System voltage is the voltage used to determine insulation requirements and the product is intended to be used with. For example, 120 Vac, 240 Vac, 480 Vac, 690 Vac, can be single-phase or a multiphase source. The product must be labeled with this voltage. For single-phase systems, the rated voltage is the value between the two phases. For 3-phase systems, the rated voltage is dependent on the type of source transformer, “delta” or “wye”.

“delta” has the same phase-to-phase voltage as the phase to ground voltage. “wye” has a different phase to phase voltage then the phase to ground voltage. For products that are only designed for “center ground wye” source, the product must be labeled such as a rating 480_277Vac. For products designed for “delta” source, the product also works on a “wye” source and is label with just the voltage such as 480 Vac. The “delta” source can also be called “corner grounded” system.

Figure 1-5 shows these two types of power source.

Figure 1-5 Delta and WYE Type of Power Source