OB/SB-1File #E2527

"4" Square Boxes

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4SP Plenum Box1'/2" Deep

Without any holesand with reset KO's

With Conduit KO's

Catalog No.Universal No.

4SU/2

WiringCu. In.

Depth Cap.

11/4" 18.0

Knockout DescriptionSides Ends Bottom

(10)V2" (5)V2»

Wt. Lbs.Per 100

61.0

Std.Pkg.

5052141Vz

4S1/2 11/2" 21.0 (12)V2" (5)1/2- 73.0 5052151V2

4SV2-DR •P/211 21.0 (12)1/2" (5V/2" 73.0 5052151V2

4S3/4 11/2" 21.0 (8)3/4"521513/4

4S3A-DR 11/2" 21.0 (8)3/4"521513/4

4SEK

4S-SPL

11/2" 21.0

11/2" 21.052151-SPL

4S-SPL-DR 11/2" 21.052151-SPL

4SP

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11/2" 21.0

(8)1/2-4 eccentric KO

(8)V2-(4)3/4"

(8)i/2-(4)3/4"

(8)1/2"(4)3/4''

(3)V2"(2)3/4"

(3)1/2"

(2)3/4"

(3)1/2"

67.0

67.0

72.0

50

50

502 eccentric KO

(3)1/2"

(2)3/4"

(3)i/2-(2)3/4"

(3V/2"

(2)3/4"

73.0

73.0

70.0

50

50

50

Copyright 1995 Printed in U.S.A.

1701 West Wellington AvenueChicago, Illinois 60657

Effective August, 1995 Page 13

OB/SB

Capacity of Steel Boxes & CoversThe number of conductors and devices allowed in a box is limited by the cubic-inch capacity of the box. Unlesssuperseded by local codes, Section 370-16 of the 1993 National Electrical Code governs the number of wires permitted.Section 370-16 is reproduced below:

370-16. Number of Conductors in Outlet, Device, andJunction Boxes, and Conduit Bodies. Boxes shall be ofsufficient size to provide free space for all conductors enclosedin the box.

The provisions of this section shall not apply to terminalhousings supplied with motors. See Section 430-12.

Boxes and conduit bodies containing conductors, size No. 4or larger, shall also comply with the provisions of Section 370-28.

(a) Standard Boxes. The maximum number of conductorspermitted in standard boxes shall be as is listed in Table370-16(a). See Section 370-28 where boxes or conduit bodiesare used as junction or pull boxes.

(1) Table 370-16(a) shall apply where no fittings or devices,such as fixture studs, cable clamps, hickeys, switches, orreceptacles, are contained in the box and where no groundingconductors are part of the wiring within the box. Where oneor more of these types of fittings, such as fixture studs, cableclamps, or hickeys are contained in the box, the number ofconductors shown in the table shall be reduced by one for eachtype of fitting; an additional deduction of two conductors shallbe made for each mounting yoke strap containing one or moredevices or equipment; and a further deduction of one conductorshall be made for one or more equipment grounding conductorsentering the box. Where a second set of equipment groundingconductors, as permitted by Section 250-74, Exception No.4, is present in the box, then an additional deduction of oneconductor shall be made. A conductor running through thebox shall be counted as one conductor, and each conductororiginating outside of the box and terminating inside the boxis counted as one conductor. Conductors, no part of whichleaves the box, shall not be counted. The volume of a wiringenclosure (box) shall be the total volume of the assembledsections, and, where used, the space provided by plasterrings, domed covers, extension rings, etc., that are markedwith their volume in cubic inches, or are made from boxes thedimensions of which are listed in Table 370-1 6(a).

(2) For combinations of conductor sizes shown in Table370-16(a), the maximum number of conductors permitted shallbe computed using the volume per conductor listed in Table370-16(b), with the deductions provided for in Section370-16(a)(1) and these volume deductions shall be based onthe largest conductor entering the box. The maximum numberand size of conductors listed in Table 370-16(a) shall notbe exceeded.

(b) Other Boxes. Boxes 1 00 cubic inches or less otherthan those described in Table 370-16(a), nonmetallic boxesshall be durably and legibly marked by the manufacturer withtheir cubic inch capacity. The maximum number of conductorspermitted shall be computed using the volume per conductorlisted in Table 370-16(b), with the deductions provided forin Section 370-16(a)(1), and these volume deductions shallbe based on the largest conductor entering the box. Boxesdescribed in Table 370-16(a) that have a larger cubic inchcapacity than is designated in the table shall be permitted tohave their cubic inch capacity marked as required by thissection and the maximum number of conductors permittedshall be computed using the volume per conductor listed inTable 370-1 6(b).

Table 370-16(a). Metal Boxes

Mjn Maximum Number of ConductorsBox Dimension, Inches Cu.ln. No. No. No. No. No. No. No.Trade Size or Type Cap. 18 16 14 12 10 8 64 x1V4 Round o r Octagonal 12.5 8 7 6 5 5 4 04x1% Round or Octagonal 15.5 10 8 7 6 6 5 04x2% Round or Octagonal 21.5 14 12 10 9 8 7 04x1% Square 18.0 1 2 1 0 9 8 7 6 04x1% Square 21.0 14 12 10 9 8 7 04x2%Square 30.3 20 17 15 13 12 10 6*41V,6x1'/4 Square 25.5 17 14 12 11 10 8 04"/,6x1% Square 29.5 19 16 14 13 11 9 04"/,6x21A Square 42.0 28 24 21 18 16 14 63x2x1%Device 7 . 5 5 4 3 3 3 2 03x2x2Device 10.0 6 5 5 4 4 3 03x2x2 ' /4 Device 10.5 7 6 5 4 4 3 03 x 2 x 2 % Device 12.5 8 7 6 5 5 4 03 x 2 x 2 % Device 14.0 9 8 7 6 5 4 03x2x3%Device 18.0 1 2 1 0 9 8 7 6 04x2%x1%Device 10.3 6 5 5 4 4 3 04 x21Ax1% Device 13.0 8 7 6 5 5 4 04x2%x21/8Device 14.5 9 8 7 6 5 4 03%x 2x2% Masonry

Box/Gang 14.0 9 8 7 6 5 4 03% x 2x3% Masonry

Box/Gang 21.0 14 12 10 9 8 7 0FS— Minimum Internal Depth

1 % Single Cover/Gang 13.5 9 7 6 6 5 4 0FD— Minimum Internal Depth

2% Single Cover/Gang 18.0 12 10 9 8 7 6 3FS— Minimum Internal Depth

1% Multiple Cover/Gang 18.0 12 10 9 8 7 6 0FD— Minimum Internal Depth

2% Multiple Cover/Gang 24.0 16 13 12 10 9 8 4

*Not to be used as a pull box. For termination only.

Table 370-16(b). Volume Required per Conductor

Size of Free Space Within BoxConductor for Each Conductor

No. 18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .5 cubic inchesNo. 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .75 cubic inchesNo. 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. cubic inchesNo. 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.25 cubic inchesNo. 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 cubic inchesNo. 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. cubic inchesNo. 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. cubic inches

Reproduced with permission NFPA.

Copyright 1989 Printed in U.S.A.

1701 W. Wellington Ave.Chicago, Illinois 60657

Effective November, 1993 Page 3