ATS BMS Integration Guide for Commercial Buildings

ATS BMS integration means connecting an automatic transfer switch to a building management system so the BMS can receive documented ATS status, alarm or operating information. The interface must be planned around the actual ATS controller and the project's required BMS points.

For LEEYEE compact 2P and 4P ATS projects, BMS functionality should be treated as a project-specific interface requirement, not assumed as a standard function of the compact transfer switch. First confirm what the building needs to monitor. Then confirm whether the selected ATS/controller provides the required contact outputs, communication interface or another approved integration method.

How This Guide Applies to a Compact 2P or 4P LEEYEE ATS

A compact ATS and a BMS communication system solve two different parts of the project. The ATS performs the source-transfer function. The BMS, when required, supervises selected operating information through interfaces provided by the ATS/controller.

The compact LEEYEE product format uses a local front operating interface with automatic/manual operation and local source or load status indication. These visible local functions should not be confused with an external BMS interface.

Why Does a Commercial Building BMS Need ATS Status?

A building management system gives operators central visibility of important equipment conditions. For an ATS, the useful question is usually: Which transfer-system conditions does the operator need to see remotely?

On suitably equipped controllers, documented information may include source availability, switch position, operating mode, alarm status or transfer-related information.[4][5] These manufacturer examples show what is possible on particular controllers. They do not prove that the same points are available on every compact ATS.

What ATS Points Should the BMS Monitor?

Build the point list around the facility's actual operating needs. Then match each requested point to a real output, terminal or documented communication value.

This is an example engineering point list. Eaton and Socomec documentation demonstrate comparable source, operating-mode, switch-position and alarm information on specific controller families.[4][5]

What Is a Dry Contact in ATS BMS Integration?

A dry contact is a voltage-free switching contact that changes between open and closed states. A BMS or PLC can monitor that state through a suitable digital input.

Dry contacts are useful when the project only needs a small number of simple status points. Typical examples may include source status, ATS position or a common alarm—but only if the selected ATS/controller actually provides those outputs.

Do not assume that the local indicator lamps on a compact ATS automatically have corresponding external dry-contact terminals.

Dry Contact vs RS485 / Modbus: Which Method Fits the Project?

RS485 is not the same thing as Modbus. Modbus is an application-layer messaging protocol, while serial implementations use a separate serial-line specification.[2]

Therefore, the presence of an RS485 terminal or connector alone would not prove that a controller supports the Modbus data required by the project. The communication protocol and register map must be verified.

How to Build an ATS BMS Point List

The best sequence is to start with what the BMS needs to know, then work backward to the ATS/controller.

1. Define the Required BMS Information

   Identify the real operating need: source availability, transfer position, alarm, operating mode or another specific status.

2. Create a Clear Point Name

   Use names such as “Normal Source Available,” “Emergency Source Available,” “Load on Emergency” or “ATS Common Alarm.”

3. Match the Point to a Real ATS Output

   Identify the terminal, contact, controller output or communication register that provides the point. If no documentation supports it, do not assume it is available.

4. Select the Interface

   Choose hardwired contacts, documented RS485/Modbus communication or another approved integration architecture according to the actual product capability.

5. Document the BMS Mapping

   Record point name, signal type, NO/NC logic where relevant, terminal or register reference, alarm meaning and any configuration requirement.

6. Verify During Commissioning

   Check that BMS indications correspond to the actual source condition, switch position and alarm state. Communication points must also match the final controller configuration.

Monitoring an ATS Is Not the Same as Controlling It

Commercial ATS controller documentation shows that some advanced controllers provide both status registers and selected control functions.[4][5] This does not mean that those functions exist on every compact ATS.

What If the Building BMS Uses BACnet?

BACnet is defined by ANSI/ASHRAE Standard 135 as a data communication protocol for building automation and control networks.[3]

If a project uses BACnet, the ATS does not necessarily need native BACnet support. On systems that provide another documented protocol, a suitable gateway may sometimes be used. Eaton, for example, documents ATS communication architectures involving Modbus and building-management gateways.[4]

Do Not Confuse ATS Information with Generator Information

In a generator-backed system, the ATS and generator controller are separate information sources. Depending on the controller, an ATS may provide emergency-source status or generator-start-related information.[4][5]

Detailed generator information—such as engine conditions, fuel information, battery data or engine-controller faults—should not automatically be treated as ATS data. If these points are required, identify whether they come from the generator controller, ATS controller or another gateway.

How IEC 60947-6-1 Relates to the Project

IEC 60947-6-1:2026 applies to transfer switching equipment used to transfer a load between power-supply sources and includes provisions covering automatic transfer switching equipment and controllers.[1]

Compliance with an ATS product standard does not prove that a particular dry contact, Modbus register, BACnet interface or remote-control command is provided. These functions remain model- and controller-specific project items.

Common ATS BMS Integration Mistakes

Assuming the compact ATS front panel proves BMS capability

Local Auto/Manual controls and status lamps show local operating information. They do not prove the existence of corresponding remote contacts or communication registers.

Approving an ATS because a quotation says “BMS compatible”

The quotation should identify the actual BMS points, terminals or communication protocol. A general phrase is not enough for engineering approval.

Assuming RS485 automatically means Modbus

Confirm the actual protocol and register documentation rather than relying only on the physical interface.[2]

Creating the BMS point list after purchasing the ATS

Define the required monitoring points before the ATS/controller is finalized. Otherwise, the project may discover too late that an output or communication function is unavailable.

Using a compact ATS where the project requires a more advanced control architecture

If the project requires extensive network monitoring, remote commands, sophisticated event data, bypass functions or high-criticality system features, confirm whether the compact ATS architecture is appropriate before specifying it.

ATS BMS Integration FAQ