Okay, let's break down this situation and explore the options and potential problems. You're right to be cautious – forcing a system to do something it wasn't designed for can lead to trouble.

Understanding the Customer's Motivation and Concerns

The customer's primary concern is backup power in the event of flooding that might disable the Generac. This is a legitimate concern, and finding a solution is important. Before diving into the "how," understanding why they're so set on a portable diesel unit and a manual transfer switch is crucial. Here are some questions to ask: Why diesel? Diesel generators are often chosen for their longevity, fuel efficiency, and ability to handle heavier loads. Is this a perceived reliability issue with the Generac? Why a rental diesel unit? Is it a cost thing? Are they expecting flooding to be a rare occurrence? If it's rare, a permanent diesel backup generator might be overkill and more expensive to maintain. Budget

Knowing the budget will drastically shape the options you can realistically offer.

Long-Term vs. Short-Term

Are they looking for a quick fix or a more permanent, reliable solution?

The Potential Problems with the Customer's Idea

Here's why Generac is likely warning you about problems: Interference with Generac Control System

Modern generators like your Generac have sophisticated control systems that monitor voltage, frequency, and load. By essentially "backfeeding" power into the system, you risk:

Confusing the Generac Controller

The Generac might try to start up while the diesel generator is already supplying power, leading to conflicts and potential damage.

Altered Sensing

The sensors designed to detect a power outage would be bypassed, possibly disabling automatic start and other safety features.

Voltage/Frequency Conflicts

If the diesel generator's output isn't perfectly matched to the Generac's or the utility's, you could have voltage or frequency conflicts that damage equipment.

Lack of Synchronization

The portable generator and the house are NOT syncronized. There may be a brief disruption of power which could be problematic for some equipment.

Warranty Issues

Modifying the system in a way that Generac doesn't approve will almost certainly void the warranty.

Safety Concerns

Backfeeding power without proper safeguards can be extremely dangerous for utility workers and anyone else who might come into contact with the electrical system.

Code Compliance

This type of setup may not meet local electrical codes, and you could face fines or be required to remove the installation.

Addressing the Questions Directly1. Has anyone come across this type of design before? Yes, in a modified version. People have tried similar things, especially in DIY situations. However, it's rarely done in a safe, code-compliant, and warranty-friendly way with modern, electronically controlled generators. People may try to manually start the generator and use the generator output breaker as a make-shift transfer switch. This is obviously not recommended.2. Secondly would the portable backup need fused protection? Absolutely! Any generator supplying power to a building needs overcurrent protection (fuses or circuit breakers) at the generator itself and at the point where it connects to the building's electrical system. This protects both the generator and the building's wiring from overloads and short circuits.

Recommended Alternatives and Considerations

Instead of trying to force this setup, here are some safer and more reliable alternatives:1. Raise the Generac

The most direct solution is to elevate the Generac generator to a level above the expected floodwaters. This could involve a concrete pad, a platform, or even relocation to a higher area on the property. The transfer switch may also have to be moved.

Pros

Simple, reliable, maintains the Generac's functionality, avoids warranty issues.

Cons

Can be expensive, may require permits, aesthetics.2.

Dedicated Portable Generator Inlet with Transfer Switch

This is the safest way to use a portable generator as backup:

Install a Proper Manual Transfer Switch

A transfer switch isolates the generator power from the utility power. This is crucial to prevent backfeeding. The transfer switch should be rated for the full amperage of the circuit(s) you want to power.

Install a Generator Inlet

A generator inlet (like a Reliance Controls inlet box) is a weatherproof receptacle specifically designed for connecting a generator. It's wired directly to the transfer switch.

Run Dedicated Circuits

Decide which circuits in the building are essential during an outage (lights, refrigerator, furnace, etc.). These circuits should be wired to the transfer switch.

Pros

Safe, code-compliant, relatively inexpensive, allows for using any portable generator of the appropriate size.

Cons

Requires manual operation, requires the customer to understand how to operate the transfer switch and generator safely. This would require a SEPARATE generator inlet that is NOT connected to the Generac in any way. Be sure to size the generator properly for the load, and provide all required over-current protection.3.

Full Replacement with a Flood-Resistant Generator

If flooding is a frequent concern, consider replacing the Generac with a generator specifically designed for flood-prone areas. These generators are typically elevated and sealed to protect them from water damage.4.

Battery Backup System

For essential loads like lighting and critical equipment, consider a battery backup system (UPS). These systems provide instant power during an outage and can be used in conjunction with the Generac or a portable generator.

Important Considerations Before Proceeding Permits and Inspections

Any electrical work must be done in compliance with local codes and regulations. This will likely require permits and inspections.

Licensed Electrician

All electrical work should be performed by a licensed and insured electrician.

Load Calculation

Accurately calculate the load you need to power during an outage to ensure the generator is properly sized.*

Safety Training

Provide the customer with thorough training on how to safely operate the generator and transfer switch.

In Summary

While the customer's idea is understandable, it's fraught with potential problems and safety concerns. Backfeeding power into the Generac system is not recommended and could void the warranty and create hazardous situations. Instead, focus on safer and more reliable alternatives like raising the Generac, installing a dedicated portable generator inlet with a transfer switch, or replacing the generator with a flood-resistant model. Prioritize safety, code compliance, and proper installation by a licensed electrician. Flag for review