Circuit breakers do more

Edited by the Engineeringtalk editorial team Oct 30, 2006

The primary role of MCCBs is circuit protection, but the latest products can do much more, says John Towersey, Technical Director of Moeller Electric.

Moulded-case circuit-breakers (MCCBs) work by monitoring the current in the circuit they are protecting.

Information about that current is useful as a guide to system performance and as an aid to faultfinding but, with ordinary MCCBs, providing access to this information means fitting costly monitoring equipment.

MCCBs with electronic trips are changing this situation, since they can be designed to capture and store data.

This means that engineers investigating a breaker trip can now have easy access to diagnostic information and, even better, users can be given advance warning of impending trip conditions.

What should users look for in data-equipped MCCBs?.

Products from reputable suppliers can be relied on to provide good protection performance, so we'll concentrate on additional functionality.

Facilities for extracting detailed information are invaluable, but it' s equally important to be able to assess the breaker's status at a glance.

This can be achieved, for example, with an LED which shows when the load reaches 70, 100 and 120% of the trip value.

Often, however, more detail is needed, and a convenient solution is a plug-in terminal with a display to show key parameters.

An alternative is to use a laptop PC to inspect and extract data, which are then available for export to standard office programs.

Let's look at the types of data needed.

Real-time current information is essential as is, in the event of a trip, a clear indication of the trip type.

Additionally, historical information is invaluable and should include a time-stamped log of events like trips and trip warnings.

Details of how the current has changed in the run up to a trip are an important diagnostic aid, and are usually provided by continuously recording current data in a revolving store.

In modern applications, MCCBs are now often used alongside networked automation systems, and it is highly desirable that they can communicate with these systems.

Interfaces for popular networking standards should, therefore, be available.

Network connections can do more than provide users with access to data.

They can also allow the data to be accessed by control systems which can then be configured to react appropriately to fault conditions.

Network connections can also be arranged to allow MCCBs to be accessed remotely via, for example, an Internet connection.

The options discussed in this article were all considered in the development of Moeller Electric's latest NZM range of MCCBs.

With ratings from 40 to 1600A, and breaking capacities up to 150kA, these innovative breakers provide comprehensive communication and data management options.

They support the emerging FDT (field device tool) standard for remote diagnostics, and can be accessed from PCs running Moeller's XPC-Soft software.

An easy-to-use data terminal, suitable for handheld use or panel mounting, is also available.

Effective protection will always be the key requirement for specifiers of MCCBs but, as we've seen, they should now expect a whole lot more.