Aluminum Wiring

The Problem

In the Vietnam War era there was a shortage of copper for wire because they needed it for military matters. As a result, aluminum was used to wire millions of homes built in the 1960s through the mid-1970s. After several years problems began to be detected. Homes with aluminum wiring were having electrical overheating problems at a rate of 55 times those of homes wired with copper wiring. The problems occurred where the aluminum wiring was connected to devices (switches, outlets, etc.) and to itself (and copper wires) in junction boxes with wire nuts, not with the wire itself.

Burnt Outlet from Poor Aluminum Wire Connection (Used with permission)

What Was Discovered

After some research a couple things were discovered. One was that corrosion on aluminum wiring is different than corrosion on copper wire. The corrosion that forms on aluminum, just by being exposed to air, is non-conductive. It inhibits the flow of electricity. Corrosion on copper, on the other hand, is conductive. Another factor that is important is that aluminum expands and contracts at a different rate when exposed to heat. They have different coefficients of thermal expansion. When copper wire was replaced with aluminum the devices (switches, outlets, wire nuts, etc.) were not changed in any way because these differences were not taken into account.

To illustrate what happened I’ll discuss a typical failure at an electrical outlet. Imagine a TV plugged into an outlet that is wired with aluminum wiring. The home owner has the TV on for hours at a time, every day, then it’s off at night. When the TV is operating electricity is flowing through the wire and the wire heats up. As the wire heats up, it expands. The wire is connected to an outlet by placing the wire under a screw and the screw is tightened down on it. As the aluminum wire expands it exerts pressure on the screw that it’s under as it tries to expand. The screw is stronger than the aluminum wiring so the wiring deforms a bit by expanding out from under the screw head to accommodate the thermal expansion. This is called creep and it’s like blowing up a balloon between two large pieces of concrete. Once the balloon expands to touch the concrete blocks it can’t move the concrete blocks so the balloon expands out the sides. Then, back to our scenario, the TV is turned off at night and the wire cools. When this happens the wire shrinks a bit because it’s no longer heated up. When it shrinks, since the wire was deformed a bit by the heat and screw pressure, a small gap is left between the screw and wire. Well, electricity doesn’t flow real well through air so an electric arc is created between the screw and the wire. Electric arcs are very hot, like fire hot. This is what caused the overheating of the connection. This was also compounded by corrosion forming on the aluminum wiring where it was exposed to air because, as stated earlier, the corrosion on aluminum does not conduct electricity well. But the corrosion problem was secondary to the creep problem. This process of expansion, contraction and gap formation took several years to actually be a problem in most cases, so it took a while to discover the problems.

Does My Home Have Aluminum Wiring?

If you’re wondering, does my home have aluminum wiring, keep reading. There are four good places to look for aluminum wiring.

  1. In your electrical panel(s)
  2. Inside outlet or switch boxes
  3. On cables in unfinished areas of the home
  4. In junction boxes

Look for Aluminum Wires in Electrical Panels

First, it’s best to ask an electrician, or home inspector, to look for aluminum wiring in your home for you. This is because doing some of the things I’m going to suggest can put you at risk of electric shock. If you go forth on your own, beware!

Inside electrical panels is probably the best place to look for aluminum wiring. Be sure to shut off power to the panel before opening it up. After you remove the front cover look for aluminum (silver-ish) colored wires. In most panels you will find aluminum wires at 220 volt circuits, which we’re generally not worried about. These are the circuits where two circuit breaker handles are connected together so that if one trips, the other trips too. These 220 volt circuits serve larger appliances like ranges, water heaters, air conditioners, sub-panels, dryers, etc. We’re concerned about the circuits that server lights and outlets in the home.

Below is a picture of aluminum wires in a panel. Inside the lower left red box you can see the bare single-strand aluminum wires along with some single strand copper wires. These bare wires are the ground wires. Seeing these is a clear indication that there is aluminum wiring in this home. Note that this panel is unusual in that we see both copper and aluminum wiring. Most panels will have one or the other. When they are mixed like this, it suggests that a remodel may have been done in the home.

The upper right red box in the photo shows some multi-strand aluminum wires (center-bottom). These are likely associated with 220 volt circuits, which aluminum wiring is still used for today. You can also see white-insulated wires with single-strand aluminum wires coming out of them. This is another indication we look for to see if there is aluminum wiring in a panel. You can also look at the wire that is inserted in to the breakers themselves, but sometimes the wire is inserted into the breaker too far to actually see the wire color.

Aluminum wiring inside an electrical panel

Look for Aluminum Wiring in Outlet and Switch boxes

To look for aluminum wiring inside an outlet or switch box you need to remove the cover of one of these boxes. This is a lot safer than removing the cover of an electrical panel, but it can still be dangerous. So, turn off the breaker for the outlet or switch before removing the cover.

When looking inside the box, if you see an aluminum colored wire wrapped around the screw-down connection, you have aluminum wiring in the home. In the picture below you can see the aluminum wire underneath the screw head. You can also see charring, or overheating, of the connection which is a perfect example of the problem with aluminum wiring.

Aluminum wiring in an outlet box with charing
Overheated connection is the main problem with aluminum wiring.

Find Aluminum Wiring by Looking on the Cable’s Sheath

In an unfinished area of the home, like a basement, garage, attic or crawlspace, you often see electrical wires. These wires have markings indicating several pieces of data. One of those data is the type of wire it is. If it’s aluminum, it will be marked “AL” in places along the wires length. If you see “CU” marked on the cable, the wire is copper.

Wire in sheath showing label on outside of sheath
“CU”, meaning copper, is indicated on the cable. Aluminum would be indicated as “AL”

Now keep in mind that even in new homes aluminum wire is still used for larger wires. So you will see AL on some wires in most homes. We are concerned about finding aluminum wires in the size of 12 and 10 gage. This is the size wire that is used for 120 volt circuits. So if you see “AL” on wires that are marked “12 AWG” (AWG = American Wire Gage – how wires are sized) or “10 AWG” you have aluminum wiring on 120 volt circuits. If you see AL marked on cables that are also labeled “8 AWG” or lower numbers (the lower numbers mean larger wires) then these wires are likely for 240 volt circuits and we generally don’t need to worry about them.

Finding Aluminum Wire in Junction Boxes

The last place to look for aluminum wires is in electrical junction boxes. Junction boxes are where wiring connections are made in a closed box. They’re just like the boxes that switches and outlets are in, there’s just no switch or outlet. Just a blank cover. You may have these in your home and you may not.

How to Fix Aluminum Wiring

There are several ways to repair the wiring in a home wired with aluminum wiring. But first, you should know that repairs are only recommended on single strand aluminum wires which are usually on 120 volt circuits, not 240 volt circuits. 240 volt circuits are typically for dryers, stoves, electric water heaters, etc. These are wired with stranded aluminum wiring and that is generally not problematic. In fact stranded aluminum wiring is still used all the time in newly built homes to wire these types of devices.

So, how do you fix a home with aluminum wiring? Like I said above, there are several ways. Here’s a list:

  • Replace all the wiring with copper – This is the best option, and the most expensive. It is rarely done due to the amount of work that would need to be done. It’s really only practical on a major remodel where walls are ‘taken down to the studs’. And, this is generally unnecessary.
  • Pigtail aluminum wires with copper – This is a process of attaching a small piece (about six inches long) of copper wire onto the end of an aluminum wire. Instead of the aluminum being connected to devices, the copper is. This is the most common way to repair aluminum wiring. Pigtailing can be done in a few different ways:
    • COPALUM Crimps – This is a method of smashing the end of a copper wire with the end of an aluminum wire so that they are essentially welded together. Then putting a ‘crimp ring’ around the connection, and then an insulating sleeve. This needs to be done with a special tool designed for this purpose and the installers need to be specially trained. This is considered the Cadillac of repairs and is sometimes done. It’s also the most expensive. It is considered a permanent repair.
      COPALUM crimp - before insulationCOPALUM crimp - before heat shrinkCOPALUM crimp - insulation shrunk
    • Purple Wire Nuts – These are specially designed wire nuts that have an anti-corrosion compound in them that envelop the wire connection when it is inserted into the wire nut. You can find many pictures on the web where these devices have failed but all of them, according to the manufacturer, were not installed according to the instructions. This is a very popular repair because it is the least expensive, and if done right, can stand the test of time. Note though that these are considered a ‘temporary repair’ by the CPSC (US Consumer Product Safety Commission). So these connections should be inspected periodically for problems.
      Wire nut for aluminum wire repairs
    • AlumiConn Aluminum to Copper Lug – This is the latest offering as a solution to this problem. The AlumiConn lug is a small block with three ports for wires. Each port has a corrosion inhibiting gel in it that envelops the wire when it is inserted. It also has a small screw that clamps down on the wire, and a plastic casing for insulation. This is generally considered a permanent solution and approved by the CPSC, but since it is fairly new some folks are reserving judgement. One challenge that this device faces is that it is a bit bulky and may be hard to fit into existing junction boxes. If I had a home with aluminum wiring I would likely choose this option where possible and the Purple Wire Nuts for areas this would not fit.
      AlumiConn connector for aluminum wire repair
  • Use CU/ALR devices – When aluminum wiring was being installed switches and outlets were not designed to accommodate the unique properties of aluminum wire. Since then updated designs have become available. They are designated with the imprint “CU/ALR”. This stands for “Copper/Aluminum Revised”. The initial CU/AL switches and outlets had some problems, hence the revised versions. CU/AL is still an acceptable designation on circuit breakers and some other devices, but don’t use CU/AL rated 120 volt outlets and switches
    CO/ALR SwitchCO/ALR text on switch

Aluminum Wiring and Insurance

One other detail about aluminum wiring is that some insurance companies are (rightly) concerned about aluminum wiring in the homes they insure. It’s hard to overlook that aluminum wiring in homes has caused 55 times more overheating conditions in homes than copper. So, some insurance companies what to know if the home contains aluminum wiring and if it has been fixed in any way. Apartment buildings and condominium associations will often get a discount on insurance if their aluminum wiring has been repaired in some way. I haven’t heard if that is true for single family homes.

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