Delta vs Wye: Line and Phase Calculator
Convert between line and phase values for wye (star) and delta three-phase configurations. The √3 factor shows up in the voltage relationship for wye and in the current relationship for delta — mixing them up is one of the most common sources of a calculation that is off by 1.732.
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Delta vs wye at a glance
| Property | Wye (Star) | Delta |
|---|---|---|
| Line vs phase voltage | V_line = √3 × V_phase | V_line = V_phase |
| Line vs phase current | I_line = I_phase | I_line = √3 × I_phase |
| Neutral available | Yes — serves single-phase loads | No (unless center-tapped) |
| Grounding | Solid reference at the neutral point | Ungrounded or corner-grounded |
| Triplen harmonics | Sum into the neutral conductor | Circulate within the delta |
| Typical use | Building distribution, 208Y/120, 480Y/277 | Transformer primaries, motor loads, older plants |
Why the √3 moves between voltage and current
In a wye connection, each winding sits between one line and the shared neutral point. Measuring line to line puts two windings in series, but they are 120 degrees apart, so the vector sum is √3 times one winding rather than twice it. Current has nowhere else to go — it flows straight through the winding to the line, so phase and line current are equal.
In a delta connection the windings sit directly between the lines, so the line voltage is the winding voltage. But each line connects to two windings, and the currents from those two combine at 120 degrees — giving the √3 factor on the current side instead.
Delta vs wye: frequently asked questions
What is the difference between delta and wye?
They describe how the three windings are connected. In a wye (star) connection each winding runs from a line to a common neutral point, so line voltage is √3 times phase voltage while line and phase current are equal. In a delta connection the windings form a closed triangle between the lines, so line voltage equals phase voltage while line current is √3 times phase current.
Why is 480Y/277 V written that way?
It is a wye system where 480 V is the line-to-line voltage and 277 V is the line-to-neutral (phase) voltage. 480 ÷ √3 = 277. The same notation gives 208Y/120 V, where 208 ÷ √3 = 120 — which is how a single distribution system serves both three-phase equipment and standard 120 V receptacles.
Which configuration should I use?
Wye is standard for distribution where you need a neutral for single-phase loads and a solid ground reference for protection. Delta is common on the primary side of transformers and in older industrial plants, and it isolates triplen harmonics in a circulating path rather than passing them to the neutral. Most modern North American building distribution is wye.
What is a high-leg or wild-leg delta?
A 240 V delta with a center tap on one winding, giving 120 V from two legs to neutral and about 208 V from the third — the high leg. NEC 110.15 requires that conductor to be marked orange. Connecting a 120 V load to the high leg puts 208 V across it, which is a common and expensive field mistake.
Does the configuration change the power formula?
No. Three-phase power is √3 × V_line × I_line × pf for both configurations. The √3 appears in the voltage relationship for wye and the current relationship for delta, and the two effects cancel in the power equation.
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