Wye delta

[A.D]

I am trying to figure out this wye delta configuration but just not grasping it. I came across a 3 phase panel with the c phase as a high leg. Phase A to ground was 120v phase B to ground was 120v phase c to ground was 240v. Can someone explain to me in simple terms the reason for this and advantage if any. Also how would 3 phase machinery get connected to this since the phases are not balanced. Thank you

 

[infinity]

The high leg should be 208 VAC to ground.

 

[roger]

I am trying to figure out this wye delta configuration but just not grasping it. I came across a 3 phase panel with the c phase as a high leg. Phase A to ground was 120v phase B to ground was 120v phase c to ground was 240v.

You actually have a center grounded delta and the high leg voltage would have been close to 208.

Can someone explain to me in simple terms the reason for this and advantage if any.

The advantage was that it could provide some 120v loads with a three phase delta system, the high leg provides no advantage and is just a bi-product of the transformer configuration.

Also how would 3 phase machinery get connected to this since the phases are not balanced. Thank you

The phases are balanced as far as L-L is concerned so three phase loads see 240v A-B-C.

Roger

 

[A.D]

Thanks roger. It's starting to make a little more sense now

 

[roger]

Thanks roger. It's starting to make a little more sense now

You're welcome and here is an illustration that will help.

Roger

 

[A.D]

Nice illustration!

 

[jumper]

Okay now that Roger has answered your original question, I have a comment:

High leg should be on B phase.

408.3(E) Phase Arrangement. The phase arrangement on
3-phase buses shall be A, B, C from front to back, top to
bottom, or left to right, as viewed from the front of the
switchboard or panelboard. The B phase shall be that phase
having the higher voltage to ground on 3-phase, 4-wire,
delta-connected systems.

 

[A.D]

Thats why I was confused when the high leg on c phase on the panel that I opened.... Thanks jumper.... The smoke is getting clear now

 

[Smart $]

Thats why I was confused when the high leg on c phase on the panel that I opened.... Thanks jumper.... The smoke is getting clear now

A lot of POCO's configure there Line C with the hi leg because it is required there for metering. It's up to the electrician to transpose the hi leg to Line B.

 

[Fulthrotl]

I am trying to figure out this wye delta configuration but just not grasping it. I came across a 3 phase panel with the c phase as a high leg. Phase A to ground was 120v phase B to ground was 120v phase c to ground was 240v. Can someone explain to me in simple terms the reason for this and advantage if any. Also how would 3 phase machinery get connected to this since the phases are not balanced. Thank you

There is no advantage to the consumer.
It allows the poco to provide 3ph service using only two transformers.

If the customer needs more juice, the poco adds a third xfmr. If not, they save the money