How ABB NDBU Series Supports Stable DDCS Fiber-Optic Communication in Multi-Drive Production Lines

INDUSTRIAL AUTOMATION  |  DRIVE COMMUNICATION

01Why Communication Matters Across Multiple Drives

In a multi-drive line, each motor has its own task, but none works in isolation. On a paper machine, drives across different sections must follow the production sequence without creating excessive web tension. In a rolling mill, a disturbance in one stand can affect material movement through the next. Conveyors present a similar challenge: upstream and downstream equipment must respond consistently when the line starts, slows or stops.

Drive controllers handle the motor control. The communication network carries the commands, status information and diagnostic messages they need to exchange. An NDBU branching unit does not calculate torque or regulate motor speed; its role is to distribute DDCS messages through the optical network. That distinction matters when a fault occurs. Replacing a drive will not repair a damaged fiber link, while replacing a branching unit will not correct a control parameter error.

Fiber-optic communication is useful around large drives because the link is electrically isolated and less susceptible to the electromagnetic interference commonly associated with power equipment. It also allows engineers to organize connections across a line instead of relying on a single chain of devices. ABB describes the NDBU-95 as a way to implement a star topology: in the documented configuration, one connected drive can lose power without disabling communication to all the others. That is a valuable network property, although the overall line may still need to stop for process or safety reasons.

The practical issue for a plant is visibility. If a drive reports intermittent communication faults, maintenance staff need to determine whether the cause is the drive, its optical connection, the branching unit, its power supply or a network setting. A documented DDCS topology makes that investigation much faster.

02Where NDBU-85C and NDBU-95C Fit in the Network

The NDBU-85C and NDBU-95C listed by Evolo Automation belong to ABB's family of DDCS branching units. In a typical arrangement, messages travel from a master device to the branching unit and then along individual optical links to connected drives. Replies return through the network to the master. More than one branching unit may be used where the installation requires a larger or differently arranged network.

The two units should not be selected by appearance alone. ABB's configuration instructions distinguish optical components used in NDBU-85 and NDBU-95 arrangements and show tree, parallel and mixed network examples. The instructions also warn that 5 MBd and 10 MBd optical components cannot simply be mixed, even though their cable connectors may look alike. Cable material, link length, channel settings and device addresses must therefore be checked against the installed configuration.

That is especially relevant to plants with equipment from different drive generations. ACS600, ACS800, DCS600 and DCS800 are drive platforms that may appear in discussions of DDCS networking; they are not NDBU models. A plant should confirm its specific controller, drive interface and optical hardware before ordering a replacement branching unit. A matching connector is only one part of compatibility.

For an engineer planning a line extension, the same checks apply before commissioning. The number of drives, desired topology, optical component type and cable route should be established first. The branching unit can then be specified as part of the complete communication path, rather than treated as an isolated spare part.

03Turning Network Design into Easier Maintenance

Communication reliability depends as much on installation and records as it does on the branching unit. Optical cables should be routed and protected according to the applicable ABB instructions. Connectors need to be kept clean, and technicians should avoid sharp bends or unnecessary strain when working inside a drive cabinet. The unit's supply and channel indicators provide useful first checks, but an indicator alone does not identify every possible fault.

Consider an intermittent alarm on one drive in a paper line. The first step is to identify the affected channel and review the event history. The team can then check the drive's power and interface, inspect both ends of its fiber link, and compare the branching unit's settings with the approved network drawing. If several drives lose communication together, the investigation may shift toward a shared unit, power supply or upstream link. This sequence helps avoid changing serviceable hardware on suspicion alone.

Spare-parts planning should be equally precise. A useful record includes the full ABB part number, the installed optical component types, channel assignments, addresses, cable specifications and configuration settings. These details reduce uncertainty during a short shutdown window and help prevent a physically similar but unsuitable unit from being installed.

For plants modernizing in stages, keeping that network record current has another benefit: engineers can see which parts of the DDCS installation can be retained and which require redesign as drives are replaced. This supports a measured upgrade without assuming that every older and newer component will communicate in the same way.

Related Catalog Models

Selected models listed on Evolo Automation. The three columns are catalog references, not interchangeable parts or compatibility recommendations.