I've had alot calls for electrical repairs over the years.  During holidays and cold weather times, the remodeling business turned into service calls for about three months.  Since I lived in an area composed of fourty to eighty year old houses and tenement buildings, I had many of my calls related to electrical service and repair. 

      More than fifty percent of these service calls were related to previous work, addons (additional circuits) and reversed polarity wiring to outlets and light fixtures.  Work performed by who knows who.  The two most common mishaps I have seen have to do with the improper distribution of amperes and voltage (watts) and dangerous reveesed polarity in recepticle outlets in homes and especially apartments.

      Where a 220VAC line enters a building, there are two separate verticle circuit bars (left/right) inside the Breaker box which recieve a phased voltage of 110VAC each and one neutral for the return voltage and ground wires from interior electrical fixtures (lights/outlets).  A simple inspection behind the circuit plate will reveal the three main wires of the source in the case of 220VAC and whether too many circuits are mounted on one side (bar) or the other.  This would include extra load where more than one circuit is attached to a single breaker.  In this case, someone may have found it necessary to replace say, a 20AMP breaker with a 30Amp breaker, because the extra load created heat that tripped the circuit breaker.  Not good! 

      The scenario involving miswired, reversed polarity outlets, light and ceiling fan fixtures is quite dangerous.  It means first of all, that the ground is hot wired with a black (positive) wire instead of an actual ground wire which is meant to protect a person from electrical shock.  Now, don't let this confuse, but, even the ground wire goes back to the box and is connected to the negative (white) wire, the other side of your normal house current.  So, in effect, your ground is always hot too.  This is the reason for disconnecting the bare or green ground wire before working on any electrical device.  Even before disconnecting the hot black wire.  When installing an electrical fixture, that same reasoning applies and the ground is the last wire to be connected, after the hot wires are covered with tape and/or wire nuts.  Reverse polarity outlets will be impossible to connect to a ground as the hot wire is now where the ground would be andthis would be a dead short.  The best way to test it is to purchase a little device that plugs into the outlet and via a series of small lights, tells you if the outlet is wired correctly. 

      It's a great diagnostic tool which requires only the expertise to plug it in and follow the chart.