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    Re: Test your magnetic compass.
    From: Lu Abel
    Date: 2012 Nov 17, 08:59 -0800
    Electrical conduit (pipe holding wires) and the spiral sheathing found on flexible BX cable are both make of steel -- it's way cheaper than aluminum.

    There was a brief period from the late 1960s to the late 1970s when the price of copper skyrocketed and houses were wired with aluminum wire.   They then discovered that the aluminum expanded and contracted with changes in temperature, loosening connections.   Aluminum is also subject to surface corrosion.   Loose, corroded connections create a sparking hazard and can cause fires.   Aluminum wire was promptly banned from residential construction.   All of which is a long-winded way of saying that unless your house was built during that period, you don't have aluminum wiring.

    From: "eremenko@math.purdue.edu" <eremenko@math.purdue.edu>
    To: NavList@fer3.com
    Sent: Friday, November 16, 2012 8:34 PM
    Subject: [NavList] Re: Test your magnetic compass.

    Dear Lu,

    > Magnetic deviation when bringing a compass near a light switch may
    > have nothing to do with electrical flow. Instead, depending on the age
    > of your house and the building codes in effect, it may be due to either
    > metallic sheathing around the wires (BX cable) and/or metal electrical
    > boxes holding the switch.

    I thought all this is of aluminium. But I will experiment more:-)

    > Most stud finders work on the basis of ultrasound.

    I like low-tech things (this is one reason why I am on this list:-)
    The stud finder I use is a little piece of
    metal on a pivot. Similar to a compass needle. It definitely reacts on
    iron nails.


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