If I had my druthers, aluminum wire and terminal blocks would not be used also .... But cheapness pervades..
I've been doing control and power engineering work for about 30 years now and I have only seen a few instances where alum entrance cable has screwed up. Usually because it wasn't prepped properly. But you are right, if you want bullet proof reliability you don't use alum in electrical installation. I am sure that the space shuttle does not have any aluminum terminal blocks in it! Still, try and find a heavy junction power block for industrial use that is not alum.... It is pretty much impossible. That is also pretty much all the power company will run any longer. I have some new 15KV lines on the poles in front of my place and they are all twisted alum cable. >>Chuckle, with suitable emphasis on the cheap part Dave. Copper is plumb outta sight now. Actually it has come down a lot. A 500 ft roll of THHN 10 gauge stranded was over a hundred bucks a roll for a while. The last I checked it is about $55 now. It is sort of like gas at $2.30 a gallon, it is cheap compared with $4.50! ;-) The copper ground/neutral bus bars I bought at the local home store recently for a star ground central point were about $6.50 each. Cheap by industrial prices ... I was talking with a customer of mine today... They were talking about some slide mechanisms that had to be replaced on a machine I helped install last year.. The replacement parts being discussed were "only" about $10K they said.... So everything is relative. :-) Dave Gene Heskett wrote: > On Tuesday 06 October 2009, Dave wrote: > >>>> This relaxes the joint pressure, air gets in, and >>>> >> alu does what it normally does when exposed to the oxygen in the air, form >> an insulating film with 100% coverage, and a 30-50 volt breakdown in about >> one millisecond. Alu is great, in its place, but inside an electrical box >> of any kind its just a damned fire starter with a long fuse timing. >> << >> >> While I agree that copper is much superior to alum. and alum wiring when >> used in places like house wiring didn't turn out so well, however alum >> power cable is pretty much the standard for service entrances. Also many >> panel power components are made of alum - often with plating to prevent >> the oxidatation problems. >> > > Even for power drops they are a fire starter. In my 25 years of being the CE > at WDTV, we were knocked off the air and had to replace all the 750mcm cable > from the substation pole to the tx building twice due to grand and glorious > fireworks from a Burndy Hy-Press installed alu sleeve failing just outside > the weather head. Twice. The last time the fire went largely un-noticed by > the operator on duty in the building, and the heat telegraphed down our > copper 750mcm so well that when we laid the weather head on the ground and > pulled it apart, the insulation was cooked for about 3 feet into the weather > head. The power guys wanted to run alu into the weather head and into the > meter base inside the building, but I scrounged up enough 750mcm in copper > that we could rebuild it in copper. But they refused, claiming they didn't > have any copper that heavy, to string anything but alu from the weather head > to the substation pole. And only 600mcm to boot. I was seen as grumbling > about it when I walked away, defeated cuz that run wasn't ours. > > My house is all copper, but the service drop they replaced with a heavier > cable when I added a 200 amp service 4 years ago, is alu.. And every time > I'm on the roof, I 'cop a feel' of each crimp sleeve to make sure there's no > heat. So far, so good, like the guy that plans to live forever said. > > I bought a house in Nebraska that had alu jumpers from the meter head > outside, to the service box inside, about an 8 inch run. I put out 2 fires > in the middle of the night in that box or in the meter head, the 2nd time > they got replaced with some 000 I had at the transmitter, color code be > damned. And its a felony to break the seal on a meter head in Nebraska. I > called Ron, the line super at Wayne County Public power the next morning both > times and told him to send somebody by with a new seal. He already knew me > well, so the next question was "what the hell were you doing in there?" > knowing the answer was related to alu wire before he asked it. > > >> It's like everything else, if you do it the right way, no problems, ignore >> the rules and they will come back and bite you. >> > > If one goes around and inspects it, tightening loose connections, it can be > pretty good. The average home owner cannot do that and has no clue that it > needs to be done from time to time. He gets his wake up call when his > insurance denies his claim because there was alu wire found in the ashes of > what was a $350k home.. > > >> Most alum terminal blocks and even the grounding/neutral bars you can buy >> at home depot etc are either tin plated copper or tin plated alum. >> > > Even tin plated alu would scare me, cuz that tin plate can't have a > continuous metal to metal connection to the alu. Cleanly cut alu will form > an oxide coating in a millisecond that is good for 40 volts, and if it lays > around a day between machining and plating, it will be good for 400 volts. > alu oxide is two things, first the second hardest substance commonly > available, and second, a good enough insulator that it has been used as a > replacement for the mica or silicon rubber insulators between power > transistors and their heat sinks. I've actually seen it use in older > transistorized tv's under the horizontal output transistor, which may have as > much as 1600 volts on it at the instant its turned off at anywhere from 15 to > 120 khz. > > >> The ones I have used before are tin plated copper. They work great and >> they are cheap. >> > > Chuckle, with suitable emphasis on the cheap part Dave. Copper is plumb > outta sight now. > > >> Dave >> >> >> --------------------------------------------------------------------------- >> --- Come build with us! The BlackBerry® Developer Conference in SF, CA >> is the only developer event you need to attend this year. Jumpstart your >> developing skills, take BlackBerry mobile applications to market and stay >> ahead of the curve. Join us from November 9-12, 2009. 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