Preventive maintenance the key to motor control center reliability

The low-voltage motor control center is a key element in electrical control systems because of the vital operating role they play in controlling motors and production processes. Over the years, MCCs have evolved from cabinets that housed basic electro-mechanical devices such as circuit breakers, contactors and overload relays to centers of automation that may include variable frequency drives, ...

By Bernardino R. Martinez, Rockwell Automation, Milwaukee, WI September 1, 2005

Sections: Using infrared thermography Maintaining de-energized equipment Maintenance after a fault TheBottomLine…

Sidebars: Guidelines to replace an older MCC Selecting networked MCCs Square D marks 50 years in Cedar Rapids Siemens completes Robicon acquisition Fuel Cell Summit 2005 promotes development

The low-voltage motor control center is a key element in electrical control systems because of the vital operating role they play in controlling motors and production processes. Over the years, MCCs have evolved from cabinets that housed basic electro-mechanical devices such as circuit breakers, contactors and overload relays to centers of automation that may include variable frequency drives, soft starters and programmable controllers.

Because failure or malfunction of electrical systems — specifically MCC-housed equipment — can present a serious hazard to personnel and property, it is imperative to comprehend how MCCs are maintained. By shifting from reacting when equipment fails to proactively maintaining machinery through preventive and predictive practices, manufacturers can help mitigate such risks and prevent failures from occurring (Fig. 1).

Using infrared thermography

Regular maintenance of MCCs occurs in two ways — by inspecting energized or de-energized equipment. One of the most common methods of inspecting energized equipment is infrared thermography. While infrared thermography can be part of an overall preventive or predictive maintenance program, it is not the only method of inspection.

Infrared thermography is a non-invasive inspection technology that uses an infrared camera to monitor temperatures and thermal patterns while equipment is running at full load to detect changes in temperature. This is often a telltale sign that equipment is performing out of spec. Used on a wide variety of equipment, including MCCs, this technology helps manufacturers predict equipment failure and plan corrective action before a costly shutdown, equipment damage or personal injury can occur.

Infrared also can be used to detect potential electrical fault conditions such as loose or corroded connections (hot spots), poor contacts, unbalanced loads, overloading and overheating (Fig. 2). Electrical fault conditions can lead to electrical system failures, arcing, equipment fires and high level short-circuits.

This inspection method can be difficult, and equipment relatively costly. To gain the best results from an infrared program, it’s important that inspection personnel are properly trained to perform the task.

Safety is another concern because electrical equipment must be scanned during operation with enclosure doors open. If equipment is scanned while enclosure doors are open and the equipment running, personnel may be required to wear personal protective equipment. As an added safety measure, some users install special camera ports on MCC enclosures. Infrared ports allow scanning of devices without requiring open enclosure doors. These cameras can be installed during manufacturing or by the user in the field (Fig. 3).

Maintaining de-energized equipment

The second type of MCC preventive maintenance is inspecting de-energized equipment. This requires more training than visual inspections. To begin, engineeers must follow specific guidelines on de-energizing, isolating and grounding the equipment to be inspected.

When performing maintenance on de-energized equipment, refer to the following general guidelines: (For a complete list of specific maintenance steps, always check the manufacturer’s user or installation manual, as well as NEMA and NFPA standards).

Structure — Check for moisture or any signs of dampness or drippings inside the MCC. Condensation in conduit and moisture from an outside source is a common cause of MCC failure. Eliminate any source of moisture and seal off conduit, cracks and openings that have allowed or could allow moisture to enter the MCC. Dry, replace and/or clean wet insulation material. Replace damaged or malfunctioning parts. Ensure that you’ve identified and eliminated the source or cause of wetness or contamination.

Buses and splice connections — For horizontal to vertical bus connections, some manufacturers do not require servicing for the life of the MCC. Follow your equipment manufacturer’s specific recommendations. For MCCs that permit servicing bus connections, check the integrity of the bus splice connections (Fig. 4). Bus splices are normally identified with labels on the MCC structure or referenced in the MCC elevation drawings or user manuals. You’ll usually find recommended torque values on the structure, in wiring diagrams or in the manufacturer’s user manual.

Wiring and branch circuit protection devices — Assure conductors are not damaged, worn or obstructing moving mechanical parts. Check wires and cables for signs of overheating such as discolored insulation; inspect fuses for discoloration and check for loose power and control connections (Fig. 5). If any of these conditions are present, determine the cause and reposition/replace wiring as necessary.

Disconnect handle mechanisms — Check for proper function and freedom of movement of the disconnect handle and door interlock mechanisms (Fig. 6). Lubricate as directed according to the manufacturer’s instructions. Replace broken, deformed, malfunctioning or badly worn parts.

Starters and contactors — Check for excessive wear and dirt accumulation on starters and contactors. Vacuum or wipe components with a soft cloth to remove dirt (Fig 7). Do not use compressed air to clean these components because they may become damaged in the process. Also, do not use contact spray cleaners, which may cause sticking on magnetic pole faces.

Generally, discoloration and/or slight pitting do not harm contacts. If contacts are overly worn, replace (not repair) them in pairs to avoid misalignment and uneven contact pressure. Be very careful about filing contacts; doing so can easily damage them and reduce their life expectancy.

Maintenance after a fault

If a fault occurs, the excessive current may damage the MCC structure, components, bus or conductors. After a fault occurs, de-energize, disconnect and isolate all involved equipment to prevent accidental contact with live parts. Verify with a DMM or VOM that power has been removed. Sometimes tie breakers, or other power sources that may not have been properly documented can back-feed a system.

Inspect and (if needed) repair all involved equipment before placing it back into service. Verify that all replacements have proper ratings and are suitable for each application. For a complete list of items to review after a fault, refer to NEMA Standards Publication No. ICS 2, Annex A (Maintenance of Motor Controllers After a Fault Condition.)


Regular maintenance of MCCs includes inspecting energized and de-energized equipment.

Infrared thermomgraphy is one common way to inspect energized equipment.

Inspecting de-energized equipment requires specialized training, especially in safety.

Safety is also an issue if a fault occurs. De-energize, disconnect and isolate all involved equipment to prevent accidental contact with live parts.

If you have questions about MCC maintenance you may contact Mr. Martinez directly at (414) 382-4857 or at . Article edited by Jack Smith, Senior Editor, PLANT ENGINEERING magazine, (630) 288-8783, .

Guidelines to replace an older MCC

It’s not always easy to determine when and with what to replace an older MCC. Some users consider MCCs to be old or out of date after 10 years of service. Other users base equipment updates on application and duty cycles. Technological improvements, such as process speed control with VFDs, feedback monitoring and network interfaces can provide incentives to upgrade older equipment.

Modern MCCs are designed to accommodate a variety of user needs, ranging from complete replacement to integration with older existing equipment. For example, many newly designed MCCs are ideal for installation in older facilities because they are built to the latest industry standards and technological updates. Conversely, sometimes, newer MCC designs can be retrofitted into structures built 30 years ago.

MCCs often contain intelligent power and control components that monitor load current, provide diagnostic feedback and valuable input/output functions. For example, some intelligent MCCs feature electronic maintenance support and allow users to remotely monitor and control operations via an industrial network such as DeviceNet or Ethernet.

Optional software includes MCC layout and schematic diagrams; instruction manuals, spare parts and maintenance data log information. The software permits users to conduct remote monitoring and troubleshooting, reducing their exposure to hazardous voltage and current. In this way, users can be warned of impending faults and proactively maintain their equipment.

When replacing older MCC equipment, consider:

Solid-state components that offer I/O, protective functions and valuable system information

Built-in pre-tested and preconfigured networks that can help reduce startup time

Real-time monitoring software that eliminates costly programming time

Unit designs that reduce floor space

Application and duty cycle.

Selecting networked MCCs

Because of the comprehensive array of control and monitoring devices they contain, some modern MCCs incorporate control schemes and present users with an opportunity to transform islands of data into useful information that minimizes downtime. With the easier maintenance, increased safety and remote diagnostic capabilities of networked MCCs, it may make sense to consider them for your next equipment upgrade.

The plug-and-play technology of modern networked MCCs enables you to reduce installation time and experience smoother startups. These MCCs include devices such as solid-state overloads, drives and soft starters, with built-in communication capabilities, providing valuable diagnostic and predictive failure information.

A networked MCC generally consists of three main elements: built-in communication media, intelligent motor control components and MCC monitoring software.

Networks greatly simplify wiring, installation and startup time by replacing wire bundles with a single network cable. Users can easily remove or add networked units, significantly reducing wiring and testing time.

Programmable controllers or distributed control systems are often part of a networked MCC configuration. Monitoring software or HMI applications access critical information through device-level networks, such as DeviceNet and FOUNDATION Fieldbus. Users can bridge these networks to higher-level networks, such as ControlNet, Ethernet and Profibus by using gateways.

Networked MCCs can simplify installation by providing access to critical information and reducing safety hazards. A maintenance person can troubleshoot units without having to open enclosure doors. Users can “plug into” an MCC and monitor data, such as current, time to trip and percentage of thermal capacity used, and remotely access diagnostic information from a maintenance laptop, a control room or even an engineer’s desk.

There are many reasons why upgrading to networked MCCs makes sense. For example, a user might upgrade MCC equipment to replace a controller, eliminate costly interconnect wiring or obtain more operational information. Also, it may be necessary to upgrade a controller because of a change in network architecture.

Consider how networked MCCs could ease maintenance practices. Traditional hardwired installation is difficult to maintain and does not readily facilitate changes. But by replacing costly control wire bundles with a single network cable, users can increase system flexibility and reduce maintenance time.

Upgrading to newer programmable controllers that pass more information at faster communication rates will help increase your uptime. Also, adding solid-state overload relays to provide diagnostic information, as well as valuable input/output status, is another upgrade that makes good sense.

Square D marks 50 years in Cedar Rapids

It was part birthday celebration, part family reunion in Cedar Rapids, IA on Aug. 4. Square D marked its 50th anniversary of its plant opening, and the 50th birthday of it QO circuit breaker at a ceremony on the plant floor. It was also a chance for Square D retirees to renew old acquaintances and reconnect with a facility that had been a major part of their lives over the past half-century.

Dave Petratis , president and CEO of Schneider Electric’s North American Division and the parent company of Square D, praised the workers who helped start Square D on its way. “They are reflective of the fabric of our company,” said Petratis, himself an Iowa native. “They’ve gone through transition, they’ve gone through a lot of pain, and the future shines brightly.”

The Cedar Rapids facility opened in 1955 with 112,000 square feet. It has expanded to 270,000 square feet over the years, and the internal facility is undergoing yet another transformation. The Cedar Rapids facility will be one of three research and development centers for Schneider Electric worldwide. The two other facilities are in Shanghai and Grenoble, France. — Bob Vavra

Siemens completes Robicon acquisition

Siemens Energy & Automation , Inc. has completed the acquisition of Robicon Corp.’s assets including the stock of its foreign subsidiaries. The purchase of Robicon’s assets will strengthen Siemens’ ac drive and industrial power control product lines, as well as provide greater access to global markets for Robicon products.

Robicon’s strengths are its advanced technology in medium voltage drives and power supplies, and its strong market positions in oil and gas, water and wastewater, energy and pipeline applications. The world market for drives has a volume of approximately $33 billion , with an annual growth rate of around 2.5%.

In the U.S., the Robicon business will be integrated as a business unit of Siemens Energy & Automation, Inc. The Robicon international subsidiaries will become part of the Siemens Regional Companies, under Siemens Automation & Drives Group’s leadership. Siemens will continue to use “Robicon” as the existing product line name.

Fuel Cell Summit 2005 promotes development

The Society of Manufacturing Engineers and the Connecticut Clean Energy Fund are partnering to present, Fuel Cell Summit 2005 , which is designed to accelerate fuel-cell development. The event will take place Oct. 23—25, at the Mohegan Sun Casino & Resort, Hartford, CT.

Fuel Cell Summit 2005 combines SME’s “Manufacturing Alternative Energy’s Future” and CCEF’s “Moving Fuel Cells Into the Mainstream.” Manufacturers will learn their role in the growing fuel cell industry.

Register for the Fuel Cell Summit 2005 at