[TowerTalk] Fwd: shack wiring

[Paul Christensen]

> ##  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