I've recently determined that I need to use #2 gauge copper wire. I've been looking at THWN, and I'm curious what the equivalent aluminum wire would be. I'd be very interested if you know of any online resources with resistance tables for various aluminum wire types. Thank you for your help!
Comments
Anon, happy to help you.
#2AWG THWN copper @ 75C is rated for 115A.
Rule of thumb for aluminium conductors is 2 trade sizes larger.
1/O THWN aluminum @ 75C is rated for 120A
Hope that helps and if you have any questions just let me know.
Anonmymous,
While using aluminum wire will save you about 50% in wire cost, there are negatives that you need to factor in as well. First, you must use much larger wire. As Adam mentioned 1/0 aluminum will carry as much current at #2 copper, but it has a cross sectional area of 100.80 mm2 vs 33.60 mm2 for the copper. This means you must use a MUCH larger conduit, which when you factor in that cost, your savings may be a wash. Another thing you need to watch out for is that whatever you are connecting at both ends is UL listed to support aluminum wire. Most breakers are, as are most load centers, but a lot of things aren't, expecially things that vibrate like motors, air conditioners, etc... Then you have to periodically check the torque of those connectors and make sure that the anti-oxidant gel is still in place.
Steve
Download the Southwire wire sizing app, it will tell you sizing and losses, aluminum wire has higher loss over copper. Its a great tool, and free from the playstore.
Just use the NEC tables, they provide ampacity for both Cu and Al conductors in the same table.
Make sure you know how to use the Al conductor according to the manufacturers requirements. There is usually a requirement to use an anti-oxident on the terminations and making sure the terminals are listed for Al conductors. The new Al alloys being used have the same expansion as Cu so there is much less of a problem with terminals loosining up over time. There were a lot of problems with Al conductor in the past that have been solved.
Sorry, Steve Felker, but you should not retorque aluminium wire!!!! You will damage it.
From the FAQ at: http://www.aluminum.org/resources/electrical-faqs-and-handbooks/electrical
Q10) Do aluminum connections need to be periodically tightened to maintain a good electrical connection?
No. Connections on either aluminum or copper should not be retightened after installation following manufacturers’ installation instructions. Connector test performance requirements are based upon no retightening.
NFPA 70B, Recommended Practice for Electrical Equipment Maintenance, does not call for retightening aluminum conductors. Connections should only be tightened if there is evidence of a loose connection. Both over-tightening and under-tightening can cause failure of aluminum or copper connections. Unwarranted re-tightening of screw-type connectors can lead to failure of the connection with either aluminum or copper conductors.
Thanks for clearing that up.. I'd always believed the ali 'flowed' under the compressive pressure of the screw/clamp and that periodic re-compressing back to the same torque was neccessary, but that FAQ led me to think that wasn't the case. My main problem is galling of screws in Siemens breakers where the thread seems to fuse with the nut and no amount of force will undo it or, for that matter tighten it. (Not specific to Ali, also seen with Cu.. ) I have a box of Siemens where I've had to cut the wire, remove the breaker and fit a new one if modification is needed. A PITA if it was an expensive breaker for sure.
Colin