You're asking a great question about generator classifications and requirements, and it's important to get this right to ensure code compliance and, more importantly, the safety and well-being of the residents.Here's a breakdown of the considerations and how to determine the proper generator classification

1. Understanding Generator Classifications (NEC Article 700, 701, 702)
Emergency Systems (NEC Article 700)

These are legally required systems intended to automatically supply illumination, power, or both to designated areas and equipment essential for safety to human life in the event of failure of the normal supply. Think fire pumps in tall buildings, exit lighting in theaters, etc. This is almost certainly NOT what you need. Emergency systems are often legally mandated by building codes or other regulations.

Legally Required Standby Systems (NEC Article 701)

These are legally required systems that automatically supply power to designated loads when the normal power supply fails. These are installed where local, state, or federal laws require them to maintain essential operations during power outages. Examples include: Sewage treatment plants. Communication systems. Some types of elevators in certain jurisdictions. Sometimes, critical processes in manufacturing. This is the one to be most careful about ruling out.



Optional Standby Systems (NEC Article 702)

These systems supply power to designated loads either automatically or manually. They are intended to supply power to facilities that are not legally required to have standby power. Examples include: Residential generators for comfort and convenience. Power for specific equipment in commercial buildings for business continuity (e.g., computers, freezers). This is likely the category your client's generator will fall into.
2. Key Factors in Determining the Correct Classification



Legal Requirements

This is the most crucial factor.

Is there any local, state, or federal law, code, ordinance, or regulation that mandates a backup water supply system (or specifically, a generator for a water booster pump) for these houses? This is what you need to investigate with the AHJ. Talk to the AHJ (Authority Having Jurisdiction)

This is essential. Contact your local building department, electrical inspector, or fire marshal. Explain the situation and ask if there are any regulations requiring standby power for this type of water supply system. Provide the AHJ with details regarding the elevation, number of homes affected, are the homes equipped with fire sprinkler systems. Their answer is the definitive one. Document their response in writing.



Review Local Codes and Ordinances

Carefully examine local building codes, plumbing codes, fire codes, and any other relevant ordinances. Look for sections that address water supply reliability, especially in areas with varying elevations or fire suppression requirements.

Life Safety Implications

Does the lack of water to these higher elevation houses during a power outage create a direct and immediate threat to life safety? Consider the following:

Fire Suppression

If the houses have fire sprinkler systems, the lack of water pressure during a fire could be catastrophic. This can easily push the system into the "Legally Required Standby" category. The AHJ will be very concerned about this.

Medical Needs

Are there residents with medical conditions that rely on a constant water supply for life-sustaining equipment?

Accessibility

How difficult would it be for emergency services to reach the houses if a fire occurred during a power outage and without adequate water pressure?

Water Pressure Requirements

What is the required water pressure at the highest house to meet code requirements? If a booster pump is essential to meet those requirements, the reliability of that pump becomes more critical.

3. Why Residential Doesn't Automatically Mean "Optional Standby"

You're right that residential generators are often optional standby systems. However, that's a general rule, not an absolute one. A residential generator can be legally required if it serves a load that is mandated by law to have backup power. The critical factor is the load the generator is powering, not the location of the generator (residential vs. commercial).

4. Steps to Take


Contact the AHJ immediately. This is the most important step.2.

Document, Document, Document

Keep detailed records of all conversations with the AHJ, including the date, time, who you spoke with, and what was discussed. Get their determination in writing if possible.3.

Review Local Codes

Thoroughly research all applicable local codes and ordinances.4.

Assess Life Safety

Evaluate the potential life safety implications of a water supply failure. Consider fire suppression, medical needs, and accessibility.5.

Consult with a Qualified Engineer

Consider hiring a professional engineer (PE) experienced in electrical and fire protection systems to review the project and provide a formal opinion on the appropriate generator classification.

In summary: While it might be optional standby, the potential for legally required standby is very high because you're dealing with a water supply system for multiple homes at different elevations. The possibility of fire suppression issues makes this a serious concern, and the AHJ will likely want to be heavily involved in the decision. Err on the side of caution and get a definitive answer from the AHJ before* proceeding. Ignoring this step could result in costly rework or, worse, a dangerous situation. Flag for review