Applies To

• Galaxy Series UPS (VS, VL, VX, VM, etc.)
• Symmetra MW UPS
• Three‑phase critical power systems
• TN‑S and TN‑C‑S grounded installations
• Single‑mains and dual‑mains UPS architectures

Purpose

This article explains Schneider Electric’s position on downstream protection coordination for UPS systems and why no generic relay‑setting or selective coordination guides exist for Symmetra MW or Galaxy UPS products. It also outlines expected UPS behavior during downstream short‑circuits and lists engineering best practices for designing selective coordination in UPS‑supported electrical systems.

Summary

Schneider Electric does not publish standard relay settings, breaker trip curves, or selective coordination templates for downstream devices fed by Symmetra MW or Galaxy UPS systems.
This is because downstream coordination must always be determined through a site‑specific power system study, which considers the unique characteristics of each installation.

Available UPS documentation (installation manuals, operation manuals, technical specifications) describes system behavior but does not include coordination guidance.
Examples of documentation that confirm this include:

• • Symmetra MW product documentation focuses on modular design, power capacity, and operational behavior without describing downstream coordination requirements.
    
    
  • Symmetra MW technical catalogs describe overload and fault‑clearing capability but provide no relay or breaker setting recommendations.
    
    
  • Galaxy UPS manuals specify that they are not substitutes for detailed site‑specific development or engineering planning.
    
    

Background

In three‑phase UPS systems, the inverter is a current‑limited source, while the static bypass is a high short‑circuit capacity source directly connected to the utility or generator.

Because of this difference:

• • • Downstream protection devices cannot be coordinated based on inverter fault current.
    • Short‑circuit clearing must assume the UPS will transfer to static bypass during severe downstream faults.
    • The correct settings depend on available upstream short‑circuit current, cable lengths, breaker types, load configuration, and grounding system.

UPS Behavior During Downstream Short Circuits

UPS products such as Symmetra MW and Galaxy respond to severe downstream faults as follows:

1. Inverter Fault Current Limitation

Inverters provide limited short‑circuit current and cannot trip high‑rated downstream protective devices.

2. Static Bypass Transfer

For high‑energy faults, the UPS transfers to static bypass, allowing the upstream mains source to supply the necessary fault current for clearing.

This behavior is consistent with Schneider Electric guidance that severe electrical abnormalities trigger protective reactions including source disconnection and bypass transfers.

3. Upstream Device Clearing

Once on bypass, the fault is cleared by the appropriate downstream or upstream protective device based on the system’s selective coordination design.

Why No Generic Relay‑Setting Guide Exists

1. Site Electrical Characteristics Vary Widely

Differences include:

• • • Upstream transformer/generator impedance
    • Cable distances
    • Breaker models and trip units
    • Fault level availability
    • System grounding
    • Load configuration

These factors make it impossible to publish a universal relay or breaker setting guide.

2. Industry Standards Require Engineering Studies

Proper coordination requires:

• • • Short‑circuit study
    • Time‑current curve analysis
    • Selective coordination study
    • Arc‑flash labeling study

These must be performed by qualified engineering professionals.

3. UPS Documentation Is Purposefully General

Per Galaxy UPS documentation, manuals are not substitutes for detailed design or site‑specific engineering.

Recommended Engineering Practices

1. Perform a Full Selective Coordination Study

Include:

• • • Short‑circuit current analysis
    • Time‑current curve (TCC) evaluation
    • Arc flash analysis
    • End‑to‑end system review from utility to final distribution

2. Coordinate Based on BYPASS Short‑Circuit Levels

Because inverter fault current is limited, assume that:

• • • Faults will be cleared while the UPS is in bypass mode.
    • Downstream breakers must be chosen and set based on the upstream/bypass fault capacity.

3. Use Current‑Limiting Protective Devices Where Practicable

This reduces stress on UPS electronics, especially inverter modules and static switch components.

4. Ensure Adequate Inverter Capacity Online

If modular UPS systems operate with minimal active inverter capacity, inverter components are exposed to higher stress before transfer to bypass.

Documentation That Can Be Referenced

The following documentation is appropriate to provide when explaining UPS behavior (but does not include coordination settings):

• • • Symmetra MW Installation Manual
    • Symmetra MW Technical Specifications
    • Galaxy UPS Installation and Operation Manuals
      (documentation reinforces the need for site‑specific engineering studies)
      [productinf...ectric.com]

Available Services

Schneider Electric Professional Services can provide:

• • • Short‑circuit and TCC (Time‑Current Curve) studies
    • Selective coordination studies
    • Arc flash studies
    • UPS behavior and distribution system modeling
    • System design recommendations

These services ensure safe and compliant coordination tailored to each electrical installation.

Conclusion

Schneider Electric does not supply generic relay‑setting or selective coordination guides for Symmetra MW or Galaxy UPS systems due to the highly site‑specific nature of electrical system protection.
Downstream selective coordination must be developed through engineering analysis, using the UPS documentation only as reference for UPS behavior.