Aluminum wiring.

Most people are aware of safety issues surrounding Aluminum electrical wiring.  Because Aluminum is considerably lighter than Copper, it has been used for years in high power lines and it is still being used without any problem. .  If the use of Aluminum wiring is so common, what is the problem?  There is not really any problem with stranded wires.  As the name implies, stranded wire is made up of numerous strands.
The picture on the right shows a sample of both Copper and Aluminum stranded wire.  This type of wiring (only much larger) is used in high power lines.  It is also used for larger appliances like electric dryers or stoves.  Each bundle of strands like these makes one conductor.

  In the early sixties the price of Copper rose much more than the price of Aluminum with the result that using Aluminum instead of Copper became even more attractive so Aluminum wiring began to be used for the regular circuits in houses.  This wiring is not stranded but solid.  The picture on the left shows a sample of this.  Each one of these single wires is one conductor.
It is with this type of wiring that safety issues occur. 

Without getting into too much detail; wiring will heat up a bit when electricity flows through it.  When it heats up, it will expand and it contracts again once it cools off.  Aluminum expands and contracts at a different rate than the connecting terminals in breakers and switches etc.  That is where the problem comes in.  With each expansion and contraction cycle the wiring will slowly loosen in the connectors.  A loose connections means a poor connection.  Poor connections cause heat, excessive heat.  The connection can get hot enough to actually start a fire. 
At a home inspection in Wellington county last week, I found evidence of this overheating.  Here are two pictures of the inside of the fuse box.
Do you see where the red insulating covering of the wiring looks like it has melted?  Well...that's because it has melted.  The combination of the plastic and the cobwebs would have made a great source of fuel.

The picture on the right is in the same panel.  This bundle of wires came frightfully close to lighting on fire. 

  (It is not only the working loose of the wiring that is a problem.  Connecting dissimilar metals creates issues that add to the problem, but that is a topic for another time.)

One of the outlets in this house would light up the tester if I pushed it one way but it wouldn't if I pushed it another way.  I am thinking that the connections at this outlet were loose as well. There are ways to make Aluminum wiring safe.  Special outlets, switches and connectors have been developed to prevent the wires from working loose.  This house wiring apparently didn't have the benefit of these safety features.  I don't very often recommend "further evaluation before closing."  Usually I explain the problem and possible ways to correct the problem.  Here I recommended to have an electrician come in so my client would at least have an idea what it would cost to make this wiring safe.  I don't know if the deal ended up going through or not.  I suspect it did because when I left, the buyer and seller were discussing which electrician to use for this.  I don't set out to be a deal killer but I certainly don't want to be an "accomplice" in getting my client killed.  I hope he took my advise. 

Submitted by Bert, for Benchmark Home Inspection Services.  Your Kitchener, Waterloo, Guelph and Orangeville area home inspector