Okay, let's break down the code references and your situation to clarify the sizing of your neutral conductor. It's important to be precise with code interpretations.

Your Situation Recap



200 Amp Residential Service

You're dealing with a residential service.

2/0 AWG Feeders

You've used 2/0 AWG conductors for your ungrounded (hot) service entrance conductors, based on 310.15(B)(7) (formerly 310.15(B)(6)), which is specific to residential services.

#4 AWG Neutral

You want to use a #4 AWG neutral.

Inspector Requires #1 AWG Neutral

The inspector is requiring a #1 AWG neutral and hasn't provided a code reference.

250.102(C)(1) & Mike Holt

You believe 250.102(C)(1) allows you to use a #4 AWG neutral (or at least justifies the #1 AWG they are saying). You also cite Mike Holt's material supporting the interpretation of this section related to neutral sizing.

Understanding the Code Sections 310.15(B)(7) (formerly 310.15(B)(6)) - Residential Service Conductors

This section allows for reduced ampacity for service entrance conductors in specific residential applications (single-family dwellings or individual dwelling units of multi-family dwellings). It's this section that allows you to use 2/0 AWG for a 200A service in this situation.

Crucially, this section ONLY applies to the ungrounded (hot) conductors. It does not directly address the neutral conductor size. 250.24(C)(1) - Ungrounded Conductors in Raceway or Cable

This is the section you need to be looking at. To properly size your neutral, the wording from the NEC is below:

(1) General. The size of the grounded conductor shall not be smaller than the required grounding electrode conductor specified in Table 250.66, except that, where connected to a rod, pipe, or plate electrode(s), that portion of the grounded conductor that is the sole connection to the grounding electrode(s) shall not be required to be larger than 6 AWG copper or 4 AWG aluminum. The equipment grounding conductor shall not be smaller than required by 250.
122. 250.102(C)(1) - Grounding Electrode Conductor

This sections discusses the conductor used to connect from a building to earth, or another approved ground source. This is generally used for grounding of metal boxes and equipment.

Analyzing the Situation and Possible Inspector Reasoning1.

Inspector Concern

The inspector is likely concerned that a #4 AWG neutral is insufficient for a 200A service. Their reasoning might stem from a general understanding that the neutral should be sized to handle the potential unbalanced load.2.

250.24(C)(1) - The Correct Section for Neutrals

This is the code section governing the neutral. As noted above, the neutral is based on Table 250.66.
3.

Unbalanced Load

The neutral conductor carries the unbalanced load in a system. In a purely balanced 200A, 240V (or 120/240V) single-phase residential service, the neutral would carry zero current. However, realistically, loads are never perfectly balanced. Appliances and circuits draw different amounts of current on each leg, and the neutral carries the difference.

Addressing the Inspector1.

Be Respectful and Inquire

Start by respectfully asking the inspector for the specific code section they are using to justify the #1 AWG requirement. Understanding their reasoning is crucial.2.

Present Your Case Based on 250.24(C)(1)

Explain that you've sized the ungrounded conductors per 310.15(B)(7), which allows the 2/0 AWG for a 200A residential service. Then, reference Table 250.66, which is determined based on the ungrounded conductors.
3.

Example Scenario

"Inspector, I've used 2/0 for my ungrounded service entrance conductors based on 310.15(B)(7). According to 250.24(C)(1), I use Table 250.
66. Based on the 2/0, Table 250.66 requires at least a #4 for the neutral. Can you help me understand where I am mistaken?"

Important Considerations

Local Amendments

Always be aware of local amendments to the NEC. Some jurisdictions might have stricter requirements than the national code.

Inspector Discretion: Ultimately, the AHJ (Authority Having Jurisdiction) has the final say on code interpretation.I hope this helps clarify the code sections and gives you a better understanding of how to approach the inspector. Good luck! Flag for review