Powering Motor Control Centers

Motor control centers are now being designed that provide the best alternative for grouping motor control, associated control and distribution equipment. Today, more and more electrical contractors are realizing the new opportunities that exist from design-build to total system integration and capitalizing on them.

Today’s most recent trend favors electrical contractors (ECs), rather than owners. ECs are quickly becoming the specifiers on motor control assemblies due in part to the trend toward outsourced maintenance. These motor control centers contain combination motor control units, which have protective devices such as circuit breakers and disconnects.

As the economy slowly turns around, more electricians are needed to install and maintain electrical devices and wiring in residential and commercial applications. The rapid growth in new technology is also expected to continue to stimulate the demand for electrical contractors.

Assembling motor control centers and determining power requirements is relatively easy. Only one set of incoming power wires should be routed to the prewired motor control center, which, in turn, distributes power to all the devices through its power bus network. Instead of mounting these units to the wall, more contractors are opting for quicker installations by mounting them to the floor.

When a problem is detected and determined to be associated with the control unit, which are often designed to handle much larger loads, it can easily be unplugged, and a spare backup unit put in its place.

Before the inception of control units, contractors were forced to wire each device. But today, productivity and installation techniques have improved.

ECs are realizing several advantages in installing these units. Mounting drives in motor control centers reduces installation costs and system complexity because a variety of these motor controllers can be fed by a single incoming feeder, which can supply several drives with incoming power. As a result, a reduction in wiring and labor will likely offset any additional costs associated with the motor control center structure.

Individual enclosed motor controls should be installed on the plant floor next to the motor being controlled. Separate auxiliary system devices, including alarms and sensors, are then wired directly to the enclosed motor controller. Therefore, many separate auxiliary devices such as safety switches can be eliminated. Electrical contractors are finding system integration and installation to be simpler and more flexible for future reconfiguration.

Rockwell Automation produces several motor controls, including DeviceNet-enabled units that provide diagnostics and troubleshooting information to assist users in maintenance applications.

“Within Rockwell Automation, ever since the last recession in 1998, there has been a move towards downsizing and increased automation moving abroad,” said Al Collins, product and business development manager for Rockwell Automation. “People who used to hire and maintain an engineering staff have now given the contracts to electrical contractors. It is hard to keep the product specification in place, but there is an increased cost savings for electrical contractors as they pay as you go.”

Motor control enclosures consist of rigid steel channel framework assembled into standardized vertical sections and bolted together to form a complete shipping section. Most structures include horizontal and vertical bus, insulation and isolation barriers, horizontal and vertical isolated wiring troughs, cable entrance areas, and space for inserting starter and control equipment.

While plugging units into a motor control center is easy and most efficient, it can also have some complexities associated with the installation. Because each enclosure must be mounted to the wall individually, contractors should plan on an increased mounting time. In addition, incoming power must be configured to each enclosure. The best alternative is to mount the motor control unit and wire it in a single large enclosure to reduce space constraints.

Some companies even provide safeguards against voltage drops or power interruptions to prevent against accidental machine start-ups. Branch-circuit sizing, overload protection and rating of the motor disconnect must be considered when installing a motor circuit for proper overcurrent protection.

“Design-build plays an important role for electrical contractors,” Collins said. “They are more focused on installations on a case-by-case basis, which has become a larger opportunity for institutional facilities. There is a leveraging capability for design-build work and electrical contractors have complete expertise with not only design-build but many also have a mechanical and drafting staff so they are positioned to provide complete solutions.”

Motor control centers have become the preferred choice to provide a convenient, economical enclosure for motor control and branch-circuit protection in commercial and industrial facilities. However, over the past few years, motor controls have evolved from cabinets that once housed basic electrical devices, such as circuit breakers, to a fully based automation center, which includes programmable controllers.

“There was a survey done not too long ago on the U.S. and Canada on where people see electrical contractor’s growth and over half of the response was in automation,” Collins said. “Electrical contractors are now being forced to get involved in a bidding war with industrial automation. They have to find a way to differentiate from the competition. Some may opt for design work and others may work on a time-and-material basis while working for institutional and commercial facilities. The three main areas for electrical contractors today are power, lighting and security. There is a broad portfolio of power and lighting controls along with security but it is finding the right person available to meet your needs.”

Electrical contractors are finding ways to take a motor control project from an idea or design, prepare a wiring diagram, determine the components for the enclosure and complete a fully automatic control system for a variety of commercial or industrial applications. For residential applications, system integration includes the automation of lighting, blinds, awnings, home theater and computer systems using software and hardware.

Electrical contractors must now focus on ensuring total system functionality for building systems. Companies such as Johnson Controls assist contractors by providing custom control and instrumentation panels used in control rooms and nerve centers in power plants, industrial process automation systems and security monitoring and control centers in commercial buildings.

Typically, the electrical contractor asks the following questions to determine a motor control system’s usage. How and when do you want your lights to turn on? Do you want to run several machines from one location? Would you like the convenience of outlets located where you need them, not just where the Code requires them to be? Would you like to bring in enough electrical power for the expansion you are planning next year?

Rockwell’s SMC-Flex controller incorporates, as standard, electronic motor overload protection. When installed and coordinated with the proper short circuit protection, overload protection is intended to protect the motor, motor controller and power wiring against overheating caused by excessive overcurrent. As a result, OEMs and system-level users will be able to improve performance and simplify power-circuit configuration with new Allen-Bradley Bulletin 1503E medium voltage (MV) OEM component kits. These OEM component kits are the latest of three medium-voltage Allen-Bradley SMC Flex solutions, including the Bulletin 1562E complete motor control solution.

It is also important to note that these motor control units should be de-energized regularly for maintenance. Once the busbars are adequately protected by bus closing plugs or other equivalent means, then it becomes safe to work inside the individual motor starters or any other unit that may be plugged into the main control center.

Other trends in the motor control industry include the placement of a human machine interface touch screen panel near the equipment, so operators may monitor the machinery properly. The controls should be networked to a centralized location where an operator may then monitor operations, oversee system operation, schedule production and control inventory. The controllers can also be networked together with a centralized “host” computer system where plant operations are monitored and controlled from a control room environment.

As with every industrial and residential control application, electrical contractors should be aware of the fact that using the right motor controls can either make or break a project. While every client is looking for a cost-effective solution, each is also seeking reliability and optimum performance. It is clear the opportunities for electrical contractors and motor control installations are increasing as they become used in more nontraditional applications. EC

SPEED is a freelance writer based in Weymouth, Mass. She can be reached at 617.529.2676 or kkspeed@aol.com.


About the Author

Kellie K. Speed

Freelance Writer
Kellie Speed is a freelance writer based in Weymouth, Mass. She can be reached at 617.529.2676 or kkspeed@aol.com .

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