Okay, let's break down your generator system and address your questions. It sounds like you're grappling with some critical grounding and bonding considerations, which are essential for safety and proper operation.

Understanding Separately Derived vs. Non-Separately Derived Systems Correct Assessment

You are

correct that your existing configuration, with 3-pole ATSs and 3-wire feeders from both the utility service and the generator to the ATSs, classifies this as a non-separately derived system. A key characteristic of a separately derived system is that the neutral is switched by the ATS.

Generator to Switchboard Connection EGC from Generator

You are

correct. Since your generator's circuit breaker is inside the generator's cabinet, the conductor from the generator to the switchboard is an Equipment Grounding Conductor (EGC). This ensures a low-impedance path for fault current back to the source (generator) to facilitate the operation of the overcurrent protective device (circuit breaker).

Floating System and Code Violations Floating System Concerns

You've identified a critical issue. While a 3-wire delta system can sometimes operate without a neutral (depending on load types), a 480V wye system generally requires a reference to ground for safety and overvoltage protection. If you don't have a neutral connection or a grounding electrode conductor (GEC) at the generator to establish a ground reference, the phase voltages can "float" relative to ground, leading to overvoltages, insulation stress, and potential equipment damage. This may be a violation of NEC 250.20(B).

Delta System? I suspect that your generator is not a 480/277V wye source, as the switchboard is only 3-wire. Your system is likely operating as a delta system, and it should be corner grounded.

Proper Grounding and Neutral Treatment for the Generator The Core Problem

Your system should have a grounding point. If your generator voltage is actually 480/277 wye, and it is being operated as a delta system, it is not compliant.

Option 1: Keep the 480/277V Wye Generator. (NOT RECOMMENDED) Neutral Connection

This requires you to run a neutral from the generator to the switchboard.

Neutral-to-Ground Bond

At the generator, you will bond the neutral to the generator frame. You would also need a grounding electrode conductor (GEC) from the generator frame to a suitable grounding electrode system (e.g., ground rod, building steel, etc.) per NEC 250.50, .52 and .
54.

Overcurrent Protection

This might require an overcurrent device on the neutral conductor per NEC 230.90

ATS Issues

You would have to swap out all 3-Pole ATSs for 4-pole ATS.

Option 2: Change Generator to a Corner-Grounded Delta. If the generator is a corner grounded delta source, then one phase should be grounded to earth through a grounding electrode conductor. The ATS systems should work well with this. If the generator is indeed a delta system, there must be a grounded conductor.

Important Considerations NEC 250.20(B)

This section of the National Electrical Code is crucial. It outlines the requirements for grounding AC systems. A 480V wye system generally needs to be grounded.

NEC 250.30

This section addresses grounding separately derived systems. While your system isn't technically separately derived, the principles regarding bonding the neutral to the enclosure and connecting a GEC are highly relevant for ensuring a proper ground reference.

NEC 250.35

This covers grounding of systems that are not separately derived. This section is crucial for your application.

Recommendations and Next Steps1. Verify Generator Voltage and Wiring Configuration

Absolutely critical. Confirm with the generator manufacturer or qualified electrician the exact voltage configuration (wye or delta) and internal wiring.2.

Engage a Qualified Electrical Engineer or Licensed Electrical Contractor

This is not a DIY project. A professional experienced in generator systems is essential to: Perform a thorough site assessment. Verify the voltage type of the generator and your loads. Develop a compliant grounding and bonding design. Ensure the generator is safely integrated into your existing system.3.

Documentation and Labeling

Once the system is correctly grounded, document the changes and label the grounding points clearly.

In summary, your concerns about a "floating" neutral and potential code violations are valid. The system needs to be properly grounded for safety and reliable operation. Get a professional involved to assess your system and implement the correct grounding solution.Disclaimer: Always consult with a qualified electrical engineer or licensed electrical contractor for any electrical system design, installation, or modification. Flag for review