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

In my area, it's all wye, and looks just like Greg's photo. MV on top, then the 3x 240V residential lines below (I forget which is the neutral out my way.) No protective grounded conductor on top, and plenty of blinking lights every time there's a lightning storm. This way, they only have to run one MV wire conductor out, and can share the grounded neutral for both the MV and LV lines.

They also seem to love to undersize them. Lessee... per NEC, my house requires a 200A service and is a dedicated fridge circuit from bumping up to a 400A service, and my two neighbors are similar... so of course the POCO puts a 25kVA pole pig up that's only rated for 104A to feed us all.

5 new houses just down the street, each with electric heat and requiring 200A service? CW (and NEC) says 240kVA. POCO puts a 50kVA on the pole. And we wonder why the power fails so much on really hot or really cold days...

They seem to have 25s for 2 houses, 37s for 3 and 50 for 4.
Just looking out the window, there are none of those "insulators" between the two transformers I can see from here. I will get up the street to look at the rest in a little while.

Albert was right. Every segment is isolated one way or the other and those are insulators in front of that transformer. I love it when I learn something. Thanks.

Ahh that all looks almost identical to what we have here in my city.. For single phase stuff the trannies are hooked to a neutral common to both the primary and secondary, and phase voltage is anything as low as 2400V all the way up to 16,000V depending on where you live in the area.
Greg: 4 houses to a 50 KVA transformer?? In an older area of the city my parents live in, ( built in 1967) there are 13 houses on a 50!! Mine is probably no better ( Cant tell they are all back yard drops) but at least the PoCo recently upgraded all the primary conductor and plunked in 75KVA cans.

A.D

Yup they are pretty consistent 2 on 25, 3 on 37 and 4 on 50.

I suppose it might be because we are all electric. Everything we have spins the meter. I did a load calc on my house and it comes out close to 200a with the original method and 150 or so with the optional. My house is actually on the small side compared to anything built in the last quarter century.

It's interesting how much smaller the utility's secondary wires are in contrast to the houses' service entrance conductors, which are governed by the NEC.

Part of that is the free air aspect of a service drop. I agree I still don't think it explains all the liberties they take. They do have a lot of experience so they are probably right

It comes to economics. A WO is issued to reconnect a service upgrade. Unless it specically says replace the tri-plex, they won't. If someone made the effort in the field and it was not on the WO, someone will be "on the carpet" for it. New construction they typically carry a couple of sizes of wire and no one on the POCO side will take the time to crunch any numbers. It is the sparkies installation that usually throws the peception off. We have a 200 amp service with either 2/0, 3/0, or a 4/0 cable hanging out for the POCO to connect to. How often does residential service draws enough power to require such a size? 99.999% of the time, never. In theory the service will never reach it's demand level let alone maxing the service out.

Look at a electric stove circuit for example. A 12kW stove has only a 8kw ciruit and when was the last time the breaker tripped on it?

The POCO's takes advantage of the demand load on the service. Partly to save cost on wire and to minimize strain on the anchors holding the tri-plex at both end.

At my house in Palm Bay, there are 8 houses on one pole pig. I can't remember what us stamped on it, but it is only 25 or 35 KW. All of these houses are 150 amp service min. with the newer houses at 200A. I am surprised that the tranny doesn't glow in the dark sometimes.

I don't think I have ever seen a house served with anything but 2ga triplex since they started replacing the 3 strands with the triplex 30 years ago. I know when I did my service upgrade ("bootlegged 100" to 200) I asked the engineering department at FPL about my drop and all they asked was if it was twisted.