If the appliance uses 220/240V only and there is no use of 110/120V , then a neutral is not necessary. In this case 3 wires should suffice. There should always be a safety ground installed that does not carry current in normal operation. If the appliance uses 220V and 110V, then one should use 4 wires. 220V, 220V , neutral and safety ground. In this case , neutral will be carrying current and may or may not be at ground potential. There should always be a safety ground installed that does not carry current in normal operation. Gus > On Dec 11, 2009, at 6:55 PM, Mark Perri wrote: > > We had to rewire our dryer from a 4 prong to 3 prong outlet for our > house (built before the 4-prong code). It is hot/hot/neutral > (black/red/white if I remember correctly), with the case wired to the > neutral. I believe 110 is used to run the small stuff (light and > buzzer), and 220 runs the heavy stuff. If you go to the local > hardware > store they sell both 3 and 4 wire cords and you can look at the color > scheme. > > Mark > > On 12/11/2009 5:27 PM, Sean Breheny wrote: >> Hi Mark, >> >> I just looked up what you said and it seems that the distinction is >> not between houses and mobile homes, but between new and old >> construction: >> >> http://fixitnow.com/appliantology/dryercords.htm >> >> This says that the latest codes require a 4-prong plug >> (hot,hot,neutral,gnd) for 220V appliances in the US. Older homes >> usually have only 3-prong plugs (hot,hot,neutral) for 220V circuits, >> and as you say, in these cases, the neutral is connected to the case >> of the appliance. >> >> Interesting, because I don't think that connecting the neutral to >> something "human touchable" is very safe since there could be a >> single >> point of failure which would electrify the case (an open neutral in >> the connection back to the breaker box). I always thought that >> three-prong 220V outlets were hot,hot,gnd not hot,hot,neutral. If you >> have no 110V stuff in the appliance, neutral isn't needed. >> >> Sean >> >> >> On Fri, Dec 11, 2009 at 8:05 PM, Mark wrote: >> >>> My brother does appliance installation. In the USA there is two >>> standards for wiring appliances. One is when they are installed in a >>> frame built home and another when they are installed in places like >>> mobile homes. In frame built homes the plugs are 3 pronged. The >>> outer >>> two connections are HOT (red, black) at 120V each or 240V between >>> the >>> two and the middle is neutral (white). Ground (green) of the >>> appliance >>> is tied to this same neutral. In a mobile home a 4 pronged plug is >>> required, where the outer two connections are still HOT (red , >>> black) at >>> 120V but the neutral (white) is not connected to the frame and the >>> 4th >>> prong (green) supplies an extra ground which connects to the metal >>> frame. >>> >>> If you look on something like a electric dryer where the >>> connections are >>> you will find a metal tab that can be connected to the center >>> neutral to >>> bond the frame to the neutral wire if installed in a home. When >>> installed in a mobile home that tab is removed and the green wire is >>> attached to the frame. >>> >>> Good Luck >>> Mark >>> >>> >>> >>> >>> >>> PICdude wrote: >>> >>>> FWIW, I opened the outlet, and the three wires are green (tied to >>>> the >>>> back of the case), then red and black. >>>> >>>> So I'm confused as to what to do now. I don't mind getting an >>>> outlet >>>> wired in here, but need to test this thing in the next few days >>>> before >>>> my DOA warranty runs out. >>>> >>>> Not sure where else I can find 220V to test this. >>>> >>>> Cheers, >>>> -Neil. > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist