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Motor Control Center (MCC) Explained

What is a Motor Control Center?

A motor control center is often referred to as an MCC.

MCC’s are a critical component in electrical power distribution systems. An MCC has a centralized assembly comprising one or more enclosed sections with motor control units as their core and a shared power bus. Each enclosed section is designed to manage and protect the electric motors in the system, enabling the functionality of equipment and machinery from a single central location.

MCC’s are installed in a control room for easy access or maintenance, typically in a separate air-conditioned room.

Components of MCC and features

MCC typically comprises the following components and features:

  1. Motor control units: They house the switches and circuits to run the MCC starter, relays, contactors, and other control parts for operating individual motors. Operators can start, stop, and monitor motors using these control panels.
  2. The horizontal bus: This connects the main power source of the MCC panel across the length of the panel to the individual vertical bus sections.
  3. The vertical bus: Also known as the power bus, it enables power connections to several starter units in the MCC. It manages the collective loads of all the motors and control units it serves.
  4. Control and monitoring: A safety mechanism for remote operations and diagnostics is achieved on modern MCCs with integrated features for monitoring and control such as network connectivity, programmable logic controllers (PLCs), variable frequency drives (VFDs), and soft starters that safeguard motors against overloads and other risks.

The VFDs and soft starters also save energy and reduce operating costs by reducing the speed of the motor when full speed is not required.

Benefits of using an MCC

  • Centralized control: Multiple motors can be easily controlled from a centralized point, enabling simpler maintenance and operation flow. Operating various motors from a single, centralized location enhances operational efficiency and effectiveness.
  • Improved safety: Electrical hazards are significantly reduced by centralizing motor controls because the need for human contact with the motors is less likely. Personnel are, therefore, taken away from the risks associated with being in close proximity to the motors.
  • Enhanced efficiency: By precisely controlling motor speeds and consuming less power during periods of lower demand, integrating VFDs and other smart devices into MCCs can result in significant energy savings.
  • Maintenance simplicity: One of the leading design considerations for MCCs is enabling easy access to control units and components for maintenance.

What is an MCC bucket?

A Motor Control Center (MCC) bucket is a modular element or component that houses the protection and control mechanisms for a single motor. Usually, a circuit breaker or fused disconnect switch, control circuitry, overload protection, and a motor starter are all included in one bucket. Together, these parts enable a motor to be started, stopped, protected, and controlled. Because MCC buckets are made to slide into and out of the MCC framework, they may be easily installed, maintained, replaced, or upgraded without interfering with the functionality of other MCC-controlled motors.

However, some MCC buckets are fixed, so the input wiring is hardwired into the bucket rather than the unit being able to slide out. Drawers, on the other hand, generally do slide in and out, but even then, there are some that are fixed-style drawers.

Key features and parts of an MCC bucket

  • Motor starter: Depending on the motor application, this can be a VFD, a soft starter, a star/delta starter, or a straight online starter. It is used to start the motor running.
  • Overload protection: The motor is shielded from currents that exceed its rated capacity, which could result in overheating and damage by devices such as thermal or electrical overload relays.
  • Disconnect switch or circuit breaker: In an emergency or for repair, this offers a safe way to cut the motor control components within the bucket from the power source.
  • Control circuitry: This can contain push buttons, indication lights, contactors, and other components that allow the motor to operate manually or automatically.  
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What's the difference between an MCC drawer and an MCC bucket?

Motor control center in-bucket and in-drawer options are modular units designed to simplify the installation and replacement of motor controllers. The MCC 'bucket' is typically square or cube-shaped, while the drawer is precisely what you might imagine: drawer-shaped. The primary reason for these two component design options is how they are mounted and the standard they comply with: MCC buckets are ANSI-compliant for North America and some selected regions, and MCC drawers are IEC-compliant, typically covering the rest of the world.

Both MCC buckets and drawers are typically made of metal and are intended to keep the motor control center safe from external elements and provide a simpler and more versatile way of providing motor control for electrical power distribution.

Causes of MCC failures

  1. Electrical overload: Protection devices known as overloads detect an excessive amount of electrical current in the motor circuit and trip the MCC to stop damage. They occasionally malfunction or are unable to detect an electrical overload, which can be caused by a mismatch between the motor and the MCC's capability, resulting in overheating, damage to the insulation, and, eventually, component failure.
  2. Component aging: MCC electrical components may deteriorate with time as a result of mechanical wear, heat stress, and environmental exposure. Older equipment is more likely to break down, especially if it is improperly maintained.
  3. Mechanical failures: When a mechanical motor component fails, for example, when a bearing fails or a motor-driven system is misaligned, it can cause excessive vibration, noise, and eventually the physical stress that breaks down electrical components.
  4. Faulty installation and loose connections: Operational failures may result from improper MCC installation, which includes bad wiring, insufficient grounding, and disregarding the manufacturer's instructions.
  5. Environmental conditions: MCC components can become corroded when exposed to harsh external factors such as high humidity, high temperatures, dust, and corrosive atmospheres. For instance, excessive humidity may result in condensation inside the MCC, which may short-circuit and corrode electrical components.

Solutions to MCC failures

  • Continuous thermal monitoring and predictive maintenance: Installing smart sensors and IIoT (Industrial Internet of Things) technology for the continuous monitoring of MCC components can help in the prevention of MCC failures and enhance overall safety. These technologies predict failures by monitoring trends like temperature, vibration, and so on for anomalies and alerting the maintenance team for maintenance checks. Optimizing maintenance schedules and reducing unplanned downtime can be achieved by implementing predictive maintenance approaches that rely on real-time data analytics on the MCC condition.
  • Regular maintenance and inspections: Issues like loose connections, wear and tear, or corrosion can be identified and corrected by implementing a scheduled maintenance routine to inspect and test MCC components before they lead to failures.
  • Load management: Constantly monitoring and regulating the load on each MCC unit is crucial to track the performance and load status of motors controlled by the MCC for overload prevention. This may include redistributing loads or upgrading the MCC to handle rising electrical demands.
  • Implementing redundancy: Including redundancy in the MCC design for critical operations, such as backup units or dual power sources, is crucial to mitigating MCC solutions. This guarantees that activities will be minimally disrupted in the case of a failure.
  • Installing protective devices: To protect against overloads, short circuits, and voltage spikes, it is important to install the necessary protective devices, such as circuit breakers, fuses, and surge protectors. Regular checks and testing of these devices help to ensure that they're working correctly, and replacement is done when there's wear and tear.

MCC is critical for managing multiple electric motors in industrial or commercial settings, offering centralized control, safety, and efficiency in motor-driven operations. With several issues that can cause its failures, adopting advanced maintenance technologies like Continuous Thermal Monitoring (CTM) with other maintenance measures to reduce the likelihood of potential failures increases asset reliability, thereby enhancing operational efficiency, safety, and flexibility in motor control applications.

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