Older homes frequently have two-prong receptacles instead
	of the more modern three.  These receptacles have no safety
	ground, and the cabling usually has no ground wire.  Neither
	the NEC or CEC permits installing new 2 prong receptacles anymore.

	There are several different approaches to solving this:
	    1) If the wiring is done through conduit or BX, and the
	       conduit is continuous back to the panel, you can connect
	       the third prong of a new receptacle to the receptacle
	       box.  NEC mainly - CEC frowns on this practice.
	    2) If there is a metallic cold water pipe going nearby, and
	       it's electrically continuous to the main house ground
	       point, you can run a conductor to it from the third
	       prong.  You MUST NOT assume that the pipe is continuous,
	       unless you can visually check the entire length and/or
	       test it.  Testing grounds is tricky - see "Testing
	       Grounds" section.
	    3) Run a ground conductor back to the main panel.
	    4) Easiest: install a GFCI receptacle.  The ground lug
	       should not be connected to anything, but the GFCI
	       protection itself will serve instead.  The GFCI
	       will also protect downstream (possibly also two prong
	       outlets).  If you do this to protect downstream outlets,
	       the grounds must not be connected together.  Since it
	       wouldn't be connected to a real ground, a wiring fault
	       could energize the cases of 3 prong devices connected
	       to other outlets.  Be sure, though, that there aren't
	       indirect ground plug connections, such as via the sheath
	       on BX cable.

	The CEC permits you to replace a two prong receptacle with a three
	prong if you fill the U ground with a non-conducting goop.
	Like caulking compound.  This is not permitted in the NEC.

	The NEC requires that three prong receptacles without ground
	that are protected by GFCI must be labelled as such.

	See the next section about computers on GFCI-protected groundless
	outlets.