Pole Mounted Transformer Primary Winding

[MD Automation]

Based on what I know from the pole outside my house...

If you look at this nameplate from my transformer, you can see (like Don says above) one side (top right) of the Primary winding is marked as GND and bonded to the can.




The Secondary neutral is also typically bonded, but outside and not internally. Like this...




In the pic below - (disregard the blown cutout) - you can see what I call the MGN (multi-grounded neutral) wire. It's the one underneath the transformer. This runs along the whole path, mostly below the 7680V primary, but also sometimes on the same level depending on if there is a crossbar on the pole.


That MGN is the neutral for both primary and secondary. And if my transformer served any other houses up or down my road, it would have the 2 hot secondary legs mounted above and below that MGN heading out right and left - and it would look exactly like any of the pics you posted. In fact they even have the standoffs for the top and bottom secondary wires in place, in my case they are simply used to secure the connections to my service laterals.

The bulk of all the return current from the primary is going back on that MGN. Sure some part of it goes down my well casing, or back thru the cable TV shield, or the ground rod(s) sunk into the soil, or any of the other myriad connections up and down the road. But I would think most is taken up by that MGN. It's certainly the lowest "resistor" in all the hundreds of paralleled "resistors" that try to return the primary current back to the source.

And for pad mounted transformers you asked about, that MGN is brought down to the HV connection along with the primary. It's the "N" in a CN (Concentric Neutral) cable. It's unwrapped and separated at the loadbreak connector.

 

[electrofelon]

And here is the data plate for my transformer. It is dual voltage (4800 and 7620) so they can use the transformer for both systems which would cover the vast majority of installs for this utility. IT is two bushing, since it would be needed for the 4800V delta system. The second bushing, although not required when used on the 13.2/7.62 MGN system, is used for the neutral. Clearly they find it worth ordering two voltage transformers rather than stocking two different units.

 

[electrofelon]

And here is a picture of my service, the 4800 delta system. I was doing some maintenance so I had pulled the cutouts with a hot stick. Its kinda a bad picture because the second cutout and second transformer bushing are both not visible! But both those conductors are ungrounded conductors. ITs somewhat rare around here to see a single phase delta system run that way, usually they are on crossarms and not one above one below like this.

 

[W@ttson]

Based on what I know from the pole outside my house...

If you look at this nameplate from my transformer, you can see (like Don says above) one side (top right) of the Primary winding is marked as GND and bonded to the can.

View attachment 2563881


The Secondary neutral is also typically bonded, but outside and not internally. Like this...

View attachment 2563882


In the pic below - (disregard the blown cutout) - you can see what I call the MGN (multi-grounded neutral) wire. It's the one underneath the transformer. This runs along the whole path, mostly below the 7680V primary, but also sometimes on the same level depending on if there is a crossbar on the pole.
View attachment 2563883

That MGN is the neutral for both primary and secondary. And if my transformer served any other houses up or down my road, it would have the 2 hot secondary legs mounted above and below that MGN heading out right and left - and it would look exactly like any of the pics you posted. In fact they even have the standoffs for the top and bottom secondary wires in place, in my case they are simply used to secure the connections to my service laterals.

The bulk of all the return current from the primary is going back on that MGN. Sure some part of it goes down my well casing, or back thru the cable TV shield, or the ground rod(s) sunk into the soil, or any of the other myriad connections up and down the road. But I would think most is taken up by that MGN. It's certainly the lowest "resistor" in all the hundreds of paralleled "resistors" that try to return the primary current back to the source.

And for pad mounted transformers you asked about, that MGN is brought down to the HV connection along with the primary. It's the "N" in a CN (Concentric Neutral) cable. It's unwrapped and separated at the loadbreak connector.

View attachment 2563884


View attachment 2563886

Woah, thanks for all this info and for the really clear pictures. What kind of camera do you have that you were able to zoom up so much!?

 

[W@ttson]

And here is a picture of my service, the 4800 delta system. I was doing some maintenance so I had pulled the cutouts with a hot stick. Its kinda a bad picture because the second cutout and second transformer bushing are both not visible! But both those conductors are ungrounded conductors. ITs somewhat rare around here to see a single phase delta system run that way, usually they are on crossarms and not one above one below like this.

I like that you have a hot stick laying around just incase you need to do some maintenance around the house!

 

[electrofelon]

I like that you have a hot stick laying around just incase you need to do some maintenance around the house!

I does come in handy. I DECIDE!

 

[garbo]

Not quite. The most common installation in the US has a 'multi-earth neutral' wire that hits all the poles, is connected to grounding electrodes, and serves as the neutral for both the high voltage distribution system and the transformer secondary voltage. This MEN wire is continuous going back to the substation

The 'SWER' system doesn't have that 'multi-earth-neutral' returning to the substation. You might have a small local neutral acting as the local low voltage neutral and the utility high voltage grounded conductor, but it doesn't return back to the substation

Jon

Sure in my area that the Ultility transformers only have one primary wire, three wires that supply 120/240 volt secondary on what we were taught called an Edison system then a flimsy aluminum ground wire that goes to a ground rod at nottom.of pole. I know that the Ultility companies do not have to follow the NEC but always thought that practice and only supplying a oversized primary fuse and no secondary protection. When I brought up the in my the dangerous large only primary fuse to a linemen he told me that they would rather have your house burn down in the event of say your service cable shorting out then to blow one of their fuses and require them to send a bucket truck.out. I'm sure that my copper water service always having a current flowing thru it reduces its life span. I never saw where local utility company tied in neutrals from nearby by neutrals from other transformers.