Info to backup safety of aluminum wiring?

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.

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.

On 16 Aug 2005 14:20:41 -0700, snipped-for-privacy@aol.com Gave us:

It will if it gets "noisy" enough.

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.

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

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--

This was the problem with the 1350 alloy of the early 70s but the AA

8000 series of alloys don't have this problem. In fact an aluminum conductor might actually perform better than copper in the aluminum lugs that are common these days. Testing seems to demonstrate that.

Proper torque is the biggest issue. That is not "as tight as you can get it"

I think it was more than that. Al has a different coefficient of expansion than Cu. So when a connection warmed up, the Al would 'extrude' it self out from under the screw. Then when it cooled, you had a loose connection with all the hazards that go with that. A couple of friends had houses built with Al wiring. Whenever that reported a 'flickering' light or 'staticcy' radio, we would check the wall outlet and find the connections 'lose'. Could usually get between a quarter and half turn (no, we weren't overtorquing, the things were just lose).

Proper devices rated for Al are able to accomodate the expansion/contraction of Al better without loosening over time.

daestrom

On Sat, 20 Aug 2005 11:07:09 GMT, "Den Corfield" Gave us:

Ever heard of metallic creepage? Malleable metals creep away from impingement over time. It is not merely a too tight or too loose scenario.

On Sat, 20 Aug 2005 11:07:09 GMT, "Den Corfield" Gave us:

Not even a word.

"The most common..."

Sounds like the AFCI folks sold the NEC a bill of goods!

From

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--

In our country, bare AL cable is used for HT overhead which is carried

500MVA (main line) to reduced voltage losses. Meanwhile, Cu wire is used for LV and below (include small signal).

proposed Gold materials to reduce almost losses.

Tks

magic