The transfer time specification for an Automatic Transfer Switch (ATS) from utility to generator power is typically found in several places:1. ATS Product Specification Sheet (Cut Sheet)

This is the most direct and reliable source. The manufacturer will clearly state the typical and maximum transfer times in the product's technical specifications. Look for sections like: "Transfer Time" "Operating Time" "Interruption Time" "Switching Time"Be aware of the definition of this timing, it should be based on ANSI standards and defined.2.

ATS Installation and Operation Manual

The manual often contains performance characteristics, including transfer times.3.

ATS Testing Reports

If the ATS has been factory-tested or field-tested, the test reports should document the actual transfer times achieved during testing. Request this from the manufacturer or vendor.4.

Manufacturer's Website

Look up the specific model number of your ATS on the manufacturer's website. They often have downloadable datasheets and manuals.5.

Single-Line Diagrams and Control Schematics

Sometimes, the single-line diagram or control schematic will reference the ATS model and its transfer time specifications.6.

Project Specifications

In the original project design documents for the building or system, there may be requirements for the ATS transfer time.

Important Considerations



UL Standard

UL 1008 is the standard for transfer switch equipment. Compliant ATSs will be rated according to this standard. UL 1008 does not explicitly mandate a specific transfer time. However, it does define performance requirements and testing procedures. The manufacturer specifies the transfer time based on these tests.

Application

Critical applications (like hospitals or data centers) often have stricter transfer time requirements than general-purpose applications. For example, life safety systems will likely be using Level 1 equipment to meet transfer time requirements.

Types of ATS

There are different types of ATS technology.

Open Transition (Break-Before-Make)

This is the most common type. There's a brief interruption of power during the transfer.

Closed Transition (Make-Before-Break)

These briefly parallel the utility and generator sources. They require careful synchronization and are used where no power interruption is allowed. They might also be called "soft load transfer" switches.Closed-transition ATSs usually have very fast transfer times, often measured in milliseconds, but they require more sophisticated control systems.

Testing and Maintenance

Regular testing of the ATS is crucial to ensure it continues to meet the specified transfer time. Factors like contact wear, control system degradation, and battery condition can affect performance.

How to Address the Inspector's Requirement


Locate Documentation

Start by finding the ATS model number and then search for the manufacturer's specification sheet.2.

Verify Transfer Time

Check the specification sheet to see if the rated transfer time meets the inspector's 10-second requirement.3.

Provide Documentation

Present the documentation to the inspector as proof of compliance.4.

If Exceeds 10 Seconds

If the rated transfer time exceeds 10 seconds, you'll need to: Discuss the discrepancy with the inspector. There might be a misunderstanding of the requirements, or the inspector might be basing the requirement on a specific code or standard. Determine if the ATS can be adjusted. Some ATSs have adjustable settings for transfer delay. However, changing these settings could affect other aspects of the system's performance.* Consider replacing the ATS with one that meets the requirement. This is the most drastic option but may be necessary if the existing ATS cannot meet the performance criteria.5.

Field Testing

If there is concern that the transfer time isn't met under real-world conditions, consider a field test to measure the actual transfer time. This should be performed by a qualified electrician or ATS technician.

Example:

Let's say your ATS is a "Cummins OTTC-100." You would search for the "Cummins OTTC-100 Specification Sheet" online. This sheet should tell you the typical and maximum transfer times.By doing the above, you should be able to determine whether your ATS meets the inspector's requirement and provide the necessary documentation. Remember, safety is paramount, and any electrical work should be performed by qualified personnel. Flag for review