#### applepieordie

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can someone explain to me the whole 'two wires' thing in single phase circuit and why the impedance is 2 times.

Thanks in advance

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- Thread starter applepieordie
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can someone explain to me the whole 'two wires' thing in single phase circuit and why the impedance is 2 times.

Thanks in advance

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Here is the problem im talking about. doesnt look like it attached properly in my first post

can someone explain to me the whole 'two wires' thing in single phase circuit and why the impedance is 2 times.

Thanks in advance

View attachment 9785View attachment 9786

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View attachment 9790

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yes this makes sense and is much easier to see when the circuit is drawn out as is in your reply rather than the one line diagram in the solution. thank you all for the replies.

View attachment 9790

To make this easy to remember for instant recall during the exam, use this:

"Single-Phase is Two Times, and Three-Pase is One Times."

...or, "1 is 2 and 3 is 1."

Kinda clumsy, but it got me through Circuits II. ?

The "1 is 2 and 3 is 1" monicker means "single phase counts 2 times the conductor length and 3 phase counts 1 times the conductor length."

The OP was confused about why the conductor length was doubled.

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One phase conductor connecting the load

Another phase conductor/neutral conductor connecting the load

Should we count 2 transmission line (2 conductors) for 3-phase system?

In a single-phase system, current travels to the load on the line conductor and returns on the neutral conductor, so this "series" circuit voltage is dropped across both the line and neutral conductors.

One phase conductor connecting the load

Another phase conductor/neutral conductor connecting the load

Should we count 2 transmission line (2 conductors) for 3-phase system?

In a three-phase system, you have two conditions: balanced and unbalanced. In a balanced three-phase system, there is no current in the neutral conductor (each phase's current cancels the other two phase's currents). Some examples of balanced 3-phase loads include 3-phase motors, pumps, and VFDs.

Conversely, with an unbalanced 3-phase system, current

I'm happy to talk to this and prove what I just claimed, but I'll spare the community until pressed to do so, but I will conclude with this: a three-phase system is not a series system; it's a parallel system, so the math is considerably more complicated than a single phase analysis, and the kicker is that you can do the math and calculate the true 3-phase voltage drop of an unbalanced 3-phase system, but the results of these calculations will leave you wondering why you even bothered.

Finally, it helps to understand why "Voltage Drop" is such a hot topic. Is it because it's a code requirement? It's not a code requirement, but rather a recommendation. It is absolutely true that too much voltage drop will cause the load to behave erratically, and can even be a very dangerous (and even deadly) situation for craftspersons working at the load; nevertheless, it's not a "CODE REQUIREMENT." The NEC recommends no more than a 3% voltage drop on the branch circuit and no more than 2% on the feeder. Voltage drop calculations are essential to the difference between a true engineered design and a classroom assignment.

There are two types of 3-phase configurations: delta and wye. In a delta configuration, there is no neutral, so that was easy - just one conductor length is considered.

In a wye configuration, there is a neutral. The return current on the neutral in a grounded-wye three-phase system is a vector sum of the three (3) phase currents.

In a

In an

But the

When performing 3-phase voltage drop calculations in

The issue is only and only of application of KVL. You trace your path of current and apply KVL whether three phase or single pahse, you get the answer. But all may not understand the concept properly and so for them thumb rules are handy to solve the problem to pass PE exam. So once we say that unbalanced (slightly) three phase problem is not asked in PE axam the rules of thumb being followed and being reiterated by @BigWheel are good enough.

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In a single-phase system, current travels to the load on the line conductor and returns on the neutral conductor, so this "series" circuit voltage is dropped across both the line and neutral conductors.

In a three-phase system, you have two conditions: balanced and unbalanced. In a balanced three-phase system, there is no current in the neutral conductor (each phase's current cancels the other two phase's currents). Some examples of balanced 3-phase loads include 3-phase motors, pumps, and VFDs.

Conversely, with an unbalanced 3-phase system, currentisproduced in the neutral; however an unbalanced 3-phase system is rarely (if ever) calculated considering the line and neutral impedances because the effort to perform the calculations isn't worth the results.

I'm happy to talk to this and prove what I just claimed, but I'll spare the community until pressed to do so, but I will conclude with this: a three-phase system is not a series system; it's a parallel system, so the math is considerably more complicated than a single phase analysis, and the kicker is that you can do the math and calculate the true 3-phase voltage drop of an unbalanced 3-phase system, but the results of these calculations will leave you wondering why you even bothered.

Finally, it helps to understand why "Voltage Drop" is such a hot topic. Is it because it's a code requirement? It's not a code requirement, but rather a recommendation. It is absolutely true that too much voltage drop will cause the load to behave erratically, and can even be a very dangerous (and even deadly) situation for craftspersons working at the load; nevertheless, it's not a "CODE REQUIREMENT." The NEC recommends no more than a 3% voltage drop on the branch circuit and no more than 2% on the feeder. Voltage drop calculations are essential to the difference between a true engineered design and a classroom assignment.

in a single-phase system, current travels to the load on the line conductor and returns on the neutral conductor, so this "series" circuit voltage is dropped across both the line and neutral conductors.

In a three-phase system, you have two conditions: balanced and unbalanced. In a balanced three-phase system, there is no current in the neutral conductor.

(each phase's current cancels the other two phase's currents)

I'm happy to talk to this and prove what I just claimed, but I'll spare the community until pressed to do so, but I will conclude with this: a three-phase system is not a series system; it's a parallel system, so the math is considerably more complicated than a single phase analysis, and the kicker is that you can do the math and calculate the true 3-phase voltage drop of an unbalanced 3-phase system, but the results of these calculations will leave you wondering why you even bothered.

three-phase system is not a series system; it's a parallel system

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