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 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. 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. -- nestork

OK..


in the diagram, the top of the primary is connected to 7200Volts and the bottom of the primary is connected to ground. THe voltage on the wire connected to ground is close to 0. It doesn't matter that some of the current passing through that wire started out at 7200 Volts. As long as the wire is connected to ground, it is ground. So someone can touch that wire with no problem.

BUT.. if the ground connection to the wire should come loose, then the wire will have a high voltage on it and would be dangerous, becuase it has current in it "that is trying to get to ground" and can't.

That is actually the same danger in the 3 wire dreyer circuit. The ground and neutral share the same wire and if the connection to that wire comes loose, the "ground wire" will have dangerous voltage on it.

On the pole transformer, ther bottom side of the primary coil is connected to ground, but the wire you see running down the pole is NOT the ONLY connection to ground. All the grounds in the entire distribution system are connected together so if the ground to one particular pole should come loose, the wire is still probably at ground due to all the other connections. But if I saw a loose ground wire running down a pole, I still would not want to touch it.

Mark