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 <mark@cgmark.us> 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. =A0I 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.
>>
>>
>>
>>
>>
>>
>
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