Dear Colleagues,

As an engineering professional, you have no doubt come across MCCs (or motor control centres) at some time in your life. This is an assembly of one or more enclosed sections having a common power bus, mainly containing motor control units. This can include variable frequency/speed drives, PLCs and metering. Typically, but not exclusively, used for low voltage 230 Vac to 600Vac motors. Each motor controller contains a contactor, overload relays, fuses or circuit breaker to provide short-circuit protection and an isolator. Traditionally, everything is hardwired and electromechanical components are still common practice.

Over the past few years, there has been rapid growth in the new intelligent MCC which provides far more now, with three main components – a communications network, hardware and software. Intelligent MCCs provide real-time monitoring and detailed diagnostics – monitoring motor current and thermal capacity, providing protective troubleshooting functions and detailed diagnostics to identify and correct problems. All in one seamless integrated package.

Intelligent MCCs can thus provide great cost savings in terms of quicker and easier design, installation and documentation and often arrive on-site pre-configured and almost ready to operate. There is also a significant reduction in cabling requirements, the plethora of terminal boxes and control system I/O.

A few pointers below in your next MCC design…. if you don’t know them already:

Over the past few years, there has been rapid growth in the new intelligent MCC which provides far more now, with three main components – a communications network, hardware and software. Intelligent MCCs provide real-time monitoring and detailed diagnostics – monitoring motor current and thermal capacity, providing protective troubleshooting functions and detailed diagnostics to identify and correct problems. All in one seamless integrated package.

Communications networks – a great array of new protocols here. Go for the one which is supported by a trusted vendor; but ensure it is one of the more common ones based around Profibus-DP/ProfiNet/Modbus/DeviceNet/Ethernet TCP/IP. Don’t let anyone bully you into a particular protocol unless there are very good reasons for it. And ensure it is open and widely supported. Take especial care with earthing/grounding and isolation with fiber preferable to avoid those intermittent communication drop outs due to electrical spikes/surges.

Maximum Network efficiency. You can now configure devices to report data as often as you want. Obviously don’t report data unnecessarily – a rapidly changing process could require an update every 50 milliseconds and a slow moving process could mean every 60 seconds. Or communicate only on a change of state. Diagnostics information can be accessed whenever convenient.

Online changes when the system is running. Many network configurations don’t allow real device changes (and we make them all the time especially when commissioning the system); so ensure you can reconfigure/ add in new devices or modify existing parameters without having to shut down the whole intelligent MCC system. So the traditional daisy-chain topology may not be ideal for a robust reconfiguration of one or two devices while the system is running.

Documentation. Nothing is more tedious than tracking down documentation relating to a part. Ensure that the electronic documentation is stored on the intelligent MCC system and accessible from your PC where you can not only view real time status of the system, but CAD drawings (as built – not three versions out of date), manuals and spare parts information.

These new intelligent MCCs are hopefully not so advanced as to fall into Arthur C. Clarke’s suggestion:
Any sufficiently advanced technology is indistinguishable from wizardry.

Thanks to Wikipedia for great references.

Yours in engineering learning

Steve