Control Panel Component Selection
How Components Are Selected for Industrial Control Panels
Selecting components for an industrial control panel involves considerably more than producing a list of electrical parts.
Every component needs to be suitable for its electrical duty, operating environment and role within the wider control system. The interaction between components also needs to be considered, including electrical protection, heat generation, available space, communications and future maintenance requirements.
A component that is technically capable of performing a particular function is not automatically the most appropriate choice for the finished panel.
Good component selection considers the complete lifecycle of the control system: how the panel will operate, how engineers will maintain it, whether replacement parts will remain available and how future modifications may affect the original design.
This guide explains some of the major considerations involved in selecting components for industrial control panels.
Start with the Control System Requirements
Component selection should begin with the application rather than a preferred manufacturer or parts list.
The designer first needs to understand what the panel is expected to control.
Requirements may include:
Supply characteristics.
Connected loads.
Motors.
Instrumentation.
PLC I/O.
Control voltages.
Variable Speed Drives.
Safety functions.
Industrial communications.
Environmental conditions.
Operator controls.
Future expansion.
The requirements of the machinery or process determine the electrical architecture, which then determines the components required within the panel.
Selecting components too early can result in equipment being specified before the actual electrical and automation requirements are understood.
Selecting the PLC and I/O
The PLC is often one of the most important automation components within the control panel.
Selection may be influenced by:
Number of digital inputs and outputs.
Analogue I/O requirements.
Processing requirements.
Communication protocols.
Remote I/O.
Safety requirements.
Motion requirements.
HMI and SCADA integration.
Existing site standards.
Engineering software.
Future expansion.
The wider installed automation environment should also be considered.
For example, introducing a different PLC manufacturer may require additional programming software, licences, spare parts and engineering knowledge.
In many applications, standardising around an existing PLC platform can provide lifecycle benefits even where several technically suitable controllers are available.
Electrical Protection
Protective devices need to be selected according to the electrical system and circuits they are protecting.
Depending on the panel, this may include:
Circuit breakers.
Fuses.
Motor protection.
Control circuit protection.
Surge protection.
Protective devices associated with individual loads.
Selection involves more than the normal operating current of the equipment.
Designers may need to consider:
Supply characteristics.
Load current.
Fault current.
Cable and conductor protection.
Breaking capacity.
Coordination.
Inrush characteristics.
Manufacturer requirements.
The protective system needs to be considered as part of the complete electrical design rather than as a collection of independently selected devices.
Contactors, Relays and Motor Control
Contactors and relays remain fundamental components within industrial control panels.
They may be used for:
Motor switching.
Load switching.
Control functions.
Isolation between circuits.
PLC interface functions.
Equipment interlocks.
Selection should consider the type of load being controlled and the electrical duty the device will experience.
Motor loads, for example, can create significantly different switching conditions from small control loads.
Where motors are involved, the wider motor control arrangement may also include overload protection, circuit protection and PLC feedback.
The objective is to create a coordinated motor control circuit rather than selecting each component independently.
Variable Speed Drives
Variable Speed Drives are increasingly common within industrial control panels.
They can provide controlled operation of motors used for:
Pumps.
Fans.
Conveyors.
Process equipment.
Material handling.
Manufacturing machinery.
Drive selection may consider:
Motor characteristics.
Load.
Required speed range.
Starting requirements.
Control method.
Communication protocol.
Environmental conditions.
Installation requirements.
Safety functions.
Harmonics and EMC considerations.
Drives can also generate significant heat.
Their inclusion can therefore influence enclosure size, component spacing, ventilation and the wider thermal design of the panel.
Power Supplies and Control Voltages
Industrial control systems frequently use DC power supplies for PLCs, sensors, relays and other control equipment.
A common example is a 24 V DC control system.
Power supply selection should consider both normal demand and the behaviour of the system under changing load conditions.
Considerations may include:
Total connected load.
Starting or peak loads.
Power reserve.
PLC requirements.
I/O requirements.
Field devices.
Relays and contactors.
HMI equipment.
Network equipment.
Future expansion.
Simply adding together nominal device ratings may not always provide the complete picture.
The control power architecture should also consider how a power supply failure would affect the automation system.
Safety Components
Where machinery requires safety-related control functions, the panel may contain dedicated safety equipment.
Depending on the machine design and risk assessment, this might include:
Safety relays.
Safety PLCs.
Emergency stop interfaces.
Guard monitoring.
Safety contactors.
Safe drive interfaces.
Safety I/O.
Safety component selection should follow the requirements established by the machine risk assessment and the applicable safety-related control system design.
It is important not to select a "safety component" in isolation and assume that this makes the complete safety function compliant.
The architecture, diagnostics, component behaviour and complete safety function need to be considered together.
Industrial Networking Components
Modern control panels increasingly contain networking equipment connecting the PLC with other automation systems.
This may include:
Industrial Ethernet switches.
Communication modules.
Protocol gateways.
Remote I/O interfaces.
Network connectors.
Fibre equipment where applicable.
Networks may support technologies such as:
PROFINET.
EtherNet/IP.
Modbus TCP.
PROFIBUS.
Other industrial protocols.
Component selection should consider the wider network architecture and not simply whether a device has the correct physical connection.
Managed network equipment, diagnostics, environmental suitability and future expansion may all become relevant depending on the application.
Terminals, Conductors and Internal Wiring
Terminals and wiring can appear relatively simple compared with PLCs and drives, but they have a major influence on the maintainability of a control panel.
Good design should consider:
Conductor sizing.
Current requirements.
Terminal ratings.
Segregation.
Protective conductors.
Identification.
Cable entry.
Field wiring.
Spare terminals.
Wiring routes.
Clear terminal and conductor identification can significantly reduce the time required for installation and future fault finding.
Space should also be considered.
A technically adequate terminal arrangement that leaves insufficient room for field wiring can make installation and maintenance unnecessarily difficult.
Enclosure Size and Thermal Management
Component selection cannot be separated from enclosure design.
The enclosure needs sufficient space for the equipment while also allowing for:
Wiring.
Cable ducts.
Terminals.
Component spacing.
Heat dissipation.
Maintenance access.
Future modifications.
Heat-producing components may include:
Variable Speed Drives.
Power supplies.
Transformers.
Contactors.
Protective equipment.
Other power electronics.
The thermal effect of the complete assembly therefore needs to be considered.
Depending on the application and environment, thermal management may involve natural heat dissipation, ventilation, fans, heat exchangers or other appropriate measures.
Environmental protection requirements also need to be considered alongside cooling, because increasing ventilation can affect enclosure protection.
Availability, Standardisation and Obsolescence
A component may meet every immediate technical requirement and still be a poor long-term choice.
Industrial control panels can remain operational for decades.
Component selection should therefore consider:
Availability:
Can the component be readily obtained when replacement is required?
Lifecycle:
Is the product current, mature or approaching obsolescence?
Standardisation:
Is the same equipment already used elsewhere on the site?
Spares:
Does the organisation already hold compatible replacement components?
Engineering knowledge:
Can internal and external engineers support the equipment?
Software:
Does the component require specialist configuration software or licensing?
Replacement:
Is there a clear migration path if the product is discontinued?
Standardisation can be particularly valuable across PLCs, drives, protection and control equipment.
However, component selection should still be based on the technical requirements of the application rather than choosing a standard component where it is unsuitable.
Why Component Selection Matters in Control Panel Design
Control panel reliability is influenced by thousands of individual engineering decisions.
Selecting the PLC affects software and communications. Selecting a drive affects thermal performance and motor control. Protective devices influence the electrical design. Enclosure selection affects environmental protection and heat dissipation.
These decisions cannot be considered independently.
A good industrial control panel therefore needs to be engineered as a complete assembly around the requirements of the machinery or process it controls.
Component selection should also consider applicable standards and project requirements. Depending on the application, this can include the BS EN IEC 61439 series for low-voltage switchgear and controlgear assemblies and BS EN 60204-1 for the electrical equipment of machinery.
As a control panel manufacturer, Stratos combines electrical design, panel manufacture and automation engineering, allowing PLCs, drives, industrial networking and other control components to be selected in the context of the wider automation system.
Need Help Specifying an Industrial Control Panel?
The components inside a control panel determine far more than its initial functionality.
PLC platform, electrical protection, drives, networking, thermal performance, component lifecycle and maintainability all influence how reliably the control system can be operated and supported over the years that follow.
Stratos provides industrial control panel design and manufacture alongside PLC and automation engineering, helping manufacturers develop panels around the electrical, automation and lifecycle requirements of the application.
Speak to our engineers about control panel design, component selection, manufacture, refurbishment or modernisation.
Frequently Asked Questions
What components are used in an industrial control panel?
An industrial control panel may contain PLCs, I/O, circuit protection, power supplies, contactors, relays, Variable Speed Drives, safety equipment, industrial network devices, terminals and other electrical control equipment. The exact components depend on the application.
How do you choose a PLC for a control panel?
PLC selection should consider I/O requirements, processing capability, communications, safety or motion requirements, HMI and SCADA integration, existing site standards, engineering software and future expansion.
Why is thermal management important in control panels?
Electrical components generate heat, particularly equipment such as Variable Speed Drives and power supplies. Excessive internal temperatures can affect equipment operation and component life, so enclosure design and thermal performance need to be considered as part of the complete panel design.
Should control panels use standardised components?
Where technically appropriate, standardisation can reduce spare parts requirements, engineering software, training and maintenance complexity. However, components should not be standardised where they are unsuitable for the electrical or operational requirements of the application.
Should obsolete components be used in a new control panel?
Generally, new designs should consider the expected lifecycle and availability of components. Selecting equipment already approaching obsolescence can create future support and spare-parts risks, although existing site standards and compatibility requirements also need to be considered.