Let's break down the relevant code sections and standards to address your concern.

Understanding the Components MCP (Motor Circuit Protector)

A type of circuit breaker specifically designed for motor circuits. It provides short-circuit and ground-fault protection but generally does not include overload (OL) protection.

MCC (Motor Control Center)

A modular assembly of motor starters, controllers, and protection devices.

VFD (Variable Frequency Drive)

Controls the speed of an AC motor by varying the frequency and voltage supplied. VFDs often incorporate electronic overload protection.

OL (Overload) Protection

Protection against excessive current draw that is below short-circuit levels but high enough to cause overheating and damage to the motor over time.

NEC (National Electrical Code) Requirements

The NEC primarily focuses on overall motor circuit protection. The key sections are: NEC Article 430 (Motors, Motor Circuits, and Controllers)

This article is the core of motor circuit protection.

NEC 430.52 (Motor Circuit Short-Circuit, Ground-Fault, and Overload Protection)

This section requires both short-circuit/ground-fault and overload protection.

NEC 430.52(C)(3) (Instantaneous Trip Circuit Breaker)

This section allows instantaneous trip circuit breakers (like MCPs) to be used as short-circuit and ground-fault protection for a motor. However, it

explicitly requires that overload protection be provided separately. NEC 430.102 (Motor Disconnecting Means)

This section requires a disconnecting means be placed in sight from and within 50 ft of the motor.

Analysis based on the NEC

Your proposed installation can be compliant with the NEC, but only if the overload protection is properly coordinated and meets all the NEC requirements. Here's how:1. Short-Circuit and Ground-Fault Protection

The MCP in the MCC bucket provides the required short-circuit and ground-fault protection.2.

Overload Protection

The VFD must have overload protection features that are listed and labeled as suitable for motor overload protection and meet the NEC requirements. This includes: Being properly set to the motor's nameplate FLA (Full Load Amps). Having a trip characteristic that will protect the motor from damaging overloads. Being properly coordinated with the MCP.3.

Compliance Statement

The manufacturer of the VFD and the MCC including the installed MCP must provide a compliancy statement that supports the coordination of the installed equipment.4.

Disconnecting Means

Ensure a disconnecting means is placed in sight from and within 50 ft of the motor, as required by NEC 430.102. This can be a disconnect switch near the motor or, potentially, the VFD's integrated disconnect, if it is lockable and meets the requirements.

UL Considerations (UL 508A, UL 845) UL 508A (Industrial Control Panels)

This standard applies to the construction of industrial control panels. If your MCC and/or the downstream enclosure with the VFD are UL 508A listed, they must meet the requirements of that standard. UL 508A relies heavily on the NEC for application requirements. It does

not mandate that overload protection be in the same bucket as the MCP. The overall system design needs to meet the NEC. UL 845 (Motor Control Centers)

This standard covers the construction and performance of MCCs. Like UL 508A, UL 845 primarily focuses on the manufacturing aspects. It doesn't specifically dictate that overload protection must be in the same bucket. However, an MCC built to UL 845 is expected to provide a system that meets the NEC requirements when used according to its instructions and listing.

Key Concerns and Recommendations1. Coordination

Proper coordination between the MCP and the VFD's overload protection is critical. The MCP must not trip before the VFD's overload protection acts in an overload situation. The MCP should only trip in a short-circuit or ground-fault condition. This should be verified by the VFD manufacturer and confirmed through a coordination study.2.

VFD Overload Protection Listing

Ensure that the VFD's overload protection is listed and labeled for motor overload protection. Not all VFDs offer this feature or have a listing for it. Check the VFD's documentation and UL listing.3.

Documentation

Keep thorough documentation of the entire system, including the MCP's specifications, the VFD's overload protection settings, coordination studies, and any letters from the manufacturers supporting the installation.4.

Authority Having Jurisdiction (AHJ)

Always consult with the local AHJ (electrical inspector) to ensure that your installation meets their specific requirements and interpretations of the NEC.5.

Panel Labeling

Make sure the MCC and/or downstream panel are clearly labeled to indicate that the overload protection is provided by the VFD in the downstream panel.

In summary:

It is not inherently a violation of the NEC or UL to have the MCP and overload protection in separate enclosures. The NEC cares about the overall* motor circuit protection. However, the system must be designed and installed to meet all the NEC requirements, including proper coordination, listed components, and suitable overload protection. Consult with the manufacturers and the AHJ to ensure compliance. The burden is on the design professional to prove that the system is compliant. Without documentation from the manufacturer that shows compliance, an AHJ may not allow it. Flag for review