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Old 03-21-2017, 01:24 AM   #21
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In the simplest terms, you're essentially shorting (bolted fault) the secondary of the transformer together through the breaker. That's why the breaker trips.
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Old 03-21-2017, 01:26 AM   #22
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Quote:
Originally Posted by sparkiez View Post
http://www.annsgarden.com/poles/JP0-PS-Schematic.jpg

That image shows the two Line taps on a standard pole transformer. If you look, you will see that one is +120V and the other is -120V relative to the neutral on the transformer's secondary. That is how you get 240V potential between L1 and L2.
You have a 240v secondary across L1 and L2. Don't worry about the neutral - it confuses most people. It's just a reference.
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Old 03-21-2017, 01:30 AM   #23
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Originally Posted by brian john View Post
Depending on the voltage the exact thing does not happen with a ground fault, at higher voltages a ground fault can become an arcing ground fault which will not generate sufficient current to operate SOME Over current protection devices. This fault can be a long term event with devastating results
This was today's job. 5kv cable fault. Probably was arcing for a period of time based on the condition of the cable.

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Old 03-21-2017, 07:51 AM   #24
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Default Theory Query

If i may, i'd like to throw the theoretical monkey wrench in, a real stumper that an EE presented in an effort to enlighten the great unwashed....

What if on tied all three legs of a perfectly balanced 3 phase system together? perfectly vectored, if you will....

Think something low enough in terms of R value here.

Wouldn't said perfect balance simply cancel each other out?

~CS~
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Old 03-21-2017, 09:30 AM   #25
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Quote:
Originally Posted by chicken steve View Post
If i may, i'd like to throw the theoretical monkey wrench in, a real stumper that an EE presented in an effort to enlighten the great unwashed....

What if on tied all three legs of a perfectly balanced 3 phase system together? perfectly vectored, if you will....

Think something low enough in terms of R value here.

Wouldn't said perfect balance simply cancel each other out?

~CS~
I don't see how. Phases are not diametrically opposed. Unless said conductors happened to be laying in a coil I don't think there would be enough induction forces to reread ****** electron flow. Thought experiments rule btw, thanks.

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Old 03-21-2017, 09:34 AM   #26
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Originally Posted by Flyingsod View Post
I don't see how. Phases are not diametrically opposed. Unless said conductors happened to be laying in a coil I don't think there would be enough induction forces to reread ****** electron flow. Thought experiments rule btw, thanks.

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This is dead on. If you put the three separate phases completely in phase, their magnitudes would combine.
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Old 03-21-2017, 09:36 AM   #27
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Quote:
Originally Posted by Flyingsod View Post
I don't see how. Phases are not diametrically opposed. Unless said conductors happened to be laying in a coil I don't think there would be enough induction forces to reread ****** electron flow. Thought experiments rule btw, thanks.

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Omg political correctness should not override real words. "Reread *******" should of course be re. Tard
Quote:
Originally Posted by Flyingsod View Post
I don't see how. Phases are not diametrically opposed. Unless said conductors happened to be laying in a coil I don't think there would be enough induction forces to reread ****** electron flow. Thought experiments rule btw, thanks.

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Old 03-21-2017, 10:08 AM   #28
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Quote:
Originally Posted by chicken steve View Post
If i may, i'd like to throw the theoretical monkey wrench in, a real stumper that an EE presented in an effort to enlighten the great unwashed....

What if on tied all three legs of a perfectly balanced 3 phase system together? perfectly vectored, if you will....

Think something low enough in terms of R value here.

Wouldn't said perfect balance simply cancel each other out?

~CS~
Quote:
Originally Posted by Flyingsod View Post
I don't see how. Phases are not diametrically opposed. Unless said conductors happened to be laying in a coil I don't think there would be enough induction forces to reread ****** electron flow. Thought experiments rule btw, thanks.
I don't even get it. I thought it would be either tie them together in a star or a triangle.
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Old 03-21-2017, 11:28 AM   #29
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Originally Posted by chicken steve View Post
What if on tied all three legs of a perfectly balanced 3 phase system together? ~CS~
It would blow up.
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Old 03-21-2017, 12:07 PM   #30
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Quote:
Originally Posted by chicken steve View Post
If i may, i'd like to throw the theoretical monkey wrench in, a real stumper that an EE presented in an effort to enlighten the great unwashed....

What if on tied all three legs of a perfectly balanced 3 phase system together? perfectly vectored, if you will....

Think something low enough in terms of R value here.

Wouldn't said perfect balance simply cancel each other out?

~CS~
I think you are conflating the effect of magnetic fields cancelling each other out, and current flow, which does not. They are apples and tractors (as in not apples and oranges, which at least are both fruits). With current flow, all you need is a path from one source to return to that source or to earth. With your perfect bolted fault on all three phases the paths from one phase to the next are going to exist and current flow in each phase will immediately jump to being all of the available fault current in the system at that point.

The only difference is that if this bolting of all three phases took place at EXACTLY the same moment and was a PERFECT connection between phases (meaning exactly the same resistance), the fault current wave forms would be symmetrical, not asymmetrical. In the past, things like breakers would have a rating for asymmetrical vs symmetrical fault current because the amount of current relates to the physical stresses exerted on the breaker when trying to open under a fault. The symmetrical rating was always a higher value, but of course was something that never happened in real life. Yet people got confused with that and would use the higher ratings by mistake, so they stopped providing that information. Fault interrupting ratings are now always asymmetrical.
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Old 03-21-2017, 12:54 PM   #31
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Quote:
Originally Posted by Flyingsod View Post
Wha?
Yeah…that’s pretty fücking rich.

Quote:
Originally Posted by sparkiez View Post
http://www.annsgarden.com/poles/JP0-PS-Schematic.jpg

That image shows the two Line taps on a standard pole transformer. If you look, you will see that one is +120V and the other is -120V relative to the neutral on the transformer's secondary. That is how you get 240V potential between L1 and L2.
I like to see when people try to explain something by posting to someone else’s interpretation as well…


...this interpretation brought to you by the Society of Broadcast Engineers, courtesy of the Ann's Garden...wth??? What kind of a reference is that?

Quote:
Originally Posted by sparkiez View Post
This is dead on. If you put the three separate phases completely in phase, their magnitudes would combine.
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Old 03-21-2017, 07:18 PM   #32
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Quote:
Originally Posted by triden View Post
In the simplest terms, you're essentially shorting (bolted fault) the secondary of the transformer together through the breaker. That's why the breaker trips.
The OP mentioned touching the conductors together, in terms of fault current this MAY BE somewhat different that a true bolted fault.
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Old 03-22-2017, 12:54 AM   #33
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Quote:
Originally Posted by brian john View Post
The OP mentioned touching the conductors together, in terms of fault current this MAY BE somewhat different that a true bolted fault.
I guess it's possible fault current could be worse upstream closer to the transformer. Also, if we are talking arc flash, the location of the actual bolted fault may not have the worst incident energy.

Last edited by triden; 03-22-2017 at 01:48 AM.
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Old 03-22-2017, 06:58 AM   #34
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Perhaps a lame Q , but does the definition of 'bolted fault' mean actual bolted parts, ocpd's, etc....?

~CS~
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Old 03-22-2017, 08:08 AM   #35
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Originally Posted by chicken steve View Post
Perhaps a lame Q , but does the definition of 'bolted fault' mean actual bolted parts, ocpd's, etc....?

~CS~
Bolted means the conductors in the fault are connected with a mechanical strength greater than the fault's ability to seperate them through explosive or magnetic force.
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