On Jan 6, 2006, at 9:10 AM, John Popelish wrote:
> R. Measures wrote:
>> On Jan 5, 2006, at 2:08 PM, John Popelish 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,
>>
>> • In a 240v appliance, why would it?
>
> If there is actually no load of any kind connected to the neutral and
> that line is dedicated to that appliance (not shared with any other
> loads) then it is effectively an equipment grounding conductor, not a
> neutral. But many 240 volt ranges, for instance, also contain clocks
> and timers and oven lights that use the neutral as a load carrying
> conductor, so this precludes that line from being a legitimate
> equipment grounding conductor.
>
>>> 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).
>>
>> • For a shock hazard to exist, the person would also need to be
>> grounded. The Neutral wire on the 240v outlet in my radio room is
>> #6-ga. What would make the resistance of the Neutral go high and
>> simultaneously connect one Line wire to the enclosure?
>
> A lose connection at either end would be the most common cause of a
> high resistance neutral.
What if the cause of loosening the connection screw on the Neutral wire
also loosened a screw on the Ground?
> If that neutral had also been used as an
> equipment grounding conductor (safety ground) than the case would be
> hot the moment the equipment was turned on.
>
> Even if the neutral is well connected, in the event of a line to
> neutral fault in the equipment, the two sides of the line circuit
> would each drop about half of the line voltage till the over current
> device opened, and you could receive a shock during that moment.
Provided one was standing in water, yes, for about one second.
> This
> case of shock hazard also applies to safety ground conductors, and in
> many cases is worse, because safety ground conductors are allowed to
> be smaller than line conductors, in many cases.
True, usually about two AW gauges smaller.
>
> Even when the neutral is intact, there must be some voltage drop
> (resistive and inductive) across it because of load current. You
> would get some very nasty ground loop currents when different pieces
> of grounded equipment were connected together (with signal wiring or
> just incidental contact), if each used its own neutral as case ground.
Electric ranges can share circuits with other 240v appliances?
>
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>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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