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Old 03-14-2017, 10:03 PM   #1
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Default Wiring up a transformer question

A 240/480 to 120/240-volt, single-phase transformer is supplied from a 480-volt circuit and delivers power to a 120-volt load. X2-X4 is connected to 120-volt load terminal L1 and X1-X3 is connected to load terminal L2. If X1-X3 is also connected to a grounding electrode conductor, ___.
I. the secondary voltage to ground is stabilized
II. the secondary fuses will open if the secondary is fused
III. the secondary windings will rapidly overheat and burn in two, unless the secondary is fused

This is a question I have in school. Not looking for any freebies! I just want to talk about it because I'm a bit confused, I'd like to figure it out though!

So... Okay I'm not exactly fresh when it comes to wiring up a transformer. But the question says that if X1 and X3 are connected to the grounding electrode conductor, wouldn't that make it the neutral and X2 and X4 will become the Hot?

I might be going in the total wrong direction with this.. Why would II and III even be an option, or did they just throw it in there to throw me off. Wouldn't I (1) be the only logic scenario to happen... What am I missing, I'm sort of confused
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Old 03-14-2017, 10:16 PM   #2
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480::120 is a 4:1 transform, so the XFMR must be a multi-tap puppy.

Grounding one leg of such a secondary establishes it to 0 VAC.

Making the other leg Hot at 120 VAC relative to ground potential.

Draft a wiring diagram based on that... and your answers flow.
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Old 03-14-2017, 10:28 PM   #3
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I drew it out. So bonding X1 and X3 together would give it 0, and X2 and X4 would give it 120v. I put them in parallel to give it the 120v. Bonding 1 side to the grounding conductor establishes it as the neutral. So walla all is good? So answer is 1 (I)? Am I thinking this correctly :S
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Old 03-14-2017, 10:53 PM   #4
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It really is not a neutral it is a grounded conductor.

You can ground X1-X3 OR X2-X4 makes no difference what terminal you ground.

THOUGH it could be argued that the grounded conductor is carrying the unbalance of the "hot" conductor
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Old 03-14-2017, 10:59 PM   #5
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Appreciate all your help. I was right, answer is I (1) only. WOO! I figured they were trying to throw me off in this question. I guess it worked because it made me overthink it and post this lol. But then again grounding and bonding is incredibly difficult to understand when your talking about all the principles involved with it. I don't know, this semester is going to be a challenge... Again thanks for your help!
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Old 03-17-2017, 07:19 AM   #6
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JasonCo,

I am curious. Is your instructor inaccessible to you. While it is a good thing to ask more than one source for help, and most people on the forum are genuinely interested in helping others, it seems that a good instructor would be itching to teach you this. I am curious because I worry about some of the people teaching the up-and-comers.
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Old 03-17-2017, 08:00 AM   #7
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Quote:
Originally Posted by Corysan View Post
JasonCo,

I am curious. Is your instructor inaccessible to you. While it is a good thing to ask more than one source for help, and most people on the forum are genuinely interested in helping others, it seems that a good instructor would be itching to teach you this. I am curious because I worry about some of the people teaching the up-and-comers.

They seem to be few and far between.
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