Single-Phase vs Three-Phase UPS:
Choosing the Architecture
UPS systems are described by their input and output phases: 1:1, 3:1 or 3:3. Choosing the right architecture depends on your electrical supply, the size of the load and whether your critical equipment is single-phase or three-phase. Here is how to decide.
Phase configuration is written as input:output. A 1:1 UPS takes single-phase in and delivers single-phase out. A 3:1 UPS takes three-phase in and delivers single-phase out. A 3:3 UPS is three-phase in and three-phase out. Picking the right one avoids oversizing, phase imbalance and installation problems.
Single-phase (1:1) UPS
Single-phase UPS systems cover roughly 600 VA to 10 kVA and protect single-phase loads. Routing by use case: LT1E (line-interactive) for small office, POS, CCTV, routers and small IT loads; TM11E (online tower) for servers, network rooms and critical single-phase loads; RM11E (online rack/tower) for IT racks; RM11E PRO for rack lithium options by model; and the PowTerra outdoor cabinet for project-configured outdoor sites (not a standard indoor 1:1 UPS).
Three-phase input, single-phase output (3:1)
A 3:1 UPS is the right answer when the building has a three-phase supply but the critical equipment is single-phase. Drawing from all three phases balances the load on the incoming supply and supports larger single-phase output than a 1:1 unit. ATENCO’s TM31E (10 to 20 kVA tower) and RM31E (6 to 10 kVA rack) are 3:1 online UPS systems for exactly this case.
Three-phase input and output (3:3)
When both the supply and the load are three-phase, you need a 3:3 UPS. This covers data-center halls, industrial plants, large telecom rooms and building services. ATENCO 3:3 architecture options include the TM33E 10–40 kVA and TM33E 50–200 kVA towers, the RM33E 10–50 kVA rack, the transformer-based TM33-ET 10–800 kVA for galvanic isolation, and TM66E modular UPS platforms up to 1.2 MW.
Comparison at a glance
| Architecture | Input : Output | Typical range | Best for |
|---|---|---|---|
| Single-phase | 1 : 1 | 1 to 10 kVA | Servers, racks, edge IT, security, small sites |
| Three-phase input | 3 : 1 | 6 to 20 kVA | Three-phase supply feeding single-phase critical loads |
| Three-phase | 3 : 3 | 10 kVA to 1.2 MW | Data centers, industrial, large telecom, building services |
How to choose
- Identify your supply. Single-phase or three-phase at the point of installation?
- Identify your load. Is the critical equipment single-phase or three-phase?
- Match them. Single-phase supply and load → 1:1. Three-phase supply with single-phase critical load → 3:1. Three-phase supply and load → 3:3.
- Check the size. Above around 10 kVA, three-phase input often makes sense for supply balance, subject to the site electrical system and load type.
If you are not sure how your supply and load map together, the UPS Selector filters by phase, or you can send the details to ATENCO for a project recommendation. See also the deeper dive on line-interactive vs online topology.
Key takeaways
- Phase notation is input:output – 1:1, 3:1 or 3:3.
- 1:1 single-phase covers about 600 VA to 10 kVA across LT1E line-interactive and TM11E / RM11E / RM11E PRO online series.
- 3:1 suits a three-phase supply feeding single-phase critical loads (TM31E tower / RM31E rack).
- 3:3 covers three-phase supply and load from 10 kVA up to 1.2 MW – including TM33E, RM33E, TM33-ET (transformer-based) and TM66E modular platforms.
Which ATENCO UPS Series Fits Each Phase Architecture?
LT1E 600 VA to 3 kVA
Best for small office, POS, CCTV, routers and small IT loads where AVR backup is enough.
TM11E 1 to 10 kVA
Online tower UPS for servers, network rooms, security systems and critical single-phase loads.
RM11E / RM11E PRO
Rack/tower online UPS for IT racks; RM11E PRO covers the lithium rack option by model.
TM31E / RM31E
Three-phase input with single-phase output for sites with 3-phase supply feeding 1-phase critical loads.
TM33E / RM33E
Three-phase online UPS for data rooms, telecom, industrial control and facility critical-power loads.
TM33-ET 10–800 kVA
Transformer-based 3:3 UPS for galvanic isolation, neutral re-derivation and isolation-specific projects.
TM66E Modular UPS
Scalable modular three-phase UPS platforms from compact systems to 1.2 MW centralized critical power.
Related Guides
Need Help Choosing the Right UPS?
Tell ATENCO your load, runtime target, input/output phase and site conditions. ATENCO will help shortlist the right UPS architecture and product series, or you can compare options in the UPS Selector.