Transformer Fundamentals
Single Phase vs Three Phase Power
Compare the electrical arrangement, rated voltage and demand before deciding which transformer family fits the installation.
Choose single phase or three phase equipment from the available supply and the loads it must serve. Compare the electrical arrangement, rated voltage and demand before deciding which transformer family fits the installation.
Start with supply and load requirements
A single-phase load uses one alternating voltage across its terminals. A balanced three-phase system has three phase voltages displaced by 120 degrees. Check the utility service and every major load nameplate, including motors, drives and auxiliary single-phase loads.
Compare current on a consistent basis
For an illustrative 100 kVA load at 480 V, single-phase current is about 208 A; balanced three-phase line current is about 120 A. The comparison uses the same apparent power and line voltage. Conductor quantities, loading balance and installation conditions belong to the complete design.
| Item or condition | What to compare | Input or result |
|---|---|---|
| Single phase | 100 kVA at 480 V | About 208 A illustrative current |
| Balanced three phase | 100 kVA at 480 V line-to-line | About 120 A illustrative line current |
| Selection inputs | Utility service and load nameplates | Phase, voltage and demand |
Example — same apparent power and voltage
Single phase: I = 100,000 VA / 480 V ≈ 208 A
Balanced three phase: I = 100,000 VA / (√3 × 480 V) ≈ 120 A
These illustrative currents use apparent power and the stated voltage basis. Confirm system voltage, load, conductors and protective-device sizing with the project designer.
Prepare the product selection
Use a single-phase pad-mounted family where the service and load require that configuration. Use a three-phase unit for a specified three-phase supply. A transformer connection must match the network and equipment; phase conversion is a separate system design decision.
For a closer look at balanced three-phase ratings, see Three Phase Transformers and Connections.
Frequently Asked Questions
Which is better for my site?
Match the utility supply, load requirements and expansion plan. The appropriate choice follows those project conditions.
Can a three-phase system serve single-phase loads?
It can when the specified voltage and connection support them. Allocate the loads and assess phase balance in the design.
Match the transformer to the service
Share the utility service, voltage basis, load schedule, major motor and drive ratings, demand and installation arrangement.