Can someone please explain this to me?

[GoldDigger]

Why do you keep saying return? I dont comprehend this return calculation?

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The current goes from source to load along one conductor and returns over a second conductor.
Most often these are the hot conductor and the neutral, but that limits the discussion too much.

It is arbitrary which you call the supply and which the return when AC is involved.

 

[Daniel malack]

The current goes from source to load along one conductor and returns over a second conductor.
Most often these are the hot conductor and the neutral, but that limits the discussion too much.

It is arbitrary which you call the supply and which the return when AC is involved.

Apply it to the initial question is what im asking for!

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[Daniel malack]

Apply it to the initial question is what im asking for!

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What is the the return on a 240 volt 2 wire circuit? You have 120 v on each leg and no neutral way back?

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[Little Bill]

What is the the return on a 240 volt 2 wire circuit? You have 120 v on each leg and no neutral way back?

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The "return" on a 240V 2-wire is the "other wire"

 

[Daniel malack]

The "return" on a 240V 2-wire is the "other wire"

What other wire? 120v phase A to ground, 120v phase B to to ground. 240 v phase A to phase B.
Which one is return wire?

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[ActionDave]

What other wire? 120v phase A to ground, 120v phase B to to ground. 240 v phase A to phase B.
Which one is return wire?

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Power goes out on the red wire, comes back on the black wire, no white wire needed to complete the circuit.

Back in the old days we would hook up water heaters with 10-2 romex and put the black wire on one pole of a two plole breaker and the white wire on the other pole, even if you never did land the bare copper equipment ground the elements would get their 240V and the water would get hot.

That used to really confuse a lot of plumbers because they didn't think the water could get hot unless there was a ground. I guess being able to understand why it worked is how I ended up an electrician instead of a plumber.

 

[oldsparky52]

What other wire? 120v phase A to ground, 120v phase B to to ground. 240 v phase A to phase B.
Which one is return wire?

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Our (USA) AC power completes 60 cycles per second. Each cycle has a moment when A-phase is positive 240V nominal to B-phase being negative, then vice versa. So each cycle has current flow going one way, then reversing going the other way and it does this complete cycle 60 times every second.

60 times each second, A-phase will be the "source", then turn around and be the "return". The current just goes back and forth, back and forth, 60 times per second.

So, thinking of a wire being a return is just not quite how things work and may confuse someone when digesting other phenomenon in our work.

 

[roger]

Our (USA) AC power completes 60 cycles per second. Each cycle has a moment when A-phase is positive 240V nominal to B-phase being negative, then vice versa. So each cycle has current flow going one way, then reversing going the other way and it does this complete cycle 60 times every second.

60 times each second, A-phase will be the "source", then turn around and be the "return". The current just goes back and forth, back and forth, 60 times per second.

So, thinking of a wire being a return is just not quite how things work and may confuse someone when digesting other phenomenon in our work.

This is what Daniel is not seeing, hopefully this post will give visualization.

Roger

 

[Daniel malack]

Our (USA) AC power completes 60 cycles per second. Each cycle has a moment when A-phase is positive 240V nominal to B-phase being negative, then vice versa. So each cycle has current flow going one way, then reversing going the other way and it does this complete cycle 60 times every second.

60 times each second, A-phase will be the "source", then turn around and be the "return". The current just goes back and forth, back and forth, 60 times per second.

So, thinking of a wire being a return is just not quite how things work and may confuse someone when digesting other phenomenon in our work.

this has nothing to do with the main question at hand. and is not in the formula of NEC voltage drop. the NEC voltage drop requirement conciders these facts in determining their requirements. that is why they have a code. i dont add what i know to the code because it is already concidered by a panel of electrical profecionals. i just have to comprehend the wording of the established CODE. And apply it. not add to it.

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[roger]

this has nothing to do with the main question at hand.
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It has everything to do with the question at hand, it is basic AC theory.

Roger

 

[Daniel malack]

Lets just apply the code requirements. to the original question. what conductor size is required by (CODE) 100 foot frome source, 230 volt, 30 amp load. what codes apply to give you #8 AWG?

I understand that when you are in the field the art of electricity applys! But when you are taking the Masters test apply the answer to the question.

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[Daniel malack]

Power goes out on the red wire, comes back on the black wire, no white wire needed to complete the circuit.

Back in the old days we would hook up water heaters with 10-2 romex and put the black wire on one pole of a two plole breaker and the white wire on the other pole, even if you never did land the bare copper equipment ground the elements would get their 240V and the water would get hot.

That used to really confuse a lot of plumbers because they didn't think the water could get hot unless there was a ground. I guess being able to understand why it worked is how I ended up an electrician instead of a plumber.

you are nuts!

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[roger]

But when you are taking the Masters test apply the answer to the question.

So show us the formula you use to get to the answer.

Roger

 

[Carultch]

Lets just apply the code requirements. to the original question. what conductor size is required by (CODE) 100 foot frome source, 230 volt, 30 amp load. what codes apply to give you #8 AWG?

I understand that when you are in the field the art of electricity applys! But when you are taking the Masters test apply the answer to the question.

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No code actually requires a #8 Cu, based only on the information presented in the problem. While Voltage drop is the intent of this problem, it is a recommendation, rather than a hard rule. By ampacity alone, and assuming it is a load on a 30A branch circuit that doesn't require safety factors, only #10 Cu is required, for any distance.

When you follow the NEC recommendations on voltage drop for the round trip 200 ft distance, limiting it to 3% of nominal 230V, you get 1.15 Ohms/kft required as a maximum resistance. The closest to this, without going over, is #8, per Chapter 9 Table 8 values.

 

[Daniel malack]

No code actually requires a #8 Cu, based only on the information presented in the problem. While Voltage drop is the intent of this problem, it is a recommendation, rather than a hard rule. By ampacity alone, and assuming it is a load on a 30A branch circuit that doesn't require safety factors, only #10 Cu is required, for any distance.

When you follow the NEC recommendations on voltage drop for the round trip 200 ft distance, limiting it to 3% of nominal 230V, you get 1.15 Ohms/kft required as a maximum resistance. The closest to this, without going over, is #8, per Chapter 9 Table 8 values.

apply the recommendation.

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[Daniel malack]

Answer #8

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[roger]

Answer #8

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So show us the formula you used to get that answer.

Roger

 

[ggunn]

Here's one from an electrical drawing I did today for a PV interconnection with a 240V single phase service:

200' RUN OF AWG#1/0 ALUMINUM (SOLAR LOAD CENTER TO INTERCONNECTION):
D = 200', I = 47.9A, r = 0.2Ω/1000'
Vd = IR = 2DIr = (2)(200')(47.9A)(0.2Ω/1000') = 3.83V
%Vd = (Vd/V)(100%) = (3.83V/240V)(100%) = 1.60%

75' RUN OF AWG#8 ALUMINUM (ARRAY TO SOLAR LOAD CENTER):
D = 75', I = 16A, r = 1.3Ω/1000'
Vd = IR = 2DIr = (2)(75')(16.0A)(1.3Ω/1000') = 3.12V
%Vd = (Vd/V)(100%) = (3.12V/240V)(100%) = 1.30%

TOTAL LOSSES DUE TO Vd = 1.60% + 1.30% = 2.90%

 

[Unbridled]

I am still studying for my WV Master Electricians Exam. I have been going along pretty good but I just hit a brick wall. Here is the question from my practice test.
A 30 amp 230 volt load is located 100 feet from the source. What is the minimum size branch circuit conductor required to operate within the limits for voltage drop that is recommended be the NEC?
a. # 10 conductor
b. # 8 conductor
c. # 6 conductor
d. #4 conductor

The book says the correct answer is B. I have no idea how to come to this conclusion. Can anyone help me?

Iv'e always used this easy to remember Vd formula for single phase.

Vd=2 KIL/CM

 

[Ingenieur]

you are nuts!

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perhaps
but he is correct