By Bert Newman
A UL-508-listed power distribution device aids wire management in panels and enclosures.
 Figure 1. Three-phase miniature motor controllers wired before (top) and after with the busbar (bottom). |
An array of miniature circuit breakers, motor controllers, disconnect switches and other protection devices lined up on a DIN rail on a panel can often stretch out to a meter in length. Commonly powered (line power brought simultaneously to all devices in the row or array), the wiring to this array is usually a set of jumpers cut to length, stripped, bent, individually inserted into each device along the row and then tightened down. Should there be an additional row of devices beneath the first one, the conductors for the second group must be jammed in between the rows after being similarly prepared. This is a labor-intensive process and uses a good deal more panel real estate than is optimal.
What if the power leads could be brought down just once to the end of each row and the connection could be made simultaneously to all the devices in that row without measuring, cutting, stripping and bending all of those conductors? A busbar, or multiple power jumper, that has received a UL-508 listing after nearly a year of testing accomplishes this.
 Figure 2. A power feed block module brings power to the center and doubles load capacity. |
Figure 1 shows a before-and-after view of the same array of rail-mounted devices. The top shows conventional jumper wiring to daisy chain power leads to each successive device. The bottom shows the effect of the busbar in eliminating all wire jumpers between devices. The figure illustrates a three-phase array of six miniature motor controllers tying 18 poles to their respective phase power. For these units, up to 57 poles could be connected in a single row. As noted, power is brought once to the set of power feed lugs mounted at one end of the busbar. These power feed connectors mount atop the busbar and feed into the same device terminal that admits the first three pins of the busbar copper itself.
In another configuration of power feed, the load characteristics can be doubled. By moving the power feed to the middle of the busbar, the current flow divides between the left and right halves of the busbar and rated load maximum is obtained by feeding up to 160 A to 18 mm2 lugs and 200 A to 25 mm2 lugs. To facilitate this second method of power feed, a power feed block module with a three-phase feed is available (see Figure 2).
UL-508 Listing
 Figure 3. Assembly method of powering power feed lugs to the busbar to an array of devices. |
The UL-508 listing means the busbar can be used in the field and does not need to be submitted for inspection as part of other equipment. It also means that the application of the busbar is pre-approved for loads varying up to 100 A in a single array (or 200 A if choosing to power the array from terminals in the middle of the row rather than at one end).
The busbars were submitted for Underwriters Laboratories (UL) testing at the same time as a line of dual-function miniature motor controllers/disconnect switches. As accessories to the controllers, the busbars were tested simultaneously and endured the same temperature rise, voltage withstand, dielectric testing, creepage and clearance measurements as the switching devices. All of the components passed and are listed by the UL in its "green book." Table 1 lists the sequence of individual tests performed on the busbars and provides a description of what each test entailed.
Manufacturing and Installation
The busbars are configured in an extruded plastic channel to power single-, dual- or three-phase devices with copper blades that fit the power terminal on the circuit breaker or motor controller body. The blades are spaced according to the specific array the panel maker has mapped out. The copper bars are prepared accordingly, cut to length and mounted in the appropriate width extrusion. Single, dual or triple input lugs are added and the busbars can be installed.
An alternative is for the user to procure long lengths of copper bars with formed blades of the appropriate spacings and extrusions of the right width. He then cuts them to length and assembles the array into the panel. This second method does not affect the UL approval and allows the user to adapt to changes in the number of devices on the rail or how they are positioned together.
To install the busbar, the user lines up the blades or pins with the array of devices he is powering, pushes them into the contact receptacles and tightens down the screws. Bringing a single set of power conductors to the input lugs completes the installation.
The method for assembling the busbar with its lugs and then inserting the unit into the terminals of the first (in line) three-phase circuit breaker or motor controller is shown in Figure 3. The figure implies two more units will appear to the left of the one shown and the six remaining pins will be seated similarly.
These busbars improve the appearance of a panel or enclosure, while making a contribution to reducing the cost and the time spent in assembling it. Nothing here is complex — just a good engineering approach that improves the job.
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BERT NEWMAN is Technical Consultant, Altech Corp., 35 Royal Rd., Flemington, NJ 08822-6000; (908) 806-9400; Fax: (908) 806-9406.
SPEC SHEET
End Applications:
Miniature circuit breakers, motor controllers, disconnect switches, other protection devices
Related Products:
Busbars, wire jumpers
Main Point:
What if the power leads on an array of protection devices could be brought down just once to the end of each row and the connection could be made simultaneously to all the devices in that row without measuring, cutting, stripping and bending all of those conductors? Busbars that improve the appearance of a panel or enclosure accomplish this. Nothing too complex — just a good engineering approach that improves the job.
