Plug-on motor controls save space and time

Rockwell has developed a mounting system which allows motor control equipment such as starters, circuit-breakers and drives to be plugged onto busbars without needing any holes to be drilled, or screw connections to be made. Individual items can be added or removed without having to isolate the incoming supply to the motor control panel.

Rockwell says that the Allen-Bradley 141A mounting system will save time and space, will be easier to install and maintain, and will provide greater flexibility.

The system, which forms part of the company`s MCS series of components, is expected to make type-testing much easier than in traditional installations where the busbar and control components come from different suppliers.

The modules are plugged onto 60mm-centre spaced busbars, either vertically or horizontally. Because the starters can be packed together tightly, dramatic reductions in panel space are possible, especially compared to systems in which the starters are mounted in individual cubicles.

The busbars remain covered and safe-to-touch, even if the load feeders are removed. When a module is removed, a microswitch in its baseplate interrupts the supply to the control circuit, ensuring that there is no load while it is being removed.

The system can accommodate direct-on-line, reversing and star-delta starters, as well as soft-starters and AC drives from Rockwell`s PowerFlex family. Distribution and sub-distribution are provided using MCCBs and/or MCBs. When used with Allen-Bradley`s 140M and 140-CMN current-limiting circuit-breakers, no verification of short-circuit withstand is needed.

All of the starter components are type-tested by BS EN 60 947, providing a partially type-tested switchgear and controlgear assembly complying with BS EN 60 439. The modules also allow devices to be lifted into a "test" position, allowing full functional checks to be carried out with the main circuits open.

The modules can be linked to control circuits using quick-disconnect connectors, normally top-mounted to separate the control circuitry from the motor output cabling.

The system is suitable for either conventional or "intelligent" motor control panels. Diagnostics information can be obtained via a DeviceNet network. For OEMs, the system is said to have the attraction of allowing several wiremen to work simultaneously on a project, prewiring the modules on a bench before clipping them into place.

According to Jeff Stewart, Rockwell`s commercial marketing manger, the new system will allow users to achieve a packing density similar to that of a "wardrobe" enclosure, but with the integrity of a full-blown motor control centre. "It provides MCC functions at a fraction of the cost," he says.