During the 1970's, aluminum (instead of copper) wiring became
quite popular and was extensively used.  Since that time,
aluminum wiring has been implicated in a number of house fires,
and most jurisdictions no longer permit it in new installations.
We recommend, even if you're allowed to, that do not use it for new
wiring.

But don't panic if your house has aluminum wiring.  Aluminum
wiring, when properly installed, can be just as safe as copper.
Aluminum wiring is, however, very unforgiving of improper
installation.  We will cover a bit of the theory behind potential
problems, and what you can do to make your wiring safe.

The main problem with aluminum wiring is a phenomenon known as
"cold creep".  When aluminum wiring warms up, it expands.  When
it cools down, it contracts.  Unlike copper, when aluminum goes
through a number of warm/cool cycles it loses a bit of tightness each
time.  To make the problem worse, aluminum oxidises, or corrodes
when in contact with certain types of metal, so the resistance
of the connection goes up.  Which causes it to heat up and corrode/
oxidize still more.  Eventually the wire may start getting very hot,
melt the insulation or fixture it's attached to, and possibly even
cause a fire.

Since people usually encounter aluminum wiring when they move
into a house built during the 70's, we will cover basic points
of safe aluminum wiring.  We suggest that, if you're
considering purchasing a home with aluminum wiring, or have
discovered it later, that you hire a licensed electrician or
inspector to check over the wiring for the following things:

    1) Fixtures (eg: outlets and switches) directly attached to
       aluminum wiring should be rated for it.  The device will
       be stamped with "Al/Cu" or "CO/ALR".  The latter supersedes
       the former, but both are safe.   These fixtures are somewhat
       more expensive than the ordinary ones.

    2) Wires should be properly connected (at least 3/4 way around
       the screw in a clockwise direction).  Connections should be
       tight.  While repeated tightening of the screws can make the
       problem worse, during the inspection it would pay off to snug
       up each connection.

       Note that aluminum wiring is still often used for the
       main service entrance cable.  It should be inspected.

    3) "push-in" terminals are an extreme hazard with aluminum wire.
       Any connections using push-in terminals should be redone with
       the proper screw connections immediately.

    4) There should be no signs of overheating: darkened connections,
       melted insulation, or "baked" fixtures.  Any such damage should
       be repaired.
   
    5) Connections between aluminum and copper wire need to be
       handled specially.  Current Canadian codes require that the
       connectors used must be specially marked for connecting
       aluminum to copper.  The NEC requires that the wire be
       connected together using special crimp devices, with an
       anti-oxidant grease.  The tools and materials for the latter
       are quite expensive - not practical to do it yourself unless
       you can rent the tool.

       [Note that regulations are changing rapidly in this area.
       Suggest that you discuss any work with an inspector if you're
       going to do more than one or two connections.]

    6) Any non-rated receptacle can be connected to aluminum wiring
       by means of a short copper "pigtail".  See (5) above.
   
    7) Shows reasonable workmanship: neat wiring, properly stripped
       (not nicked) wire etc.
   
If, when considering purchasing a home, an inspection of the wiring
shows no problems or only one or two, we believe that you can consider
the wiring safe.  If there are signs of problems in many places,
we suggest you look elsewhere.  If the wrong receptacles are used,
you can replace them with the proper type, or use pigtails - having
this professionally done can range from $3 to $10 per receptacle/
switch.  You can do this yourself too.