In a simple 240V circuit (like you would wire for an amplifier), a neutral
is not needed but a ground is. Current flows from one hot to another so
you would have 2 hots and a ground but no neutral. If a 2 wire cable is
used, the white wire is labeled with black tape to indicate it is hot
rather than neutral. Generally, a neutral is only needed in a 120V circuit.
Some 240V circuits use a neutral because the appliance incorporates 120V
devices as well as 240V. A 3 wire cable must be used in this case so you
have 2 hots, a neutral and a ground. A range or a dryer are typical
examples. Dryers often use a 120V motor to turn the drum and the lights
are 120V but the heating element is 240V. An range may have 120V control
circuits or lights but uses 240V heating elements. In this case, the
neutral carries current because the parts of the appliance that use 120V
pass current from one hot to the neutral. So you would need 2 hots, a
neutral and a ground rather than just 2 hots and a ground.
Joe N1FCJ
At 11:26 PM 1/5/2006, you wrote:
>R.Measures wrote:
>
> > Without a ground/bond wire wouldn't connecting the Neutral wire to the
> > metal enclosure hold the enclosure to a safe potential until the
> > breaker trips?
>
>The neutral carries load current, so it may have some voltage drop at
>the appliance end, compared to the end at the power panel. And if it
>ever goes high resistance, then the moment any load is connected to
>it, it has full line voltage on it. So a single failure (open
>neutral) would produce a shock hazard if the case were attached to it,
>the moment the appliance was turned on (a moment someone is likely to
>be touching the case, also).
>
>The safety ground never carries current under normal conditions, so it
>take two failures (hot faulted to metal case and open ground
>conductor) to produce an unsafe condition.
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