1. PURPOSE
1.1 This engineering standard describes methods of selecting, sizing, installing, and supporting junction and pull boxes. In this standard a junction or pull box is identified as an electrical enclosure used to connect raceway junction points and facilitate the installation of wiring, generally without wiring splices or terminations within the enclosure.
2. SCOPE
2.1 This standard applies to all junction and pull-box applications unless otherwise required by the National Electrical Code or project-specific requirements. While directed towards Air Products‑owned and -operated facilities, it shall be considered the minimum requirements for any facility design. For sale of equipment the electrical designer shall verify these requirements with the customer representatives before proceeding with facility design.
3. RELATED DOCUMENTS
3.1 Air Products Engineering Documents
STD-P338A Low Point Drain Installation Details (2 sheets)
4AEL-620300 Electrical Work
3.2 National Fire Protection Association (NFPA)
70 National Electrical Code (NEC)
- National Electrical Manufacturers Association (NEMA)
250 Enclosures for Electrical Equipment (1000 Volts Maximum)
4. BOX SIZING
4.1 All boxes with conductors rated 600V or less shall be sized according to NEC Article 314-16.
4.2 All boxes with conductors rated above 600V shall be sized according to NEC Article 314-71.
- BOX TYPE
5.1 All boxes located outdoors shall be NEMA 4X. Aluminum is preferred because of mechanical strength, resistance to most adverse environments, and moderate cost.
5.1.1 The use of nonmetallic boxes shall be considered only when low initial cost is requested and long‑term reliability is not an issue. Air Products’ operating experience has been that, while most nonmetallic boxes are made of material that is resistant to continued exposure to sunlight and other outdoor elements, the material becomes brittle and more easily susceptible to damage after years of exposure to these elements.
5.1.2 The use of stainless steel boxes shall be considered only when required to withstand specific environmental conditions that other materials cannot withstand or by project-specific requirements.
5.2 All boxes located indoors in process areas (for example, compressor buildings, storage buildings) shall be NEMA 12, except if the area is subject to occasional hose-down for cleaning purposes. In those installations, NEMA 4 boxes shall be used.
5.3 All boxes located indoors in clean, dry, nonprocess areas (for example, control rooms, electrical rooms, office areas), where the presence of dust, dirt, or dripping noncorrosive liquid is mostly nonexistent, may be NEMA 1.
5.4 Boxes with screw or clamp covers are preferred.
6. BOX INSTALLATIONS
6.1 All boxes shall be supported securely and independent from the conduit system.
6.2 Small outlet-type boxes [less than 1640 cm3 (100 in3)] that have threaded hubs identified for the purpose and have two or more conduits threaded into the box may be supported by the conduit [refer to NEC Article 314-23(F)].
7. APPROVED MANUFACTURERs
7.1 Hoffman Engineering Company or equal.
- AIR PRODUCTS COMMONLY USED NEMA CLASSIFICATIONS
Standard (NEMA) Enclosure Types
Enclosures for Non-hazardous Locations
| Type | Description | Application |
| NEMA-1 | General Purpose | Enclosures constructed for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment and to provide a degree of protection against falling dirt. |
| NEMA-3R | Rainproof and sleet-resistant | Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow; and that will be undamaged by the external formation of ice on the enclosure. |
| NEMA-4 | Watertight and dust-tight | Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow, windblown dust, splashing water and hose-directed water, and that will be undamaged by the external formation of ice on the enclosure. |
| NEMA-4X | Watertight, dust-tight, and corrosion-resistant | Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow, windblown dust, splashing water, hose-directed water, and corrosion, and that will be undamaged by the external formation of ice on the enclosure. |
| NEMA-12 | Industrial use, dust-tight, and drip-tight | Enclosures constructed (without knockouts) for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt; against circulating dust, lint, fibers and flyings; and against light splashing of liquids. |
| NEMA-13 | Oil-tight and dust-tight | Enclosures constructed for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt; against circulating dust, lint, fibers, and flyings; and against the spraying, splashing, and seepage of water, oil, and noncorrosive coolants. |
Enclosures for Hazardous Locations
| Type | Description | Application |
| NEMA-7 | Class I, Groups A, B, C, or D
(indoor only) |
Enclosures constructed for indoor use in hazardous locations classified as Class I, Division 1, Groups A, B, C, or D, as defined in NFPA 70 (NEC). |
| NEMA-8 | Class 1, Groups A, B, C, or D
(indoor or outdoor use) |
Enclosures constructed for either indoor or outdoor use in hazardous locations classified as Class I, Groups A, B, C, or D, as defined in NFPA 70 (NEC). |
| NEMA-9 | Class II, Groups E, F, or G | Enclosures constructed for indoor use in hazardous locations classified as Class II, Division 1, Groups E, F, or G as defined in NFPA 70 (NEC). |