Let's break down your questions about using industrial controls for load stepping on generator systems.1. Is there any issue with using industrial controls to step generator loads on emergency, legally required standby, and optional standby systems? Optional Standby Systems

For optional standby loads, using industrial controls like PLCs or relay systems for load stepping is generally

acceptable and often cost-effective. You have the flexibility to implement your own load management strategy, prioritizing which loads come online first and controlling the timing. The key is to ensure reliability and proper coordination with the generator's control system. Emergency and Legally Required Standby Systems

For these critical systems,

ATS switches are generally preferred and often mandated by codes and regulations. Here's why: Reliability

ATS switches are specifically designed for emergency power transfer and are inherently more reliable than a custom-built PLC or relay-based system. They are robust, tested, and designed for continuous operation in emergency situations.

Simplicity

ATS switches provide a straightforward and dependable transfer mechanism. They're less prone to software glitches or control system failures that could occur with a more complex PLC system.

Code Compliance

Building codes (like the NEC in the US) often have specific requirements for emergency and legally required standby systems, including the use of listed and labeled transfer switches (which typically means ATSs). Using a PLC system might make it harder to demonstrate code compliance.

Speed

ATS switches are designed to transfer loads quickly, minimizing downtime in an emergency. PLC-based systems can be fast, but they may introduce delays that are unacceptable for critical applications.

Overall Considerations



Redundancy

If you do consider using a PLC/relay system for critical loads, redundancy is essential. This would mean having a backup PLC or control system that can take over in case of a failure. This starts increasing the cost and complexity.

Safety

Ensure the control system is designed with safety interlocks and fail-safe mechanisms to prevent damage to the generator or connected equipment in case of a control system malfunction.

Generator Protection

Coordinate your load stepping strategy with the generator's protection relays (overcurrent, overvoltage, etc.) to prevent nuisance tripping.

2. From a contract document standpoint, has anyone seen industrial control systems like PLCs or relay switching systems specified on plan? Was it just a detail/sequence of operation or were you given a detailed wiring diagram?

Yes, it's not uncommon to see industrial control systems specified for load stepping, especially on larger or more complex generator installations. Here's what you might see in contract documents: Sequence of Operation (SOO)

This is the minimum you should expect. The SOO will describe the order in which loads are to be connected, the time delays between steps, and any conditions that need to be met before a load is energized. It will outline the what and when of the load stepping process.

Functional Description

More detailed than the SOO, this describes how the system is supposed to work. It might include information about the PLC's inputs and outputs, the logic used for load control, and any fault detection or alarm features.

One-Line Diagrams

The electrical one-line diagram will show the generators, ATS switches (if any), distribution panels, and the loads that are being stepped. It may not show the detailed wiring of the PLC or relay system, but it should indicate the points where the PLC/relays interface with the electrical system.

Wiring Diagrams/Schematics

Ideally, you'll have detailed wiring diagrams or schematics for the PLC/relay system. These diagrams will show all the connections between the PLC, relays, contactors, sensors, and other components. This is crucial for installation, troubleshooting, and maintenance.

PLC Programming

For PLC-based systems, the contract documents might include the PLC program listing (or a description of its structure). This allows you to understand the control logic and make modifications if necessary. In some cases, the owner may want to retain the rights to the PLC program to ensure future flexibility.

Bill of Materials (BOM)

A list of all the components used in the control system, including the PLC, relays, contactors, power supplies, enclosures, and wiring.

Specification Sections

A dedicated specification section for the load management system outlining performance criteria, component approvals, testing, and commissioning requirements.

Tips for dealing with contract documents



Review carefully

Thoroughly review all contract documents to understand the scope of work and the required functionality of the load management system.

Ask questions

If anything is unclear, don't hesitate to ask the engineer or owner for clarification.

Submittals

Prepare detailed submittals for the proposed control system, including wiring diagrams, PLC programming details (if applicable), and component specifications.*

Testing and Commissioning

Plan for thorough testing and commissioning of the load management system to ensure it operates correctly and meets the specified requirements.

In summary: While using industrial controls for stepping optional standby generator loads is viable, weigh the cost savings against the reliability and code compliance benefits of ATS switches, especially for critical loads. When specified, expect thorough documentation detailing the system's operation and wiring. Flag for review