Is my CCA wire really a copper claded aluminum ?

[rafael.x55]

I have CCA CAT5 cable, resistance seemed little high, so I did an experiment. Randomly cut the length and took the conductors out.

9m twisted pair from connected at the end so total length is 18m. Metal core is 0.49mm

Powered from 5V and current is 1.05A, resistance 4.76ohm or 0.26ohm/m. Resistivity 0.26 * PI*0.49e-3^2/4 = 4.9-8 ohm x m

Aluminum should be 2.82e-8. https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

What am I calculating wrong ? Or did they sneak in some iron to shave few cents off ?

 

[jpanhalt]

The primary use of the wire is for AC. Perhaps you should do the analysis using AC, not DC.

https://en.wikipedia.org/wiki/Copper-clad_aluminium_wire

As for pure aluminum, I did not find the alloy that is used in common wire. Because aluminum is soft and difficult to machine, it is possible that a harder, more machinable alloy is used in CCA. That alloy could likely have lower conductivity.

John

 

[RadioRon]

You measured 4.76 ohms for the entire circuit. It is possible that you have significant resistance in your connections to the wire that you are not accounting for. Also, what kind of power supply was used (I'm wondering what the internal resistance of the supply was). Did you measure exactly 5.00V at the ends of the wire with a good voltmeter?

 

[jpanhalt]

RadioRon, I agree and though of adding a comment about adding a control, but didn't. A control might be a "pure copper" CAT5 cable treated the same way.

John

 

[rafael.x55]

Some good points here, thank you. Original measurements were done on 30V/3A lab power supply with 3 digit panel meters for current and voltage, but I forgot to consider the leads.

Reference measurement was performed:
CAT6 pure copper wire, exactly 10ft. Untwisting 1m yielded 1.04m, so exact length of twisted pair was 2 x 10ft x 0.305 x 1.04 = 6.34m
The diameter measured 0.52mm, the area is 0.212 mm2
Measured 1.67V / 3.10A = 0.544 ohm. Resistivity = 0.544 ohm * 0.212e-6 m2 / 6.34 m = 1.82e-8
The result is 3.5% higher, which can be explained by increased temperature. Wire was distinctively warm, alpha for copper is 3.9e-3/C, so 20 degrees adjustment brings the resistivity dead on.
The voltage measurements were done with generic XL830L

Checked my power supply panel meters, current was within 0.5% from DMM, the 5.0V was 4.89 on DMM, correction -2.2%
Also during the reference measurement above, power supply leads were determined to be 0.052 Ohm (1.83V - 1.67V) / 3.10A, correction to original measurement 4.76 ohm -1.1%
The original measurement was 74% higher than expected so even with corrections above and accounting about 4-5% for temperature increase, it is still way off.
It is not attracted by the magnet.

Conclusion: mystery alloy

On practical side, I have been continuously dissipating 12W/m entire day today using this mystery wire. Not so great for 1Gbps networking, but works well for de-icing

 

[tomizett]

I'm sure you're right. It's fairly rare to come across pure aluminium as an engineering material - I doubt that it would make very decent wire as it has a very low tensile strength.
Perhaps you could measure the tensile strength, elasticity or breaking strain to get a better idea of what it might be?

 

[steveB]

Perhaps you could measure the tensile strength, elasticity or breaking strain to get a better idea of what it might be?

Hey! Who let a mechanical engineer into the forum? (joking)

 

[rumpfy]

raf,
I'm not sure that CAT5 cable was ever specified to be Copper clad aluminium (aluminum?)
This communications cabling system grew out of the use of PVC insulated internal telephone cable wiring for data transmission. That wire used a 0.5 mm diameter solid copper conductor. Your measurement of 0.49 mm confirms to me, that the wire is solid copper of 0.5 mm diameter. The constraint on wire diameter is severe because the cabling system was designed to use the US Bell systems RJ45 8 pin connector.
With CAT 6 cable, I think the conductor size was also 0.5 mm and the crosstalk requirements were tightened from the CAT5 spec. Your measurement of 0.52 mm for CAT6 is consistent with a nominal size of 0.5 mm and solid copper.
hope this helps.