Steel City 521911234RD 4SQ-3.5DP, RED

The red finish on this 4 inch square steel box is the standard color convention for fire alarm and life safety circuits, so inspectors and other trades can tell the fire system boxes apart from general power and lighting at a glance. Electrically it is the same 4 x 4 x 3-1/2 inch steel box as a standard gray one; the color is what separates it on the job.

This box has 46 cubic inches of volume, which is the deep 3-1/2 inch version of the 4 inch square. Using the NEC box fill volumes, that supports 23 No. 14 conductors, 20 No. 12, or 18 No. 10 before any deductions. Every device yoke, clamp set, and ground group takes its own allowance off that total, so a box with a mud ring and a couple of devices will land well under those raw counts.

Eighteen knockouts total, spread across the four sides and the back, which is what lets a deep 4 square serve as a junction or pull point with multiple raceway or cable entries. The count is generous enough that you rarely need to add a second box on a crowded fire alarm or branch circuit run.

Yes. It is a standard 4 x 4 inch square steel box, so any 4 inch square flat cover, raised device ring, or plaster ring built to that footprint mounts to it. The extra depth is all behind the mounting plane and does not change the cover pattern. Covers and rings are separate items; the box is sold each.

Buy it that way. The 521911234RD comes from the factory in red, so there is no field painting step and no risk of paint fouling the grounding surfaces or the cover screw threads. Jurisdictions that require fire alarm boxes to be identified by color are satisfied by the factory finish.

Steel. That matters because a steel box bonds to metallic raceway through the knockout connections and becomes part of the equipment grounding path, which a nonmetallic box cannot do. It is also what lets it take a grounding screw in the tapped hole and hold device screws under repeated service.

Sold each, so you can order the exact count for a job rather than a full carton. On a fire alarm rough-in where only a handful of devices need a red box, that avoids carrying extra.