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Re: [TowerTalk] Fwd: shack wiring

To: w9ac@arrl.net, towertalk@contesting.com
Subject: Re: [TowerTalk] Fwd: shack wiring
From: TexasRF@aol.com
Date: Mon, 2 Aug 2010 10:00:25 EDT
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Paul, with 2 phases, wouldn't they be phased at 120 degrees apart instead  
of 180?
 
Seems that would cause problems with 220/240vac loads.
 
73,
Gerald K5GW
 
 
 
In a message dated 8/2/2010 7:36:13 A.M. Central Daylight Time,  
w9ac@arrl.net writes:

>  ##  If the business's  don't get a neutral... then how do the  business's
> obtain 120 vac ??

The neutral for premise  distribution is created at the utility transformer 
secondary.   Speaking of electrical distribution and use of neutrals, this 
evolution of  plant step-down architecture has always bothered  me:

http://72.52.250.47/images/power-tap.gif

http://www.psc.state.fl.us/consumers/utilitypole/images/utilitypole5.jpg

In  the U.S., the HV primary on a pole transformer feeding a home is tapped 
 
between one phase of a three-phase system and a Multi-Ground Neutral  
(MGN). 
The photo in the top link shows only one phase on the pole  insulator. 
Often, the other two phases are not passed in deeper  residential 
distribution.

At each pole, a grounding conductor  (shown in the second link) is run from 
the MGN to earth to keep the  distribution's MGN ground line at earth 
potential.  That's a good  thing because if a ground fault occurs, it's 
possible that the pole  grounding conductor (runs from the top of the pole 
to 
the ground stake)  would elevate to the full 7200V delivered by the 
distribution phase  through the transformer primary.  During a fault 
condition, a person  standing on the ground while touching the pole's 
grounding conductor would  be guaranteed electrocution.

Albeit more expensive for utility  companies, it makes more sense to me 
that 
for new neighborhood  construction, two phases should be carried to the 
home 
transformer's HV  primary, and not between one phase and the MGN.   This is 
 
especially the case where 3-phase is available on the pole.  Yet, in  cases 
where a residential transformer is mounted on a 3-phase pole, the  utility 
companies still use the MGN instead of a second phase. The safety  of the 
exiting distribution is wholly dependant on the bonding quality of  all 
components between the MGN, the pole grounding conductor, and the  earth 
grounding rod.  Tapping two phases instead of one eliminates  the deadly 
ground fault condition.  Then again, just how many  accidents or deaths 
result each year from such a ground fault?  In  areas of *well-maintained* 
plant, probably not too many.

Paul, W9AC  

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