Section 500.7(A) through (L) shall be acceptable protection techniques for Electrical and electronic equipment in hazardous (classified) locations shall be protected by one or more of the techniques in 500.7(A) through (P).
(K) Combustible Gas Detection System. A combustible gas detection system shall be permitted as a means of protection in industrial establishments with restricted public access and where the conditions of maintenance and supervision ensure that only qualified persons service the installation. Where such a system is installed, equipment specified in 7(K)(1), (K)(2), or (K)(3) shall be permitted.
(1) General Any gas detection system utilized as a protection technique shall meet all of the requirements in 500.7(K)(1)(a) through (K)(1)(e).
(a) The gas detection equipment used shall be listed for Class I, Division 1 and listed for the detection of the specific gas or vapor to be encountered.
(b) The gas detection system shall not utilize portable or transportable equipment or temporary wiring methods.
(c) The gas detection system shall only use pointtype sensors. The system shall be permitted to be augmented with open-path (line-of-sight)–type sensors, but open- path–type sensors shall not be the basis for this protection technique.
(d) The type of detection equipment, its listing, installation location(s), alarm and shutdown criteria, and calibration frequency shall be documented where combustible gas detectors are used as a protection technique.
(e) The applications for the use of combustible gas detection systems as a protection technique shall be limited to 7(K)(2), or (K)(3), or (K)(4).

[see NEC for (4) Informational Notes here]

(1)(2) Inadequate Ventilation.
(2)(3) Interior of a Building or Enclosed Space.
(3)(4) Interior of a Control Panel.

(see NEC for complete Code text)

Section 500.7(A) through (L) shall be acceptable protection techniques for Electrical and electronic equipment in hazardous (classified) locations shall be protected by one or more of the techniques in 500.7(A) through (P).
(L) Inherently Safe Optical Radiation “op ” This protection technique shall be permitted for equipment in Class I or II, Division 1 or 2 locations for which the equipment is identified.
Informational Note: The identified class and division depends on the intended explosive atmosphere and the number of faults applied as part of the protection technique evaluation.
(M) Protected Optical Radiation “op pr.” This protection technique shall be permitted for equipment in Class I or II, Division 2 locations for which the equipment is identified.
Informational Note: The identified class and division depends on the intended explosive atmosphere as part of the protection technique evaluation.
(N) Optical System With Interlock “op sh.” This protection technique shall be permitted for equipment in Class I or II, Division 1 or 2 locations for which the equipment is identified.
Informational Note: The identified class and division depends on the intended explosive atmosphere and the number of faults applied as part of the protection technique evaluation.
(O) Protection by Skin Effect Trace Heating “IEEE 844.1.” This protection technique shall be permitted for skin effect trace heating equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 2 for which it is listed.

(see NEC for complete Code text) 

(A) Class I, Division 1.
(1) General. In Class I, Division 1 locations, the following wiring methods in (a) through (f) shall be permitted:
(a) Threaded rigid metal conduit (Type RMC) or threaded steel intermediate metal conduit (Type IMC). (see NEC for complete details)
(b) Type MI cable (see NEC for complete details)
(c) Type MC-HL cable (see NEC for complete details)
(d) Type ITC-HL cable (see NEC for complete details)
(e) Optical fiber cable Types OFNP, OFCP, OFNR, OFCR, OFNG, OFCG, OFN, and OFC (see NEC for complete details)
(f) In industrial establishments with restricted public access, where the conditions of maintenance and supervision ensure that only qualified persons service the installation, for applications limited to 600 volts nominal or less, and where the cable is not subject to physical damage, and terminated with fittings listed for the location, Type TC-ER-HL cable. Type TC-ER-HL cable shall be listed for use in Class I, Division 1 or Zone 1 locations and shall be installed in accordance with 336.10.
Informational Note: See the information on construction, testing, and marking of cables and cable fittings in ANSI/UL 2225-2013, Cables and Cable- Fittings for Use in Hazardous (Classified) Locations.
(g) In industrial establishments with restricted public access, where the conditions of maintenance and supervision ensure that only qualified persons service the installation, listed Type P cable with metal braid armor, with an overall jacket, terminated with fittings listed for the location, and installed in accordance 337.10.
Informational Note No. 1: For information on construction, testing, and marking of Type P cable, see ANSI/UL 1309-2017, Marine Shipboard Cable.
Informational Note No. 2: For information on construction, testing, and marking of cable fittings, see ANSI/UL 2225-2013, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations.

(C) Marking. Equipment shall be marked in accordance with 505.9(C)(1) or (C)(2).
(2) Zone Equipment. Equipment meeting one or more of the protection techniques described in 505.8 shall be marked with all of the following in the order shown:
(1) Class I (equipment shall be permitted to omit the Class I marking)
(2) Zone [in accordance with Table 9(C)(2)(4)]
(3) Symbol “AEx”
(4) Protection technique(s) in accordance with Table 9(C)(2)(4)
(5) Applicable material group in accordance with Table 505.9(C)(1)(2) or a specific gas or vapor.
(6) Temperature classification in accordance with 9(D)(1)
(7) Equipment protection level (EPL)
Table 505.9(C)(2)(4) Types of Protection Designation Equipment Suitability

(see NEC for complete Code text and table)

All 125-volt, single-phase, 15- and 20-ampere receptacles installed in areas where electrical diagnostic equipment, electrical hand tools, or portable lighting equipment are to be used shall have Ground-fault circuit-interrupter protection for personnel shall be provided as required in 210.8(B).

(D) Areas Suitably Cut Off and Ventilated. Adjacent areas in which flammable liquids or vapors are not likely to be released, such as stock rooms, electrical control rooms, and other similar locations, shall be unclassified where adequately ventilated and mechanically ventilated at a rate of four or more air changes per hour, or designed with positive air pressure, or where effectively cut off from the hangar itself by walls or partitions..

(A) Emergency Electrical Disconnects. Fuel dispensing systems shall be provided with one or more clearly identified emergency shutoff devices or electrical disconnects. Such devices or disconnects shall be installed in approved locations but not less than 6 m (20 ft) or more than 30 m (100 ft) from the fuel dispensing devices that they serve. Emergency shutoff devices or electrical disconnects shall disconnect power to all dispensing devices; to all remote pumps serving the dispensing devices; to all associated power, control, and signal circuits; and to all other electrical equipment in the hazardous (classified) locations surrounding the fuel dispensing devices. When more than one emergency shutoff device or electrical disconnect is provided, all devices shall be interconnected. Resetting from an emergency shutoff condition shall require manual intervention and the manner of resetting shall be approved by the authority having jurisdiction. [30A:6.7]
The emergency shutoff device shall disconnect simultaneously from the source of supply, all conductors of the circuits, including the grounded conductor, if any. Equipment grounding conductors shall remain connected.
Exception: Intrinsically safe electrical equipment need not meet this requirement. [30A:6.7].

Part II shall not apply to the following:
(1) Business offices, corridors, waiting rooms, and the like in clinics, medical and dental offices, and outpatient facilities
(2) Areas of nursing homes and limited care facilities wired in accordance with Chapters 1 through 4 of this Code where these areas are used exclusively as patient sleeping rooms
(3) Areas used exclusively for any of the following purposes:
(a) Intramuscular injections (immunizations)
(b) Psychiatry and psychotherapy
(c) Alternative medicine
(d) Optometry

Informational Note: See NFPA 101-2015 2018, Life Safety Code®.

An isolated ground receptacle, if used, shall not defeat the purposes of the safety features of the grounding systems detailed in 517.13. [99:6.3.2.2.5(A)]

(A) Inside of a Patient Care An isolated grounding ground receptacle shall not be installed within a patient care vicinity. [99:6.3.2.2.7.1(B)] [99:6.3.2.2.5(B)]
(B) Outside of a Patient Care Vicinity. Isolated ground receptacle(s) installed in patient care spaces outside of a patient care vicinity(s) shall comply with 517.16(B)(1) and (B)(2).
(1) The equipment grounding terminals of isolated ground receptacles installed in branch circuits for patient care spaces shall be connected to an insulated equipment grounding conductor in accordance with 250.146(D) in addition to the equipment grounding conductor path required installed in a wiring method described in 13(A).
The equipment grounding conductor connected to the equipment grounding terminals of isolated ground receptacles in patient care spaces shall be clearly identified along the equipment grounding conductor’s entire length by green insulation with one or more yellow stripes.
(2) The insulated equipment grounding conductor required in 517.13(B)(1) shall be clearly identified along its entire length by green insulation, with no yellow stripes, and shall not be connected to the grounding terminals of isolated equipment ground receptacles but shall be connected to the box or enclosure indicated in 517.13(B)(1)(2) and to non–current-carrying conductive surfaces of fixed electrical equipment indicated in 517.13(B)(1)(3).
Informational Note No. 1: This type of installation is typically used where a reduction of electrical noise (electromagnetic interference) is necessary, and parallel grounding paths are to be avoided.
Informational Note No. 2: Care should be taken in specifying a system containing isolated ground receptacles, because the grounding impedance is controlled only by the grounding wires of the effective ground-fault current path is dependent upon the equipment grounding conductor(s) and does not benefit from any conduit or building structure in parallel with the equipment grounding path conductor. [99:A.6.3.2.2.7.1].

(A) Applicability (see NEC for complete text)
(B) Feeders (see NEC for complete text)
(C) Selectivity (see NEC for complete text)
(D) Testing. When equipment ground-fault protection of equipment is first installed, each level shall be performance tested to ensure compliance with 517.17(C). This testing shall be conducted by a qualified person(s) using a test process in accordance with the instruction provided with the equipment. A written record of this testing shall be made and shall be available to the authority having jurisdiction.

The life safety branch of the essential electrical system shall meet the requirements of Article 700, except as amended by Article 517.
(1) Section 700.4 shall not apply.
(2) Section 700.10(D) shall not apply.
(3) Section 700.17 shall be replaced with the following: Branch circuits that supply emergency lighting shall be installed to provide service from a source complying with 700.12 when normal supply for lighting is interrupted or where single circuits supply luminaires containing secondary batteries.
(4) Section 700.32 shall not apply.
Informational Note No. 1: For additional information, see NFPA 110-2013 2019, Standard for Emergency and Standby Power Systems.
Informational Note No. 2: For additional information, see 517.29 and NFPA 99-2015 2018, Health Care Facilities Code.

(A) Two Independent Power Sources. Essential electrical systems shall have a minimum of the following two independent sources of power: a normal source generally supplying the entire electrical system and one or more alternate source(s) sources for use when the normal source is [99:6.4.1.1.4] [99: 6.7.1.2.2]
(B) Types of Power Sources.
(1) Generating Units. Where the normal source consists of generating units on the premises, the alternate source shall be either another generating set or an external utility [99:6.4.1.1.5] [99:6.7.1.2.3]
(2) Fuel Cell Systems. (see NEC for complete text).
(3) Battery Systems. Battery systems shall be permitted to serve as the alternate source for all or part of an essential electrical system.
Informational Note: For information on installation of battery systems, see NFPA 111-2016, Standard on Stored Electrical Energy Emergency and Standby Power Systems.

(A) Separate Branches (see NEC of complete text)
(B) Transfer Switches (see NEC of complete text)
(C) Wiring Requirements
(1) Separation from Other Circuits. The life safety branch and critical branch of the essential electrical system shall be kept entirely independent of all other wiring and equipment and shall not enter the same raceways, boxes, or cabinets with each other or other wiring. [99:6.7.5.2.1]
(a) Raceways, cables, or enclosures of the life safety and critical branch shall be readily identified as a component of the essential electrical system (EES). Boxes and enclosures (including transfer switches, generators, and power panels) shall be field- or factory-marked and identified as a component of the EES. Raceways and cables shall be field- or factory-marked as a component of the EES at intervals not to exceed 6 m (25 ft).
(b) Conductors of the life safety branch or critical branch shall not enter the same raceways, boxes, or cabinets with each other or any other wiring system. It shall be permitted for the branch conductors to occupy common equipment, raceways, boxes, or cabinets of other circuits not part of the life safety branch and critical branch where such wiring complies with one of the following:
(1) Is in transfer equipment enclosures
(2) Is in exit or emergency luminaires supplied from two sources
(3) Is in a common junction box attached to exit or emergency luminaires supplied from two sources
(4) Is for two or more circuits supplied from the same branch and same transfer switch
(c) The wiring of the equipment branch shall be permitted to occupy the same raceways, boxes, or cabinets of other circuits that are not part of the essential electrical
(d) Where Category 2 (general care) locations are served from two separate transfer switches on the essential electrical system in accordance with 517.18(A), Exception 3, the Category 2 (general care) circuits from the two separate systems shall be kept independent of each other.
(e) Where Category 1 (critical care) locations are served from two separate transfer switches on the essential electrical system in accordance with 517.19(A), Exception No. 2, the critical care circuits from the two separate systems shall be kept independent of each other.

Illumination shall be provided for all working spaces about fixed service equipment, switchboards, switchgear, panelboards, or motor control centers installed outdoors that serve assembly occupancies. Control by automatic means only shall not be permitted. Additional lighting outlets shall not be required where the workspace is illuminated by an adjacent light source. 

Dimmers shall comply with 520.25(A) through (D).
(A) Disconnection and Overcurrent (see NEC for complete text)
(B) Resistance- or Reactor-Type Dimmers. Resistance- or series reactor-type dimmers shall be permitted to be placed in either the grounded or the ungrounded conductor of the circuit. Where designed to open either the supply circuit to the dimmer or the circuit controlled by it, the dimmer shall then comply with 404.2(B). Resistance- or reactor-type dimmers placed in the grounded neutral conductor of the circuit shall not open the
(C) (B) Autotransformer-Type (see NEC for complete text)
(D) (C) Solid-State-Type Dimmers. (see NEC for complete text).

(G) Protection. Flexible cords or cables accessible to the public shall be arranged to minimize the tripping hazard and shall be permitted to be covered with nonconductive matting secured to the walkway surface or protected with another approved cable protection method, provided that the matting or other protection method does not constitute a greater tripping hazard than the uncovered cables. It Burying cables shall be permitted to bury cables. The requirements of 300.5 shall not apply.

Part II. Relocatable Structures
545.20 Application Provisions. Relocatable structures shall comply with Part II of this article and the applicable sections of Part I.
545.22 Power Supply.
(A) Feeder.
(B) Number of Supplies.
(C) Identification.
(D) Grounding
545.24 Disconnecting Means and Branch-Circuit Overcurrent Protection. (A) Disconnection Means.
(B) Branch-Circuit Protective Equipment and Panelboards.
545.26 Bonding of Exposed Non-Current-Carrying Metal Parts.
545.27 Intersystem Bonding.
545.28 Ground-Fault Circuit-Interrupters (GFCI).

(See NEC for complete Code text).

(G) Receptacles. All 125-volt, single-phase, 15- and 20-ampere receptacles installed in the locations listed in (1) through (4) shall have Ground-fault circuit-interrupter protection shall be provided as required in 210.8(B). GFCI protection shall not be required for other than 125-volt, 15- and 20-ampere receptacles installed within the following areas:
(1) Areas having an equipotential plane
(2) Outdoors
(3) Damp or wet locations
(4) Dirt confinement areas for livestock.

A distribution point shall be permitted to supply Any agricultural building or structure for livestock located on the same premises shall be supplied from a distribution point. More than one distribution point on the same premises shall be permitted. The overhead electrical supply shall comply with 547.9(A) and (B), or with 547.9(C). The underground electrical supply shall comply with 547.9(C).
Any existing agricultural building or structure for other than livestock and any existing buildings and structures not under the scope of Article 547 shall be permitted to be supplied in accordance with 250.32(B)(1) Exception No. 1.
(A) Site-Isolating (See NEC for complete Code text)
(B) Service Disconnecting Means and Overcurrent Protection at the Building(s) or Structure( s). (See NEC for complete Code text)
(C) Service Disconnecting Means and Overcurrent Protection at the Distribution Where The service disconnecting means and overcurrent protection for each set of feeders or branch circuits are shall be located at the distribution point, the. The service disconnecting means shall be installed in accordance with Part VI of Article 230. The feeders or branch circuits supplied to buildings or structures shall comply with the provisions of 250.32 and Article 225, Parts I and II.
Informational Note: Methods to reduce neutralto- earth voltages in livestock facilities include supplying buildings or structures with 4-wire single- phase services, sizing 3-wire single-phase service and feeder conductors to limit voltage drop to 2 percent, and connecting loads line-to-line.
(D) Identification. Where a site is supplied by more than one distribution point, a permanent plaque or directory shall be installed at each of these distribution points denoting the location of each of the other distribution points and the buildings or structures served by each..

(B) Ground-Fault Circuit-Interrupters (GFCI). All 125-volt, single-phase, 15- and 20- ampere receptacle outlets installed in the locations specified in 550.13(B)(1) through (5) shall have GFCI protection for personnel. Ground-fault circuit-interrupter protection shall be provided as required in 210.8(A). GFCI protection shall not be required for other than 125-volt, 15- and 20-ampere receptacles installed within a mobile or manufactured home in the following areas:
(1) Outdoors, including Compartments accessible from outside the unit
(2) Bathrooms, including receptacles in luminaires
(3) Kitchens, where receptacles are installed to serve countertop surfaces
(4) Sinks, where receptacles are installed within 1.8 m (6 ft) of the outer edge of the sink
(5) Dishwashers
Informational Note: For information on protection of dishwashers, see 422.5.

(E) Additional Receptacles. Additional receptacles shall be permitted for connection of electrical equipment located outside the mobile home, and all such 125-volt, single-phase, 15- and 20-ampere receptacles shall be protected by a listed groundfault circuit-interrupter. Receptacles located outside a mobile or manufactured home shall be provided with ground-fault circuit-interrupter protection as specified by 210.8(A). Where receptacles provide power to a mobile or manufactured home in accordance with 550.10, ground-fault circuit- interrupter protection shall not be required.

(A) General (see NEC for complete Code text)
(B) Materials and (see NEC for complete Code text)
(C) Ground-Fault Circuit-Interrupter (see NEC for complete Code text)
(D) Reverse Polarity Device. A reverse polarity indicating device that provides a continuous visible or audible signal shall be installed in the recreational vehicle in accordance with the installation instructions and shall respond to the reversal of the ungrounded and the grounded conductors in the 120-volt ac system..

(F) GFCI Protection
(1) All 125-volt, single-phase, 15- and 20-ampere receptacles shall have listed ground- fault circuit-interrupter protection for personnel. The GFCI devices used in RV site electrical equipment shall not be required to be weather or tamper resistant in accordance with 9 and 406.12.
Informational Note: The percentage of 50 ampere sites required by 551.71 could be inadequate for seasonal recreational vehicle sites serving a higher percentage of recreational vehicles with 50 ampere electrical systems. In that type of recreational vehicle park, the percentage of 50 ampere sites could approach 100 percent.
(2) Thirty- and 50-ampere receptacles used in recreational vehicle site equipment shall not be required to meet the requirements of 210.8(B)..

The definitions in this section shall apply only within this article.
Berth.
Boatyard.
Bulkhead.
Crane.
Docking
Facility.
Electrical Datum Plane. (Previous definition at 555.2 moved to 682.2) (New definition for Electrical Datum Plane added to Article 100 and assigned to CMP-7)
Floating Building.
Marina.
Marine Marina Power Outlet. An enclosed assembly that can include equipment such as receptacles, circuit breakers, fused switches, fuses, a watt-hour meter(s), panelboards, and monitoring means approved identified for marine marina use. [303:3.3.13]
Monorail.
Mooring(s).
Shore Power.
Slip.
Storage,
Dry Stack.
Wharf.

(See NEC for complete definitions and Code text)..

All metal parts in contact with the water, all metal piping, and all non-current-carrying metal parts that are likely to become energized shall be connected to the grounding bus in the panelboard using solid copper conductors; insulated, covered, or bare; not smaller than 8 AWG. Connections to bonded parts shall be made in accordance with 250.8. (This was 553.11 in the 2017 NEC.).

(A) Ground-Fault Protection. For other than floating buildings, ground-fault protection for docking facilities shall be provided in accordance with 555.35(A)(1) through (A)(3).
(1) Receptacles Providing Shore Receptacles installed in accordance with 555.33(A) shall have individual GFPE set to open at currents not exceeding 30 milliamperes.
(2) GFCI Protection for All 125-volt, single-phase, 15- and 20-ampere receptacles for other than shore power shall be protected in accordance with 555.33(B)(1) and (B)(2).
(3) Feeder and Branch-Circuit Conductors with GFPE. Feeder and branch-circuit conductors that are installed on docking facilities shall be provided with GFPE set to open at currents not exceeding 100 milliamperes. Coordination with downstream GFPE shall be permitted at the feeder overcurrent protective device.
Exception to (3): Transformer secondary conductors of a separately derived system that do not exceed 3 m (10 ft) and are installed in a raceway shall be permitted to be installed without ground-fault protection. This exception shall also apply to the supply terminals of the equipment supplied by the transformer secondary conductors.
(B) Leakage Current Measurement Device. Where more than three receptacles supply shore power to boats, a leakage current measurement device shall be available and be used to determine leakage current from each boat that will utilize shore power.
Informational Note No. 1: Leakage current measurement will provide the capability to determine when an individual boat has defective wiring or other problems contributing to hazardous voltage and current. The use of a test device will allow the facility operator to identify a boat that is creating problems. In some cases a single boat may cause an upstream GFPE device protecting a feeder to operate even though multiple boats are supplied from the same feeder. The use of a test device will help the facility operator prevent a particular boat from contributing to hazardous voltage and current in the marina area.
Informational Note No. 2: An annual test of each boat with the leakage current measurement device is a prudent step toward determining if a boat has defective wiring that may be contributing hazardous voltage and current. Where the leakage current measurement device reveals that a boat is contributing hazardous voltage and current, repairs should be made to the boat before it is permitted to utilize shore power. 

555.50 Service Conductors.
555.21 Feeder Conductors.
555.52 Installation of Services and Feeders
(A) Flexibility
(B) Wiring Methods
555.53 Ground-Fault Protection.
555.54 Grounding.
(A) Grounding of Electrical and Nonelectrical
(B) Installation and Connection of Equipment Grounding
(C) Identification of Equipment Grounding
(D) Grounding Electrode Conductor
555.55 Insulated
555.56 Equipment
(A) Electrical
(B) Cord-Connected Appliances..

(G) A box, conduit body, or other enclosure, with a cover installed, shall be required for all splices except where:.
Exception No. 1: On construction sites, a box, conduit body, or other enclosure shall not be required for either of the following conditions:
(1) The circuit conductors being spliced are all from nonmetallic multiconductor cord or cable assemblies, provided that the equipment grounding continuity is maintained with or without the box.
(2) The circuit conductors being spliced are all from metal-sheathed cable assemblies terminated in listed fittings that mechanically secure the cable sheath to maintain effective electrical continuity.
Exception No. 2: On construction sites, where permanent wiring in framed walls and ceilings is GFCI protected and used to supply temporary power or lighting:.
(1) A cover shall not be required for splices installed completely inside of junction boxeswith plaster rings.
(2) Listed pigtail-type lampholders shall be permitted to be installed in ceiling-mountedjunction boxes with plaster rings.
(3) Finger safe devices for supplying and connection to devices shall also be permitted.

(A) Where Reused. Where overcurrent protective devices that have been previously used are installed in a temporary installation, these overcurrent protective devices shall be examined to ensure these devices have been properly installed, properly maintained, and there is no evidence of impending failure.
(B) Service Overcurrent Protective Devices. Overcurrent protective devices for solidly grounded wye electrical services of more than 150 volts to ground but not exceeding 1000 volts phase-tophase shall be current limiting.
Informational Note: The phrase “evidence of impending failure” means that there is evidence such as arcing, overheating, loose or bound equipment parts, visible damage, or deterioration. The phrase “properly maintained” means that the equipment has been maintained in accordance with the manufacturers’ recommendations and applicable industry codes and standards. References for manufacturers’ recommendations and applicable industry codes and standards include but are not limited to NEMA AB 4-2017, Guidelines for Inspection and Preventative Maintenance of Molded- Case Circuit Breakers Used in Commercial and Industrial Applications; NFPA 70B-2019, Recommended Practice for Electrical Equipment Maintenance; NEMA GD 1-2016, Evaluating Water-Damaged Electrical Equipment; and IEEE 1458-2017, IEEE Recommended Practice for the Selection, Field Testing, and Life Expectancy of Molded-Case Circuit Breakers for Industrial Applications.