Aluminum wiring in an older house

A copper shortage in the mid-1960s led builders to use aluminum wire for the everyday 15- and 20-amp circuits in houses, not just the heavy circuits for dryers and ranges. Homes built before 1965 are unlikely to have aluminum branch wiring. Cables put in between 1965 and the mid-1970s may have it, in new houses, in additions and in circuits added or rewired then.

The danger is at the connections. A national survey found that homes built before 1972 and wired with aluminum were 55 times more likely than copper-wired homes to have at least one outlet connection reach fire hazard conditions. Those conditions meant cover-plate screws heating to 300°F, sparks from the outlet, or charred material around it. The survey only looked at outlets, and other aluminum connections and splices fail too.

Why the connections fail

Several processes at an aluminum wire connection slowly raise its resistance to current. The damage builds up over time. The higher resistance makes the connection overheat when current flows, sometimes to dangerous levels. It happens at outlets, switches and junction boxes, and where major appliances such as dishwashers and furnaces connect.

Failing aluminum connections seldom give clear warning first, and some overheat with no earlier sign of trouble. Signs of a problem in any wiring include:

• Outlet or switch cover plates that are hot to the touch
• Flickering lights
• Circuits that stop working
• A smell of burning plastic at an outlet or switch

If you notice any of them, have a qualified electrician find the cause. Don't try it yourself, since you could be electrocuted or make the problem worse.

How to tell if you have it

Aluminum wire was almost always installed as plastic-sheathed cable that looks just like copper cable. Look at the printing on the outer jacket where the cables are exposed, such as an unfinished basement or garage. A flashlight held at a low angle helps you read embossed letters. Aluminum cable is marked "Al" or "Aluminum" every few feet along one side.

Read as much of the marking as you can. "CU-clad" or "Copper-clad" next to "Al" means copper-coated aluminum wire, which isn't covered by the repairs below. If you can't tell what you have but suspect aluminum, have an electrician check.

The repairs

It's highly recommended that a qualified electrician do the work. Three methods are recognized as permanent repairs:

• Rewiring with copper. New copper circuits replace the aluminum ones, which can be left in the walls. It's the best method, but in many houses it's impractical or very expensive.
• COPALUM connectors. A short copper wire, called a pigtail, is joined to the end of each aluminum wire with a special crimp connector and tool. Every aluminum connection and splice in the house is done, including outlets, switches, dimmers, fixtures, appliances and junction boxes. Only electricians trained by the manufacturer may install it.
• AlumiConn connectors. Where COPALUM isn't available, pigtailing with this setscrew connector is the next best alternative. It has done well in tests but has a shorter track record.

These repairs apply to the 15- and 20-amp branch circuits, not the larger aluminum wire for the service entrance, the dryer and the range.

Fixes that fall short

• Twist-on connector pigtails. Many overheated badly in testing, and some may fail more often than the original connections.
• "CO/ALR" switches and outlets. They do better than ordinary devices with aluminum wire but have still failed in tests. They also don't exist for every part of the system, such as hardwired appliances and ceiling fixtures.
• Ordinary crimp connectors from a hardware store. None have been evaluated for joining copper to aluminum.

Twist-on pigtails or CO/ALR devices can serve as an emergency stopgap for one failed connection. Have the whole system repaired by a recognized method soon after.

An annotated example

What to do next

If your house was built or rewired between 1965 and the mid-1970s, read the cable jackets in the basement or garage for "AL" or "Aluminum". If you find it, or see any warning signs, have a qualified electrician assess it, and ask which of the three recognized repairs they'll use. Electrical panel checks and warning signs covers other signs of trouble.