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Four Wire Delta Circuits

A four-wire delta (4WD) electrical service is a three-phase delta service with a center-tap on one of the transformer windings to create a neutral for single-phase loads. Motors loads are commonly connected to phases A, B, and C, while single-phase loads are connected to either phase A or C and to neutral. Phase B, the "high" leg, is not used for single phase loads.

This type of service, which is also known as a "high-leg", "wild-leg", "stinger leg", or "wild phase" service, is common in older manufacturing facilities with mostly three-phase motor loads and some 120 volt single-phase lighting and plug loads.

120/208/240 Volt Service

Three Phase Four Wire 480 Volt Delta Electrical Service
Compatible WattNode Models
Any 240 volt delta (3D) model

This is the most common four-wire three-phase delta service and is essentially a 240 volt, three-phase, three-wire delta service with one of the 240 volt transformer winding center tapped to provide two 120 Vac circuits, which are 180 degrees out of phase with each other. The voltage measured from this center tapped neutral to the third "wild" leg is 208 Vac.

This service almost always has a neutral connection, but in some rare situations, the neutral conductor is not available. It generally exists at the service entrance, but may not run to the panel or load. In theory, a four-wire delta without neutral is just a three-phase delta, but there is one difference. In a normal three-phase delta, ground will either be the center voltage or one one leg, but a three-phase delta derived from a four-wire delta transformer will have ground halfway between two legs. Delta model WattNode meters are the best choice, as they will work with or without a neutral connection.

Four-wire delta connection diagram

240/415/480 Volt Service

Three Phase Four Wire 480 Volt Delta Electrical Service
Compatible WattNode Models
Any 480 volt delta (3D) model

This is much less common, but we do occasionally get requests to measure this type of service, which is essentially identical to a 120/208/240 service, but with all the voltages doubled.

General Notes

See Also

 

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