Subpanel Electrical Fire

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wrote:

is
Ah, yes...I was wondering how long it would take for the qualifications to be made. I've been very clear all along the contexts I've been talking about and have said more than once that aluminum is sub-optimal for home wiring. But, hey, nice try at a misdirection after being painted into a corner. Now that the tactic is just to start making up things I never said, I'll just bow out.
todd
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It was somewhere outside Barstow when "Todd Fatheree"

--
Smert' spamionam

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"Andy Dingley" wrote in message

"Bad" for home wiring because of termination issues, but good enough for transmission lines.
--
www.e-woodshop.net
Last update: 11/06/04
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Hi Andy,
Just out of curiousity what is the "Superb ring system".
Pat
On Sun, 06 Mar 2005 12:18:10 +0000, Andy Dingley

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toller wrote:

<snip>
OK, you want the techie explanation, here goes:
1) Aluminum wire oxides in the atmosphere.
2) The oxidization increases the resistance of an electrical connection.
3) The increased resistance generates heat which causes "cold flow" of the aluminum, thus reducing termination pressure, which also increases the electrical resitance of the connection.
It is a never ending vicious cycle resulting in the melting of the aluminum wire about 2"-3" up inside the insulation on the wire and often a fire results.
The above is why aluminum conductor has not been used in buildings for years.
Proper use of antioxidant compounds such as Alnox and larger conductors, above 2/0 minimum, allow use of aluminum in many high current applications, but definitely not branch circuits in housing applications.
HTH
Lew
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The rating info on the sheathing of the feed cable is very difficult to read over the section of the cable that is exposed to view. But, it appears to be either 8 or 6 gauge. Given that 8 gauge is rated, I believe for only 40 Amps and this is off of a 50A breaker on the main panel, I must assume it to be 6 gauge.
Also, all of the houses in our little development have the same central air conditioning units, so I assume the feed line is original to the house and was accepted as code-compliant in the mid 70's timeframe.
Thanks for your info, CDW
toller wrote:

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I just had a home built and I noticed that the power company used aluminum cable which they trenched underground from the pole to my house.
writes:

Al
wire.
They
to
is
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You simply CAN'T assume that. You have NO assurance that the person who installed that matched the breaker to the conductors correctly, and, from what you've posted so far, it sounds to me like he did NOT.
Furthermore, you said in your original post that your feed wire is aluminum. 8ga COPPER is rated 40A; aluminum conductors have lower ratings than copper conductors of the same gauge.
The current rating (ampacity) depends on the material, the wire gauge, and the temperature rating of the insulation.
To carry 50A in aluminum, you need either (a) 4ga wire of any conductor temperature rating, or (b) 6ga wire with a conductor temperature of at least 75 deg C. 8ga aluminum is NOT Code-approved, nor is it safe, for carrying 50A regardless of the conductor temperature.

You can't assume that either.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Doug Miller wrote:

You're right, of course. I guess what I was trying to say was that, trying to evaluate the possible causes of the problem, I look for the most likely events and go from there. If that does not pan out, I examine the less likely events.
You may be correct, there, also, in that the failure of the installer to perform the job correctly coupled with the failure of the municipal inspector to catch the error may be more likely than I expected. I realise they are not necessarily independent probabilities; i.e. neither of them were necessarily doing their job conscientiously.
Thanks for pointing this out!

Unfortunately, I just cannot make out more of the info on the sheathing than the 6 or 8 gauge point. So, I just do not know the temp rating.

Point taken...thanks... CDW

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In that case, it would be prudent to remove it, and replace it with 6/3 copper with ground - the point being that, given that the wire is aluminum, if it's 8ga it's unsafe, period, and if it's 6ga you're unable to determine whether it's safe or not. OTOH, 6ga copper is safe for 50A regardless of conductor temperature.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Lew Hodgett wrote:

both Al

This isn't true Lew. Go down in your breaker panel and look at what comes into it - aluminum. Look at what feeds your sub panel if you have one - aluminum. It's the combination of aluminum and copper in pigtails that caused problems in the 60's, not aluminum wire feeding panels. The OP posted a problem with a branch circuit that was copper. The aluminum feed lines coming into his sub panel hae nothing to do with the copper branch circuits.
-Mike- snipped-for-privacy@alltel.net
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Mike wrote:

Totally different world.
Utilities commonly use Al conductors as service entrance feeders as well as distribution cables; however, that is a totally different application which the utilities address by using specific terminations crimped with tools designed specifically for Al cable.
Take a look at the terminations made by the utility at the weather head of a typical service entrance. (You don't find those terminations at Home Depot)
Attempting to use Al conductor in a clamp type termination found on a typical plug-in c'bkr of a residential load center or the same clamp type termination found on the neutral and ground bus bars for branch circuits is a totally different world.
Cold flow and ultimately melt down are just a matter of time.
Lew
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True, but only in the sense that *much* more care is required in installation.

Nonsense. Cold flow occurs when a connection is over-tightened. A connection that is not overtorqued will not cold flow. Aluminum conductors, in terminals designed for use with same, are safe enough when tightened to the proper torque specification and no further, and of course when an appropriate anti-oxidant is used.
_Properly_installed_ aluminum wiring is safe. Trouble is, it's a _whole_lot_ more difficult to install aluminum properly, as compared to copper. For starters, - use only devices, terminals, and connectors rated for use with aluminum - use anti-oxidant paste everywhere - use a torque wrench on *every* termination to avoid overtightening (that includes the screws on receptacles and switches)
With copper, you don't have to worry about any of that: copper doesn't cold-flow, any listed device is OK to use with copper, and copper oxide is nearly as good a conductor of electricity as copper itself (aluminum oxide, OTOH, makes a reasonably decent electrical *insulator*).
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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I don't know if it has been mentioned but another strike against Al wire in branch circuits is that the wire is very disagreeable about being bent. Al wire will weaken and crack if flexed too often, as can happen while attaching devices (pulling, twisting. folding, stuffing back in the box, etc.)
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Lew wrote...
Totally different world.
Utilities commonly use Al conductors as service entrance feeders as well as distribution cables; however, that is a totally different application which the utilities address by using specific terminations crimped with
tools designed specifically for Al cable.
Take a look at the terminations made by the utility at the weather head
of a typical service entrance. (You don't find those terminations at Home Depot)
Attempting to use Al conductor in a clamp type termination found on a typical plug-in c'bkr of a residential load center or the same clamp type termination found on the neutral and ground bus bars for branch circuits is a totally different world.
Cold flow and ultimately melt down are just a matter of time.
Lew
So then I said...
Not really different Lew. The meter channel uses crimped lugs like you're talking about, but your service panel uses aluminum feeders that just clamp down in the main and on the buss bar the same way that your copper branch circuits do. The same way that I believe the OP is describing his sub panel to be.
The point the OP made - at least as far as I recall, is that his branch circuites are copper. It's only his feed that is aluminum. That would be essentially what you see in your primary panel. The buss bar is aluminum, so he would not have any problems clamping an aluminum feeder down. It's when you put copper in there that you contend with issues of dissimilar metals and have to use products like no-ox to prevent them.
-Mike-
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Mike Marlow wrote:

Mike, Yes, the subpanel is set up as you describe with Al Feeder and, all copper to the subpanel circuits.
You also say the buss bar is Al. My material recognition is not up to par, so, I really cannot tell. It certainly looks like it could be Al. The grounding bar appears to be the same material as do the hot terminals. The set screws in the neutral and ground buss appear to be the same material, but the set screws in the hot terminals have a color that looks about half way between Al and Brass. BTW, the bracket that connects the grounding buss to the case is the same material as the set screws on the hot terminals.
So, what is it about the construction of this subpanel that allows it to be rated for AL or Cu wire, the Al bus terminals?
Charlie

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Well Charlie, I'm no metallurgist so I take the easy way out - I rely on the label in the box. I'm guessing it's the clamping that allows for either wire. It's when copper and aluminum are twisted together that the joint will fail over time (heat). Most panels are rated for AL or Cu. There's nothing special about yours. It's just the way most are made.
--

-Mike-
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The quality of the termination of the wires that burned was poor , a result of an untight connection, corrosion of the conductor, or the inside of the terminal, etc. Since this poor connection added a resistance to the circuit, it caused heat to build up at that point. The circuit breaker didn't trip because you weren't pulling more current through it than it was rated for. Whenever you re-use old wiring or panels all of the terminations need to be cleaned thoroughly before they are assembled. In the case of aluminum wire this is even more important. It's also necessary to coat the aluminum conductor terminations with a special grease type compound that has been developed to prevent oxygen in the air from oxidizing the aluminum when it warms up from carrying heavy currents. This has to be done when you do the installation. Now it will be necessary to dis-assemble the problem connections, cut back the wires far enough to find undamaged insulation and conductors. Replace any terminal that shows any damage, and then clean and re-assemble all of the connections again applying the special grease to the aluminum connections. Make sure that you have every connection good and tight before you re-apply power and it should all be OK again. It's a good idea to inspect the panel connections every so often to try to catch this type of problem before it gets this bad. It's a good thing that you caught it when you did. It wasn't your wiring, but the poor electrical connection that caused the heat to build up and damage the wiring.
--
Charley




"Seawulf" < snipped-for-privacy@cox.net> wrote in message
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I want to thank all of you who responded. I even enjoyed the playful wrestling with characteristics of Al wiring.
Having thought about this for a few days, now - before reading all of your stimulating comments - I had begun to conclude that the charring of the insulation on the neutral wire for the dust collector circuit was perhaps,not the cause, but the result of the underlying problem. The clue to the problem, I began to think was the melted plastic around the neutral bus bar and the problem was the connection of the 50A feed Neutral to the subpanel Neutral bus bar.
So, after reading your comments, especially Charley's - I believe that to be the case. I think that the faulty connection heated the bus and the dust collector wire had its insulation touching the bar, which would explain why it was so charred and the feed and other circuit neutrals' insulation was not affected.
I also take onboard the comments about the potential danger of Al wire.
Thanks for your help
Charley wrote:

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You're very welcome (I say for the others), and from the volume and intensity of the replies, you now know why this is rec.electrical.woodworking. Other than, possibly, staining cherry, few posts get as many quick responses as electrical issues, and this has been the case here for many years. Interestingly though, IMO the quality of the responses is much better than several years ago; one might almost assume some of you guys know what you're talking about:-) GerryG An EE who has nothing more to add, since several already said it all.

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