17.5 Spray Areas, Aircraft Hangars, Hazardous-Location Bonding & Intrinsic Safety (Articles 500, 504, 513 & 516)
Key Takeaways
The interior of a spray booth or spray room and the interior of its exhaust ducts are Class I, Division 1 (or Class II, Division 1 for powders) under Article 516.
In hazardous locations, locknut-bushing and double-locknut connections may not be relied on for bonding; bonding jumpers or other approved means must be used all the way back to the service or separately derived system (500.30 in the 2026 NEC).
In a Class I, Division 2 location, the bonding jumper around listed LFMC may be omitted only if the LFMC is 6 ft or less with listed fittings, the circuit is protected at 10 A or less, and the load is not a power utilization load.
Aircraft hangar floor areas are Class I, Division 2 up to 18 in. above the floor, and pits or depressions below the floor are Class I, Division 1 (513.3).
Intrinsically safe circuit conductors must be separated from nonintrinsically safe conductors by at least 2 in., a grounded metal partition, or an approved insulating partition, and may be identified with a light blue color (504.30 and 504.80).
Spray application, dipping, and coating (Article 516)
Article 516 covers places where flammable paints, finishes, or combustible powders are sprayed, dipped, or coated, such as auto body paint booths and industrial finishing lines.
Area classification
| Location | Classification |
|---|---|
| Interior of a spray booth or spray room, its exhaust ducts, and any area in the direct path of spray | Class I, Division 1 (or Zone 1), or Class II, Division 1 for powders |
| Around an open face of a spray booth | Class I, Division 2 within a set distance of the opening, typically 5 ft horizontally and vertically for open-faced booths |
| Around other openings (doors and access openings) | Class I, Division 2 within about 3 ft of the opening |
| Open spraying outside a booth | Class I, Division 2 for a distance around the Division 1 spray area, such as 20 ft horizontally and 10 ft vertically |
Always use the exact dimensions and figures in Article 516 for the type of booth and ventilation on the job.
Wiring and equipment
- Electrical equipment and wiring inside the Division 1 spray area must be suitable for Class I, Division 1, and no electrical equipment may be installed where it would be exposed to deposits of readily ignitible residue unless specifically approved.
- Luminaires that illuminate a spray booth are generally installed outside the booth, behind sealed, heat-treated glass panels that keep the luminaire out of the classified space; luminaires inside must be identified for the location and protected against residue buildup.
- Equipment above or near open spraying or dipping that could produce sparks or hot particles must be totally enclosed or arranged so particles cannot fall into the classified area.
- All metal parts of booths, exhaust ducts, piping, and the objects being sprayed must be grounded to prevent static ignition.
Aircraft hangars (Article 513)
| Location | Classification |
|---|---|
| Pits or depressions below the hangar floor (513.3(A)) | Class I, Division 1 (or Zone 1) up to the floor level |
| Entire floor area (513.3(B)) | Class I, Division 2 up to 18 in. above the floor |
| Around aircraft (513.3(C)) | Class I, Division 2 within 5 ft horizontally of aircraft power plants, fuel tanks, or structures containing fuel, from the floor to 5 ft above the upper surface of wings and engine enclosures |
| Areas suitably cut off and ventilated, such as stockrooms and offices | Unclassified |
2026 change (513.8): underground wiring below the hangar floor is no longer classified as Class I, Division 1. The hangar rule now matches the treatment of underground wiring at motor fuel dispensing facilities in 514.8. Equipment above the classified area must still prevent sparks from falling, and aircraft energizers and stanchions must meet Article 513.
Bonding in hazardous locations (500.30 in the 2026 NEC)
The 2026 NEC moved the separate bonding rules of 501.30, 502.30, and 503.30 into one location, 500.30, and a Tentative Interim Amendment clarified that the special bonding must extend all the way back to the service or source.
- No locknut bonding: the locknut-bushing and double-locknut types of contacts may not be relied on for bonding. Use bonding jumpers with proper fittings, bonding bushings, or other approved means.
- Extent: the bonding means apply to all intervening raceways, fittings, boxes, and enclosures between the hazardous location and the point of grounding for the service equipment or for a separately derived system, even where those parts are outside the classified location.
- Flexible metal conduit and LFMC: where used as permitted, install an internal or external bonding jumper in parallel with each conduit. In Class I, Division 2, the jumper may be omitted only where the LFMC is 6 ft or less with listed fittings, the circuit is protected at 10 A or less, and the load is not a power utilization load.
- Equipment grounding conductors are still required; wire-type EGCs are sized from Table 250.122.
Intrinsically safe systems (Article 504)
An intrinsically safe circuit cannot release enough electrical or thermal energy, under normal or fault conditions, to ignite the specific hazardous atmosphere. It needs intrinsically safe apparatus in the hazardous area and associated apparatus (such as a barrier or isolator) usually in the unclassified area.
| Rule | Requirement |
|---|---|
| Installation (504.10) | Follow the control drawing, which identifies permitted apparatus and interconnections |
| Wiring methods (504.20) | Any wiring method suitable for unclassified locations may be used, including Chapter 7 wiring methods, with sealing as required |
| Separation (504.30) | Intrinsically safe conductors must be separated from nonintrinsically safe conductors by at least 2 in. (50 mm), a grounded metal partition, or an approved insulating partition, or be in separate raceways or cables |
| Sealing (504.70) | Conduits and cables must be sealed to minimize the passage of gases and vapors, but the seals need not be explosionproof |
| Identification (504.80) | Terminals, raceways, cable trays, and enclosures marked to identify intrinsically safe wiring; light blue may be used for identification where no other conductors are that color |
| Grounding (504.50) | Associated apparatus and shields grounded per the control drawing |
Worked example: an auto body shop
A body shop adds a spray booth and a mixing room.
- Booth interior and exhaust duct: Class I, Division 1. Use threaded RMC or other Division 1 methods with seals, and only equipment identified for the location.
- Booth lighting: install luminaires on the outside of the booth roof, behind sealed glass panels, so they are outside the classified space.
- Raceways serving booth equipment: bond every raceway and enclosure from the booth back to the service with bonding jumpers or bonding bushings; locknuts alone do not count.
- Flexible connection to the exhaust fan motor: an LFMC whip needs a bonding jumper, because the fan is a power utilization load.
In a Class I location, which connection may NOT be relied on for bonding a rigid conduit to an enclosure?
A bonding bushing with a bonding jumper
A double-locknut connection
A threaded hub made up wrenchtight
A listed bonding jumper with proper fittings
What is the classification of the floor area of an aircraft hangar up to 18 in. above the floor?
Unclassified
Class I, Division 1
Class II, Division 2
Class I, Division 2
What separation is required between intrinsically safe and nonintrinsically safe conductors in open wiring under 504.30?
6 in.
12 in.
2 in., or a grounded or insulating partition
No separation, if both are in the same metal raceway
Sections you finish are checked off in the contents.