An aluminum electrical connection needs a few things to be reliable: 1) a "springy" fastener 2) mechanical precleaning 3) an oxygen blocking coating.
In the US, aluminum conductors are allowed for certain usages. We used to allow 14 and 12AWG receptacle wiring, but too many houses burned down. The receptacles were redesigned for Cu or Al, but the codes remained stubbornly against the practice. A few more times where copper prices go through the roof, and the codes will change. For larger conductors, the wire, or bar, is brightened up with Emory paper, or a stainless steel (important!) brush, and then is covered with "Gorilla Snot", or some sort of NoAlOx grease. NoAlOx is a grease made of an oxygen resistant heavy oil, and a coarse emory grit. I like to again rough things up after the NoAlOx is liberally applied. Finally, the conductors are tightened to specified torque using a springy fastener... The springy fastener is often simply an ordinary fastener with a "Bellview Washer" stack to give it compliance. The big thing that makes high current aluminum joints fail is thermal expansion. If the fastener isn't springy, the aluminum expands from the heat, finds it cannot go in the direction of the tightened fastener, and flows elsewhere. When the joint cools, and the aluminum under the fastener shrinks, the joint is now loose, and will arc when current is once again applied, evaporating more aluminum out of the joint. Soon the fire department will be coming... if you are lucky. NoAlOx prevents this issue, if you use a springy fastener. -Chuck Harris Mitch Van Ochten wrote: > I once repaired a Valhalla 2555A Current Calibrator > <https://valhallascientific.com/DataSheets/2555A_Data_Sheet.pdf> (good for > up to 100A output). It uses aluminum bus bars inside to route the current. > The junctions between the bars had become higher than normal impedance and it > could no longer deliver 100A. I disassembled all joints, cleaned them with > emery cloth, then applied a drop of Caig Deoxit and re-assembled. That was > over four years ago and no complaints from the customer so far. > > > Best regards, > > mitch > > -----Original Message----- > From: volt-nuts [mailto:[email protected]] On Behalf Of Andre > Sent: Wednesday, September 20, 2017 3:54 AM > To: Discussion of precise voltage measurement > Subject: Re: [volt-nuts] Best way to measure micro Ohms > > Hi, just my $0.02 worth. > I have some instrumentation amplifiers here also looked into low resistance > connections for my other projects. > > If I recall correctly you need to look at the electrochemical series. For > interconnects on Al you want a metal similar on the ES. > The oxide is a problem but if you connect it properly eg with an oil droplet > and clamp connnector using compatible vernier it should be fine. > > Looking at how wiring in the US is done might give you some ideas. > > Kind regards, -Andre > ________________________________________ > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
