This document defines terms related to combustible dust, wiring methods in hazardous locations, grounding requirements, and spray application processes using flammable materials. It provides definitions for combustible dust, various wiring methods permitted in Class I and Class II hazardous locations, sealing and drainage requirements, and definitions for terms like flash-off area, limited finishing workstation, resin application area, and spray area as they relate to spray application processes using flammable materials. It specifies grounding requirements for wiring in hazardous locations and classification of locations for motor fuel dispensing facilities.

1. 500. 2 Definitions
Combustible Dust. Dust particles that are 500 microns
or smaller (material passing a U.S. No. 35 Standard Sieve
as defined in ASTM E 11-09, Standard Specification for Wire
Cloth and Sieves for Testing Purposes) and present a fire or
explosion hazard when dispersed and ignited in air.
Informational Note: See ASTM E 1226–12a, Standard Test
Method for Explosibility of Dust Clouds, or ISO 6184-1,
Explosion protection systems — Part 1: Determination of explosion
indices of combustible dusts in air, for procedures for
determining the explosibility of dusts.

2. Class 1 Locations
501.10 Wiring Methods
(A) Class I, Division 1.
 (1) General. In Class I, Division 1 locations, the
wiring methods in (a) through ( e) shall be
permitted.
(e) Optical fiber cable Types OFNP, OFCP, OFNR,
OFCR, OFNG, OFCG, OFN, and OFC shall be
permitted to be installed in raceways in accordance
with 501.10(A). These optical fiber cables shall be
sealed in accordance with 501.15.

3. Class 1 Locations
501.10 Wiring Methods
(A) Class I, Division 1.
 (2) Flexible Connections. Where necessary to
employ flexible connections, as at motor
terminals, the following shall be permitted:
 (1) Flexible fittings listed for the location, or
 (2) Flexible cord in accordance with the
provisions of 501.140, terminated with cord
connectors listed for the location, or

4. Class 1 Locations
501.10 Wiring Methods
(A) Class I, Division 1.
 (2) Flexible Connections – (cont.)
 (3) 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 protected from damage by
location or a suitable guard, listed Type TC-ER-HL
cable with an overall jacket and a separate equipment
grounding conductor(s) in accordance with 250.122
that is terminated with fittings listed for the location

5. Class 1 Locations
501.15 Sealing and Drainage
 (C) Class I, Divisions 1 and 2.
 (6) Conductor or Optical Fiber Fill. The
cross-sectional area of the conductors or optical
fiber tubes (metallic or nonmetallic) permitted in
a seal shall not exceed 25 percent of the cross-
sectional area of a rigid metal conduit of the
same trade size unless the seal is specifically
identified for a higher percentage of fill.

6. Class 1 Locations
 501.30 Grounding and Bonding, Class I,
Divisions 1 and 2
Regardless of the voltage of the electrical system,
wiring and equipment in Class I, Division 1 and 2
locations shall be grounded as specified in Article
250 and in accordance with the requirements of
501.30(A) and (B).

7. Class II Locations
 502.10 Wiring Methods
 (A) Class II, Division 1.
 (1) General. In Class II, Division 1 locations, the
wiring methods in (1) through (4) shall be permitted
 (4) Optical fiber cables Types OFNP, OFCP, OFNR,
OFCR, OFNG, OFCG, OFN, and OFC shall be
permitted to be installed in raceways in accordance with
502.10(A). Optical fiber cables shall be sealed in
accordance with 502.15.d:

8. Class II Locations
 502.30 Grounding and Bonding, Class II,
Divisions 1 and 2
Regardless of the voltage of the electrical system,
wiring and equipment in Class II, Division 1 and 2
locations shall be grounded as specified in Article
250 and in accordance with the requirements of
502.30(A) and (B).

9. Intrinsically Safe Systems
 504.10 Equipment Installation
 (C) Enclosures. General-purpose enclosures
shall be permitted for intrinsically safe apparatus
and associated apparatus unless otherwise
specified in the manufacturer’s documentation.

10. Motor Fuel Dispensing Facilities
514.3 Classification of Locations
 (C) Motor Fuel Dispensing Stations in Boatyards
and Marinas.
 (1) General. Electrical wiring and equipment located at
or serving motor fuel dispensing locations shall be
installed on the side of the wharf, pier, or dock
opposite from the liquid piping system.
Informational Note: For additional information, see
NFPA 303-2011, Fire Protection Standard for Marinas and
Boatyards, and NFPA 30A-2012, Motor Fuel Dispensing
Facilities and Repair Garages.

11. Motor Fuel Dispensing Facilities
514.3 Classification of Locations
 (C) Motor Fuel Dispensing Stations in Boatyards
and Marinas – (cont.)
 (2) Classification of Class I, Division 1 and 2 Areas.
The following criteria shall be used for the purposes of
applying Table 514.3(B)(1) and Table 514.3(B)(2) to
motor fuel dispensing equipment on floating or fixed
piers, wharfs, or docks.

12. Motor Fuel Dispensing Facilities
514.3 Classification of Locations
 (D) Closed Construction. Where the construction of
floating docks, piers, or wharfs is closed so that there is
no space between the bottom of the dock, pier, or
wharf and the water, as in the case of concrete-enclosed
expanded foam or similar construction, and the
construction includes integral service boxes with supply
chases, the following shall apply:

13. Motor Fuel Dispensing Facilities
514.3 Classification of Locations
 (1) The space above the surface of the floating dock,
pier, or wharf shall be a Class I, Division 2 location
with distances as specified in Table 514.3(B)(1)(1) for
dispenser and outdoor locations.
 (2) Spaces below the surface of the floating dock, pier,
or wharf that have areas or enclosures, such as tubs,
voids, pits, vaults, boxes, depressions, fuel piping
chases, or similar spaces, where flammable liquid or
vapor can accumulate shall be a Class I, Division 1
location.

14. Motor Fuel Dispensing Facilities
514.3 Classification of Locations
 Exception No. 1: Dock, pier, or wharf sections that do not support fuel
dispensers and abut, but are located 6.0 m (20 ft) or more from, dock
sections that support a fuel dispenser(s) shall be permitted to be Class I,
Division 2 locations where documented air space is provided between dock
sections to allow flammable liquids or vapors to dissipate without traveling to
such dock sections. The documentation shall comply with 500.4(A).
 Exception No. 2: Dock, pier, or wharf sections that do not support fuel
dispensers and do not directly abut sections that support fuel dispensers shall
be permitted to be unclassified where documented air space is provided and
where flammable liquids or vapors cannot travel to such dock sections. The
documentation shall comply with 500.4(A).

15. Motor Fuel Dispensing Facilities
514.3 Classification of Locations
 (E) Open Construction. Where the construction of piers,
wharfs, or docks is open, as in the case of decks built on
stringers supported by pilings, floats, pontoons, or similar
construct ion, the following shall apply:
 (1) The area 450 mm (18 in.) above the surface of the dock, pier,
or wharf and extending 6.0 m (20 ft) horizontally in all directions
from the outside edge of the dispenser and down to the water
level shall be a Class 1, Division 2 location.
 (2) Enclosures such as tubs, voids, pits, vaults, boxes,
depressions, piping chases, or similar spaces where flammable
liquids or vapors can accumulate within 6.0 m (20 ft) of the
dispenser shall be a Class I, Division 1 location.

16. ARTICLE 516 Spray Application, Dipping,
Coating, and Printing Processes Using
Flammable or Combustible Materials
 516.2 Definitions
 Flash-Off Area. An open or enclosed area after a spray
application process where vapors are released due to exposure to
ambient air or a heated atmosphere. [33:3.3.1.1]
 Limited Finishing Workstation. An apparatus that is capable of
confining the vapors, mists, residues, dusts, or deposits that are
generated by a spray application process and that meets the
requirements of Section 14.3 of NFPA 33, Standard for Spray
Application Using Flammable or Combustible Materials, but
does not meet the requirements of a spray booth or spray room,
as herein defined. [33:3.3.15.1]

17. ARTICLE 516 Spray Application, Dipping,
Coating, and Printing Processes Using
Flammable or Combustible Materials
 516.2 Definitions – (cont.)
 Resin Application Area. Any area in which polyester resins or
gelcoats are spray applied. [33:3.3.1.2]
 Spray Area. Any fully enclosed, partly enclosed, or unenclosed
area in which ignitible quantities of flammable or combustible
vapors, mists, residues, dusts, or deposits are present due to the
operation of spray processes, including (1) any area in the direct
path of a spray application process; (2) the interior of a spray
booth or spray room or limited finishing workstation, as herein
defined; (3) the interior of any exhaust plenum, eliminator
section, or scrubber section; (4) the interior of any exhaust duct
or exhaust stack leading from a spray application process;

18. ARTICLE 516 Spray Application, Dipping,
Coating, and Printing Processes Using
Flammable or Combustible Materials
 516.2 Definitions – (cont.)
 (5) the interior of any air recirculation filter house or
enclosure, including secondary recirculation particulate
filters; (6) any solvent concentrator (pollution
abatement) unit or solvent recovery (distillation) unit.
The following are not considered to be a part of the
spray area: (1) fresh air make-up units; (2) air supply
ducts and air supply plenums; (3) recirculation air
supply ducts downstream of secondary filters; (4)
exhaust ducts from solvent concentrateur (pollution
abattement) units. [33:3.3.2.3]

19. ARTICLE 516 Spray Application, Dipping,
Coating, and Printing Processes Using
Flammable or Combustible Materials
 516.2 Definitions – (cont.)
 Spray Area – (cont.)
(5) the interior of any air recirculation filter house or enclosure,
including secondary recirculation particulate filters; (6) any solvent
concentrator (pollution abatement) unit or solvent recovery
(distillation) unit. The following are not considered to be a part of
the spray area: (1) fresh air make-up units; (2) air supply ducts and
air supply plenums; (3) recirculation air supply ducts downstream of
secondary filters; (4) exhaust ducts from solvent concentrator
(pollution abatement) units. [33:3.3.2.3]

20. ARTICLE 516 Spray Application, Dipping,
Coating, and Printing Processes Using
Flammable or Combustible Materials
 516.2 Definitions
 Spray Booth. A power-ventilated enclosure for a spray
application operation or process that confines and
limits the escape of the material being sprayed,
including vapors, mists, dusts, and residues that are
produced by the spraying operation and conducts or
directs these materials to an exhaust system. [33:3.3.14]

21. ARTICLE 516 Spray Application, Dipping,
Coating, and Printing Processes Using
Flammable or Combustible Materials
 516.2 Definitions
 Spray Room. A power-ventilated fully enclosed room
used exclusively for open spraying of flammable or
combustible materials. A spray room is a purposefully
enclosed room built for spray/coating/dipping
applications provided with dedicated ventilation supply
and exhaust. Normally the room is configured to house
the item to be painted, providing reasonable access
around the item/process. Depending on the size of the
item being painted, such rooms may actually be the
entire building or the major portion thereof. [33:3.3.15]

22. ARTICLE 516 Spray Application, Dipping,
Coating, and Printing Processes Using
Flammable or Combustible Materials
 516.2 Definitions
 Unenclosed Spray Area. Any spray area that is
not confined by a limited finishing workstation,
spray booth, or spray room, as herein defined.
[33:3.3.2.3.2]

23. 516. 3 Classification of Locations
 (A) Zone Classification of Locations.
(1) For the purposes of this article, the zone system of electrical
area classification shall be applied as follows:
a. The inside of open or closed containers or vessels shall be
considered a Class I, Zone 0 location.
b. A Class I, Division 1 location shall be permitted to be
alternatively classified as a Class I, Zone 1 location.
c. A Class I, Division 2 location shall be permitted to be
alternatively classified as a Class I, Zone 2 location.
d. A Class II, Division 1 location shall be permitted to be
alternatively classified as a Zone 21 location.
e. A Class II, Division 2 location shall be permitted to be
alternatively classified as a Zone 22 location. [33:6.2.2]

24. 516. 3 Classification of Locations
(cont.)
(2) For the purposes of electrical area classification, the
division system and the zone system shall not be
intermixed for any given source of release. [33:6.2.3]
(3) In instances of areas within the same facility classified
separately, Class I, Zone 2 locations shall be permitted to
abut, but not overlap, Class I, Division 2 locations. Class
I, Zone 0 or Zone 1 locations shall not abut Class I,
Division 1 or Division 2 locations. [33:6.2.4]

25. 516. 3 Classification of Locations
(cont.)
(4) Open flames, spark-producing equipment or
processes, and equipment whose exposed surfaces exceed
the autoignition temperature of the material being sprayed
shall not be located in a spray area or in any surrounding
area that is classified as Division 2, Zone 2, or Zone 22.
Exception: This requirement shall not apply to drying, curing, or
fusing apparatus. [33:6.2.5]

26. 516. 3 Classification of Locations
(cont.)
(5) Any utilization equipment or apparatus that is capable
of producing sparks or particles of hot metal and that is
located above or adjacent to either the spray area or the
surrounding Division 2, Zone 2, or Zone 22 areas shall be
of the totally enclosed type or shall be constructed to
prevent the escape of sparks or particles of hot metal.
[33:6.2.6]

27. Health Care Facilities
517.2 Definitions
 Life Safety Branch. A system of feeders and branch
circuits supplying power for lighting, receptacles, and
equipment essential for life safety that is automatically
connected to alternate power sources by one or more
transfer switches during interruption of the normal
power source. [99:3.3.94]

28. Health Care Facilities
517.2 Definitions – (cont.)
 Patient Care Space. Space within a health care facility wherein
patients are intended to be examined or treated.
 Basic Care Space. Space in which failure of equipment or a system
is not likely t o cause injury to the patients or caregivers but may
cause patient discomfort.
 General Care Space. Space in which failure of equipment or a
system is likely to cause minor injury to patients or caregivers.
 Critical Care Space. Space in which failure of equipment or a
system is likely to cause major injury or death to patients or
caregivers.

29. Health Care Facilities
517.2 Definitions – (cont.)
 Support Space. Space in which failure of equipment or a system is
not likely to have a physical impact on patients or caregivers.
Informational Note No. 1: The governing body of the facility
designates patient care space in accordance with the type of patient
care anticipated and with the definitions of the area classification.
Business offices, corridors, lounges, day rooms, dining rooms, or
similar areas typically are not classified as patient care space.
Informational Note No. 2: Basic care space is typically a location
where basic medical or dental care, treatment, or examinations are
performed. Examples include, but are not limited to, examination
or treatment rooms in clinics, medical and dental offices, nursing
homes, and limited care facilities.

30. Health Care Facilities
517.2 Definitions – (cont.)
 Informational Note No. 3: General care space includes areas such as patient
bedrooms, examining rooms, treatment rooms, clinics, and similar areas
where the patient may come into contact with electromedical devices or
ordinary appliances such as a nurse call system, electric beds, examining
lamps, telephones, and entertainment devices.
 Informational Note No. 4: Critical care space includes special care units,
intensive care units, coronary care units, angiography laboratories, cardiac
catheterization laboratories, delivery rooms, operating rooms, and similar
areas in which are patients are intended to be subjected to invasive procedures
and are connected to line-operated, electromedical devices.
 Informational Note No. 5: Spaces where a procedure is performed that
subjects patients or staff to wet conditions are considered as wet procedure
areas. Wet conditions include standing fluids on the floor or drenching of the
work area. Routine housekeeping procedures and incidental spillage of liquids
do not define wet procedure areas. It is the responsibility of the governing
body of the health care facility to designate the wet procedure areas.

31. Health Care Facilities
517.2 Definitions – (cont.)
 Patient Care Vicinity. A space, within a
location intended for the examination and
treatment of patients, extending 1.8 m (6 ft)
beyond the normal location of the patient bed,
chair, table, treadmill, or other device that
supports the patient during examination and
treatment and extending vertically to 2.3 m (7 ft
6 in.) above the floor. [99:3.3.139]

32. Health Care Facilities
517.2 Definitions – (cont.)
 Wet Procedure Location. The area in a patient care
space where a procedure is performed that is normally
subject to wet conditions while patients are present,
including standing fluids on the floor or drenching of
the work area, where either such condition is intimate
to the patient or staff.
 Informational Note: Routine housekeeping procedures
and incidental spillage of liquids do not define a wet
procedure location.

33. Further Information
 Wet procedure locations may also include such areas as
hydrotherapy areas, dialysis laboratories, and certain
wet laboratories at the discretion of the governing body
of the facility. The definition excludes areas such as
lavatories or bathrooms within a health care facility. For
infection control purposes, many patient and treatment
areas have a sink for hand washing, which also is not a
wet procedure location.

34. Health Care Facilities
517.19(C) Operating Room Receptacles
 (1) Minimum Number and Supply. Each operating
room shall be provided with a minimum of 36
receptacles, at least 12 of which shall be connected to
eit her of the following:
 (1) The normal system branch circuit required in
517.19(A)
 (2) A critical branch circuit supplied by a different
transfer switch than the other receptacles at the same
location

35. Health Care Facilities
517.19(C) Operating Room Receptacles
 (2) Receptacle Requirements. The receptacles
required in (517.19)(C)(1) shall be permitted to be of
the single or duplex types or a combination of both. All
receptacles shall be listed hospital grade and so
identified. The grounding terminal of each receptacle
shall be connected to the reference grounding point by
means of an insulated copper equipment grounding
conductor.

36. ARTICLE 520
Theaters, Audience Areas of Motion Picture
and Television Studios, Performance Areas,
and Similar Locations

37. 520.2 Definitions
 Stage Equipment. Equipment at any location on the
premises integral to the stage production including, but
not limited to, equipment for lighting, audio, special
effects, rigging, motion control, projection, or video.

38. 520.2 Definitions – (cont.)
 Stage Lighting Hoist. A motorized lifting
device that contains a mounting position for one or more
luminaires, with wiring devices for connection of
luminaires to branch
circuits, and integral flexible cables
to allow the luminaires
to travel over the
lifting range of the
hoist while energized.

39. 520.2 Definitions – (cont.)
 Stage Switchboard. A switchboard, panelboard, or
rack containing dimmers or relays with associated
overcurrent protective devices, or overcurrent
protective devices alone, used primarily to feed stage
equipment.

40. II. Fixed Stage Switchboards
520.21 General
 Fixed stage switchboards shall comply with 520.21(1) through
(4):
 (1) Fixed stage switchboards shall be listed.
 (2) Fixed stage switchboards shall be readily accessible but shall
not be required to be located on or adjacent to the stage.
Multiple fixed stage switchboards shall be permitted at different
locations.
 (3) A fixed stage switchboard shall contain overcurrent
protective devices for all branch circuits supplied by that
switchboard.
 (4) A fixed stage switchboard shall be permitted to supply both
stage and non-stage equipment.

41. III. Fixed Stage Equipment
Other Than Switchboards
 520.40 Stage Lighting Hoists
Where a stage lighting hoist is listed as a complete
assembly and contains an integral cable-handling
system and cable to connect a moving wiring
device to a fixed junction box for connection to
permanent wiring, the extra-hard usage
requirement of 520.44(C)(1) shall not apply.

42. ARTICLE 640
Audio Signal Processing,
Amplification, and Reproduction
Equipment
640.1 Scope
 (B) Not Covered. This article does not cover the
installation and wiring of fire and burglary alarm
signaling devices.

43. 680.22 Lighting, Receptacles, and Equipment
(B) Luminaires, Lighting Outlets, and
Ceiling-Suspended (Paddle) Fans.
 (6) Low-Voltage Luminaires.
Listed low-voltage luminaires
not requiring grounding, not
exceeding the low-voltage
contact limit, and supplied by
listed transformers or power
supplies that comply with
680.23(A)(2) shall be permitted
to be located less than 1.5 m (5
ft) from the inside walls of the
pool.

44. 680.26 Equipotential Bonding
 (C) Pool Water.
Where none of the bonded parts is in direct connection
with the pool water, the pool water shall be in direct
contact with an approved corrosion-resistant conductive
surface that exposes not less than 5800 mm2 (9 in.2) of
surface area to the pool water at all times. The conductive
surface shall be located where it is not exposed to physical
damage or dislodgement during usual pool activities, and
it shall be bonded in accordance with 680.26(B).

45. Solar Photovoltaic (PV ) Systems
690.2 Definitions
 DC-to-DC Converter. A device installed in the PV
source circuit or PV output circuit that can provide an
output dc voltage and current at a higher or lower value
than the input dc voltage and current.

46. Solar Photovoltaic (PV ) Systems
690.2 Definitions
 Direct-Current (dc)
Combiner. A device
used in the PV source
and PV output circuits
to combine two or
more dc circuit inputs
and provide one dc
circuit output.

47. Solar Photovoltaic (PV ) Systems
690.2 Definitions
 Multimode Inverter.
Equipment having the
capabilities of both the
utility-interactive inverter
and the stand-alone
inverter.

48. IV. Wiring Methods
690.31 Methods Permitted
 (B) Identification and Grouping. PV source circuits
and PV output circuits shall not be contained in the
same raceway, cable tray, cable, outlet box, junction
box, or similar fitting as conductors, feeders, branch
circuits of other non-PV systems, or inverter output
circuits, unless the conductors of the different systems
are separated by a partition. PV system conductors shall
be identified and grouped as required by 690.31(B)(1)
through (4). The means of identification shall be
permitted by separate color coding, marking tape,
tagging, or other approved means.

49. IV. Wiring Methods
690.31 Methods Permitted
 (B) Identification and Grouping (cont.)
 (1) PV Source Circuits. PV source circuits shall be
identified at all points of termination, connection, and
splices.
 (2) PV Output and Inverter Circuits. The
conductors of PV output circuits and inverter input and
output circuits shall be identified at all points of
termination, connection, and splices.

50. IV. Wiring Methods
690.31 Methods Permitted
 (B) Identification and Grouping (cont.)
 (3) Conductors of Multiple Systems. Where the
conductors of more than one PV system occupy the
same junction box, raceway, or equipment, the
conductors of each system shall be identified at all
termination, connection, and splice points.
Exception: Where the identification of the conductors is evident by
spacing or arrangement, further identification shall not be required.

51. IV. Wiring Methods
690.31 Methods Permitted
 (B) Identification and Grouping (cont.)
 (4) Grouping. Where the conductors of more than one
PV system occupy the same junction box or raceway
with a removable cover(s), the ac and dc conductors of
each system shall be grouped separately by cable ties or
similar means at least once and shall then be grouped at
intervals not to exceed 1.8 m (6 ft).
Exception: The requirement for grouping shall not apply if the
circuit enters from a cable or raceway unique to the circuit that
makes the grouping obvious.