Why Is Service Entrance Wire Aluminum

[mestagehand]

Rather then being the type of person that accepts and repeats what I am told is ok I like to know the reasoning behind it. So here is a dumb question that I haven’t come across in my research in aluminum wiring. Sense everyone out there generally feels that aluminum is unsafe, especially 12 Awg and 14 Awg branch circuits, why do we still use it in larger gauges? What stops it from loosening up in a pannel or meter box? (kind of the same question but just in case it wasn't answered) Why doesn’t the service entrance fail after several years like an outlet or switch would? The answers to those questions may lead to why there is an article in the NEC code book that still allows you to use Aluminum wiring for dryers and ovens? Is it safe, or would you prefer to see copper? What precautions should be taken when installing it?

Thanks for your help

[Wgoodrich]

Large versus small. Try and experiment project. Find a piece of steel wire say 14 awg or smaller. Then find a large steel rod say about 2" around. Now take a blow torch to each piece of steel at the same time. The little wire will heat up cherry red and you have just barely warmed that large mass of steel.

Same happens in electrical. When electricity is used carrying an electrical load the wire heats and cools as it is being used to differing degrees. This heating and cooling will cause both copper or aluminum to loosen in connections making it prudent to periodically check all connections for tightness as the years go by. Commonly not done but a real good idea.

The smaller the wire the faster it will expand and contract due to heating and cooling. The faster the heating and cooling the more likelyhood for those wiring connections to work loose due to the expansion and contraction.

Thinking of the above it then should become obvious that the larger aluminum wiring such as 8 awg and larger is much less likely to work loose as fast as smaller wire such as 12 or 14 awg wire. The aluminum wiring of older days say back in the 70s installed at that time was not as reliable for electrical installations as the aluminum wiring manufactured today.

We had a history of loose connections, damage due to heat of loose connections or corroded connections etc. with those wiring projects from the past in that era. Today the metal mix is different and most if not all the problems of the past has been addressed concerning the alloy of luminum wiring manufactured today versus the 70s era. Also the alloys of connectors made today are improved better than the connectors of that era such as receptacles, switches, wire nuts etc.

The bad feeling concerning aluminum wiring is due to the problems we found in the history of that aluminum smaller wiring [faster heating than larger wires] installed in teh 70s compared to today.

Now it is true that aluminum wiring is required to be larger in wire size than the copper ampacity with the same ampacity rating. This is due to the resistance of copper being approximately 12.8 ohms and the aluminum wiring resistance to be approximately 22.1 ohms.

This puts us to ohms law. Ohms law says approximately that a 12 awg aluminum wire is rated at 15 amps versus 20 amps for the same 12 awg copper wire. Just because the resistance is higher in copper versus aluminum does not make it better to conduct electricity. You just have to use the wire rated for the amp load being applied to that wire whether copper or aluminum. The efficiency of electricity used is the same if the ampacity is the same.

Aluminum wiring connections are more likely to corrode in wet locations thus requiring you to install per the manufacturer's installation instruction using products listed and labeled for the use. If installed correctly you should have no problems with any wire size aluimnum as long as it is 12 awg or larger in a home using the improved aluminum wiring manufactured today with the devices manufactured today.

Now to say aluminum wiring should not be used is an error. Most of the world power, up to 90% of it is delivered by the power company across large distances such as primary lines using aluminum wiring.

Almost all the electricty you have used in your life traveled on aluminum wiring as some point from the power being generated and you having used it.

The NEC still allows you to install 12 awg aluminum wiring today in a new home to power receptacles, switches, ranges, dryers and etc. Big and small aluminum is fine is installed per the manufacturer's installation instructions and the NEC rules.

HOpe this helps

Wg

[wire2]

wg, you've covered it pretty well.
I'd like to add that a large part of the low opinion of aluminum wire was due to a very high number of problems and failures of cheap wiring devices available in the 70's, (receptacles and switches). Typically they had a push-in feature that held the wire under a spring steel flap. Now you had only a steel knife edge against a 12 ga aluminum wire, with several of these in series, (daisy) in a home. I recall changing MANY of them to screw type devices after complaints of hot receptacles, flickering lights, no power, etc.
As wg stated, if the ampacity of a conductor is comparable, there's nothing wrong with aluminum wire, (versus copper), the problems arise with poor terminations.
A clean aluminum cable, coated with anti-oxidant compound will form a reliable connection for many years under normal circumstances.

[Ohm1]

anti-oxidant compound

Time plays a roll in installation. While AL is fine to install, it is far better to go with copper when dealing with branch feeds.