Voltages for 4-wire delta and 4-wire open delta are the same, where Bø is the {Orange} “high leg”
There are three "phase-to-phase" voltages
-
Aø-Bø 240V
Bø-Cø 240V
Cø-Aø 240V
There are three "phase-to-neutral" voltages
-
Aø-N 120V
Bø-N 208V
Cø-N 120V
Reference
99 NEC Article 384 — Switchboards and Panelboards §384-3 Support and Arrangement of Busbars and Conductors (e) High-Leg Marking (f) Phase Arrangement Note that Bø is the standard “high leg” per NEC.
Some older utility standards used [and may still require] Cø as the “high leg” in their meter sockets and related equipment.
480V 4-wire delta systems are rare and not generally used on new equipment, or offered by utilities for new service.
ANSI Standard C84.1-1995
Electrical Power Systems and Equipment--Voltage Ratings (60Hz) Table 1 —
Standard Nominal Systems Voltage and Voltages Ranges lists a nominal system voltage as
240/120 for 3ø 4-wire
delta systems.
https://www.electrical-contractor.net/ubb/Forum15/HTML/000054.html The first two diagrams show delta and open-delta secondary connections. Voltage relationships are the same. Open delta is useful for smaller loads.
http://www.cooperpower.com/Library/pdf/R201902.pdf Compare figures 11 using three 1ø transformers and figure 15 using two 1ø transformers. Both produce the same 240/120V 4-wire ∆ 3ø voltage.
http://home.att.net/~benmiller/elecsys.htm
Compare illustrations: CENTER-TAP GROUNDED DELTA and CENTER-TAP GROUNDED OPEN DELTA
[This message has been edited by Bjarney (edited 08-18-2003).]
