You're on the right track, but let's break down where the difference is coming from. You're focusing on the feeder size, but the key is the overcurrent protection protecting that feeder.Here's the correct reasoning and relevant code sections:1. The Key: Overcurrent Protection Device - The size of the equipment bonding jumper is based on the rating of the overcurrent device protecting the conductors, not the conductor size itself. This is a critical concept. In your question, the feeder is protected by a 225-amp breaker.2. Table 250.102(C)(1) for Equipment Bonding Jumpers - This is the correct table to use. Look at the left-hand column, "Rating or Setting of Automatic Overcurrent Protective Device in Circuit Ahead of Equipment, Conduit, etc., Not Exceeding (Amperes)."3. Finding the Correct Row - You're looking for the row where 225 amps falls. The table will likely show ranges like: 151-200 201-300 (This is the one!)4. Reading the Table - Across from the "201-300" row, the column for "Copper" will specify the required size of the equipment bonding jumper. In this case, it should be #4 CopperWhy you were initially off

You correctly identified the feeder conductor size from Table 310.16 based on its ampacity.

However, you incorrectly based your answer on the size of the feeder conductors. The code dictates that it's the overcurrent protection that determines the bonding jumper size.

Important Considerations



Main Bonding Jumper vs. Equipment Bonding Jumper

Make sure you understand the difference. The main bonding jumper (at the service equipment) is sized based on the service entrance conductors. The equipment bonding jumper (like the one in your question) is sized based on the overcurrent protection.

Local Amendments

Be aware that some jurisdictions may have local amendments to the NEC, which could change the required bonding jumper sizes. Always check with your local electrical inspector or authority having jurisdiction (AHJ) to confirm the requirements in your area.

Minimum vs. Requirement The table provides the minimum required size. You are always permitted to upsize the conductor.

In summary, the answer should be #4 copper because the 225-amp breaker is what determines the size of the equipment grounding conductor (EGC), not the 250 kcmil conductors. Flag for review