Ampacity of Copper Conductors 9

[Mbrooke]

Anyone know why Table 310.15(B)17) lists 4/0 copper at 360*C but wire spec sheets list it at 480 amps? Same for other wire sizes... what is the actual ampacity? Am I correct to think NFPA70 assumes no wind while wire manufacturers assumes wind?

 

[davidbeach]

4/0 what? Could potentially deal with CU, AAC, ACSR, ACSS (generally don't have ACSS that small). The facility ratings come out of the Planning group. For protection I just look at the highest rating, which is for the coldest ambient and make sure nothing trips at that point. Not sagging it to the ground on high load on hot days is the responsibility of the system operators.

 

[mparenteau]

Emissivity is just a measure of how well something emits thermal energy. If something is a good absorber, it is also a good reflector. Poor absorber, poor reflector.

Mike

 

[Mbrooke]

4/0 copper. Which yes I know is typically not found on any new lines- but go back 100 years it was common.

 

[Mbrooke]

mparenteau: Is this why condenser coils are black and evporator coils are white?

 

[Compositepro]

"If something is a good absorber, it is also a good reflector. Poor absorber, poor reflector."

That is not correct. A good absorber is a good emitter but a poor reflector. A reflector is a poor absorber and a poor emitter.

Shiny copper is a good reflector in the infrared, as is gold.

Condenser and evaporator coils are generally designed for convective heat transfer and not radiative heat transfer. Car radiators not really radiators, either. Heating radiators in homes are rarely black, they usually are white or silver. Go figure.

 

[waross]

Did you get your reflections mixed, CompositePro?
The condenser coils are black for best radiation, opposite of absorbtion.
The evaporator coils may be unpainted because many paints and coverings don't do well in a wet, freeze-thaw cycle.
In refrigerators, the light colours are probably to facilitate identifying and cleaning dirt.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[7anoter4]

Sometimes answering a specific question gives the impression that I do not agree with what has been said by other specialists in the field. I am sorry if I left this impression.
I do not have experience in as many fields as waross or vast and deep knowledge in the field of cables, grounding and many others like cuky2000.
Because in the 60 years since I finished my studies I only dealt with design, I got in the habit of looking for explanations by calculation and less from my own experience.
Usually the questions do not contain enough data to be able to calculate.
This is not the case with MBrooke where the accuracy of the question forces me to a precise answer.
By the way, I agree with the views expressed by all participants and consider that I have still
more to learn from my participation in this very interesting and instructive forum.

 

[FacEngrPE]

Emmissivity shows up in the formula for heat transfer by radiation.

Reference -

https://www.engineeringtoolbox.com/radiation-heat-transfer-d_431.html

For objects other than ideal black bodies ('gray bodies') the Stefan-Boltzmann Law can be expressed as

q = ε σ T[sup]4[/sup] A (2)

where

ε = emissivity coefficient of the object (one - 1 - for a black body)

 

[waross]

Thank you for the mention, 7anoter4.
I have learned quite a bit from your posts.
Keep up the good work.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[mparenteau]

@CompositePro:

Yes...thanks for keeping me honest.

To restate: Good absorber/good EMITTER is what I should have said. Poor absorber/good reflector.

Mike

PS This can be shown by the equation: a + r = 1, where:

a = absorption (or emissivity)
r = reflectivity

this assumes no transmission, else the equation is a + r + t = 1.

 

[Mbrooke]

Can I ignore conduction and radiation for short circuit calcs?

 

[Parchie]

Short circuits are just that, short! Better not worry about heat being transferred during such conditions, assume adiabatic conditions!

 

[Mbrooke]

adiabatic

Schweet!!!!!!!!!!!!

What final short circuit temp do I not want to exceed.

 

[waross]

What is the melting point of copper?
(Not as off the wall as you may think.
I remember years ago, an instruction sheet for drying the ends of mineral insulated cable prior to termination.
"If an open flame is used to dry the cable, care must be taken to not melt the copper".)

[link ]Bill[/url]
--------------------
"Why not the best?"
Jimmy Carter

 

[Mbrooke]

Good question- I don't know for hard drawn copper.

My fear is annealing.

 

[7anoter4]

See IEEE 80/2013 section 11.3.1.1 Calculation of TCAP.11.3.1.2 Resistivity of clad steel rod Table 1
Copper, annealed soft-drawn Fusing temperature Tm (°C)=1083
As far as I know above 300oC copper softens and losses its mechanical strength.
From Materials for electrical engineering by Jaromír DRÁPALA:

 

[Parchie]

Please see Onderdonk or Preece formulas for fusing of conductors!

 

[Mbrooke]

Need some more info Parchie- I like where you're going with this.


Any idea how much strength hard drawn loses at 300*C?

 

[7anoter4]

Sorry. In my post of 21 july 8:01 it is noted:
"In the same conditions[Ta=25oC,no sun,2ft/s] I=580 A.
I meant this:
In the same conditions[Ta=25oC,full sun,2ft/s] I=580 A.[ε=0.23,α=0.23]].Sorry.

 

[Mbrooke]

580 amps is not bad at all. Thanks for crunching these numbers! Debt noted, I owe you now.!