Ask Me Help Desk - Current capacity of cold wires.

Current capacity of cold wires.

Someone asked this before, it wasn't answered, and I am curious. Hypothetical question, you are in Anartica where cold can be extreme, There are no inspectors or code to deal with, But need to power Mining equipment How much current could a #2 wire handle at
0 Degrees, Freezing. And how much would it handle in free air? Are their calcs for this?

You planning on doing some moonlight work at the South Pole? Be sure to bring some "anti-freeze".

The concept is that an ambient temperature of less than normal, typically code uses 86 Deg F, the resistance of a conductor will be less.

This is what the Superconductor method uses, by immerssing a conductor in liquid nitrogen, gets the wire temp down to close to -400 Deg F.

Here is some info:

Temperature Coefficient of Resistance

Superconductors

You mention Zero. While the temp will bring the resistance down some, I think it will be negligible to allow more current on the #2.

I will let you have fun with the calcs, and get back with the answer.

Kiss I bet either has done this or will know exactly what to do. Hopefully he sees this and can add whatever knowledge he has.

I need to get going on a re-bid for some changeorders, or my a** is grass.

Yep, that was Johnny5 who gave me a reddie because I answered based on building codes rather than a hypothetical question.

Current carrying capacity is basically self heating and the ambient temperature and some safety margin. A bare conductor totally supported in free air could theretically have a higher current capacity than a wire insulated with teflon or PVC. It also is going to depend on the number of wires in a confined space such as a conduit or jacket.

So, that out of the way, you could calculate the power loss of the wire at the rated code temperature using the Resistance of the wire at that temperature.

Then back out I from the resistance at the lower temperature. P and V are constants.
You want the same power loss at the rated temp and the lower temp. This will mean that the voltage drop is the same at both temperatures. You know R at both temperature, You know I designed and you want to find the new I for the lower temperature.

But, since you know P=(V^2)/R and V is a constant. It's really going to be the ratio of the two resistances and it would raise the rated current by that ratio.

A #2 could carry 300 Amps?
Kiss, how much current could it handle, theroetically. And even at 40 below,how much.

Copper has a temperature coefficient of 0.004041/deg C
86 F = 30 C
-40 F = = -40 C

Delta T = 70 C

=1/(70*0.004041) = 3.535192845

Thus 300 * 3.53 = 1060 amps

Why did you make me work so hard?

Kiss, you missed my comment directed to Strat:

Quote:

Originally Posted by tkrussell

I will let you have fun with the calcs, and get back with the answer.

Tk:
I forgot about it.

Strat:
Could you have figured it out on your own?

TK, did you ban Johnny5 or just close his question when he got smart?

In hindsight, I'd probably add the same safety margin of 86-75, so I'd probably add 61 degrees converted to centegrade or 11 degrees C from the delta T value. i.e. rate the wire below the 11 degrees below the operating pont.

Bal, I had a hissy fit and just closed the post. I cannot ban anyone, I need to bring that task, if necessary, to powers higher than me. My observation is something has to be very abnormal to be banned.

I am just a lowly moderator.If he was banned, I am not aware of it.

All I ask is poster answer the questions that invariably are asked to help clarify their original question.

The "or not" comment rang my bell.

But I digress.

Kiss, 1000 amps?

Quote:

Originally Posted by KeepItSimpleStupid

tk:
I forgot about it.

Strat:
Could you have figured it out on your own?

Didn't know formula before, and Math hurts my brain any more. Would have figured, or found through research, plus poster pm'd me curious to the answer, and I also was, I have said things and had taken wrong, forget how the other post went, not important, it was a good question and got good answers. Thanks, Take Care

Quote:

Originally Posted by tkrussell

Bal, I had a hissy fit and just closed the post. I cannot ban anyone, I need to bring that task, if necessary, to powers higher than me. My observation is something has to be very abnormal to be banned.

I am just a lowly moderator.If he was banned, I am not aware of it.

All I ask is poster answer the questions that invariably are asked to help clarify their original question.

The "or not" comment rang my bell.

But I digress.

Kiss, 1000 amps?

Thanks TK

Quote:

Originally Posted by ballengerb1

TK, did you ban Johnny5 or just close his question when he got smart?

Mr ballengerb1 I think the dust has settled I am sorry

Quote:

Originally Posted by ballengerb1

Yep, that was Johnny5 who gave me a reddie because I answered based on building codes rather than a hypothetical question.

What's a reddie

A reddie is a mark that is added to someone's profile when you "Rate this Answer",when someone clicks disagree, it leaves a red mark, if you agree with the answer, you can leave a green. Many get reds wrongfully. (it was a good answer, but they didn't like the answer. Many won't give reds unless really deserved, Some will post a green as a "Balancer' to counter an reddie not deserved.
I give green's, no reds, unless they gave me one unnecessarily. Take Care,Good Luck

I have resigned myself to not giving any greens or reds at all to anyone.

Any accurate or inaccurate advice is best dealt with in a post, where the topic can be discussed in a more direct manner, is my opinion.

The Rep system, while available, and I understand it's purpose, is not utilized properly to begin with, causing it do be somewhat irrelevant, and the "balancer" system is even more useless, in my opinion.