Common ATS Specification Mistakes — And How to Avoid Them
Specifying an Automatic Transfer Switch (ATS) incorrectly is more common than most project teams realize. The consequences range from failed factory acceptance tests and delayed commissioning to equipment damage and costly field replacements. This article covers the most frequent ATS specification mistakes and how to avoid each one.
1. Undersizing the Current Rating
The most common and most expensive mistake in ATS specification is selecting a unit with an insufficient ampere rating for the actual load.
Why it happens: Project teams often size the ATS based on the connected load at the time of specification, without accounting for future capacity expansion, motor starting currents, or harmonic loading.
How to avoid it: Calculate the maximum demand current including all connected loads, apply a safety margin of at least 20-25%, and confirm whether any loads have high inrush or starting currents. Always specify the ATS for the full switchboard capacity, not just the current load.
2. Ignoring Neutral Switching Requirements
In three-phase four-wire systems, failing to specify a 4-pole ATS when neutral switching is required is a serious oversight that can create safety hazards and compliance failures.
Why it happens: Engineers sometimes default to 3-pole units because they are simpler and less expensive, without fully evaluating the neutral current characteristics.
How to avoid it: In systems with multiple power sources, high neutral current, or where generator and utility neutrals are both solidly grounded, a 4-pole ATS is required. Confirm the grounding scheme before specifying pole configuration.
3. Specifying Open Transition When Closed Transition Is Required
Open transition (break-before-make) transfer is standard for most applications. However, sensitive electronic equipment, process control systems, and motor loads may not tolerate the brief interruption.
Why it happens: Open transition ATS units are more widely available and lower in cost. The distinction is sometimes overlooked in early specification stages.
How to avoid it: Review the sensitivity of connected loads. If the load includes servers, PLCs, variable speed drives, or medical equipment, evaluate whether closed transition transfer is required.
4. Selecting the Wrong IP Rating for the Environment
Specifying an ATS enclosure with an insufficient IP rating for the installation environment leads to premature failure from moisture, dust, and contamination.
Why it happens: Standard indoor enclosures (IP30-IP31) are often specified by default, even when the unit will be installed in an outdoor or industrial environment.
How to avoid it: For outdoor installations, specify a minimum of IP54. For dusty industrial environments, IP55 or higher is typically required. Always verify environmental conditions at site before finalising the enclosure specification.
5. Failing to Confirm Generator Compatibility
An ATS that is not compatible with the generator control system can result in failed automatic start sequences, incorrect transfer logic, or repeated nuisance alarms.
Why it happens: ATS units and generators are sometimes procured from different suppliers without confirming interface compatibility.
How to avoid it: Obtain the generator control panel documentation before specifying the ATS. Confirm the start signal type, ready-to-load signal, and interlocking requirements.
6. Overlooking Certification Requirements for the Destination Country
For export projects, failing to specify the correct certifications for the destination country can result in equipment being held at customs or rejected by local authorities.
Why it happens: Certification requirements are often addressed late in the procurement process, after the equipment has already been ordered.
How to avoid it: Confirm certification requirements (CE, UL, SABS, SASO, etc.) at the start of the specification process. Include them in the technical specification and purchase order.
7. Not Specifying a Manual Bypass for Critical Loads
Without a manual bypass provision, the ATS cannot be maintained or replaced without interrupting the load — unacceptable in hospitals, data centers, or 24/7 manufacturing operations.
Why it happens: Manual bypass options add cost. They are sometimes omitted to reduce budget without considering operational implications.
How to avoid it: For any ATS protecting a critical or continuous load, specify a manual bypass switch — either integral or as a separate bypass panel.
8. Incorrect Transfer Time Specification
Specifying a transfer time that is too slow for the connected load leads to operational problems. Specifying unnecessarily fast transfer adds cost without benefit.
Why it happens: Transfer time requirements are sometimes copied from previous projects without evaluating the specific load characteristics.
How to avoid it: Review the ride-through capability of all critical loads. Standard contactors typically drop out after 50-100ms of power loss. For loads that cannot tolerate any interruption, a static transfer switch may be more appropriate.
How MEGI Consultancy Can Help
MEGI Consultancy provides project-based ATS specification support for industrial, commercial, and infrastructure projects worldwide. We review your requirements, identify specification gaps, and coordinate supply from verified manufacturers with pre-shipment verification and full export documentation.
Contact our team at sales@megiconsultancy.com with your technical requirements. We are happy to provide guidance at no obligation.