Quote:
Originally Posted by DWRAT
4 prong is the newer code where 3 prong is the older code.
Either will work fine.
The newer 4 prong basically has a extra ground wire.
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What is here is the fact. But if you are looking carefully you will see that the three prong connection adds a shunt from the neutral (white) to the chassis ground (where on the 4 wire, the green wire connects).
DO NOT FORGET THIS OR YOU WILL DIE. SERIOUSLY. I'M NOT KIDDING.
The code changed to use a true earth ground (the green wire) on appliances. Previously the electrical connectivity was the equivalent of inside the breaker box - at the termination, neutral and ground were connected on the same bus bar. The new code separates the earth ground and neutral at the appliance. This is for appliances like ranges and dryers only. True 220V devices like air conditioners maintain the traditional 220V connection: 2 hot plus ground (no neutral)
The reason that dryers and ranges split is that they actually (within the appliance) split the 220V into 2x120V circuits. This allows control panels, etc. to run on 120V and the neutral (when the dryer/range is on) actually carries a slight current. In a pure inductive load (the Air Conditioner or other 220V motor with 2xlive and ground) the current is on one (red or black) at a time, and the other (black or red) provides return. The same concept is used in the so-called "edison" 220V -> 2x120V circuit (which is now disallowed by the code).
As recommended, if you are not absolutely comfortable making this conversion, get your electrician back.