You're describing a system with a primary and secondary generator, where the secondary kicks in only if the primary fails. This is generally achievable but requires careful planning and adherence to code. Let's break down the considerations

Here's a breakdown of the system and potential issues:
Concept



Primary Generator (Lead)

Normally provides backup power to the load through its ATS.

Secondary Generator (Lag)

Monitors the primary generator's status. If the primary generator fails (e.g., voltage drop, loss of signal), the secondary generator starts and the ATS switches to it.

ATS Configuration

The tricky part is how the ATS units are configured to achieve this. The customer wants one panel and both ATS units to act together for both generators.

Potential Methods to Achieve the Desired Functionality


PLC or Custom Control System



Description

The most reliable and flexible approach. A Programmable Logic Controller (PLC) monitors the status of both generators and the utility power. It controls the ATS units based on a pre-programmed logic sequence.

Operation

Utility failure triggers the primary generator to start. If the primary generator fails after starting and transferring the load, the PLC initiates the secondary generator start sequence and then commands the ATS to switch to the secondary generator. The PLC can also handle time delays, alarms, and other sophisticated functions.

Advantages

Highly customizable, reliable, and provides good monitoring and control.

Disadvantages

More complex and requires a skilled programmer and electrician to implement.2.

Cascade ATS Configuration (Requires Specific ATS Capabilities)



Description

This might be possible with certain ATS units that have advanced control inputs/outputs and can be configured to communicate with each other.

Operation

The primary ATS would operate as normal, detecting utility failure and starting the primary generator. The secondary ATS would monitor the output of the primary generator (voltage, frequency, etc.). If the primary generator fails, the secondary ATS would start its generator and transfer the load.

Challenges



ATS Compatibility

This relies heavily on the capabilities of the ATS units. You need to ensure they can communicate and be configured to act in this way. Not all ATS units have this capability.

Control Wiring

Requires carefully planned control wiring between the two ATS units.

Code and Safety Considerations (Important!) NEC (National Electrical Code) Compliance



Article 700 (Emergency Systems) or 701 (Legally Required Standby Systems)

Determine if this is an emergency system (e.g., hospital) or a legally required standby system (e.g., fire pumps). These articles have very specific requirements for generator systems, testing, and reliability.

700.12(D) or 701.11(C) Overlapping Coverage

Pay attention to sections that discuss multiple generators supplying a system. You need to ensure proper coordination and control.

700.12(B)(3) or 701.11(B)(3) Capacity

The generator(s) must have sufficient capacity to supply all connected loads. You may need to demonstrate this with load calculations.

ATS Listings

The ATS units must be listed for their intended use.

Short-Circuit Current Rating (SCCR)

The ATS units and the panel they feed must have a SCCR adequate for the available fault current.

Grounding

Proper grounding of the generators, ATS units, and panels is essential for safety.

Neutral Switching

Determine if neutral switching is required based on the application and local codes.

Coordination and Selective Coordination



Overcurrent Protection

Ensure that the overcurrent protective devices (circuit breakers or fuses) are properly sized and coordinated to protect the equipment and prevent nuisance tripping. Selective coordination is particularly important in emergency systems.

Load Calculations

Perform accurate load calculations to determine the size of the generators needed. Consider both the connected load and the starting kVA requirements of motors and other equipment.

Transfer Time

The transfer time from utility to generator and generator to generator should be as short as possible, especially for critical loads.

Maintenance and Testing

The system must be regularly tested and maintained to ensure its reliability.

Concerns with the "Series" Description

The customer's description of "wiring in series" is likely not accurate. ATS units don't typically get wired in electrical series in the way that components in a circuit are. Instead, the ATS units control the source of power feeding the load, and their operation is coordinated through control wiring and logic, as described above.

Why Direct Wiring is Not Recommended



Risk of Damage

Directly wiring the outputs of two generators together is very dangerous and can damage the generators due to circulating currents and synchronization issues. The generators must be synchronized before being connected.

ATS Design

ATS units are not designed to be wired in series in the conventional sense. Doing so would likely void their listings and create safety hazards.

Recommendations


Clarify Customer Requirements

Get a very clear understanding of the customer's goals. What loads need backup power? What is the acceptable downtime? Why do they want a lead/lag configuration?2.

Consult with Generator and ATS Manufacturers

Talk to the technical support teams of the generator and ATS manufacturers. They can advise you on the best way to achieve the desired functionality with their equipment. Get written confirmation that the proposed configuration is supported and compliant.3.

Engage a Qualified Electrical Engineer

A qualified electrical engineer with experience in generator systems can perform load calculations, design the control system, specify the equipment, and ensure that the system is code-compliant and safe. This is crucial for a system with this level of complexity.4.

Detailed Drawings and Documentation

Create detailed drawings and documentation of the system, including wiring diagrams, control logic diagrams, and testing procedures.5.

Thorough Testing

After installation, thoroughly test the system under various conditions to ensure that it operates correctly and reliably.

In conclusion, achieving a lead/lag generator setup with ATS units is possible, but it requires careful planning, appropriate equipment, and adherence to code. A PLC-based control system is generally the best approach, but a cascaded ATS configuration might* be feasible with specific ATS models. Do not attempt to directly wire the outputs of the generators together. Consulting with experts and following code requirements are essential for safety and reliability. Flag for review