OK american homeowners, here's some tips to straighting out your household electrics:
Most homes will have 2 mains, one neutral, and one ground coming into the MAIN breaker panel for the house.
Look, don't touch if you have NO experience with this
One main should be BLACK, ~120 volts.
The other main wil be another COLOR, usually RED, ~120 V.
The neutral should be WHITE, 0 Volts conditionally (this is important, do not trust it to be 0 volts).
Mains and Neutral should be the same size (gauge) wire.
The Ground wire can be either GREEN or BARE (no insulation) and may be a different size than Mains or Neu.
The BLACK Main is your primary power HOT, and will pass through the MAIN BREAKER to a metal buss that your individual breakers attach to.
The RED (other COLOR) main is also routed through the MAIN BREAKER to a DIFFERENT metal buss, usually a mirror of the other breaker buss, and will power another series of 120V circuits or used in conjunction WITH the primary main to give ~240 Volts to appliances like a clothes dryer or water heater.
The WHITE NEUTRAL should be connected to a TOTALLY SEPERATE buss, niether a POWER buss NOR the GROUND buss. The NEUTRAL is meant to be the RETURN conduit for the MAINS in a proper AC circuit. it does NOT need to be routed through MAIN BREAKER
The GREEN or BARE GROUND wire MUST be connected to a SEPERATE buss, and MUST be ALSO connected to the BREAKER BOX itself.
TWO COMMON PROBLEMS THAT CREATE NOISE:
1) The WHITE NEUTRAL is used AS A (THE) GROUND in the BREAKER BOX. technacally, the white neutral IS a ground of sorts and will work as a ground does, but is NOT MEANT TO DO SO AT THE USER (house) END. the main drawback to this wiring scenario is that it compromises the INTEGRITY OF THE GROUND CIRCUIT. AC voltage must complete a circuit with a ground to "flow", and the WHITE NEUTRAL is there to complete that circuit. If it is connected to the GROUND in any way, AC NOISE wil be introduced into the GROUND circuit where it does not belong.
This CROSS WIRING is usually found in the breaker box, but it is common to find it at individual outlets where someone was too lazy to properly run ground wires.
2) The (BLACK) "hot" wire and the (WHITE) "neutral" wire are juxtapposed at the (wall) outlet. this is called "OUT OF PHASE" On your 2 or 3 prong outlet, the small slot is the "hot", the larger slot the "neutral". The connecting screws on the back of the receptical correspond to this as the BLACK "hot" wire should connect to the dark "brass' colored terminal screw, the WHITE 'neutral' wire should connect to the lighter "silver" colored terminal screw.
On a three prong grounded outlet, the GREEN or BARE wire is connected to the GREEN colored terminal screw, found at the top or bottom on the back of the receptical. This wire may either terminate directly to the groung screw on the receptical or it simply may come out of the conduit, be looped around the ground screw, and go back through the conduit to another receptical at another location in the house. THIS IS OK. Another OK ground wire route is to have the ground wire to go directly from the ground screw on the recepticle to a screw on the RECEPTICAL BOX IN THE WALL, but ONLY IF THE RECEPTACAL BOX IS METAL ANDIF THE HOUSE CONDUIT IS METAL ALL THE WAY BACK TO THE MAIN BREAKER PANEL!
SIMPLE PHASE TEST AT THE RECEPTICALS:what you want
With a multi-meter set to AC volts auto range:
Small slot to large slot: ~120 V
Small slot to Ground slot: ~120 V
Large slot to Ground slot: 0 volts or you may see some stray varying low volt/amperage voltage indicated on the meter, because the wire to the large slot is on the circuit channeling electricity back to the source (it's supposed to).
Odds are that there will be some neutrals connected to the ground circuits in your home. That will be evident if you do a "continuity" check (set the multimeter to audible signal) and test from the large slot to the ground slot. What I have described above would be ideal perfect conditions, a rarety.
Above all: if you are in doubt of DOING ANY WIRING WORK, HIRE A QUALIFIED, LICENSED ELECTRICIAN!
