1) DELTA DELTA CONNECTION 1. Suitable for both un-grounded and effectively grounded sources. 2. Suitable for a three-wire service or a four-wire service with a mid-tap ground. 2) DELTA WYE CONNECTION 1. Suitable for both un-grounded and effectively grounded sources. 2. Suitable for a three-wire service or a four-wire grounded service with X O grounded. 3. With X O grounded, the transformer acts as a ground source for the secondary system. 4. Fundamental and harmonic frequency zero-sequence currents in the secondary lines supplied by the transformer do not flow in the primary lines. Instead the zero sequence currents circulate in the closed delta primary windings. 5. When supplied from an effectively grounded primary system does not see load unbalances and ground faults in the secondary system. 3) WYE DELTA CONNECTION 1. Suitable for both un-grounded and effectively grounded sources. 2. Suitable for a three-wire service or a four-wire delta service ...