[TowerTalk] Fwd: shack wiring

TexasRF at aol.com TexasRF at aol.com
Mon Aug 2 07:41:39 PDT 2010

Sorry Paul, I misunderstood your information. I see now that you were  
talking about neighborhood primary power distribution, not individual home  
secondary power source.
I see the single phase primary distribution running for miles and miles out 
 in the rural areas around here. As new and upgraded facilities are 
installed I  see three phase distribution replacing the old plant.
This part of Texas is seeing growth like southern California back 30 to 40  
years ago and the older power distribution systems are being replaced at a 
rapid  pace. 
Gerald K5GW
In a message dated 8/2/2010 9:21:52 A.M. Central Daylight Time,  
w9ac at arrl.net writes:

>  "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"

The transformer's secondary winding creates the 180-degree phase  
relationship on the 120/240 side -- not the transformer's primary.   

Paul, W9AC

In a message dated 8/2/2010 7:36:13 A.M.  Central Daylight Time, 
w9ac at 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:


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 
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 

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 
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 
for  new neighborhood construction, two phases should be carried to the 
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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