grounding conductor requirements for areas outside a patient vicinity. The IG equipment grounding conductor is in addition to the two paths required in 517.13 and must be identified using the color green with one or more yellow stripes.
Section 517.29 Type 1 Essential Electrical Systems
Section 517.29 and its title were revised to specifically address Type 1 Essential Electrical Systems and to align with NFPA 99. Type 1 EES are required for Category 1 (critical care) spaces. Category 1 (critical care) spaces shall not be served by a Type 2 EES.
Section 517.31(C) Wiring Requirements
Item (1)(a) provides an identification requirement for raceways, cables and enclosures of an essential electrical system at intervals not exceeding 25 feet. Item (3)(f) has been revised and broadened to all types of ceiling structures. Luminaires are now permitted to be wired using flexible metal raceways or metal-sheathed cable assemblies.
Section 518.6 Illumination
New Section 518.6 requires illumination for all equipment working spaces installed outdoors. Assembly occupancies typically locate service and distribution equipment outdoors. Section 110.26(D) generally requires illumination of working spaces installed indoors only.
About The Author

Michael Johnston
NECA Executive Director of Codes and Standards (retired)JOHNSTON, who retired as NECA’s executive director of codes and standards in 2023, is a former member and chair of NEC CMP-5 and immediate past chair of the NEC Correlating Committee. Johnston continues to serve on the NFPA Standards Council and the UL Electrical Council. Reach him at [email protected].