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A fusible bus plug is a switch and a set of fuse holders in one enclosure: it taps power from the busway, disconnects the load, and protects the load circuit with fuses fitted inside the plug. A non-fusible bus plug has no fuses. It is either a circuit breaker plug, where a molded case breaker does the protecting, or a plain switch or tap that depends on an overcurrent device somewhere else. BRAH Electric lists 504 fusible bus plugs as substitutes for 11 busway families from General Electric, Siemens / ITE, Square D and Cutler Hammer / Eaton / Westinghouse, shown by brand in the table further down.
Fusible vs non-fusible bus plugs side by side
The table compares the two types that carry their own protection: the fusible plug and the circuit breaker plug.
| Fusible bus plug | Circuit breaker bus plug | |
|---|---|---|
| Overcurrent protection | Fuses fitted inside the plug | A molded case circuit breaker inside the plug |
| Disconnecting the load | A switch worked by the plug handle | The breaker, worked by the plug handle |
| What sets the protection | The fuse class and ampere rating you fit, up to the amperage of the plug | The frame and trip rating of the breaker |
| After a fault | Find the cause, then replace the blown fuses with the same class and rating | Find the cause, then reset the breaker |
| Wear parts | Fuses, fuse clips, switch contacts, stabs | The breaker, operating hardware, stabs |
| What to match on a replacement | Busway family, amperage, voltage, wires, ground, fuse class | Busway family, breaker type and rating, voltage, wires, ground |
| Product standards that apply | UL 857 for the plug-in unit, UL 248 series for the fuses | UL 857 for the plug-in unit, UL 489 for the breaker |
The third kind, an unfused switch or tap box, has no overcurrent device of its own. It can only be used where the circuit it feeds is protected in a way the electrical code allows, which is a design question for an engineer and the authority having jurisdiction, not a purchasing choice.
How a fusible bus plug protects the load
Inside a fusible plug the current passes from the stabs through a switch, then through one fuse per phase, then out to the load lugs. Opening the handle opens the switch, which lets you change fuses with the load side dead. The line side of the switch and the stabs stay live for as long as the busway is energized.
The plug decides the largest fuse that will physically fit. The fuse decides the protection. Fuse class fixes the dimensions of the fuse and its interrupting rating, which is why the fuse class accepted is listed for every plug. Current-limiting classes can clear a high fault current very quickly and reduce the energy that reaches the equipment downstream. Whether your system needs that is answered by a short-circuit and coordination study, not by a rule of thumb.
For more on fuse choice, see fuse classes in bus plugs and how to choose bus plug fuses.
What non-fusible means: breaker plugs and unfused switches
A circuit breaker plug uses a molded case breaker as both the disconnect and the overcurrent device. After a trip the breaker is reset instead of fuses being replaced, and nobody has to keep the right fuses in the storeroom. The breaker has its own interrupting rating, and it has to be adequate for the fault current available at that point on the busway.
A breaker plug is identified by its busway family and by the breaker inside it, so a replacement has to match the breaker type and trip rating as well as the plug. A fusible plug is identified by its switch rating and fuse class. The two are not interchangeable without checking the protection again, because the time-current behavior of a fuse and a breaker of the same ampere rating is not the same.
Fusible bus plugs in the BRAH catalogue by brand and family
Every part in the fusible bus plugs listing is a 3-phase fusible switch plug listed as a direct substitute for one busway family. Each family is listed in 30A, 60A and 100A, in 240V and 600V versions, as 3-wire or 4-wire, with or without a ground. The last column links three parts from each family.
| Busway brand | Busway family | OEM plug type | BRAH series | Amperages | Voltages | Fuse classes accepted | 600V, 3-wire examples (30A, 60A, 100A) |
|---|---|---|---|---|---|---|---|
| General Electric | Armor Clad | AC | BEC | 30A, 60A, 100A | 240V, 600V | H, R, J | BEC3603, BEC3606, BEC3610 |
| General Electric | Spectra | SB | BEB | 30A, 60A, 100A | 240V, 600V | H, R, J | BEB3603, BEB3606, BEB3610 |
| General Electric | Spectra Low-Amp | SL | BEL | 30A, 60A, 100A | 240V, 600V | H, R, J | BEL3603, BEL3606, BEL3610 |
| General Electric | Type FVK (Flex-A-Plug) | FVK | BEK | 30A, 60A, 100A | 240V, 600V | H, R, J | BEK3603, BEK3606, BEK3610 |
| ITE / Siemens | BD Series | BOS | BES | 30A, 60A, 100A | 240V, 600V | R, H, K | BES3603, BES3606, BES3610 |
| ITE / Siemens | XL-U Series | UV | BUV | 30A, 60A, 100A | 240V, 600V | R, H, K | BUV3603, BUV3606, BUV3610 |
| ITE / Siemens | XL-X Series | RV | BRV | 30A, 60A, 100A | 240V, 600V | R, H, K | BRV3603, BRV3606, BRV3610 |
| Siemens | Sentron Series | SXID, SLID, SLVB, SLVBH | BVB | 30A, 60A, 100A | 240V, 600V | H, R, J | BVB3603, BVB3606, BVB3610 |
| Square D / Schneider Electric | I-Line I & II | PQ | BPQ | 30A, 60A, 100A | 240V, 600V | H, R, J | BPQ3603, BPQ3606, BPQ3610 |
| Cutler Hammer / Eaton | POW-R-WAY III | P3F | B3F | 30A, 60A, 100A | 240V, 600V | H, R, J | B3F3603, B3F3606, B3F3610 |
| Westinghouse / Cutler Hammer / Eaton | POW-R-WAY I & II | ITAP | BIP | 30A, 60A, 100A | 240V, 600V | R | BIP3603, BIP3606, BIP3610 |
The fuse class column matters when you stock fuses. The Square D, General Electric, Sentron and POW-R-WAY III parts are listed as accepting Class H, R and J fuses. The ITE / Siemens BD, XL-U and XL-X parts are listed for Class R, H and K, and the POW-R-WAY I & II parts for Class R.
The records for the BEC, BEB, BEL and BES series each describe the plug as a UL Listed assembly, complete with a UL Recognized internal switch and components. Many parts also come in a version with weather stripping for drip protection, with a W at the end of the part number. For anything not in the table, call (855) 355-2724 with the part number.
Parts listed for breaker type bus plugs
Several BRAH parts are made for circuit breaker plugs or for moving a plug from one type to the other:
- GEBPBRKRCK: mounting hardware for converting a fusible General Electric Armor Clad, Spectra or Spectra Low-Amp plug in a 30A, 60A or 100A can to circuit breaker type. The breaker is sold separately.
- TED-SEBRKT: operating toggle hardware for General Electric breaker type plugs fitted with TED or THED breakers.
- N250BT: neutral kit for General Electric breaker type plugs up to 250A used with Spectra SF Series breakers.
- PFA100GK and PKAG250: ground kits for Square D I-Line breaker type plugs, types PFA, PFH and PFC up to 100A and types PKA, PKH and PKC up to 250A.
- PFA100NK and PKAN250: neutral kits for the same Square D breaker type plugs.
Replacement bus plug stabs for General Electric plugs are listed for both fusible and circuit breaker types. The GE bus plug replacement guide has the full list of GE kits.
How to choose between a fusible and a non-fusible plug
If you are replacing a failed plug, replace like with like. The protection for that load was designed around the device that was there, and the drawings, labels and arc flash study assume it. Order the same type, family and rating.
If you are adding a load or redesigning a line, the choice belongs to whoever is responsible for the protection study. The questions they will ask are practical ones:
- What fault current is available at that point on the busway, and does the fuse or breaker have the interrupting rating for it?
- Does the load need the device to coordinate with protection upstream so a fault trips only that plug?
- Is it a motor circuit, where a blown fuse on one phase has to be considered?
- How fast must the line restart after a trip, and who will be on site to do it?
- Will the right fuses be stocked and controlled, so nobody fits the wrong class?
Cost follows from those answers. Comparing purchase price alone leaves out fuses, spare breakers and the price of a line standing still.
What to check before you order a fusible bus plug
- Busway brand and family: from the busway nameplate. A plug fits one family only.
- OEM catalog number: from the plug label, complete with suffix letters.
- Amperage: 30A, 60A or 100A.
- Voltage: 240V or 600V version. Use the 600V part on a 480V system.
- Wires and ground: 3-wire or 4-wire, with or without ground.
- Fuse class: the classes the plug accepts, compared with the fuses you use now.
- Location: whether the old plug has weather stripping.
BRAH Electric is an aftermarket manufacturer, not an authorized distributor of the OEM brands named here. Its bus plugs are designed in-house, tested at its Carlsbad, California facility, and covered by a 2-year warranty from the invoice date. Orders for in-stock parts placed before 3:00 PM Pacific ship the same business day.
Safety with either type of plug
Fuses and breakers protect the load circuit. They do nothing for the person handling the plug, because the stabs sit on live bus bars whenever the busway is energized. Before a plug of either type is installed, removed or opened beyond its fuse compartment, the busway has to be de-energized, locked and tagged out, and tested for absence of voltage by a qualified person.
Fusible and non-fusible bus plug FAQs
What is the main difference between fusible and non-fusible bus plugs?
A fusible plug protects the load with fuses inside the plug. A non-fusible plug has no fuses: a circuit breaker plug protects the load with a breaker, and an unfused switch relies on protection provided elsewhere in the circuit.
Can I replace a fusible bus plug with a circuit breaker plug?
Only after the protection has been checked by a qualified engineer, because the two devices respond differently to overloads and faults. For General Electric Armor Clad, Spectra and Spectra Low-Amp plugs in 30A, 60A and 100A cans, kit GEBPBRKRCK provides the mounting hardware for the conversion.
Is a non-fusible bus plug less safe than a fusible one?
Not in itself. Either type is safe when its interrupting rating suits the available fault current and the load circuit is protected as the electrical code requires. The risk comes from an unfused switch used where nothing else protects the circuit, or from fuses or breakers of the wrong rating.
Which fuse classes do fusible bus plugs accept?
It depends on the plug. In the BRAH listing the General Electric, Square D, Sentron and POW-R-WAY III parts accept Class H, R and J. The ITE / Siemens BD, XL-U and XL-X parts accept Class R, H and K, and the POW-R-WAY I and II parts accept Class R. Check the product page for the part you order.
Do fusible bus plugs need more maintenance?
They have more parts that are handled: fuses are replaced after a fault, and fuse clips can lose tension or overheat over the years. A breaker plug has a breaker that should be exercised and inspected as its maker recommends. Both types need their stabs, handle mechanism and enclosure checked during planned outages.
References
- UL 857, Busways: the UL standard for busways and plug-in units.
- UL 248-1, Low-Voltage Fuses, General Requirements: general requirements of the standard series that defines low-voltage fuse classes.
- UL 489, Molded-Case Circuit Breakers, Molded-Case Switches and Circuit-Breaker Enclosures: the UL standard for the molded case breakers used in circuit breaker plugs.
- NFPA 70, National Electrical Code: the installation code that sets overcurrent protection requirements for busway and the circuits tapped from it.