Quote:
Originally Posted by brian015
Jerry - my 240V home wall-unit air conditioner only has three plugs - leading me to conclude it does not need a connection to neutral - it is two-phase 120V (plus a ground plug). I would guess your microwave would have same plug (for household use).
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Air conditioners are generally rated for less than 15amps. An electrician can chime in on this but I'm pretty sure it's not required to have both a neutral and a ground conductor with this amp draw. Although 4 conductor plugs and cords with separate neutral and grounds are available.
For higher amp draw, homes built before 1996 (or any additional wiring installed before then) are also allowed to use only 3 conductors combining ground and neutral. But newer homes and wiring have 4 conductors (separate ground and neutral) and 4 prong plugs for 220/240v use in circuits 30amps and above such as dryers and electric stoves.