While complex process and motor control enclosures are generally outsourced to a third-party controls contractor, many times small and mid-size industrial control panels that house motor controllers, variable frequency drives (VFD) and automation modules are built and wired in-house. Since no two production or industrial process lines are exactly the same, rarely will a pre-fabricated control panel fit all your electric motor control needs for machinery, compressors, fans, pumps and process control.
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Robust power components such as VFDs, transformers, and power supplies generate heat. The resulting temperature rise can wreak havoc on delicate control panel devices, including your programmable controller, solid state relaying devices and your communications wiring. Consider following industry best practices for the physical layout of the control cabinet back panel to manage the cabinet temperature rise due to heat dispersal of power electronics.
Active Thermal Management for Electric Motor Control Cabinet
Industry best practices dictate design and layout strategies to effectively combat ambient temperature heat rise and to manage the thermal effects of heat generating devices. Avoid overcrowding your back panel, and allow at least two inches between power generating devices (VFDs, transformers, power supplies) for good airflow. Always follow the manufacturer's suggested clearances for power electronics.
If your floor operations are considered 'hot manufacturing lines', or if outdoor temperatures frequently rise above 90 degrees, then active thermal management solutions should be considered. Enclosure fans can be installed near the top of panels (since heat rises) to increase the air circulation. Also consider an enclosure mounted cooling unit for motor control panels that contain a transformer, power supplies, and VFDs to help maintain a consistent cabinet temperature.
VFDs will generate the most heat, and similar to transformers, heat sinks can be used to keep the air surrounding these components cooler. Good thermal management means putting some distance between sensitive electronic components which can fail if the inside motor control panel temperature gets too high. Always follow the manufacturer's guidelines for clear spacing around, above, and below VFDs and transformers to promote proper ventilation and keep the drives properly cooled. Manufacturers will offer multiple mounting configurations for VFDs, leaving the controls designer with flexibility in the panel layout.
The Panel Layout as a Passive Heat Management System
When an electrical enclosure is also housing automation controls and relay technology such as starters and contactors - which may require different voltage levels, there are a number of factors that can be considered to promote good air flow and reduce the temperature inside the panel:
- Choose an enclosure size large enough to accommodate the current layout of devices and still have space for future devices in case of new machinery or additional motor installations.
- Locate heat generating devices away from solid state components - transformers and 480V power devices are usually placed at the top of cabinet for ease of power connections and to segregate high voltage components from low-power devices.
- Keep a minimum spacing between power devices to avoid arc flash, and to allow adequate clear space for cable bending radius, which also gives electricians enough space to wire device terminals.
- Provide enough terminal blocks for PLC control inputs/outputs, field device wiring, and spares to prevent cabinet overcrowding in the future.
As a final note, the performance of your electrical cabinet can be negatively affected by interactions between control wiring and 480V power wiring. High power circuit cables will induce enough of an electromagnetic field surrounding the cables to produce an effect on low-voltage control conductors that are within that magnetic field.
A resulting voltage can be induced into the control circuit, known as electromagnetic interference (EMI). A false EMI-induced voltage can cause VFDs and the PLCs to malfunction from the false signal that is generated. For this reason, 24V low power and 120V control wiring should be segregated by location and by wire color. Follow the NEC for proper wire colors for each voltage level.
When designing an electric motor control panel, contact Mader Electric. We are experts in VFD installations and provide a full line of motor control devices and programmable controls to meet all your process machinery and industrial motor and pump control panel needs.