Okay, let's break down these questions regarding your generator feed and grounding.

Question 1: 3 Sets of 3/0 vs. 2 Sets of 350 kcmil

Here's a comparison to help you decide: Current Capacity (Ampacity)

3 sets of 3/0 Copper (THHN in conduit): Assuming 90°C rating and derating per 310.15 (B)(3)(a) based on the number of current-carrying conductors in the raceway, you'll need to check the exact ampacity after derating. A very rough estimate for each 3/0 would be around 200-225A per conductor after derating. 3 sets of 3/0 would get you close to, but likely not quite 600A. You will need to do the actual calculations to ensure you have adequate ampacity, which depends on conditions of use and cable type. 2 sets of 350 kcmil Copper (THHN in conduit): Similar to above, you need to do the ampacity derating calcs. A very rough estimate for each 350 would be around 280-300A per conductor after derating. 2 sets of 350 would likely get you to 600A after derating, though again, you would need to check the specific conditions.

Ease of Handling (Your Primary Concern)

3/0 is significantly easier to pull, bend, and terminate than 350 kcmil. This is a major advantage, especially with limited help and a long, complex run. The smaller diameter and greater flexibility of 3/0 will make the job much physically easier. 350 kcmil is heavier and stiffer, requiring more strength and more careful bending. This will be harder to manage, especially going up the building and through the attic.

Cost

3/0 copper is generally less expensive per foot than 350 kcmil copper. However, you'll be using more feet of it. Get actual quotes to compare the total material cost.

Voltage Drop

For long runs, voltage drop is a critical consideration. Larger conductors (350 kcmil) will have less voltage drop than smaller conductors (3/0) for the same current. Use a voltage drop calculator to determine if either conductor size meets code requirements for your length and load. There are many online.

Termination Space

Check the termination lugs on your generator and the other end of the run (at the load). Ensure that your lugs can accommodate the conductors you select. Terminating 350 kcmil can sometimes be more challenging in tight spaces.

Recommendation

Given your emphasis on ease of handling, and the fact that you have minimal help, 3 sets of 3/0 is likely the better choice, provided you can meet the ampacity and voltage drop requirements after doing the proper calculations. The physical strain of working with the larger conductors will slow you down and increase the risk of injury. If you find that the 3/0s don't have enough capacity, you may need to increase the number of sets to 4. This will likely still be easier than running 2 sets of 350's.

Crucially, DO THE AMPACITY DERATING AND VOLTAGE DROP CALCULATIONS before making a final decision!Question 2: Grounding Electrode Conductor (EGC) in Parallel Runs

Your understanding is mostly correct, with a small but important clarification: EGC Sizing

You are correct that the EGC size is based on the overcurrent protective device (OCPD) protecting the circuit, per NEC 250.122. For a 600A OCPD, 1 AWG copper is indeed the minimum size required. 250.122(B) requires that the EGC be increased in size proportionately to the increase in size of the ungrounded conductors.

EGC in Each Raceway



YES, an EGC is required in each raceway. NEC 300.3(B) and 250.122(F) explicitly state this. The EGC must be run in parallel with the phase conductors in each conduit or raceway. Important Notes

The EGC in each raceway must be at least 1/N of the size determined in 250.122, where N is the number of parallel sets. For 3 parallel sets of 3/0, you would need three 1 AWG EGCs. If you go with 4 parallel sets of 3/0, you would need four 1 AWG EGCs.

NEC 250.122(F)(1) states that if the parallel conductors are installed in separate raceways or cables, the equipment grounding conductor shall be installed in the same raceway or cable as the circuit conductors.In summary, for a 600A feed using parallel conductors, you MUST have an EGC sized according to 250.122 in each* raceway containing the phase conductors. Each EGC must be a minimum of 1 awg if you are running 3 sets of parallel conductors. Flag for review