Transformer internal wiring question

[JasonCo]

Out of 80 questions that have been incredibly difficult, I'm down to 1 last question and as much as I've looked over it and have tried drawing it out, its got me stumped! I almost feel like none of them are correct based on the way the connections are. The only one that makes any sense at all to me is III.

The reason I say III is because that is the only one where the Neutral is connected for a Wye system. The other ones make no sense to me, although I guess I don't know a whole lot about this stuff. We have to read over 50 pages and I swear no where does it talk about this at all, its just a random question thrown into the homework... **** I hate posting a homework question but I'm ready to learn, not just get an answer. My goal is to learn, sorry for posting homework but I'm totally stuck and I'm too stubborn to just guess.. Also it defeats the purpose of school. Thanks for your help

 

[Fnewman]

Although you are connrect that I is a corner grounded delta connection with no neutral, I would suggest study the other two a bit closer.

 

[JasonCo]

Well I learned the hard way haha, Answer defiantly isn't C which I thought it was. III being a Wye connection. II being center tapped Delta? I I'm confused with. Anyways Answer must be B I guess. You just can't win with a question like this...

 

[ActionDave]

I was taught that the only true neutral was a wye or star connected three phase and to stop calling grounded conductors neutral conductors, so I agree with III being the correct answer. Then the NEC went and defined neutral in a stupid way and screwed all that up. I agree it is a flawed question but it did get you to did hard and for that reason it is a good study question.

 

[infinity]

I don't see any system bonding jumpers so are any of the neutrals technically grounded conductors?

 

[ActionDave]

Well there is the green text that says To the grounding electrode.

 

[Smart $]

I was taught that the only true neutral was a wye or star connected three phase and to stop calling grounded conductors neutral conductors, so I agree with III being the correct answer. Then the NEC went and defined neutral in a stupid way and screwed all that up. I agree it is a flawed question but it did get you to did hard and for that reason it is a good study question.

I agree that the wye configuration of III is the only one which has a true neutral. However, II being a high-leg delta configuration has by convention and NEC definition a neutral point and conductor. I doubt the test or study guide is authored from a purist point of view. I believe that rather uncommon in our trade.

 

[Smart $]

Well there is the green text that says To the grounding electrode.

A main or system bonding jumper is not required to make a neutral... but a connection to a grounding electrode is required to make a grounded secondary [neutral] conductor, which is the point of the problem... but FWIW an MBJ/SBJ would thus be required consequentially.

@infinity
For reference, a main or system bonding jumper connects the grounded conductor to the EGC. Only by exception is the GEC connection permitted to be made on the EGC side of the MBJ/SBJ.

 

[NewtonLaw]

Typical Utility Connections

Typical Utility Connections

Out of 80 questions that have been incredibly difficult, I'm down to 1 last question and as much as I've looked over it and have tried drawing it out, its got me stumped! I almost feel like none of them are correct based on the way the connections are. The only one that makes any sense at all to me is III.

The reason I say III is because that is the only one where the Neutral is connected for a Wye system. The other ones make no sense to me, although I guess I don't know a whole lot about this stuff. We have to read over 50 pages and I swear no where does it talk about this at all, its just a random question thrown into the homework... **** I hate posting a homework question but I'm ready to learn, not just get an answer. My goal is to learn, sorry for posting homework but I'm totally stuck and I'm too stubborn to just guess.. Also it defeats the purpose of school. Thanks for your help

The correct answer is "B". Both II and III have have a typical utility service grounded neutral. II is a 4 wire Delta supply that gives you 240 volts three phase and 120/240 volt single phase. For this configuration, A phase to ground would be the high leg reading 208 volts to ground and is not typically used. III - is a simple 4 wire Wye service.

Of course I am assumming 120/240 or 208Y/120 volt secondary.

Hope this helps,

Newton Law

 

[infinity]

The correct answer is "B". Both II and III have have a typical utility service grounded neutral. II is a 4 wire Delta supply that gives you 240 volts three phase and 120/240 volt single phase. For this configuration, A phase to ground would be the high leg reading 208 volts to ground and is not typically used. III - is a simple 4 wire Wye service.

I think that you meant B phase to ground is the high leg.

 

[NewtonLaw]

Thank you

Thank you

I think that you meant B phase to ground is the high leg.

You are correct, I meant B-Phase would be the high leg.