A control panel drawing can be technically complete and still leave important questions unresolved. The wrong component may have been selected. An enclosure may be too tight for service access. The I/O list may not match the field devices. A network connection may be missing.

That is why shop control panel drawing review should be on your checklist before fabrication begins. This confirms that the panel being built for production is the right panel the project.

Start With the Current Project Requirements

Before reviewing individual drawings, make sure everyone is working from the same scope.

The latest equipment list, control description, electrical requirements, customer specifications, and approved substitutions should be available.

AEC’s Custom Control Panel Checklist covers many of the items that should be reviewed before a panel is ordered.

A common mistake is reviewing each sheet in isolation. A schematic may look correct by itself but conflict with the bill of materials. The package needs to be reviewed as one system.

Review the Power Distribution First

Power problems are expensive to correct after fabrication begins, so start with the incoming electrical requirements.

Confirm the supply voltage, phase, frequency, main disconnect, branch protection, control power, power supplies, and motor loads.

For motor-heavy applications, compare the design against the actual horsepower and starting method of each motor. A motor operated across the line requires a different arrangement than one controlled by a soft starter or VFD. AEC’s Motor Control Panel Components Explained provides additional detail on disconnects, starters, overload relays, VFDs, soft starters, and related panel components.

Check SCCR Against the Installation Requirements

The shop control panel drawing package should identify the panel’s required Short Circuit Current Rating, or SCCR, where that information is known.

The reviewer should confirm that the design requirement is appropriate for the available fault current at the installation location.

SCCR is not simply a label added after construction. Component selection and protective device combinations can affect the final rating. AEC explains the calculation and the components that commonly limit the rating in Understanding Short Circuit Current Rating (SCCR) on Industrial Control Panels.

Review the Schematic as an Operating System

Electrical schematics should be reviewed for more than drafting accuracy.

What happens when the operator presses Start? Which interlocks have to be satisfied? What happens if an overload trips? Which devices continue operating after another part of the process stops?

Emergency stops, safety circuits, permissives, alarms, HOA selectors, local and remote control, and reset functions should match the intended operation. If the project includes an HMI or PLC, hardwired functions should also agree with the programmed control philosophy.

The drawing should make troubleshooting possible later. Wire numbers, terminal numbers, device tags, and cross-references need to be consistent enough that a technician can trace a circuit without reverse-engineering the panel.

Panel Layout Drawings Need a Maintenance Review

A layout drawing shows whether the components fit. Look at spacing around disconnects, breakers, PLC hardware, drives, power supplies, terminal blocks, and wireways. Components that require adjustment or replacement should be accessible without removing unrelated equipment.

VFDs, transformers, and power supplies may require specific clearances or ventilation. Packing them tightly into an enclosure because they fit on the drawing can create temperature problems in service.

Wire routing matters too. Power conductors, control wiring, and sensitive signal wiring should have a practical path through the enclosure without creating unnecessary crossings or crowded wireways.

AEC’s Industrial Motor Control Panels page shows the types of custom motor control assemblies where these layout decisions become part of the overall design.

Verify the Bill of Materials Against the Drawings

The bill of materials should match what appears on the schematics and layout.

Check manufacturer, model number, voltage rating, current rating, enclosure type, communication capability, and quantities for critical devices. If the customer has approved manufacturers or plant standards, confirm that the proposed components meet them.

Component selection can also affect future maintenance. A technically acceptable device may still be a poor choice if the facility has standardized on another manufacturer, does not have programming software for it, or would have difficulty obtaining a replacement.

The Design-Build Approach to Custom Industrial Control Panels is useful background on why engineering and fabrication decisions need to stay coordinated throughout the project.

Confirm the PLC I/O Before Fabrication

Every field device should have the correct signal type, voltage, tag, PLC address, and description. Digital inputs and outputs should be distinguished from analog signals, and analog ranges should match the instruments being supplied.

Check the list against the process drawings and equipment schedule. Missing devices often show up here before they appear anywhere else.

Spare I/O should also be planned. If capacity is being reserved for future equipment, identify it clearly instead of leaving unexplained empty points in the design.

Network and Communication Requirements Need Specifics

“Ethernet connection required” is not enough information for a finished control system.

The drawings and supporting documentation should identify which devices communicate, the network topology, required protocols, and responsibility for IP addressing where applicable.

PLC-to-HMI communication is only one part of the system. VFDs, remote I/O, operator stations, managed switches, plant SCADA, and other equipment may all share the control network.

AEC’s Automated Control Systems work includes PLC-based systems, touch-screen interfaces, remote monitoring, and plant-wide communication. The shop drawing review should make clear which of those connections are part of the current project and which are only planned for later.

Resolve Open Items Before “Approved” Goes on the Drawing

Before drawings are released for production, the project team should know the answers to the issues that could change fabrication. That includes incoming power, motor sizes, component substitutions, enclosure requirements, I/O, communications, control sequences, operator devices, listing requirements, and required panel ratings.

A useful approval package should leave the fabricator with very little interpretation.

If an item genuinely cannot be finalized, identify it clearly and decide how it will be handled.

Shop Drawing Approval Is the Last Low-Cost Time to Make Changes

Changes don’t become impossible once fabrication starts. They become more expensive.

Moving a component on a drawing takes minutes. Moving it after holes are cut and wiring is installed may require a new back panel, new enclosure work, rewiring, revised drawings, and another round of testing.

The same applies to PLC I/O, network hardware, motor starters, operator controls, and protective devices.

Once the panel is built, AEC’s Factory Acceptance Testing for Industrial Control Panels provides the next verification step. FAT confirms that the completed panel operates as intended before shipment. After installation, the Control Panel Commissioning Checklist for Startup and System Handoff covers field verification and startup.

For a new control panel project, send the panel builder current drawings, equipment information, electrical requirements, preferred components, control descriptions, communication requirements, and known installation constraints before shop drawings are finalized. Then review the package as an operating system, not simply as a set of drawings waiting for a signature.

Related Engineering Resources

Factory Acceptance Testing (FAT) for Industrial Control Panels

Design-Build Approach to Custom Industrial Control Panels

Custom Control Panel Checklist

Motor Control Panel Components Explained

Understanding Short Circuit Current Rating (SCCR) on Industrial Control Panels

Control Panel Commissioning Checklist for Startup and System Handoff

Industrial Motor Control Panels

Automated Control Systems