Okay, let's break down the neutral situation in your 400A parallel service with aluminum conductors and address why your power company might suggest only one neutral conductor. I can't make a video right now, but I'll provide a comprehensive explanation you can follow.

Understanding the Basics Parallel Conductors

You're using parallel conductors (two sets of 4/0 Al for the hots and neutrals) to handle the high current of a 400A service. This is common practice because it's often more practical and cost-effective than using a single, very large conductor.

The Role of the Neutral

The neutral conductor is the return path for unbalanced current in a single-phase, 120/240V system (which is typical for residential services). In a perfectly balanced system (where both legs of the 240V are carrying the exact same load), the neutral theoretically wouldn't carry any current. However, in reality, loads are almost never perfectly balanced, so the neutral always carries some current. It also acts as a grounding reference.

NEC Requirements (Simplified)

The National Electrical Code (NEC) is the guiding standard for electrical installations. It mandates sizing conductors based on ampacity (current-carrying capacity), proper installation methods, and safety factors. It also details when and how neutrals can be reduced in size (but we're not talking about that scenario here).

Your Situation: Two Sets of Parallel Conductors

You've run two sets of 4/0 Aluminum conductors in parallel for your hot legs AND two sets of 4/0 Aluminum for your neutrals. This means you essentially have double the neutral capacity that a single 4/0 Aluminum conductor would provide.

Why the Power Company Suggests Only One Neutral

The key reason the power company might suggest only one neutral run back to the transformer has to do with how current divides in parallel conductors and the conservative design practices often employed. Here's the breakdown:1. Current Division in Parallel Conductors

Ideally, in a perfectly installed parallel conductor system, the current will divide equally between the conductors. So, if you're carrying 200 amps on one leg of the 240V, you'd ideally have 100 amps in each of the 4/0 Aluminum conductors of that phase. The same principle applies to the neutral.2.

Redundancy and Safety Factor

Electrical design inherently includes safety factors. By running two full-size neutrals, you have a very robust neutral return path. Even if one neutral conductor were to somehow fail (due to damage, loose connection, etc.), the other would still be able to carry the neutral current.3.

Over-Sizing the Neutral

In many cases, the neutral conductor is already significantly oversized. Loads are rarely perfectly balanced, but often, the imbalance isn't drastic enough to require a neutral conductor that's the same size as the ungrounded (hot) conductors, especially in a residential setting. If you are dealing with heavy non-linear loads, this can change the situation requiring an increase of neutral size.4.

Transformer Design and Grounding

The transformer itself is grounded according to specific requirements (often through a grounding electrode system at the transformer). The neutral conductor you run to the transformer connects to this grounded point. This ensures a low-impedance path for fault currents.

Why Your Installation with Two Neutrals is Likely OK NEC Compliance (Assuming Proper Installation)

The NEC states (with some exceptions) that the neutral conductor should be sized no smaller than the ungrounded conductors. You are far exceeding this requirement.

Superior Performance

Having two full-sized neutrals in parallel provides: Lower impedance neutral return path Increased redundancy, improving reliability.

Power Company Approval

If the power company has explicitly told you it's acceptable to run both neutrals, and you have that in writing or documentation, you are likely safe.

Important Considerations and Questions to Ask Power Company's Specific Reasoning

Press the power company to explain why they suggest only one neutral. Are they simply trying to save you money on materials (which is unlikely, as they would not volunteer this information) or is there a technical reason specific to their system? It's worth understanding their reasoning.

Local Codes and Amendments

Be aware that local electrical codes or amendments to the NEC might exist in your area. Always check with your local electrical inspector for any specific requirements that apply to your installation.

Quality of Installation

Regardless of whether you use one or two neutrals, perfect installation is crucial. This means: Proper terminations: Use correctly sized and installed connectors approved for aluminum conductors. Anti-oxidant paste: Use anti-oxidant paste (like Penetrox) on all aluminum connections to prevent corrosion. Torque: Torque all connections to the manufacturer's specifications. Secure mounting: Properly support and secure all conductors.

Voltage Drop

With parallel conductors, voltage drop is generally less of a concern, but it's still a factor to consider in long runs. Having two neutrals slightly reduces voltage drop on the neutral return.

Harmonics

If there are expected harmonic currents on the neutral (usually only a concern in commercial or industrial settings with many non-linear loads), then the second neutral conductor would carry some of the harmonic currents.

In Summary

Running two full-sized neutrals in parallel is not wrong and is arguably better from a performance and redundancy standpoint. It is highly unlikely to violate NEC, given that it exceeds the minimum neutral size requirement. The power company's suggestion to use only one neutral might be based on their own conservative design philosophy, a desire to save you some money (unlikely), or a specific characteristic of their system. Definitely get clarification from them about why they are making the suggestion.

Recommendation



Document Everything

Keep records of all communications with the power company, including names, dates, and specific statements.

Consult a Qualified Electrician

If you are not completely comfortable with electrical work, hire a licensed and experienced electrician to review your installation and ensure it meets all applicable codes and safety requirements. Have them look at the whole installation not just the neutral.

Follow the NEC

Always adhere to the latest edition of the NEC and any local amendments.*

Err on the Side of Caution: When in doubt, over-sizing conductors and providing additional safety measures is almost always preferable.I hope this clarifies the situation! Let me know if you have any other questions. Flag for review