Joe,
The same applies for my 3 phase HT power supply were the 3 phase transformer
is switched in delta configuration.
No neutral needed, the 3 coils are connected to the 3 phases and the ground
lead is connected to the chassis in order to trip the differential breaker
in my mains panel if due to a failure the chassis becomes connected to one
of the phases.
Cheers, Dick
PA3DUV
----- Original Message -----
From: "Joe" <joe@jtme.com>
To: <amps@contesting.com>
Sent: Friday, January 06, 2006 6:22 PM
Subject: Re: [Amps] NEC-think.
> 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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