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fixit for aluminum branch circuits


Jim Baird
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Friends:

Having farmed out my services to "the dark side" (that is, the public sector) for some time now, I still find myself looking at existing conditions.

Asked to inspect for utility connection by a new buyer of a long unoccupied "investment" dwelling, I found evidence of meter tampering by a midnite electrician, a really strange looking super-lock on the meter can, and an inside panel that contained 99+ per cent aluminum branch circuits.

As a "code official" I can't invoke code sections on a 1979 house, but I did tell the owner to put his electrician on the case and to remedy the aluminum branches one way or another. I'm looking for the electrician's signoff on the building, either by inspection and pigtailing or verification of connections.

My post on ICC's web board elicited a response from an electric expert who said to have the electrician arc-fault every branch.

He said:

"...The development and use of the AFCI product was the solution to the improper termination of aluminum..."

Because the NEC is not a maintenance code the new technology was inserted in a logical place in new buildings, the room where most deaths occur from fires, the residential bedroom.

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Friends:

Having farmed out my services to "the dark side" (that is, the public sector) for some time now, I still find myself looking at existing conditions.

Asked to inspect for utility connection by a new buyer of a long unoccupied "investment" dwelling, I found evidence of meter tampering by a midnite electrician, a really strange looking super-lock on the meter can, and an inside panel that contained 99+ per cent aluminum branch circuits.

As a "code official" I can't invoke code sections on a 1979 house, but I did tell the owner to put his electrician on the case and to remedy the aluminum branches one way or another. I'm looking for the electrician's signoff on the building, either by inspection and pigtailing or verification of connections.

My post on ICC's web board elicited a response from an electric expert who said to have the electrician arc-fault every branch.

He said:

"...The development and use of the AFCI product was the solution to the improper termination of aluminum..."

Because the NEC is not a maintenance code the new technology was inserted in a logical place in new buildings, the room where most deaths occur from fires, the residential bedroom.

When aluminum wiring fails, it causes series arcs. The last I heard, the current generation of AFCIs only protect against parallel arcs. Has that changed yet?

- Jim Katen, Oregon

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When aluminum wiring fails, it causes series arcs. The last I heard, the current generation of AFCIs only protect against parallel arcs. Has that changed yet?

Jim, could you explain the difference please? I confess I've never heard of different types of arcs. I thought AFCI's protected against things like a loose connection at a receptacle terminal. Wouldn't that be a series arc??? What constitutes a parallel arc?

After a bit-o-google...

Arc faults can be series or parallel. Examples of a series arc are a broken wire where the ends of the broken wire are close enough to cause arcing, or a relatively poor electrical connection. Parallel arcs occur between conductors of different potential including, for example, a power conductor and a ground. Arc faults occur in series with the source and series arcs are further in series with the load. Arc faults have a relatively high impedance. Thus, a series arc results in a reduction in load current and is not detected by the normal overload and overcurrent protection of conventional protection devices. Even the parallel arc, which can draw current in excess of normal rated current in a circuit, produces currents which can be sporadic enough to yield RMS values less than that required to produce a thermal trip, or at least delay operation. Effects of the arc voltage and line impedance often prevent the parallel arc from reaching current levels sufficient to actuate the instantaneous trip function.

Am I getting that right then, that an arc at a loose terminal or wire-nut would not trip an AFCI?

PS...for those who want a headache you have to read the patent abstract...good luck!

USPTO Application #: 20080204955

Title: Arc fault circuit interrupter and method of parallel arc fault detection

Abstract: An arc fault circuit interrupter includes separable contacts, an operating mechanism, a current sensor sensing current flowing through the contacts and outputting a sensed current, and a processor determining and storing peak values of the sensed current for plural half-cycles. The processor provides arc fault detection, determines whether a first predetermined plurality of half-cycles occur in succession and correspond to non-unity power factor, and responsively inhibits the detection for a first predetermined time, and whether a second predetermined plurality of half-cycles occur in succession, each with smaller peak amplitude than that of an immediately preceding half-cycle of like or differing polarity, and responsively inhibits the detection for a second predetermined time. The processor determines that the detection is not inhibited for the first and second predetermined times, and responsively indicates that any of the half-cycles having a peak amplitude greater than a predetermined amount is a parallel arc. (end of abstract)

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When aluminum wiring fails, it causes series arcs. The last I heard, the current generation of AFCIs only protect against parallel arcs. Has that changed yet?

Jim, could you explain the difference please? I confess I've never heard of different types of arcs. I thought AFCI's protected against things like a loose connection at a receptacle terminal. Wouldn't that be a series arc??? What constitutes a parallel arc?

A series arc would occur at a loose connection or a broken wire. In a series arc, the electricity is still moving along its intended path, but it has to jump over a gap to get there. The arc's magnitude will be limited by the load on the circuit. No load = no arc. Little load = little arc (or no arc). Big load = big arc.

A parallel arc would happen with a line-to-line, line-to-neutral or line-to-ground fault. This might happen if you were to smash a staple too tightly against a romex cable. This arc's magnitude won't be limited by the load. The arc can occur even if the circuit isn't being used and, without an AFCI to protect it, it would burn till it tripped a common circuit breaker.

Early on, AFCIs only protected against parallel arcs. There was talk of improving them. I know that the newer combination type AFCIs will protect against series arcs, but I don't know the status of the breaker-type AFCIs. They might or might not protect against series arcs. I honestly don't know.

- Jim Katen, Oregon

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A series arc would occur at a loose connection or a broken wire. In a series arc, the electricity is still moving along its intended path, but it has to jump over a gap to get there. The arc's magnitude will be limited by the load on the circuit. No load = no arc. Little load = little arc (or no arc). Big load = big arc.

Series arcs are a little trickier to diagnose because tripping a switch or the brushes on a commutator both create series arcs.

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A series arc would occur at a loose connection or a broken wire. In a series arc, the electricity is still moving along its intended path, but it has to jump over a gap to get there. The arc's magnitude will be limited by the load on the circuit. No load = no arc. Little load = little arc (or no arc). Big load = big arc.

Series arcs are a little trickier to diagnose because tripping a switch or the brushes on a commutator both create series arcs.

Exactly. A truly useful AFCI will have to figure out the difference between benign arcs at, say, a vacuum cleaner motor's brushes or an excercise machine and dangerous arcs at, say, a loose, aluminum wire connection. It'll need to do it with something near 100% accuracy and it'll need to do it in a tiny fraction of a second if it's to be of any value in preventing fires. That's not an easy thing to do.

- Jim Katen, Oregon

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My question would be why there was aluminum branch wiring on a dwelling from 1979. I've never seen it on anything past 1973 or so. Then again, it wasn't ever too popular around here, maybe because we didn't (and still don't) have tract builders who literally watch every penny. Was aluminum wiring used as recently as 1979?

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My question would be why there was aluminum branch wiring on a dwelling from 1979. I've never seen it on anything past 1973 or so. Then again, it wasn't ever too popular around here, maybe because we didn't (and still don't) have tract builders who literally watch every penny. Was aluminum wiring used as recently as 1979?

Good question. As far as I know, there was never a rule or law that prohibited using aluminum wiring. The NEC still recognizes it for use in branch circuits.

I think that its use faded away as the price advantage disappeared and as bad publicity turned customers away from it. The bad publicity started in '72 with the formation of the CPSC and, as I recall, the final straw was the Beverly Hills Supper Club fire in '77. After that, no one wanted to have anything to do with aluminum wiring. The electrician who installed it in '79 must have been quite a character.

- Jim Katen, Oregon

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Well, it looks as if the combination AFCI devices are out there. These newer AFCIs are designed to protect against series arcs as well as parallel ones.

Check out Square D's version here:

http://ecatalog.squared.com/pubs/Circui ... rs%20(AFCI)/0760HO0701.pdf

And GE's version:

http://www.geindustrial.com/publibrary/ ... %7Cgeneric

And Siemens:

http://www2.sea.siemens.com/Products/Re ... agecode=en

So, I guess I'd agree with Jim Baird's associate. The new combination-type AFCIs ought to be a big help in making an aluminum-wired house safer. Though I wouldn't consider them a panacea.

- Jim Katen, Oregon

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  • 4 months later...

My question would be why there was aluminum branch wiring on a dwelling from 1979. I've never seen it on anything past 1973 or so. Then again, it wasn't ever too popular around here, maybe because we didn't (and still don't) have tract builders who literally watch every penny. Was aluminum wiring used as recently as 1979?

Good question. As far as I know, there was never a rule or law that prohibited using aluminum wiring. The NEC still recognizes it for use in branch circuits.

I think that its use faded away as the price advantage disappeared and as bad publicity turned customers away from it. The bad publicity started in '72 with the formation of the CPSC and, as I recall, the final straw was the Beverly Hills Supper Club fire in '77. After that, no one wanted to have anything to do with aluminum wiring. The electrician who installed it in '79 must have been quite a character.

- Jim Katen, Oregon

The house I inspected today had single strand aluminum wiring. The electrical permit on the cover of the service panel was dated June 1981. That's the most recent example I've come across.

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I know this isn't the kind of stuff we are used to seeing from the 60's and 70's but I have had a couple of new construction (2008) that had single strand #6 aluminum for the range. I think we may see aluminum single strand in the smaller gauges sneaking its way back into the market.

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A series arc would occur at a loose connection or a broken wire. In a series arc, the electricity is still moving along its intended path, but it has to jump over a gap to get there. The arc's magnitude will be limited by the load on the circuit. No load = no arc. Little load = little arc (or no arc). Big load = big arc.

Series arcs are a little trickier to diagnose because tripping a switch or the brushes on a commutator both create series arcs.

Exactly! And the old motors create really cool ones as they wear. When I was a kid I used to play around with the brushes on old motors and increase the distance from the commutator just to see the light show it would put on. Yes, I had a strange childhood, don't ask. - Just look into the air vents of any of those old, armor plated, 50 Lb. black and decker drills as they run, you'll see what Chad is talking about.

I think this is probably the real reason they started out only in bedrooms, no motor circuits to cause constant tripping.

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I know this isn't the kind of stuff we are used to seeing from the 60's and 70's but I have had a couple of new construction (2008) that had single strand #6 aluminum for the range. I think we may see aluminum single strand in the smaller gauges sneaking its way back into the market.

You are confusing single strand Branch circuits with single strand Dedicated circuits.

The Branch circuits have lots of points of connection. Four connections at each receptacle as hot and neutral come in and leave for the next receptacle in the circuit. Lots of places to have arcs.

Dedicated circuits had a connection at the panel and one at the receptacle. Fewer connections so few locations to arc. Very common to see single strand aluminum on dedicated circuits for ranges, dryers, A/C units, wall ovens, cook tops, etc.

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My question would be why there was aluminum branch wiring on a dwelling from 1979. I've never seen it on anything past 1973 or so. Then again, it wasn't ever too popular around here, maybe because we didn't (and still don't) have tract builders who literally watch every penny. Was aluminum wiring used as recently as 1979?

Good question. As far as I know, there was never a rule or law that prohibited using aluminum wiring. The NEC still recognizes it for use in branch circuits.

I think that its use faded away as the price advantage disappeared and as bad publicity turned customers away from it. The bad publicity started in '72 with the formation of the CPSC and, as I recall, the final straw was the Beverly Hills Supper Club fire in '77. After that, no one wanted to have anything to do with aluminum wiring. The electrician who installed it in '79 must have been quite a character.

- Jim Katen, Oregon

I believe the CPSC made wire manufacturers remove 14 and 12 AWG solid conductor aluminum wiring from the market in 1978. I would not expect to find a home built in 1979 or later wired with this material. I've only seen a few homes in my area (central PA) wired with solid conductor aluminum wiring, one of which was 2 weeks ago. http://www.cpsc.gov/CPSCPUB/PREREL/prhtml74/74040.html

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You are confusing single strand Branch circuits with single strand Dedicated circuits.

The Branch circuits have lots of points of connection. Four connections at each receptacle as hot and neutral come in and leave for the next receptacle in the circuit. Lots of places to have arcs.

Dedicated circuits had a connection at the panel and one at the receptacle. Fewer connections so few locations to arc. Very common to see single strand aluminum on dedicated circuits for ranges, dryers, A/C units, wall ovens, cook tops, etc.

I'd like to study that. Got a reference?

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