ECN Forum Forums Photo Discussion Forums Photos for General Discussion Primaries of pole mounted transformers

My place is fed by an underground service that climbs up a power pole, 2ga in conduit (for a 100A service). This pole is shared by a neighboring house, which also has an underground service using 4ga. The POCO has an overhead connection that looks fairly heavy crossing the street to get to the line that in turn goes to a 3rd pole that has the transformer. It looks like the power company gave us the heavy line to our pole because it serves 2 houses. Which makes for less voltage drop when we turn on heavy loads in our house. If we had an overhead service, that wire would likely be much thinner.

Greg's image shows the Multi Grounded Common Neutral (Refered to as "MGCN") "version" for 1Ø Medium Voltage Distribution.

I see this type of Primary feeds in Nevada (Las Vegas), and in rural areas of Oregon.

Most of California - at least Southern California, have L-L Primary Feeders for 1Ø Distribution.

Some areas with 12470Y/7200 3Ø 4 Wire Primaries will connect L-N, but this is not a Common Neutral type system - as the Grounded Conductor is not common to both the Primary and Secondary feeders of a given Transformer.

Here are a few Schematics from the Tech. Reference section, covering Residential Distribution Systems:


Fig. 1.1: Multi-Grounded Comon Neutral (MGCN)


Fig. 1.2: 3 Phase 4 Wire Distribution - typical in my area on older 4KV Circuits, and some newer 12470Y/7200 4 Wire Circuits


Fig. 1.3: 3 Phase 3 Wire "L-L" Distribution - typical in my area.

More images may be seen at Residential Distribution Systems page.
Go to the "Menu" at the Tech Reference area, and select from there

Scott

BTW: I just found out the links at the "Menu" need to be re-directed, so I perform the necessary tweeks ASAP.

Fixed Tech Reference "Menu" hyperlinks!!!

Check it out at:

Menu For Technical Reference Section

Scott

I have seen a similar scheme on some older poles around here, although I'm pretty sure they are not isolated. If multiple transformers are running on the same primary, and their secondaries run to a common bus, the load should be evenly distributed, shouldn't it?

Newer installations are all triplex, and the newest services I've seen are completely insulated with plastic (no more ceramic) hangars. They look pretty weird, as the phases and grounding conductor can't be spaced more than 12" from each other, all using the same hangar.

The transformer that supplies my house is a 25KVA, and currently has 9 service drops running from it. Most of them are probably 100A, but that's still quite a stretch.

11 amps per house? You all must be Amish

"11 amps per house? You all must be Amish"

LOL

My guess is that your light bulbs last a long time due to low voltage.

My UPS reports 120.6 VAC on the line-in. But, I haven't replaced a bulb since I moved in September.

Last Summer, Con Ed of NYC had some spectacular cascading failures in areas where they had multiple transformers feeding a common bus. Seems some of the transformers failed, and the transformers still alive had more loading, and the bus wires started literally burning up in places. A lot of underground wiring had to be replaced, and some customers had to be fed with generators Con Ed set up locally on the street. It was a mess, and the city government was rather unhappy about it.

In the U.K. the xfmr primaries are always wired phase-to-phase, since our MV/HV never distributes a neutral.

3-phase xfmrs and 240/415 Y local distribution is the norm for anywhere where there are more than a few houses, but where single-phase spurs are run for remote rural homes, the HV is always run as two phases:



Xfmr above is 11kV primary, 240V secondary.