Okay, let's break down the connection of your generator to your service panel using an interlock kit, and address the neutral bonding question, especially considering the outdoor location.

Summary of your plan



Generator

7500W running / 9500W peak, 240V, 31A.

Interlock Kit

GE (specific model not provided).

Wiring

#8 Copper (based on 31A x 1.15 = 35.65A).

Breaker

30A, 2-pole in the main panel.

Connection

L14-30R receptacle on the generator to a corresponding L14-30P plug connected to the interlock kit.

Analysis and Considerations


Wiring and Breaker Size

Your calculation for wire size is on the right track, but you're using a 1.15 factor. This factor is often used for continuous load calculations (loads expected to run for 3 hours or more). Generators are often used for backup power during outages, which can be considered continuous, so using this factor is a good, conservative approach. #8 AWG copper is appropriate for a 30A circuit (and even a 35A circuit). However, the breaker at the main panel must be rated for the wire and the receptacle. Your breaker selection of a 30A breaker is correct. Verify the amperage rating of the L14-30R receptacle on the generator. It should be rated for 30A.2.

Neutral Bonding - The Critical Question



The Goal

You want one and only one neutral-to-ground bond in your system. If you have two, you create parallel neutral paths, which can lead to circulating currents, overheating, and potentially dangerous conditions.

Your Main Panel

Your main service panel is the primary point of neutral-to-ground bonding. This is where the neutral conductor from the utility is bonded to the ground/earthing system.

The Generator's Neutral Bonding

Here's where the confusion arises. The question is whether the generator's neutral is already bonded to its frame/ground. If it is bonded, you must disconnect this bond when using it as a separately derived system connected to your main panel.

NEC References: You are correct to be looking at NEC 250.30 and 250.
34. The crux of it is that a generator used to supply a building wiring system is considered a "separately derived system" and therefore must follow those rules. How to Determine if the Generator's Neutral is Bonded



Check the Generator's Manual

This is the most important step. The manual should explicitly state whether the neutral is bonded to the frame. Look for a section on grounding.

Visual Inspection

Sometimes, you can visually inspect the generator. Look for a green grounding screw or strap connecting the neutral conductor (white wire) to the generator's metal frame. This can be inside the generator's control panel.

WARNING

Disconnect the generator from any power source before attempting any visual inspection.



Continuity Test

If the manual is unclear, and you are comfortable using a multimeter safely, you can perform a continuity test. Disconnect the generator from any power source. Set your multimeter to continuity/resistance. Place one probe on the neutral conductor of the L14-30R receptacle, and the other probe on the generator's metal frame. If you get a reading close to zero ohms (or a beep on a continuity tester), the neutral is bonded.3.

If the Generator's Neutral Is Bonded (Most Common)



You MUST Disconnect the Bond

This is the most common scenario. You will need to permanently disconnect the neutral-to-frame bond inside the generator. Refer to the generator's manual for instructions. This is often a simple matter of removing a bonding strap or screw. Do not simply cut the wire; properly disconnect it.4.

If the Generator's Neutral is Not Bonded

This is rare, but possible. If the generator's neutral is not bonded, you must drive a grounding electrode (ground rod) at the generator's location and bond the generator frame to that ground rod. This is to ensure safety in case of a fault within the generator.5.

Grounding Electrode System at Generator Location



NEC 250.34(C). The NEC generally does not require a grounding electrode (ground rod) at a portable generator that only supplies equipment connected through cord and plug. However, since you are connecting to your service panel through an interlock, the exception doesn't apply. A ground rod is required6.

Outdoor Location Considerations



Weather Protection

Since the generator is outside, ensure it is protected from the elements (rain, snow, etc.). Consider a generator enclosure or a purpose-built generator shed. Never operate a generator in an enclosed space due to the risk of carbon monoxide poisoning.

Extension Cord

Do not use extension cords to connect the generator to the L14-30 inlet connected to your panel. Run the correct wire size.

Wiring diagram

Generator L14-30R <--> Cord with L14-30P <--> Interlock Kit Inlet <--> Breaker in Main Panel

In Summary: Steps to take1.

Consult the Generator Manual

This is the single most important step.2.

Determine Neutral Bonding

Based on the manual and/or a continuity test, determine if the generator's neutral is bonded to the frame.3.

Disconnect (If Necessary)

If the neutral is bonded, disconnect it permanently and properly.4.

Run the Wiring

Install the appropriate gauge wiring to the interlock kit inlet, and connect to the breaker.5.

Test

After everything is connected, test the system.

Disclaimer: Working with electricity can be dangerous. If you are not comfortable performing these tasks, consult a qualified electrician. This information is for general guidance only and should not be considered a substitute for professional advice. Local codes and regulations may vary. Flag for review