Aluminum Cables

Thanks for the help.

Talk to you later.

Hey,

I do not have to design anything at this point. But I can design a system if i need to. I was doing some reading and came across "mcm" and just wanted to engage you guys and talk about it because it new in my lane. I am used to working with AWG, or #6, #2, or 1/0 conductors thats all. Thanks for the reply, I like this website and I like the conversation that go back and forth, take care.

P.S

Crazy Legs is the name of my fantasy football team.

I'd be cautious in using Aluminum - in the 1970's it was used as a cheaper alternative to copper but when it was implicated in some house fires, most North American jurisdictions have banned its use in home construction.

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That was solid single strand wire used in wiring a home. The wire he is talking about is for service feeds and is stranded. Has been used as an alternative for copper in large feeds.

Crazy Legs, et.al.,

The early form of aluminum that was indeed responsible for many fires was replaced by a revised alloy that had a much lower ductility. The well-known failure mode for an aluminum conductor termination is due to cyclic: heating - expansion - deformation - cooling - contraction - oxidation. The oxide layer is a good resistor, so over time the cycle is guaranteed to be self-destructive. Proper installation techniques insist on breaking the ever-present oxide layer mechanically in the presence of an oxide-inhibiting greasy product designed for this purpose. Also, one must use the proper amount of tightness, whether using crimpers and dies selected for the wire size or bolts torqued to the specified value.

In the context of this thread, the higher resistance of aluminum necessitates the use of a larger conductor to achieve the same ampacity. The enemy of an insulated wire is heat and the heat dissipation is related to the circumference of the cable instead of its cross-sectional area. In larger cables carrying AC current, the "skin effect" puts more of the current in the outermost layers of the cable and less (per unit area) in the interior. Thus, the allowable ampacity of the cables increases at a rate nearly equal to the ratio of the diameters raised to a power of 1.25 (in free air) or a power close to 1.19 (in conduit). In conduit, however, the additional problem of cooling by radiation or convection through the conduit wall makes the relationship poorer for the very largest sizes of conductors.

To carry the same current as a 500 MCM copper conductor, you would need about a 750 MCM aluminum conductor.

--John M.