Can someone please explain this to me?

[Daniel malack]

I believe I pulled it from this on-line calculator:

https://www.cirris.com/learning-center/calculators/133-wire-resistance-calculator-table



Ditto. Only way I got #8 was with Al.

They are applying 110.14(C) terminal ratings only allowing 60° C column. Gives you a #8

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[oldsparky52]

The Southwire calculator only asks if it is single ø or 3ø. so for 240V (or 230) you would think it knows there are two conductors.
It shows a #10 for 240V 30A for 100'.

I put in 200' ad it came back with #6.

So neither scenario came back with #8

I have reservations about using that OLC.

 

[steve66]

I have reservations about using that OLC.

And since this is a practice problem, I really wouldn't expect someone to use an online calculator to get the answer.

Maybe to check the answer, but when we don't get the right answer, its pretty obvious this calculator makes assumptions (like the Power Factor) that aren't part of the original problem.

 

[JFletcher]

They are applying 110.14(C) terminal ratings only allowing 60° C column. Gives you a #8

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I'm not following you. even if the terminals are 60*C, and the wire 60*C (NM), #10 is good for 30A.

 

[oldsparky52]

I'm not following you. even if the terminals are 60*C, and the wire 60*C (NM), #10 is good for 30A.

But the VD on a 100' circuit, 30A, 230V exceeds the 3% recommended VD by the NEC (which is what the test question used for the parameters).

 

[oldsparky52]

... its pretty obvious this calculator makes assumptions (like the Power Factor)...

I don't really have a handle on how PF effects VD, can you help me with that? I understand why and how it affects KW (as compared to KVA), but not VD.

Thanks.

 

[Daniel malack]

Daniel, I don't want to get into a pissing contest on this, but most breakers today (rated under 100A) are rated for both 60c and 75c terminations. I agree that other terminations need to be considered. Circuits less than 40-amps will rarely ever be used at ampacities that require a 75c termination, just the way it is. But ... it is not true that a circuit under 100A has to be calculated at the 60c termination because of the circuit breaker because most of them are also rated for 75c terminations (other current limiting terminations may be in the circuit but it's not usually the circuit breaker that needs to be considered).

I just looked on several breakers GE 40°, Sq D home line 40°, Sq D QO 40°, Siemens 40°, Cutler Hammer Ch 60-75° Cutler Hammer bolt in 60-75° most are 40°. I got no reason to lie to ya.

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[Daniel malack]

I just looked on several breakers GE 40°, Sq D home line 40°, Sq D QO 40°, Siemens 40°, Cutler Hammer Ch 60-75° Cutler Hammer bolt in 60-75° most are 40°. I got no reason to lie to ya.

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SQ December QO bolt in 40°!

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[Carultch]

I just looked on several breakers GE 40°, Sq D home line 40°, Sq D QO 40°, Siemens 40°, Cutler Hammer Ch 60-75° Cutler Hammer bolt in 60-75° most are 40°. I got no reason to lie to ya.

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I think that is the ambient temperature, not the termination temperature.

 

[oldsparky52]

I just looked on several breakers GE 40°, Sq D home line 40°, Sq D QO 40°, Siemens 40°, Cutler Hammer Ch 60-75° Cutler Hammer bolt in 60-75° most are 40°. I got no reason to lie to ya.

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Well since you must have at least a 60c connection, all of the breakers you listed may not be used ... but ... since we use them, .... maybe, just maybe you are misunderstanding some of the information you are presenting?

Most likely the 40c ratings are the ambient temperature ratings, and the 60c-75c ratings are the termination ratings. Two completely different items. One is for the air around the breaker and the other directs us as to what ampacity table we are allowed to use.

 

[steve66]

I don't really have a handle on how PF effects VD, can you help me with that? I understand why and how it affects KW (as compared to KVA), but not VD.

Thanks.

Actually, I think the Southwire calculator assumes 3 phase. That makes a bigger difference than the power factor. I don't seen anywhere on the Southwire calculator where I can choose 1 phase.

But back to the power factor - it makes some difference in the calculated impedance of the wire. If you know R and X for a wire, then Z depends on R and X and the power factor.

Z = X*PF+R*Sin(Acos(PF))

(I think that's right - I'm trying to read it from an excel formula.)

Just as an example, my Square D calculator lists L-L voltage drop per amp per 100' in magnetic copper wire: (trying to make a table, which isn't working)

....................... ..... #8 Wire #10 wire
1 phase: 90% PF. . 0 .15 ....... . 0 .23
1 phase: 80% PF ...0.13 ........ 0 .20
3 phase: 90% PF .. 0 .13 ........ 0 .20
3 phase: 80% PF... 0 .11 ........ 0 .17

 

[roger]

That was ambient temperature, not termination rating.



On page 7 you will find

Correct, the ambient is marked on the breaker, the terminal rating may or may not be found on the breaker or the terminals, but it can always be found in the manufactures tech sheets.

I think that is the ambient temperature, not the termination temperature.

Correct again.

Well since you must have at least a 60c connection, all of the breakers you listed may not be used ... but ... since we use them, .... maybe, just maybe you are misunderstanding some of the information you are presenting?

I think he has hit the nail on the head Daniel

Most likely the 40c ratings are the ambient temperature ratings, and the 60c-75c ratings are the termination ratings. Two completely different items. One is for the air around the breaker and the other directs us as to what ampacity table we are allowed to use.

:thumbsup:

Roger

 

[Daniel malack]

I looked again at breakers. You are right i do see terminal ratings below the 40° marking and they are all 60° -75° C rated terminals. What does the 40° C ambient marking mean?

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[Daniel malack]

I looked again at breakers. You are right i do see terminal ratings below the 40° marking and they are all 60° -75° C rated terminals. What does the 40° C ambient marking mean?

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How do you apply the 40° marking?

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[Ingenieur]

How do you apply the 40° marking?

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40 C (104 F) is the rated ambient operating temperature
for conductors as the temp rises above that ampacity must be derated

 

[Fnewman]

In my mind, way too much discussion for what is really a simple, possibly trick question. If it is a 30 amp load, given no other information, you have to assume continuous. That equals a #8 circuit and calculator.net gives a drop of 1.64%. The calculator instructions specifically state NOT to use round trip distance.

 

[GoldDigger]

Because the calculator figures both feed and return drop automatically.

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[oldsparky52]

Actually, I think the Southwire calculator assumes 3 phase. That makes a bigger difference than the power factor. I don't seen anywhere on the Southwire calculator where I can choose 1 phase.

But back to the power factor - it makes some difference in the calculated impedance of the wire. If you know R and X for a wire, then Z depends on R and X and the power factor.

Z = X*PF+R*Sin(Acos(PF))

(I think that's right - I'm trying to read it from an excel formula.)

Just as an example, my Square D calculator lists L-L voltage drop per amp per 100' in magnetic copper wire: (trying to make a table, which isn't working)

....................... ..... #8 Wire #10 wire
1 phase: 90% PF. . 0 .15 ....... . 0 .23
1 phase: 80% PF ...0.13 ........ 0 .20
3 phase: 90% PF .. 0 .13 ........ 0 .20
3 phase: 80% PF... 0 .11 ........ 0 .17

So, ... as PF goes farther away from 1, the resistance in the circuit becomes less? So the worse the PF the less resistance?

 

[Little Bill]

Actually, I think the Southwire calculator assumes 3 phase. That makes a bigger difference than the power factor. I don't seen anywhere on the Southwire calculator where I can choose 1 phase.

My Southwire app has a place to choose single ø or 3 ø.

 

[Daniel malack]

Because the calculator figures both feed and return drop automatically.

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

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