From here

aluminum wire hazard ring electric ottawa electrical ottawa electrician
Aluminum wire is still approved by the N.E.C. But this on the assumption that everything will be done perfect. Having said that i would like to give a little advice on using aluminum wire when you are building a new home. For the sake of saving a few dollars, it is not worth the safety hazard you face when using this wire. This is not only my opinion but the opinion of many others in the trade. Many times i have been called to repair corroded connections using this wire. Most of the time the aluminum wire had to be replaced with copper. One other piece of advice, before you consider buying a home with aluminum wire you might want to check with the insurance company. Some of them may refuse to insure a house with aluminum wire.
There are a lot of homes that have been wired with aluminum wiring and it would not be financially possible to rewire the entire house or service. There are a few things you can do to make sure that the wiring is not becoming a problem. You should be on the lookout for devices or lighting going on and off. Breakers or outlets overheating. Have the main panel checked for corrosion or loose connections. When adding copper devices or wire to aluminum, make sure this work is done by someone who knows the proper procedure for this type of wiring. A little preventative maintenance can go a long way in preventing future safety hazards.