Info to backup safety of aluminum wiring?

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SQLit wrote:

A megger only finds damaged insulation where there is a carbon path to ground (or line-to-line). I think it would find a small percentage of actual aluminum problems and no loose connections. Disconnect GFCIs if you use one.
Bud--
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Bud wrote:

If the problem is due to a loose connection or oxidation induced high resistance, then a multimeter will certainly detect that on the resistance measurement function.
Matt
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Matt Whiting wrote:

(A multimeter is different from a megger.)
I don't think it is too practical to measure the junction resistance. How do you connect to the wire that is on at least one side. Tests have shown that wirenuts fail by the contact made not wire-to-wire because of oxidation but through the steel spring. I remember the resistance being about 2 ohms, not much. Not enough to dim lights, no flicker. But the steel spring becomes a heating element that destroys insulation and can ultimately cause a fire. 2 ohms may be hard to find with a multimeter.
Bud--
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Bud wrote:

correction -this should be a drop of 2 volts at a significant current; if hte current was 10A the resistance would be 0.2 ohms
not much. Not enough to dim lights, no

0.2 ohms may be hard to find

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Bud wrote:

How is the steel spring any different for Al wire than for Cu wire? It's heating is a function of the current through it or what it absorbs from the wire, not a function of the type of metal connected to it. Heat is generated by ohmic resistance, and that comes from corrosion between the Aluminum wires or the wires and the wire nut spring, not the spring itself.
Matt
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Matt Whiting wrote:

Steel has a high resistivity, which is why it is not used as a conductor. The tests show the wires do not contact each other because of oxide on the aluminum. The steel spring breaks through the oxide to make contact with the aluminum conductors. This means all the current is going through the spring. A CPSC report at http://www.inspect-ny.com/aluminum/pl2p2.htm shows a 2 volt drop across the wire nut at 17 amps. This is only about 0.1 ohm resistance but is a 34 watt heater. At this current level the spring is red hot. This destroys the insulation on the wires and the wire nut and can start a fire. But the voltage drop is low and constant so lights are not dim and do not flicker. Later in the deterioration the the connection can totally fail, possibly with arcing that generates a lot more heat (more likely fire).
One wire nut that failed this way was the Ideal #65 twister which is listed for aluminum/copper. Cleverly the plastic shell and the antioxide paste in the wirenut are both combustible.
(The link above is part of a slide show that goes forward and back.)
http://www.inspect-ny.com/aluminum.htm links to this site and others of interest.
Bud--
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Newsgroups: misc.consumers.house
Date: Wed, 10 Aug 2005 21:30:08 -0400 Local: Wed, Aug 10 2005 9:30 pm Subject: Re: Info to backup safety of aluminum wiring?
Does anyone know if using (and regularly testing) AFCI (Arc Fault Circuit Interrupers) increases reliability aluminium wiring to that of copper wiring when the current connection mechanisms are used?
***
A very good question. I'd love to know the answer too.
Thanks, Harry
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Harry Muscle wrote:

Tests show that failure in wire nuts result from no contact between the wires because of oxide on the aluminum. The steel spring breaks through the oxide to make contact with the aluminum conductors. This means all the current is going through the spring. A CPSC report at http://www.inspect-ny.com/aluminum/pl2p2.htm shows a 2 volt drop across the wire nut at 17 amps. This is only about 0.1 ohm resistance but is a 34 watt heater. At this current level the spring is red hot. This destroys the insulation on the wires and the wire nut and can start a fire. But the voltage drop is low and constant so lights are not dim and do not flicker. Since there is no arc, there is nothing for the AFCI to see.
Later in the deterioration the the connection can totally fail, possibly with arcing that generates a lot more heat. Arcing here would be picked up by an AFCI.
(The link above is part of a slide show that goes forward and back.)
http://www.inspect-ny.com/aluminum.htm links to this site and others of interest.
Bud--
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In northern Alaska where I am at, aluminum wire is rarely used. The extreme temperatures cause too many problems with cold flow.
But the AFCI problem you bring up is interesting because according to the Zlan site the inventor of the AFCI chip had to find a way to distinguish good arcs like a light switch turning on and off from a bad arc. I wonder if he analyzed all the possible combinations of aluminum to copper connections.
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the utility of afcis is somewhat dubious to begin with.
it is supposed to detect an arc, such as might happen when an extension cord is damaged.
whether they actually do or not is not clear.
in any case they will not detect the heating that occurs on an aluminum conenction that has started to oxidize.
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On 16 Aug 2005 14:20:41 -0700, snipped-for-privacy@aol.com Gave us:

It will if it gets "noisy" enough.
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No it won't. AFCIs detect arcs, and at fairly high current levels. The oxidation that forms on aluminum connections reduces the current due to the resistance of the connection, thats what causes the heat, and the fires.
Gave us:

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TokaMundo wrote:

The manufacturers do not make it clear that AFCIs cannot detect series arcs, such as those resulting from an oxidizing connection, until they progress to a ground fault which draws at least thirty milliamperes. If the arcing connection does not cause a ground fault the AFCI cannot detect it and the heat it generates can kindle a fire. They can detect a parallel arc such as when a screw penetrates a cable and causes a high resistance arcing fault between the current carrying conductors. Such parallel arcs are not that common. -- Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison
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Member TPVFD wrote:

I keep forgetting that.
The 2005 NEC requires AFCIs with series AND parallel protection starting 1-1-2008. I don't know of any on the market now.
Bud--
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Sounds like the AFCI folks sold the NEC a bill of goods!
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John Gilmer wrote:

From http://www.cpsc.gov/volstd/afci/AFCIFireTechnology.pdf
As part of the U.S. Consumer Product Safety Commission's (CPSC's) 1994 and 1995 efforts to reduce residential electrical system fires, the CPSC sponsored work on detecting and monitoring conditions that could lead to or cause fires in homes. The work was performed by Underwriters Laboratories Inc. (UL) and was documented in a report entitled, "Technology for Detecting and Monitoring Conditions that Could Cause Electrical Wiring System Fires." The study uncovered several possible technologies and concluded that arc-fault detection combined with ground-fault protection was the most promising technology to reduce the risk of fire when combined with conventional circuit breakers. At that time, such an arc-fault circuit breaker did not exist as a commercial device. Additional research has led to the development of the AFCI as a commercial product. ------------------- Series arcs, protection for which is being added to AFCIs, include loose connections. The current is limited by the load current downstream from the arc, so they won't trip breakers. They can, however, generate a lot of heat.
The NEC is a pretty pragmatic code. Changes usually require a demonstration that the change will improve safety.
Bud--
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Harry Muscle wrote:

1971 was a particularly bad year. Aluminum wiring is just fine for feeders, service entrance conductors, and other large capacity circuits (generally, 30A and larger). The biggest problem was with 15A devices sold until about 1972 -- it was impossible to make a proper connection with aluminum wire that would not oxidize and eventually fail. Aluminum wiring to an electric stove, clothes drier, central A/C, water heater, or subpanel is probably OK (the terminals will be listed something like "CU-AL" or "AL7CU")
There are new (expensive) replacement devices that are listed for use with copper or aluminum wire that are marked "CO-ALR" (if I recall correctly) that can be used on aluminum 15A branch circuits without needing copper or copper-clad pigtails.
I believe the CO-ALR devices is a better retrofit than adding a copper pigtail unless you get special crimp connectors made especially for joining small aluminum-to-copper conductors.
I would not live in a house with 15A aluminum branch circuits unless *every* connection had been inspected and upgraded as necessary. I would rip the "easy" ones out completely and replace with copper.
Best regards, Bob (not an electrician, just opinionated :-)
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If it was done _correctly_, Al wiring has always been safe. Cu/AL rated connectors/devices have been around as long as Al wire has. The problem mostly being craftsmen who didn't follow the rules, and Al being less forgiving of poor workmanship.

BTW: "CU-AL" designations are largely obsolete, electrical standards now primarily call for CO-ALR. Considered better than CU-AL, but CU-AL is still okay

Canada has always accepted CO-ALR wirenuts alone (without anti-oxidant grease) for routine 15A circuits. But the wirenuts are becoming harder and harder to find and are quite expensive (compared to ordinary ones).
[Larger Al connections require appropriatedly rated terminal connectors/ clamp devices, and anti-oxidant grease like in the US.]
US code appears to have been fluctuating rather a lot in regards to copper pigtailing. At one point at least, the ONLY legal way to pigtail Al to copper was with a very specialized crimp connector (~$5-10 _each_) and an expensive crimping tool (>$500). IIRC, the "system" was manufactured by "AMP", and they wouldn't sell you the stuff unless you took a course on how to use it.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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OK, what I don't understand then is why a testing agency is able to proof that for example a wirenut approved for aluminum can fail when installed properly and under normal conditions. If this wire nut is part of the "proper" methods involved in installing aluminum wiring, and when done properly is supposed to be completely safe, then why are they able to prove that it's unsafe?
I'm specifically refering to the information on the Ideal wire nuts presented here www.inspect-ny.com/aluminum.htm (about half way down the page).
Thanks, Harry
***
Chris Lewis Aug 10, 9:54 am

If it was done _correctly_, Al wiring has always been safe. Cu/AL rated connectors/devices have been around as long as Al wire has. The problem mostly being craftsmen who didn't follow the rules, and Al being less forgiving of poor workmanship.

BTW: "CU-AL" designations are largely obsolete, electrical standards now primarily call for CO-ALR. Considered better than CU-AL, but CU-AL
is still okay

Canada has always accepted CO-ALR wirenuts alone (without anti-oxidant grease) for routine 15A circuits. But the wirenuts are becoming harder
and harder to find and are quite expensive (compared to ordinary ones).
[Larger Al connections require appropriatedly rated terminal connectors/ clamp devices, and anti-oxidant grease like in the US.]
US code appears to have been fluctuating rather a lot in regards to copper pigtailing. At one point at least, the ONLY legal way to pigtail Al to copper was with a very specialized crimp connector (~$5-10 _each_) and an expensive crimping tool (>$500). IIRC, the "system" was manufactured by "AMP", and they wouldn't sell you the stuff unless you took a course on how to use it. -- Chris Lewis, Una confibula non set est It's not just anyone who gets a Starship Cruiser class named after them.
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I don't know if this is an aluminum thing or not, but many electric service connections are aluminum. These done properly are applied with aluminum wire goop and then the connections are torqued to main panel manufacturer's specifications.
Yet it is not uncommon for these connections to become loose and need to be re-torqued.
The question is: Does this occur more so with aluminum main service wiring than with copper main service wiring?
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