This is a complex situation with several important considerations, and safety is paramount. Here's a breakdown of the issues, potential solutions, and the importance of a neutral break.

Understanding the Problem Multiple Services

Having two services from the utility (400A and 200A) is the core of the issue. Each service has its own grounded conductor (neutral) connected to the utility's grounding system at the transformer.

Genset as Separately Derived System (SDS)

When the generator is running, it becomes a new source of power. Because of this, it needs its own grounding electrode system. Connecting a generator to an existing system without properly isolating the utility neutral creates a potentially hazardous situation, including:

Parallel Neutral Paths

This is the biggest concern. The generator's neutral will become connected to both utility neutrals. This can lead to circulating currents through the neutral conductors, causing: Overheating of neutral conductors (fire hazard) Voltage imbalances Nuisance tripping of breakers Erroneous operation of sensitive electronic equipment

Potential Differences

The utility and generator neutrals may not be at the exact same potential. Connecting them together can create circulating currents and potential shock hazards.

Backfeed to the Utility

If not properly isolated, the generator could potentially backfeed power into the utility grid, which is extremely dangerous for utility workers.

Existing ATS

The existing 200A, 2-pole ATS does

not switch the neutral. This is a problem, as you need to completely isolate the utility neutral when the generator is running. Cost

Cost is always a factor, but safety should never be compromised. Cutting corners can lead to much larger expenses (and potential liabilities) down the road.

The Importance of a Neutral Break

A neutral break is absolutely critical in this scenario. Here's why: Eliminates Parallel Neutral Paths

By switching the neutral, you ensure that the generator's neutral is only connected to the loads it is serving, and completely disconnected from the utility neutrals. This prevents circulating currents.

Safety

A proper neutral break protects against shock hazards and potential damage to equipment.

Code Compliance

National Electrical Code (NEC) Article 702 (Optional Standby Systems) and Article 250 (Grounding and Bonding) are relevant here. While I don't know your local codes, they almost certainly require the generator to be installed as an SDS with a neutral break. Violating code can lead to fines, insurance issues, and liability.

Proper Operation

Without a neutral break, the generator may not function properly, and connected equipment could be damaged.

Why the "Shared Neutral Path" is a Problem

You ask if a shared neutral path will really be an issue. The answer is a resounding yes. The length of the underground wire run only compounds the problems. The shared neutral between the two services connected to the generator will almost certainly cause problems: Current Imbalance

The currents flowing in the neutral conductors will not be balanced. The neutral conductors could be overloaded.

Voltage Drop

The neutral conductors could experience excessive voltage drop, leading to voltage fluctuations at the loads.

Harmonics

If any of the loads are non-linear (e.g., electronic devices, variable frequency drives), the harmonics will circulate through the neutral conductors, making the problems even worse.

Fault Current Path

In a fault situation, the grounding system relies on a low-impedance path to trip the breaker. Parallel neutral paths can interfere with this, increasing the risk of shock.

Potential Solutions and Considerations1. Recommended (and Code-Compliant) Solution



Replace or Modify the ATS

This is the most robust solution. Replace the existing 2-pole ATS with a 3-pole ATS that switches both phases and the neutral. Alternatively, research if the existing ATS can be modified to include neutral switching.

3-Pole Manual Transfer Switch for the Main Farm Service

This gives the ability to isolate the farm from the utility when running on generator power.

Proper Grounding

Install a new grounding electrode system (ground rod) for the generator, bonded to the generator frame and the generator neutral.

Disconnect the Utility Neutral at the Genset

When the ATS switches to generator power, the utility neutral should be completely disconnected.

Load Calculation

Ensure the generator is properly sized for the total load of both the farm and the hog barns.2.

Less Desirable (But Possibly Cheaper) Solution (Consult with an Electrical Engineer)



Dedicated Generator ATS for Hog Barn

Keep the existing ATS for the Hog Barn, with the addition of a neutral switching relay installed by a qualified electrician.

Manual Transfer Switch for Farm Service

Install a 3-pole manual transfer switch with neutral break for the main farm service.

Proper Grounding

Install a new grounding electrode system (ground rod) for the generator, bonded to the generator frame and the generator neutral.

Important Considerations



Electrical Engineer Consultation

This is a complex installation. It is strongly recommended that you consult with a qualified electrical engineer who can perform load calculations, review the existing wiring, and design a safe and code-compliant system.

Local Codes and AHJ

Contact your local Authority Having Jurisdiction (AHJ, usually the electrical inspector) to discuss the project and ensure compliance with local codes. They may have specific requirements.

Generator Sizing

Make sure the 250A generator is adequately sized to handle the total load of both the farm and the hog barns. A load calculation is essential. Consider future load growth.

Wiring Quality

Inspect the existing wiring, especially the underground run between the farm and hog barns, to ensure it is in good condition and properly sized for the intended load.

Documentation

Keep detailed records of all work performed, including wiring diagrams, load calculations, and inspection reports.

Lockout/Tagout Procedures

Implement proper lockout/tagout procedures to ensure the generator cannot be accidentally energized while utility power is still connected.

Professional Installation

Ensure that all work is performed by a qualified and licensed electrician.

In Conclusion

While the $5,000 cost may seem high, it's a necessary investment to ensure the safety and proper operation of the generator system. Cutting corners could result in significantly higher costs (in terms of property damage, injury, and legal liabilities) in the long run. Prioritize safety, consult with an engineer, and comply with all applicable codes. Flag for review