On Mon, 13 Jul 2020 12:54:24 -0500, dpb wrote:

On 7/13/2020 12:21 PM, wrote:
On Mon, 13 Jul 2020 10:15:28 -0400, Ralph Mowery
wrote:

In article ,
says...

An important difference, like I thought a "service" is not fused.
At least not on the service size, though according to Fretwell
there is a fuse on the primary side, which makes sense. Still
since a given transformer typically serves more than one service, you
could apparently put many times the current rating of the service
conductors through it before it blows. Probably not much of an
issue, since if something happens, a direct short is probably
far more likely, which I guess would blow the xformer fuse before
damage was done to the conductors.





The purpose of the fuse in the primary of the transformer is to protect
the main line from being overloaded. While the power company would like
to save the transformer, the main thing is not to damage the main line
and put many out of power. Chances are that if there was a direct short
in one of the secondary lines it would blow that fuse before the
transformer went bad. Wiring can often stand a very high overload if
the time period is short. Fuses are usually designed to blow faster the
higher the overload.

Some transformers, especially in cities feed several houses. I lived in
the county but there were several houses close together. The power
transformer fed 4 houses. During a lightning storm the transformer blew
for some reason. With surge supressors on much of my house, all that
was damaged was the supressors and the oven. The built in oven only
blew an internal fuse and surge supressor in it. Several of the
neighbors lost their TV sets and a few other devices.


I will ask my PoCo buddy about the primary protection the next time I
see him.

I dunno about that side definitely, either...the breaker in the
connection there only protects the feeder _TO_ the house, indeed.

There's about 20-30 ft between the pole the xfmr hangs on to the
service/meter pole, the SE goes down the meter pole thru the meter then
into junction box where the house feed ties to that disconnect and runs
back up the pole where there's connections to the SE to barn, elevator
and over to the silo...there's fused disconnect on it (silo) that then
feeds the waterer heaters plus convenience outlets/lights for the
feedlot/corrals/working chute area.

Places aren't that close together out here that one transformer does
multiple farmsteads and power demands are fairly substantial in
comparison to normal residence.

Here they will put one house on a 25KVA, 2 will be on a 37 and 3 will
be on a 50. There are a couple of 50s here with 4 houses on them but I
bet that will change if they tear down those little 1300 sq/ft PreFIRM
shacks and put a 2000 Sq/Ft house there. A lot of this infrastructure
is 60 years old and predates wide spread use of A/C and other heavy
hitters.

This is the map of my primary. I am about 1/3d of the way down from
the tap off the distribution trunk.
http://gfretwell.com/electrical/Xfmr.jpg