On Tuesday, November 19, 2013 12:03:14 PM UTC-5, nestork wrote:
;3151685 Wrote:

Here's what I'm not getting at the moment. What are the connections to

that transformer? If it is 3 phase leg to neutral on the primary side,

then the center tap should be above neutral on the secondary (house)

side, right? Which would mean that house neutral is NOT at ground level.

But I'm pretty sure it is.



your confusion is becasue you don't understand how a transformer works.

The pri and secondary are isolated from each other. The center tap of

the sec has NO RELATIONSHIP to the primary. Think of the secondary as

seperate floating power supply not related to the primary. The center

tap of the secondary is neutral or ground ONLY becasue it gets connected

to ground. Since it is connected to ground the two ends become +120 and

-120 relative to neutral.



Mark



Mark:



I find the first diagram on this web page that was posted by SRN

helpful:



http://tinyurl.com/ly24tjo





Don't let krw see that. The reference clearly says that
with a spit-phase 240v/120v service, there are two phases present
and they differ by 180 degrees. He says that just can't be.




It shows the primary side of the distribution transformer connected

between the 7200 VAC carried by the single phase wire and ground.



What I can't figure out here, tho, is that if the distribution

transformer on the telephone pole is connected to ground, then it's

connected via the ground wire that goes down the pole and is wrapped

around the base of the telephone pole. So far as I know, that ground

wire is not insulated, so that anyone that touches that ground wire

would get a 7200 volt shock, which would surely kill them.


Even if it were only connected that way, you would only get a shock
if the ground wire were broken and you grabbed the energized end.
Otherwise if you grabbed an intact wire, the only voltage present
would be whatever there is due to the small resistance of the wire,
which would result in a small voltage drop across the wire run.
The 7200 volts is across the transformer. The 25 ft of copper wire
only drops a few volts, depending on the current flowing in it and
the resistance of the wire.

Actually the transformer is typically connected to a
primary neutral. The primary neutral is in turn connected
to ground much like on the secondary (house) side. It's not
necessarily at every transformer, but periodically along
the run. Other transformers connected to the same neutral,
but from different phases, will balance out and reduce the current
flowing in the neutral.



So, I think that wiring diagram is mostly correct, but I think there's a

problem with the primary side of the transformer connected to ground via

the telephone pole's grounding wire.



Yes, IMO, they should have shown the primary connected to
a neutral, not just ground.