You're asking about the legality and safety of using a single neutral conductor to a PV disconnect instead of running both the incoming and outgoing neutral conductors through the disconnect. Here's a breakdown of the code implications and best practices

Likely a Code Violation and Potentially Unsafe

Generally, using a single neutral conductor in this manner is a violation of the National Electrical Code (NEC) and poses a safety risk. Here's why: NEC 250.24(C) (Grounded Conductor for Alternating-Current Systems)

This section requires that the grounded (neutral) conductor be run to the disconnecting means for the premises or building. While you have a neutral to the disconnect, if it's not through the disconnect, you are violating the need for the neutral to be at the PV disconnect.

NEC 690.13(B) (Equipment)

This section addresses disconnecting means for PV systems. It usually requires all current-carrying conductors (including the neutral in some systems) to be opened simultaneously by the disconnect. Your setup does not open the neutral.

Neutral Current Path

The neutral conductor provides the return path for unbalanced current. By not having a continuous, controlled neutral path through the disconnect, you risk the current finding alternative paths, which could be dangerous. If the hot conductors of the system are disconnected at the disconnect for any reason, then the neutral will be carrying the entire return current.

Voltage Imbalance and Equipment Damage

A broken or compromised neutral can lead to significant voltage imbalances in the electrical system, potentially damaging equipment.

Arcing and Fire Hazard

An interrupted neutral connection can create arcing faults, posing a fire hazard.

Why You Need to Run the Neutral Through the Disconnect

The purpose of the disconnect is to completely isolate the PV system from the rest of the electrical system for safety during maintenance or emergencies. This includes the neutral conductor. Opening the neutral at the same time as the ungrounded (hot) conductors ensures no current is flowing in the PV system.

Acceptable Solutions

Here's how to properly handle the neutral connection for a PV disconnect:1. Run the Neutral Through the Disconnect

This is the standard and safest approach. Run both the incoming and outgoing neutral conductors through the PV disconnect switch. The disconnect should interrupt all current-carrying conductors simultaneously (including the neutral if required by the system design). This ensures complete isolation.2.

Neutral Disconnect Requirements by Inverter Type



Transformerless Inverters (Most Common)

Transformerless inverters do not isolate the DC side from the AC side. Therefore, the neutral must be switched in the disconnect per NEC 690.35(D)(3).

Transformer-Based Inverters

Some older inverters use transformers that provide galvanic isolation between the DC and AC sides. In this case, the neutral is not required to be switched at the disconnect if and only if the inverter is specifically designed and listed to not require a switched neutral. This is

rare with modern inverters. Always check the inverter documentation. Microinverters

Microinverters generally follow the same rules as transformerless inverters. The neutral is typically switched at the AC disconnect.

Considerations and Recommendations



Local Codes and AHJ (Authority Having Jurisdiction)

Always check with your local electrical inspector or AHJ. They have the final say on code compliance. They may have specific interpretations or requirements beyond the NEC.

Inverter Manufacturer's Instructions

Carefully review the inverter manufacturer's installation manual. It will specify the required wiring configuration, including neutral connections and disconnect requirements.

Wire Gauge

Ensure the neutral conductor is properly sized to handle the expected current. Use the same size conductor as the ungrounded (hot) conductors, or as determined by calculations based on the anticipated load.

Voltage Drop

If the distance to the disconnect is long, consider voltage drop. You may need to upsize the conductors to minimize voltage drop.

Marking

Always properly label all conductors and the disconnect itself for clarity and safety.

In Summary:

While your intent to simplify the wiring is understandable, using a single neutral conductor and bypassing the disconnect is likely a code violation and a safety hazard. Always run the neutral conductor through the disconnect switch unless the inverter is specifically designed* to not require it, and you have documentation from the manufacturer to prove it. Prioritize safety and code compliance. Consult with a qualified electrician and your local AHJ to ensure your PV system is installed correctly and safely. Flag for review