cable size calculation of allumunium cable

saha_malay

current capacity of allumunium cable of different sqmm at 40degree C ambient temperature.

securespark · Posted: Fri Sep 08, 2006 3:49 pm Post Subject:

Can you rephrase that?

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Spark123 · Posted: Fri Sep 08, 2006 3:57 pm Post Subject:

There are charts for the current ratings of aluminium conductors in appendix 4 of bs7671 which give them a current rating at 30 deg C. To find its rating at 40 degrees all we need to do is multiply it by a de-rating factor for 40 deg C. I don't know about india though.

plugwash · Posted: Fri Sep 08, 2006 5:04 pm Post Subject:

finally remember that using aluminium wiring with fittings not designed for it is very dangerous, so is putting it in the same terminal as copper even if the fitting is designed for both.

if you have figures for copper cable you should be able to derive the ones for aluminium pretty easilly, just multiply the figure for copper by the resistivity of copper at your cables temperature rating and divide by the resistivity for aluminium at that temperature.

Nige F · Posted: Fri Sep 08, 2006 6:23 pm Post Subject:

you`re not wrong, -plugwash

I had a length of ali going to my cooker from CU..........nearly set fire to the unit.....then it went to 6 mm copper via a 30A junction box.........changed it all before part P

securespark · Posted: Fri Sep 08, 2006 10:02 pm Post Subject:

If Cu & Al don't go together, how come they used to make aluminium conductors coated with copper?

Or indeed imperial cables with tinned copper conductors?

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As George Michael once said, "..if you're gonna do it, do it right, right?"

plugwash · Posted: Fri Sep 08, 2006 10:05 pm Post Subject:

securespark wrote:

If Cu & Al don't go together, how come they used to make aluminium conductors coated with copper?

i'm not sure on the details i just know special precautions are needed (american wiring sites are very hot on this as such wiring was far more common over there), maybe if the aluminium is completely covered the issues (which i belive are primerally accelerating corrosion arround the joints)

Quote:

Or indeed imperial cables with tinned copper conductors?

i presume they are tinned with tin not aluminium

securespark · Posted: Sat Sep 09, 2006 10:04 am Post Subject:

But the point you're making presumably is about dissimilar metals reacting against each other?

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plugwash · Posted: Sat Sep 09, 2006 7:00 pm Post Subject:

look, i'm not a materials scientist so i don't know exactly why its dangerous and why other metal combinations (e.g. copper and tin or copper and lead) don't pose a problem.

I DO know aluminium is strange stuff though. in air you basically won't get it to burn easilly at all (i think it may be easier if powdered though) but mix it with iron oxide (which should by rights be a reaction that releases less energy than simply burning it) and give it a bit of activation energy and you'll get a hugely intense reaction that is virtually impossible to stop.

jeepmadmike · Posted: Mon Sep 11, 2006 8:39 pm Post Subject:

Ali and copper cables can be joined without a problem as long as the joint is covered with a compound with prevents any electrolytic corrosion, ali cables will burn back during a fault, I repaired a 300mm SWA a few months ago it had been damaged during excavition work and re-buried almost 4 feet of the cores where missing.