The two types of low voltage (LV) busway are feeder and plug-in. They are commonly intermixed on runs of busway and plug into each other.
Feeder Busway
- Sometimes called low impedance busway
- Used to feed power to a distant point
- Beneficial because the voltage drop over the run is generally low (somewhat lower than plug-in and certainly lower than cable in conduit)
- Similar to an extension cord
- Indoor – connected to the facility distribution equipment and distributes power throughout the building
- Outdoor – connects from the transformer located outside the facility to the wall flange and must extend 1-foot inside the facility, then it can be connected via indoor feeder to the distribution equipment
Plug-In Busway
- Tap off of plug-in busway to feed devices
- Has plug in opening to plug in a bus plug
- More costly than feeder busway
- Similar to a power strip plugged into an extension cord
- Provides outlets every two feet for plug-in devices
- Indoor plug-in – connects to indoor feeder busway in order to “tap-off” electricity
- Sprinkler-proof plug-in – same as indoor plug-in, except it is sprinkler-proof
Length of Busway
- The most common length of busway is 10 feet.
- Ten-foot sections are used whenever possible to run power to a location.
- However, smaller lengths are available to meet the customer’s specific installation requirements.
Fittings
- Just as electrical fittings are used to turn corners, make tee connections and crosses in conduit and wire installations, special Busway Fittings (elbows, tees, and crosses), are available.
- These fittings provide the flexibility to route the bus to distribute electricity to any location in a building.
- Fittings are also used to terminate the busway.
- Some examples of termination fittings are end cable tap boxes, end closers, flanges to connect to switchboards or motor control centers, and transformer connections.
- Most fittings can be used on all types of busway. This adds flexibility should the customer need to reconfigure the bus run in the future
Elbows
Elbows enable turns and height changes in the busway system. An elbow can turn the busway system right or left, up or down.Elbows are supplied with a joint stack and covers. Elbows may be ordered as stacks or sections. Elbow stacks are joint stacks that are angled “edge wise” (for up or down changes) or “flat wise” (for left or right changes).
Tees
Tees are used to start a new section of busway in a different direction. Tees can start a new section to the right, to the left, up, or down. Tees are supplied with two joint stacks.
Crosses
A cross allows a busway run to extend in four directions.
Offsets
Offsets allow the busway system to shift left, right, up, or down while continuing in the same direction. Offsets are supplied with a joint stack. When space is tight, a single offset can be used instead of two connected elbows.
Horizontal Hangers
- Included in the purchase of busway is a hanger for every ten horizontal feet of run.
- Hangers are critical to proper busway installation as they support the weight of the busway, keeping it straight.
- The National Electrical Code® requires adequate support for busway. Busway must be supported at intervals of 1.5 m (5’) or less, unless it is specifically designed for fewer supports.
Vertical Hangers
- Hangers are also required when busway is run vertically, however they need to be priced in the bill of materials.
- A special spring suspension hanger is used, equalizing the weight supported by each hanger. its recommends that a spring hanger support be used on every floor unless the distance exceeds 16 feet. In that case, more that one support is required as the maximum distance between supports is 16 feet.
Bus Plugs
The three types of bus plug devices are described below. :
- Fusible Switch
- Used to connect a load to the busway while providing overcurrent protection for the load.
- Contains a fuse
- In the event of an overload, the element in the fuse melts, removing power form the load before damage can occur
- To restore power to the load, the fuse must be replaced
- Circuit Breaker
- Used to connect a load to the busway while providing overcurrent protection for the load
- In the event of an overload, the circuit breaker trips, removing power from the load before damage can occur
- To restore power to the load, the circuit breaker must be reset
- Specialty Plug
- Includes devices such as special circuit breakers (example, earth leakage), surge protective devices (SPD), receptacle plugs, combination contactor and starters and bolt-on devices
Busway Layout Example
In this installation, there are feeder busway sections and plug-in busway sections. Elbows, tees and crosses are used to connect the busway sections.
Low Voltage Busway Applications
Low voltage busway can be used in many applications.
Commercial / High-Rise Applications
- Commercial office and high-rise apartment buildings use busway to distribute power to the various floors in a building. Feeder bus brings the electricity inside the building to the main electrical room equipment and runs from floor to floor.
- Plug-in busway is then used at each floor to install a bus plug, such as a cable tap box or circuit breaker. The plug-in device is used to “tap-off” electricity from the busway to an electrical room for the floor or for a specific tenant
Industrial Applications
- A Industrial applications use busway to distribute power throughout the building. Feeder bus brings the electricity inside to the facilities first piece of distribution equipment. From there, indoor feeder bus distributes power throughout the building and connects to plug-in bus.
- Plug-in bus is then connected to the feeder bus in order to distribute power throughout a manufacturing floor. The plug-in bus uses a bus plug, such as a circuit breaker, to “tap-off” electricity to feed manufacturing tools and equipment.
- Note that plug-in sprinkler-proof can also be used in these applications.
Low Voltage Busway Selection Criteria
When selecting low voltage busway, make sure to ask the following questions:
- Indoor, outdoor or sprinkler-proof?
- Amp rating?
- 3 wire, 4 wire or 200% neutral?
- Total length of run, including elbows and other fittings
- Number of turns (elbows, tees, etc)
- Housing, internal or isolated ground?
- Fusible or circuit breaker bus plugs?
- Are there any wall or floor penetrations?
- What are the termination points? (end cable tap box, end close, standard flange)
- What length will be run in vertical runs requiring vertical hangers?
references :
- Siemens Technical Education Program
- Eaton Busway Guide
See also