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Home Repair - - If it ain't broken, don't fix it. Otherwise look here.
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Posted by David Nebenzahl on November 7, 2009, 3:59 pm
On 11/7/2009 11:51 AM Robert Green spake thus:
> I believe the problem most people have with shared neutrals is that
> it seems like they are adding 1 plus 1 and getting 1 as a result.
> However, since they are out-of-phase, you're really adding 1/2 plus
> 1/2 and coming out with 1. When the first circuit's amplitude is at
> its peak, the other phase is at the bottom, and the two phases cancel
> each other out. It doesn't seem to be common sense that by adding a
> load to the other half of unbalanced load that you'd actually be
> reducing the current in the shared neutral wire, but that's how it
> works. I think. (-: At least that's how my friend who designs 240VAC
> gear explained it me.
That's 'zactly right.
Being 180° out of phase, any current running in one leg of the circuit
will be cancelled by any current in the other leg. The amount of
cancellation depends on the amount of current being drawn in each leg.
The highest current possible in the shared neutral will be when only one
leg is drawing maximum current. If both legs draw maximum current, then
the current in the neutral is close to zero. In this case, the majority
of the current flow is through the two "hot" wires.
Very clever idea. However, for reasons given here many times, I think
Edison circuits are to be avoided, on account of the potential problems
they can cause.
Spend the extra 25 cents and use paired hots and neutrals.
--
Who needs a junta or a dictatorship when you have a Congress
blowing Wall Street, using the media as a condom?
- harvested from Usenet
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Posted by Doug Miller on November 7, 2009, 4:13 pm
>[...] most of the 240VAC equipment in an
>average home is not pure 240VAC. In my panel they run neutrals to power the
>oven timers, water heater igniters and other circuits needing only 110VAC.
Electric water heaters have igniters?
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Posted by The Daring Dufas on November 7, 2009, 4:41 pm
Doug Miller wrote:
>
>> [...] most of the 240VAC equipment in an
>> average home is not pure 240VAC. In my panel they run neutrals to power the
>> oven timers, water heater igniters and other circuits needing only 110VAC.
>
> Electric water heaters have igniters?
>
Some gas water heaters have electric controls and igniters
similar to a gas furnace along with a draft inducer blower.
TDD
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Posted by Nate Nagel on November 7, 2009, 5:13 pm
The Daring Dufas wrote:
> Doug Miller wrote:
>>> [...] most of the 240VAC equipment in an
>>> average home is not pure 240VAC. In my panel they run neutrals to
>>> power the
>>> oven timers, water heater igniters and other circuits needing only
>>> 110VAC.
>> Electric water heaters have igniters?
>
> Some gas water heaters have electric controls and igniters
> similar to a gas furnace along with a draft inducer blower.
>
> TDD
right, but a gas water heater wouldn't need a 240VAC circuit to serve
it, either. So still only 2 wires plus ground.
nate
--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel
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Posted by The Daring Dufas on November 7, 2009, 6:46 pm
Nate Nagel wrote:
> The Daring Dufas wrote:
>> Doug Miller wrote:
>>>> [...] most of the 240VAC equipment in an
>>>> average home is not pure 240VAC. In my panel they run neutrals to
>>>> power the
>>>> oven timers, water heater igniters and other circuits needing only
>>>> 110VAC.
>>> Electric water heaters have igniters?
>> Some gas water heaters have electric controls and igniters
>> similar to a gas furnace along with a draft inducer blower.
>> TDD
>
> right, but a gas water heater wouldn't need a 240VAC circuit to serve
> it, either. So still only 2 wires plus ground.
>
> nate
>
Perhaps there is a confusion of terminology. R. Green may be
somewhere other than The U.S. Them dang furners talk funny
ya know. *snicker*
TDD
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Page 5 of 13 < 1 2 3 > last >>
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> it seems like they are adding 1 plus 1 and getting 1 as a result.
> However, since they are out-of-phase, you're really adding 1/2 plus
> 1/2 and coming out with 1. When the first circuit's amplitude is at
> its peak, the other phase is at the bottom, and the two phases cancel
> each other out. It doesn't seem to be common sense that by adding a
> load to the other half of unbalanced load that you'd actually be
> reducing the current in the shared neutral wire, but that's how it
> works. I think. (-: At least that's how my friend who designs 240VAC
> gear explained it me.