Application Data

NOTE: For transformers with non-standard kVA ratings, increase the size to the next largest standard rating.

Single-Phase Connections—240 x 480 to 120/240 V

The following diagrams show special ways that standard 240 x 480-120/240 single phase transformers can be connected for special applications.

Two unit transformers connected in “Hoppy Hookup” for single phase lighting and single phase power loads from three phase supply.

This connection allows changeover of existing single phase service to three phase service without changing existing lighting panels or secondary neutrals. The neutral current will be the same as with the original single phase service rather than increasing by the factor of 1.73 (= √3).

NOTE: The primary common current will be the √3 x the current in the other two lines. For 480 V primary—Connect H2 to H3 in each unit. For 240 V primary—Connect H3 to H1 and H2 to H4 in each unit. Secondary kVA capacity = Total nameplate kVA of both transformers.

Three Phase Connections

NOTE: For transformers with non-standard kVA ratings, increase the size to the next largest standard rating, using single phase 240 x 480 to 120/240.

Three Units Connected Delta-Wye

For 480 V Delta primary—Connect H3 to H2 in each phase
For 240 V Delta primary—Connect H3 to H1 and H2 to H4 in each phase
For 416Y/240 V secondary—Connect X3 to X2 in each phase
For 208Y/120 V secondary—Connect X3 to X1 and X2 to X4 in each phase
Three phase kVA capacity = Total kVA of three units

Three Units Connected Delta-Delta

For 480 V Delta primary—Connect H3 to H2 in each phase
For 240 V Delta primary—Connect H3 to H1 and H2 to H4 in each phase
For 240 V Delta secondary—Connect X3 to X2 in each phase
For 120 V Delta secondary—Connect X3 to X1 and X2 to X4 in each phase

Two Units Connected Open-Delta

For 480 V Delta primary—Connect H3 to H2 in each phase
For 240 V Delta primary—Connect H3 to H1 and H2 to H4 in each phase
For 240 V Delta secondary—Connect X3 to X2 in each phase
For 120 V Delta secondary—Connect X3 to X1 and X2 to X4 in each phase
Three Phase kVA capacity = Total kVA of Two units x 0.86

Two Units Connected as Open Delta Auto Transformer for Three Phase Operation for 240–480 or 480–240 kVA Capacity = (Total kVA of Both Units x 2) x .86

Two Units Connected as Open-Delta Auto Transformer for Three Phase Operation for 600–480, 480–600, 480–380, or 380–480

Two Units Connected as Open-Delta Auto Transformer for Three Phase Operation for 575–480 or 480–400

The following diagram shows special ways that standard 600–120/240 single phase transformers can be connected for special applications.