- 1900 Electrical Box Definition: A 1900 Electrical Box is defined as a standard 4-inch square electrical switch box, used when a simple switch box is insufficient.
- Types and Capacity: There are regular and deep versions; the regular holds twelve 10 AWG wires, while the deep version offers more space.
- Design and Dimensions: These boxes have a patented design for easy cable removal and reuse. The regular box is 4×4 inches and 1.5 inches deep, while the deep box is 4×4 inches and 2.125 inches deep.
- Historical Background: The name “1900 Box” comes from a part number assigned by the Bossert Company nearly a century ago, not from its cubic inches.
- Applications: The 1900 Electrical Box is used for installations requiring higher volume boxes, flexible armored cables, and for mounting lighting fixtures, switches, or receptacles.
What is a 1900 Electrical Box?
A 1900 box is a 4-inch (4’’) square metal outlet box, also called a 4-square. The old catalogue name was a combination gas-and-electric fixture box, and that number stayed as trade slang. Today the box is electrical only and gives more room than a single-gang switch box.
Makers sell more than one depth. Two common 4-square depths are:
- 1900 Electrical Box
- 1900 Deep Electrical Box
NEC Table 314.16(A) gives a 4-inch square × 
inch box 30.3 in³. At 2.5 in³ per 10 AWG conductor that is 12 of 10 AWG, before device and clamp deductions. A 1½-inch-deep 4-square is 21.0 in³, so only eight 10 AWG conductors on that same table. Always deduct for devices, fittings and clamps.
Easy cable removal and a reusable connector appear on some listed clamps or boxes. Treat that as a maker claim, not a feature of every 1900 box.
1900 Electrical Box Dimensions
Typical 4-square sizes (nominal trade dimensions):
- Standard 4-square: 4 × 4 inches (4’’ × 4’’) and
inches deep. - Deep 4-square: 4 × 4 inches (4’’ × 4’’) and inches deep.
Many 4-square boxes are welded steel with slotted cover screws. Side and back knockouts are usually ½ inch and ¾ inch, not 1½-inch conduit. Whether you may omit a bonding jumper at concentric knockouts depends on the listing and the circuit voltage. Do not treat “no jumper” as a blanket rule above or below 250 V.
Where Did the Name 1900 Box Come From?
The name is not “19 cubic inches.” A 4 × 4 × 1½ box is listed at 21.0 in³, not 19.
A 1917 central-electric-supply catalogue lists a 1900 combination gas and electric box (see the stored label figure). That part number is the usual origin of the slang.
Trade histories credit a Bossert Company part number from about a century ago. The stored figure is the evidence this page keeps for that story.
Applications of 1900 Electrical Box
Typical uses, with the usual limits:
- Use a 4-square when a single-gang box does not have enough volume for the device and conductors.
- Some deep 4-squares include clamps listed for FMC, MC, MCI, AC or HCF. Others are knockout-only for conduit. Match the listing to the cable.
- Armored cable needs a box or connector listed for that cable. A bare 4-square KO is not, by itself, an AC/MC clamp.
- With the right plaster ring or cover they hold switches, receptacles or a fixture canopy in walls and ceilings. Support the box as the code requires for the fixture weight.
- Skip a bonding jumper only when the box and fittings are listed for that use, often up to 600 V. Concentric or eccentric knockouts can still need a jumper. Follow the listing, not this list.
