A hypothetical question about the current carrying capacity of bare copper.

[A.Justice]

From what I understand, wire mostly gets it's amp ratings based on the type of insulation, and how well it withstands heat. Obviously there's physical limitations based on the wire gauge, but the difference between cheaply insulated stuff with a low melt point, and something like PTFE or silicone are pretty big. I use mostly 10 awg, and the spec sheets for PVC or plastic are all around 40 amps. Some of the more expensive silicone can take 70-140 amps (according to the manufacturer's data sheet).

So, my thought is what if you (again, hypothetically, I'm definitely not going to do this) used solid, bare copper wire, in a location where it could safely heat up. Copper melts around 2000°f, I bet it would hold together enough to reach 1000° before any sort of mechanical wire failure.

Could bare wire be used to carry short, relatively large loads? Is there any sort of formula that could tell me the maximum theoretical current carrying capacity of a piece of copper? It's been nagging at me all day wondering if you can pass current through red-hot wires successfully, and how much.

 

[Bob B]

Voltage loss is another major consideration.

I wouldn't use small wire to carry large loads period. The heat generated has the potential to cause other problems even in a short segment.

 

[snoobler]

AWG charts list various fusing currents for wire gauges.

American wire gauge - Wikipedia

en.wikipedia.org

But as @Bob B indicated, voltage loss is directly proportional to power loss. That hot wire means you're losing energy/power.

 

[MattiFin]

Could bare wire be used to carry short, relatively large loads? Is there any sort of formula that could tell me the maximum theoretical current carrying capacity of a piece of copper? It's been nagging at me all day wondering if you can pass current through red-hot wires successfully, and how much.

Put a powerfull fan to cool the wire and you can probably push it to 10s fusing current shown here:

American wire gauge - Wikipedia

en.wikipedia.org

2000A for 1/0 cable. Hypotetically, like your question.

 

[newbostonconst]

The ratings differences could be do to the usage specs. If a wire is UL listed I would believe the numbers.

If it is not UL listed then they likely aren't testing under the same specs. You do not know at what temp it is rated at and if it is tested in open air or in conduit with other current carrying wires.

Like NM-B (aka Romex) wire is rated higher in some sizes because it really can't be put in conduit and thus has air movement around it I believe.

 

[A.Justice]

Thanks for the grease responses! I didn't realise that voltage loss would be an issue as well, besides being dangerous, it sounds inefficient as well...

 

[natec]

There is industry guidance (and mil-spec guidance) for bare bus bar ampacity. Here is one source (they also have great instruction on bus bar joints):

Electrical: Bus Bar - Table 1: Ampacities

Ampacities in the table below are for bus bars having an emissivity of 0.4.

www.copper.org

 

[A.Justice]

There is industry guidance (and mil-spec guidance) for bare bus bar ampacity. Here is one source (they also have great instruction on bus bar joints):

Electrical: Bus Bar - Table 1: Ampacities

Ampacities in the table below are for bus bars having an emissivity of 0.4.

www.copper.org

That is exactly the kind of chart I was looking for, some of those numbers are incredible. Much appreciated!

 

[MichaelK]

So, my thought is what if you (again, hypothetically, I'm definitely not going to do this) used solid, bare copper wire, in a location where it could safely heat up. Copper melts around 2000°f, I bet it would hold together enough to reach 1000° before any sort of mechanical wire failure.

Could bare wire be used to carry short, relatively large loads? Is there any sort of formula that could tell me the maximum theoretical current carrying capacity of a piece of copper? It's been nagging at me all day wondering if you can pass current through red-hot wires successfully, and how much.

In the biology field we have a term for this. It's called "natural selection". Please have a sit-down chat with your insurance agent the next time you have one of these ideas.

 

[A.Justice]

In the biology field we have a term for this. It's called "natural selection". Please have a sit-down chat with your insurance agent the next time you have one of these ideas.

I'm the kind of person who likes to know the full specifications of the materials that I work with. Knowing failure points, and not just the rated limits, but when catastrophic failure can happen is extremely important when designing a system in my own home, or working for my customers.

 

[snoobler]

In the biology field we have a term for this. It's called "natural selection". Please have a sit-down chat with your insurance agent the next time you have one of these ideas.

So... everybody using a bus bar between cells or to join batteries in parallel is acting on "one of those ideas" and should "have a sit-down chat with your insurance agent" ?

 

[MichaelK]

So... everybody using a bus bar between cells or to join batteries in parallel is acting on "one of those ideas" and should "have a sit-down chat with your insurance agent" ?

Look back at the first post where 1000 degrees gets mentioned. That's more along the lines of what I was thinking about.

 

[A.Justice]

So, my thought is what if you (again, hypothetically, I'm definitely not going to do this) used solid, bare copper wire, in a location where it could safely heat up. Copper melts around 2000°f, I bet it would hold together enough to reach 1000° before any sort of mechanical wire failure.

Look back at the first post where 1000 degrees gets mentioned. That's more along the lines of what I was thinking about.

Please re-read the first line if you are worried about me doing something dumb.

 

[MichaelK]

Please re-read the first line if you are worried about me doing something dumb.

Please don't feel offended. I've encountered what seems like more than my share of idiots online, so I tend to be overly cautious.

 

[Catvideofestival]

I second the bussbar calculations.

Also, if you are going through this thought process it is also valid to consider two more things. First being the type of connection point used as it is usually the point of highest resistance/heat and would be where the first melt/break would happen (I've seen it, google melted neutral). Second being if you are dealing with large fast changes of current there are large magnetic forces at play as well as the field expands and contracts. One example of this would be cables in a cable tray that have broken their tie-wraps because of a violent movement in a short circuit condition.

 

[Diysolar123]

From what I understand, wire mostly gets it's amp ratings based on the type of insulation, and how well it withstands heat.

no, that is not correct...
amp ratings are based on power "lost" to heat; its just I^2 * R, and you can calculate that by the resistivity of various materials.
The more heat you generate, the higher the resistance of the material gets, its not about "withstanding" heat.

electrical wiring codes are based on avoiding fires which is how the type of insulation comes into play, different thing.