Bus Plugs & Busway: A Buyer’s Guide to Power Distribution
Busway (also called bus duct) is a prefabricated electrical distribution system that uses enclosed copper or aluminum bus bars instead of individual cables and conduit to distribute power throughout a building. Bus plugs tap into the busway run to feed individual loads — panelboards, transformers, motor starters and other equipment.
Feeder Busway vs. Plug-In Busway
Feeder busway carries power from the main switchboard to a distribution point without tap-off openings. It is essentially a high-capacity power highway — straight sections bolted together, with elbows, tees and offsets for routing.
Plug-in busway has openings (plug-in ports) at regular intervals where bus plugs can be inserted. This makes it easy to add, move or remove loads without rewiring — particularly valuable in factories and data centers where load configurations change frequently.
What Is a Bus Plug?
A bus plug is a self-contained unit that clamps onto the busway and provides a circuit breaker or fusible disconnect for a single branch circuit. It typically contains:
- A molded-case circuit breaker (MCCB) or fused switch
- Bus stabs that mate with the busway bus bars
- A handle or lever for insertion/withdrawal
- An enclosure (NEMA 1 or NEMA 12)
Major Busway Systems
Busway systems are not interchangeable between manufacturers — each has a proprietary bus bar configuration. The major platforms:
- Square D I-Line — the most widely installed plug-in busway in North America. Bus plugs use the "PQ" designation (e.g. PQ3606G, PQ4620G). I-Line plugs have a distinctive "flag"-style stab pattern.
- GE Spectra — uses "Spectra" series bus plugs (DERA, DEKA). GE Armor-Clad is the older legacy system.
- Siemens / ITE — BD, XJ-L and other series. ITE busway is still common in older plants.
- Eaton / Cutler-Hammer — Pow-R-Way III and IV systems.
- Square D Speed-D — an older Square D system predating I-Line, still in service in some facilities.
Matching a Replacement Bus Plug
To find the right replacement, you need:
- Busway system — the stabs must match your specific busway run. An I-Line plug does not fit a Spectra run.
- Amperage — the plug's breaker must be sized for the branch circuit (30 A to 1,200 A+).
- Voltage — 240 V, 480 V or 600 V.
- Number of poles — 3-pole (three-phase) or 3-pole with ground/neutral.
- Breaker type — thermal-magnetic or electronic trip.
Because busway systems last for decades, many bus plugs are available only on the surplus market. We stock a deep inventory across all major platforms.