You've correctly identified the crux of the issue. NEC 240.87(A) does indeed state that overcurrent protective devices that can be set to 1200A or higher must have arc flash hazard reduction unless an exception applies.Here's a breakdown and why your reviewer might be technically correct, but practically, it's less clear: The Code Language

NEC 240.87(A) is pretty straightforward. If the breaker can be set to 1200A or higher, arc flash reduction methods are required. This includes settings for instantaneous trip, short-time trip, and ground-fault pickup. It doesn't explicitly exempt generator breakers.

Possible Arc Flash Reduction Methods

240.87 lists acceptable methods for reducing arc flash hazards. ARMS (Arc Reduction Maintenance Switching) is one option, but other methods such as zone-selective interlocking, energy reducing maintenance switches, current limiting fuses, etc. can be used in lieu of ARMS. If any of these are already present, the breaker will meet code.

Generator Breakers and Practical Considerations



Common Practice

As you mentioned, it is uncommon to see ARMS systems or other advanced arc flash reduction on generator output breakers, especially smaller generators. This is because the risk assessment might not justify the added cost and complexity.

Generator Impedance

Generators inherently have limited fault current contribution. The impedance of the generator windings limits the amount of fault current available at the output terminals. This reduced fault current magnitude means the arc flash hazard might not be as severe as with a utility source.

Coordination

Generator output breakers are typically coordinated with downstream protective devices. If those downstream devices have arc flash mitigation, the generator breaker might not need it.

Maintenance Practices

Generators are often taken offline for maintenance. This reduces the potential for arc flash during maintenance activities.

Exceptions

240.87(B) provides an exception where there is documentation that the overcurrent device is isolated such that it is not accessible to unqualified persons during operation and the means of disconnection is padlocked or password protected or the work is performed by qualified person(s) using PPE in accordance with an established hazard/risk assessment procedure.

How to Address the Reviewer's Comment


Perform an Arc Flash Study

The best approach is to conduct an arc flash study on the generator system. This study will determine the incident energy levels at the generator output breaker under various fault conditions. The study will include the generator's fault current contribution and downstream protection scheme.2.

Present Your Findings

If the arc flash study shows that the incident energy levels are within acceptable limits (based on your company's safety policies and applicable regulations) without additional arc flash mitigation, present the study and the rationale to the reviewer. Explain how the generator's impedance and the downstream protection scheme limit the fault current and incident energy.3.

Consider Other Options (If Needed)

If the arc flash study indicates a need for arc flash mitigation, consider alternative methods besides ARMS.

Current Limiting Fuses

A properly sized current-limiting fuse upstream of the generator breaker can significantly reduce fault current and incident energy.

Zone-Selective Interlocking (ZSI)

If the downstream protective devices have ZSI capabilities, this can improve coordination and reduce clearing times, thereby lowering incident energy.

Remote Operation

If the breaker can be opened remotely, this can remove the operator from the arc flash hazard.

Implement Exceptions per 240.87(B)

If all unqualified personnel are restricted from accessing the breaker while energized and it is padlocked or password protected, or all work is performed by qualified personnel in accordance with established hazard/risk assessments, then no other arc flash mitigation is needed.4.

Document Everything

Document the arc flash study, the rationale for your chosen approach, and any mitigation measures implemented.

In summary: While the reviewer's concern about NEC 240.87(A) is valid on the surface, it's important to look at the specific characteristics of the generator system and conduct an arc flash study to determine the actual risk. Often, the generator's inherent characteristics and downstream protection will provide adequate mitigation, or alternative methods can be used to comply with the code. You likely don't need ARMS, but you need to demonstrate why it's not needed. Flag for review