What is the FD in a distribution box

FD in a distribution box stands for "Ferrous Deep," indicating a deep electrical device or junction box designed for conduit connections and branch circuits.

Meaning and Purpose

An FD box is a type of cast or metal device box used in electrical installations to connect and change the direction of conduit runs, as well as to provide space for branch circuit connections . The "FD" abbreviation typically stands for Ferrous Deep, where "Ferrous" refers to the original metal construction and "Deep" indicates the box's greater depth compared to standard or shallow boxes . This extra depth allows for more wiring space, making it suitable for installations with multiple conductors or devices.

Applications

FD boxes are commonly used for:

• Indoor and outdoor installations, as they are corrosion-resistant and can be weatherproof, raintight, and dust-tight when fitted with proper covers .
• Accommodating standard flush devices such as switches and receptacles.
• Serving as pulling fittings for threaded rigid metal conduit (RMC) and intermediate metal conduit (IMC), allowing easier wire installation and maintenance .
• Branch circuit connections, where multiple circuits converge or change direction.

Comparison with FS Boxes

FD boxes are often paired with FS boxes, where FS stands for Ferrous Shallow. The main difference is depth: FS boxes are shallower (typically around 2 inches), while FD boxes are deeper (around 2.69 inches), providing more internal space for wiring . Both types may include internal grounding screws and come in single, two, or three-gang configurations.

Key Features

• Threaded hubs for secure conduit connections
• Smooth integral bushings to protect conductor insulation
• Weatherproof and corrosion-resistant construction
• Available in various gang sizes and configurations
• Compatible with standard covers, plugs, and accessories In summary, an FD box is a deep, durable junction or device box designed to facilitate safe and organized electrical connections, particularly where more wiring space is required or multiple conduits converge.