Okay, let's break down the neutral-ground bonding and docking station requirements in your scenario. This is a common and important design question.

Understanding the Neutral-Ground Bonding Situation Main Switchboard

Neutral and ground are bonded here. This is the normal service entrance bond, and it's code-required.

Permanent Generator

Neutral and ground are bonded here. This is also typically required for a separately derived system (SDS) as defined by the NEC (National Electrical Code).

4-Pole ATS

Switching the neutral means when the generator is online, the neutral is isolated from the utility neutral. When the utility is online, the utility neutral is used. This is a key part of your system design.

Docking Station

This is where the question gets tricky and it's important to do this correctly.

Docking Station Rating - Non-Service Entrance Rated

In your described setup, the docking station does not need to be service entrance rated. Here's why: The service entrance is already established at your main switchboard. The docking station is essentially an extension of your generator circuit, not a new service. You have an already existing neutral-ground bond at the permanent generator.

Neutral-Ground Bond for Temporary Generator via Docking Station

This is the critical part: The docking station MUST provide a neutral-ground bond for the temporary generator WHEN the temporary generator is connected and the permanent generator is offline. This is how you keep your system safe and code-compliant.

How to accomplish the temporary generator N-G bonding



Dedicated N-G Bonding Jumper in the Docking Station

The simplest and most reliable approach is to include a robust neutral-to-ground bonding jumper within the docking station enclosure. This jumper is permanently connected to the neutral and ground buses/bars within the docking station.

Relay Controlled N-G Bonding Jumper If you are concerned about circulating currents when both the permanent generator and the temporary generator are connected to the docking station, then you could install a relay controlled N-G bonding jumper. Permanent Generator as a Reference

When the permanent generator is online, the temporary generator will use the N-G bond at the permanent generator.

Permanent Generator and Temporary Generator Both Offline

No N-G bond is established.

Important Considerations and Best Practices Short-Circuit Current Rating (SCCR)

The docking station must have an appropriate SCCR rating for the available fault current at its location.

Grounding Electrode System (GES)

Ensure your permanent generator is properly connected to the building's grounding electrode system per NEC Article 250. This helps provide a low-impedance path to ground for fault currents.

Signage

Clearly label the docking station with instructions on proper connection procedures, the requirement for the temporary generator to have its neutral properly bonded to ground within the docking station when the permanent generator is offline, and any other relevant safety information.

Qualified Personnel

All connections and switching operations should be performed by qualified personnel familiar with electrical safety procedures and the specific requirements of your system.

NEC Compliance

Always adhere to the latest version of the National Electrical Code (NEC) and any applicable local codes. Specifically, pay close attention to Articles 250 (Grounding and Bonding), 445 (Generators), and 700, 701, or 702 (Emergency, Legally Required, or Optional Standby Systems).

Coordination Study

Conduct a coordination study to ensure that all overcurrent protective devices (OCPDs) are properly sized and coordinated to minimize outages and maximize safety. This is especially important with multiple generators and ATSs.

Inspection

Have the complete installation inspected by a qualified electrical inspector.*

Check with equipment manufacturers

The manufacturer will be able to provide details and technical assistance for the installation of their equipment.

In summary: Use a non-service entrance rated docking station. Internally bond the neutral and ground buses/bars of the docking station. That way, the temporary generator will always have a neutral-ground bond when it is connected and the permanent generator is offline.This information is for general guidance only. A qualified electrical engineer should be consulted for the final design and to ensure compliance with all applicable codes and regulations. Flag for review