NEMA OS 1-2013 Sheet-Steel Outlet Boxes Device Boxes Covers and Box Supports.pdf

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1、NEMA Standards PublicationNational Electrical Manufacturers Association$16,1(0$266KHHW6WHHO2XWOHW%RHVHYLFH%RHV cabinets or cutout boxes; pull boxes; floor boxes; flush device plates; boxes, plates and covers designed for use with surface metal raceway systems only; and boxes larger than 1650 cubic c

2、m (100 cubic in.) in volume except multiple gang device boxes. 1.2 REFERENCES The following publications are adopted in part, by reference in this publication, and are available from the organizations below. Unless otherwise noted, references are to the most recent edition. National Electrical Manuf

3、acturers Association 1300 N. 17thStreet, Suite 900 Rosslyn, VA 22209 NEMA OS 3 Selection and Installation Guidelines for Electrical Outlet Boxes National Fire Protection Association 1 Batterymarch Park Quincy, MA 02169 ANSI/NFPA 70 National Electrical CodeUnderwriters Laboratories LLC 333 Pfingsten

4、Road Northbrook, IL 60062 ANSI/UL 514A Metallic Outlet Boxes 1.3 DEFINITIONS blank cover: an outlet box cover having no knockouts or openings, other than those used to mount to a box. These covers complete the enclosure. blank/knockout cover: an outlet box cover that contains a knockout which can be

5、 removed to accommodate a fitting for a pendant cord, etc. When left in place it may serve as a blank cover. box (electrical): a part of an enclosure provided with means for mounting a cover, cover-plate, accessory, etc. OS 1-2013 Page 8 2014 National Electrical Manufacturers Association box extende

6、r: an accessory installed in or on a box that is mounted in a finished structure. The box extender rests on the edge of the existing box (fixed depth) or extends into the box (adjustable depth). It is not mechanically secured to the box. The flange of the box extender, if provided, rests on the fini

7、shed surface. box support: a means for securing an outlet or device box to the building structure (e.g. bracket) or finished surface. Supports can be an integral part of the box, attached to the box, or entirely separate. bracket: a box support for securing an outlet box or device box in place in wa

8、lls or ceilings, or to wall studs, building structures, or structural members. cable box: an outlet box provided with clamps for use with metallic or nonmetallic cables or flexible nonmetallic tubing, or any combination of said cables and tubing. (See outlet box.) clamp: a part of, or an accessory t

9、o a cable box to secure metallic or nonmetallic cables or flexible nonmetallic tubing (Loom), or any combination of said cables and tubing to the box. concrete box: an outlet box especially intended for support in concrete, typically constructed to allow end-to-end extension and the application of c

10、overs on two sides. This box is not intended for floor installation. conduit box: an outlet box designed with circular knockouts for conduits or fittings for conduit, tubing or cable. device box: a box which is designed to receive and support switches, receptacles, and similar devices. The term “dev

11、ice box” includes the following specific types: a. Single gangfixed sides, accommodates a single device b. Two gangfixed sides, accommodates up to two devices c. Three gangfixed sides, accommodates up to three devices d. Four gangfixed sides, accommodates up to four devices e. Gangablepermits the re

12、moval of one or both sides of the box to join (or gang) as many sections as required device mounting covers: a device box cover that provides a mounting platform for a wiring device. The device is mounted on top of the cover. The cover may be raised. These covers are also sometimes referred to as mu

13、d rings. A wallplate is required to complete the enclosure. exposed work cover: a device box cover that is typically raised having cutouts to accept and support wiring devices. The devices are mounted to the underside of the cover. These covers also complete the enclosure. flush-mounted box: a box t

14、hat is so designed as to have a minimal front projection from the surface surrounding the box opening. hung-ceiling box: a box that consists of a ring and a back plate with supporting bars for use with rigid metal or nonmetallic conduit, electrical metallic or nonmetallic tubing, flexible metallic c

15、onduit, armored cable, flexible nonmetallic tubing, or nonmetallic sheathed cable above suspended ceilings. junction box: a junction box with a volume up to 1650 cm3(100 cu. in.) is considered an outlet box. knockout: a portion of the wall of a box that can be removed readily in order to provide an

16、opening for the entry of tubing, conduit, or cable. OS 1-2013 Page 9 2014 National Electrical Manufacturers Association listed: equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with evaluation of p

17、roducts or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that the equipment, material, or services either meets appropriate designated standards or has been tested and found suitable for a spec

18、ified purpose. outlet box: a box used in an electrical wiring system for containing wire, taps, splices, or devices. It has provisions for the entry of conduit, tubing, or cable assemblies and for the attachment of a separate cover, which is used to close the box or provide support for the devices o

19、r fixtures. Note: The function of an outlet box, when completely closed by a cover or part of a wiring device acting as a cover, is to guard live parts against outside incidental contact, to protect the surrounding environment from faults occurring within the outlet box, to permit inspection of the

20、wiring system, and to provide a safe means for replacement of wiring devices. Normally, outlet boxes have provisions for the entrance of conductors through conduit, cable, or tubing. Outlet boxes also have a provision for fastening covers, which are separate or a part of a wiring device. The fasteni

21、ng means is not a hinge and provides for future removal. An outlet box also provides one or more of the following: a. Support for luminaire (fixture) assemblies and lampholders b. Access to the raceway system for which it is designed c. Extension of existing raceway or wiring systems d. Ground conti

22、nuity within the raceway or the wiring system e. Utilization of accessories such as fixture studs, clamps, bar hangers, extension rings, and such. outlet box cover: a cover intended to close the face of a box. surface-mounted box: a box designed and intended to be mounted on a surface and to be expo

23、sed to sight rather than recessed in a wall, ceiling, or partition. OS 1-2013 Page 10 2014 National Electrical Manufacturers Association OS 1-2013 Page 11 2014 National Electrical Manufacturers Association Section 2 SPECIFICATIONS 2.1 MATERIAL 2.1.1 The thickness of boxes and covers of flat rolled s

24、heet steel shall be not less than 1.59 mm (0.0625 inch) except that: a. The minimum thickness at or within 6.35 mm (1/4 in.) of any right-angle bend in a drawn sheet-steel box shall not be less than 1.04 mm (0.041 in.). b. The average thickness of the sides and ends (see 2.13) of a drawn box shall b

25、e permitted to be 1.47 mm (0.058 in.) based on three measurements made on the side and end of the box not less than 19.1 mm (3/4 in.) from a right-angle bend. The three measurements are to be made in a line perpendicular to the front of the box at a point 6.35 mm (1/4 in.) from the front, at a point

26、 6.35 mm (1/4 in.) from the right-angle bend at the back, and at a point equidistant between the two. c. Listed boxes and covers shown to have equivalent strength and characteristics shall be permitted to be made of thinner sheet steel. 2.1.2 A flush device box extender of flat rolled sheet steel sh

27、all be permitted to be 0.76 mm (0.030 in.) minimum thickness. See Figure 202. 2.2 CORROSION PROTECTION The surfaces of sheet-steel boxes, covers, and supports (except tapped holes, the area under the heads of screws securing the sides of a gangable device box, pieced holes and cut edges formed from

28、zinc-coated stock, and hangers made of steel bar stock) shall be protected against corrosion. 2.2.1 Outside Surfaces The average thickness of a zinc coating shall be not less than 0.013 mm (0.0005 in.), and not less than 0.0102 mm (0.0004 in.) on box supports, external clamps, and the outside surfac

29、e of boxes and covers. Alternate coatings may be approved. Note: See UL 514A for method of determining compliance. 2.2.2 Inside Surfaces The average thickness of a zinc coating shall be not less than 0.0038 mm (0.00015 in.), and not less than 0.0025 mm (0.0001 in.) on internal clamps and the inside

30、surface of boxes and covers. The coating thickness on interior surfaces not able to be contacted by a 19.1 mm (3/4 in.) diameter ball is not specified but the presence of a coating is to be determined by visual inspection. Alternate coatings may be approved. Note: See UL 514A for method of determini

31、ng compliance. 2.2.3 Screws Screws of ferrous material shall be protected against corrosion by a zinc coating. 2.2.4 Spot or Injection Welds The thickness of coating on spot or injection welds is not specified, but the presence of a coating shall be determined by visual inspection. OS 1-2013 Page 12

32、 2014 National Electrical Manufacturers Association 2.3 OPENINGS 2.3.1 Conduit Knockouts Conduit knockout openings provided in boxes or covers for the entrance of conduit shall be effectively closed to afford protection practically equivalent to that of the box walls; however, the knockouts shall be

33、 so cut that they can be removed without deforming the box or cover in which they are located. Such knockout openings shall be located in flat surfaces of the boxes to permit locknuts, bushings, or fittings to be seated fully against these surfaces when installed as intended. Note: The drawings in t

34、his publication illustrate the placement of conduit knockouts in a side, end, bottom, or cover of a box. These drawings show typical knockout locations but are not intended to be required locations. Knockouts shall effectively cover the openings in which they are located and the clearance between th

35、e knockout and the opening shall not be more than 0.25 mm (0.010 in.). 2.3.2 Cable-Size Knockouts Cable-size knockouts openings which are provided in boxes for the entrance of tubing or cable shall be effectively closed to afford protection practically equivalent to that of the box walls; however, t

36、he knockouts shall be so cut that they can be removed without deforming the box in which they are located. Clamps shall be installed in all cable boxes to firmly secure the cable or tubing. Cable-size knockouts shall have pryout openings not more than 25.8 mm (0.040 in) in area. The drawings shown i

37、n this publication illustrate the minimum number of cable-size knockouts considered adequate. Additional knockouts may be provided. 2.3.3 Diameters of Knockouts The actual diameters for five nominal sizes of knockouts shall be as shown in Table 1. Table 1 DIAMETER OF KNOCKOUTS Trade Size of Diameter

38、, mm (Inches) Knockout Nominal Minimum Maximum Cable Pryout* 16.662 (0.656) 16.535 (0.651) 16.789 (0.661) 1/2 (16) 22.225 (0.875) 21.819 (0.859) 22.606 (0.890) 3/4 (21) 28.169 (1.109) 27.788 (1.094) 28.981 (1.141) 1 (27) 34.925 (1.375) 34.519 (1.359) 35.712 (1.406) 1-1/4 (35) 44.044 (1.734) 43.663 (

39、1.719) 44.856 (1.766) *The maximum dimension of horseshoe-shaped cable-size knockout (pryout), perpendicular to a flat side, shall be considered its diameter. 2.3.4 Open Holes No dimension of an open hole in a box shall exceed 6.747 mm (17/64 in.). The total area of open holes shall not exceed the v

40、alues shown in Table 2. In computing the area of openings, the oblique portion of a bevel-cornered box shall be considered as a part of the integral end. OS 1-2013 Page 13 2014 National Electrical Manufacturers Association Table 2 OPENINGS IN A BOX Type of box, Maximum area of openings, mm (in.) num

41、ber of gangs All openings Openings in bottom Single 291 (0.45) 215 (0.33) 2 355 (0.55) 270 (0.42) 3 420 (0.65) 330 (0.51) 4 484 (0.75) 385 (0.60) 5 549 (0.85) 450 (0.70) 6 613 (0.95) 515 (0.80) 7 678 (1.05) 580 (0.90) 8 742 (1.15) 645 (1.0) a aaNote 1: A pryout slot in the area of the box where a cl

42、amp is provided shall be disregarded, except when the pryout slot extends outside the area of the knockout, in which case, one-half of the area of the pryout slot or opening not covered by the clamp shall be used in computing the total area. Note 2: An opening adjacent to an integral ear provided fo

43、r die clearance only shall be disregarded in computing the total area. aFor each additional gang over 8, add 65 mm (0.100 in.) to all openings and the openings in the bottom. 2.4 SUPPORTS Boxes shall be so designed that they can be securely fastened in place without depending on the support furnishe

44、d by any system of wiring. A box support provided as a part of a box shall be so designed and constructed as to provide ample strength and rigidity. A box support that is provided separately shall be so designed and constructed as to securely attach to the box for which it is intended and provide am

45、ple strength and rigidity. The means necessary to attach the support to the box shall be provided with the support. Provision for supporting a device within the box shall be independent of the means used to support the box. 2.4.1 Supporting Ears Supporting ears shall be of flat-rolled sheet steel no

46、t less than 0.91 mm (0.036 in.) in thickness (or equivalent in strength) and suitably attached to the box. 2.4.2 Stud Face Brackets Brackets shall be capable of supporting a mass of 23 kg (50 lbs.) for 5 minutes without breaking or pulling loose from the box. 2.4.3 Stud Side Brackets Brackets shall

47、be capable of supporting a mass of 23 kg (50 lbs.) for 5 minutes without breaking or pulling loose from the box. 2.4.4 Bar Hangers (Adjustable or Fixed) Bar hangers shall be so constructed as to be capable of supporting a mass of 91 kg (200 lbs.) for 5 minutes. OS 1-2013 Page 14 2014 National Electr

48、ical Manufacturers Association Bar hangers having only the provision for mounting from a ceiling grid (such as for a drop ceiling) shall be so constructed as to be capable of supporting a mass of 23 kg (50 lbs.) for 5 minutes without breaking or pulling loose from the box. 2.4.5 Holes Provided for M

49、ounting Holes provided in the sides of a box for through-nailing shall be so located as to permit without interference, the installation of typical wiring devices, so as not to restrict of designed wiring capacity. 2.5 COVER SCREWS Cover screws shall be long enough to engage at least two full threads in the metal of the ears or box. 2.6 BOXES FOR SUPPORTING EQUIPMENT OR ACCESSORIES A box that is intended to provide a means for support for equipment such as a luminaire (lighting fixture), c