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Bus Plug Buying Guide
Introducing Bus Plugs
Bus plugs provide access to a busway's electrical power, and provide electrical protection for the machine the bus plug is feeding. Additionally a bus plug can be turned on or off to control the electricity flow.
What Are Bus Plugs?
Bus plugs are electrical components of a busway system which plug into the bus duct through a port to allow connection to the electrical power within the bus duct.
Designed for three-phase power, the bus plug's "stab" plugs onto each phase (A, B, C) in the electrical bus duct. A bus plug may also have a stab for a neutral bus bar.
Designed for three-phase power, the bus plug's "stab" plugs onto each phase (A, B, C) in the electrical bus duct. A bus plug may also have a stab for a neutral bus bar.
By Another Name
- Bus plugs are referred to by many different names:
- Buss plug
- Swingjack
- Disconnect Bus box
How Do Bus Plugs Work?
Bus plugs work by attaching to the busway bus bars (one for each phase) and allowing connection to the electrical power being carried by the bus duct. The bus plug allows the flow of power to be turned on and off with a handle and switching mechanism.
Bus plugs provide overcurrent protection through installed fuses or a circuit breaker with a maximum ampere limit. The fuses or circuit breaker will interrupt the flow of electricity if the amperes flowing through the bus plug exceed its maximum.
The bus plug safety mechanism locks the door when the bus plug is in the on position.
The Benefits of Bus Plugs
Flexibility
One advantage of a busway system and a bus plug is the flexibility to plug the bus plugs anywhere along the bus duct. Bus plug ports are standard every two feet on both sides of a plug-in section of busway.
If a machine is moved, a bus plug can be relocated anywhere along the duct to accommodate the machine in its new location.
A standard 10 foot section of bus duct has five plug-in ports for bus plugs on each side. A section of GE Spectra SL busway is shown.
Over Current Protection
Bus plugs provide over-current protection through one of two means, fuses or a circuit breaker to protect the machine or component from excess current. Fusible bus plugs are more common.
A Cutler Hammer fusible CP4 bus plug on the left and a GE breaker style Armor Clad bus on the right.
On-Off Handle
Modern bus plugs have a handle to turn the bus plug on and off without opening the bus plug. This style of bus plug is sometimes referred to as "floor operated" because rope or chains can be attached to the handle to actuate the bus plug from the floor.
Bus plugs contain a safety lock mechanism preventing the door from opening when the bus plug is in the "on" position.
Safety Lockout
Bus plugs provide the option to secure the bus plug with a padlock to the bus plug from being actuated. The handle and the door latch provide a hole for a standard padlock on most bus plug series. This is a common feature on floor-operated bus plugs.
The lockout on a GE Spectra SB bus plug allows for a padlock to secure the bus plug’s On-Off position.
Bus Plug Sizing?
The size of a bus plug is determined by the amperage the bus plug is designed to handle.
Bus plug size is based on the amperage and fuses or circuit breakers required to handle the electrical load. Larger amperages require larger conductors, which result in larger (and heavier) bus plugs.
Fusible Bus Plug Sizes
Fusible bus plugs run in standard sizes to match the size of the fuses providing the overcurrent protection.
- Standard sizing for fusible bus plugs:
- 30 amp maximum and below
- 25 amp to 60 amp max
- 65 amp to 100 amp max
- 110 max to 200 amp max
- 225 amp to 400 amp max
- 425 amp to 600 amp max
- 700 amp to 800 amp max.
- 1000 amp max
- 1200 amp max
- 1600 amp max
Not all manufacturer's series offer fusible bus plugs above 600 amps.
Circuit Breaker Bus Plug Sizes
Bus plugs using circuit breakers for overcurrent protection are sized based on the size of the circuit breaker frame. For many manufacturers a 30 amp to 100 amp circuit breaker bus plug will be the same size because the circuit breakers are the same size.
A Square D PFA36040G bus plug. The FA circuit breaker provides the overcurrent protection.
What About Volts?
Volts do not matter for the size of the bus plug. A 60 amp bus plug used on a 240 volt busway system will be the same size as the unit for a 480 volt system.
However, the required fuses will be different. Therefore the internal blocks will be configured differently to accommodate the different size fuses.
A 240-volt fuse will be smaller compared to a 600 volt fuse (480 volt).
Identifying Bus Plugs?
Identifying the correct bus plug saves time, money, and frustration. Part of the process at Legacy Industrial Electric LLC is to understand what bus plug is needed to eliminate wasting time and money.
- What information is needed?
- Busway Manufacturer and Series
- Voltage
- Amperage
- Wire
- Ground
Major Manufacturer's Busway Series
| Bull Dog / ITE Gould Siemens | Square D | GE ABB | Westinghouse Cutler Hammer Eaton |
| BD Busway | SD Busway | FVK | Lifeline / Standard |
| XL-X | I-Line I | DE | Pow-R Way |
| XL-U | I-Line II (800A & up) | DH | Powerbus |
| XJ-L | Armor Clad | Pow-R Way III | |
| Sentron | Spectra SL | ||
| Spectra SB |
Voltage
What voltage is being fed into the busway from the distribution? In North America there are two choices, 240 volt maximum and 480/600 volt maximum. The bus plug fuse blocks need to be set to accept the correct fuses
For circuit breaker bus plugs, the circuit breaker needs to be rated for the voltage to ensure the circuit breaker trips correctly, providing the required protection.
Amperage
The amperage determines the size of the bus plug. Higher amperage require larger bus plugs.
Amperage ranges from 5 amps to 1600 amps for most bus plug series. Bus Plugs are offered in standard sizes with the fuses or circuit breaker providing the maximum amperage the bus plug will tolerate before causing the overcurrent protection to trip.
Wire
How many connections are needed. Bus plugs have a connection for each phase in the bus duct (A, B, C). Some busway has a neutral, requiring a fourth connection.
- A bus plug requiring connection to the A, B, C phase is referred to as 3 wire.
- A bus plug requiring connection to the A, B, C phase, and a neutral is referred to as 4 wire.
Ground
Some busway systems have a mechanical connection to ground. The busway will be mechanically connected to the grounding in the electrical distribution. Newer busway systems all facilitate a ground connection.
For busway systems with a ground, the bus plug will have a "tab" to physically connect to the busway grounding. A ground lug will be accessible inside the bus plug.
A dedicated ground is most often noted in the bus plug's catalog number by the letter "G".
Example: Square D PQ3603G
This bus plug will have a ground tab that plugs into the bus duct.
Older (vintage ?? ) busway systems may not have dedicated grounding. Siemen's BD series and Westinghouse's Lifeline/Standard bus duct systems usually do not have grounding inherent in the busway.
In these situations the system may be grounded by using the housing. For the bus plug, a ground lug may be attached to the bus plugs enclosure after scraping away the paint to create the connection to the bare metal.
We cannot vouch for this method as a suitable method of grounding a busway system, but we have seen it done in practice.
NOTE: We are not electrical contractors.
Catalog Number
Each manufacturer has a system for naming the busway system components. The systems are similar, but slightly different for each manufacturer, and for each bus duct system. The catalog number is normally on the outside label on the bus plug.
With the catalog number, a bus plug or the bus duct can normally be identified. If one bus plug catalog number is known, or the busway catalog number, the required bus plug can be identified.
Parts of a Bus Plug
Reconditioned Square D PQ3603G bus plug.
This article was written by Legacy Industrial Electric LLC for the purpose of helping visitors understand electric busway bus plugs.
If you discover issues or problems with this article, please email us at [email protected].
If you have questions about bus plugs, please contact us
