High Leg Deltum Wiring Diagram
If the secondary is a four wire delta the fourth wire originating at a center tap on one of the legs of the delta is grounded.
High leg deltum wiring diagram. It is used when both single and three phase power is desired to be supplied from a three phase transformer or transformer bank. The high leg conductor is also called the wild leg stinger leg or bastard leg other important nec rules relating to the high leg are as follows. 3 phase delta power. The nec code requires that the high leg be identified by an orange color it was often referred to as a red leg delta or by other effective means and is usually the b phase.
For example a 120v delta transformer will have a 208v leg. Many call it a high leg system because the voltage from line 2 to ground is higher than that of the other legs. Most utility companies will not hook up 3 phase delta on the customer side anymore because the the high or wild leg which as shown in the diagram runs a good deal higher than 120 volts to neutral. Hello i am working on a project at a local hospital.
Hook up a high leg to a single phase 120 volt piece of equipment and wait for the power supply to blow up. Double delta connections always provide 240 120v single phase t3. U n w w2 w6 v6 w1 v2 w5 u1 u2 u5 u6 v1 v v 240v 12 lead double delta. Figure 10 illustrates the wye delta connection either as three single phase transformers or as a single three phase unit.
We are adding a new 150 amp 208y 120v panel board for the it server ups and hvac. The primary wye windings are typically grounded. A change to the 2008 nec now allows the high leg of a four wire three phase delta service to be labeled as the c phase instead of the b phase. The utility service is 240 120 3 phase 4 wire high leg and the emergency generator is 208y 120 3 phase 4wire 208v line to line and 120v line to neutral.
It s important to note that the line current from a delta transformer doesn t equal the phase current. Both bushing labels and polarity dots are shown. In this example the line current is 87a and the phase.