Can you explain a 6 wire service

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topper

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Most of my experience with 6 wire service involves replacing them. Lately we have run into quite a few of them. It is my understanding that these were most likely built in the 40's. In our area if they get disconnected for any reason, the poco will not turn them back on. Since they may be called something else in different areas, let me try to describe what they are. They typically are fed from transformers that are typically located on separate poles. One is a single phase 120/240 transformer. The other is a 3 phase set up with three transformers, but the center phase is bolted to ground. It is my understanding that the disconnect should not have a fuse in the center phase, which has been the case in about half of the services that I have seen. It seems that one person explained that these service came about when 3 phase became needed for shop equipment, but the old equipment needed single phase 240v. I can understand that, but why not just use a 240 Delta? Why the grounded center phase? I really don't need to know this for anything I am needed to do, especially since we are generally tearing these out, I am just curious and want to understand them.

Thanks,

Jim
 
topper said:
The other is a 3 phase set up with three transformers, but the center phase is bolted to ground. It is my understanding that the disconnect should not have a fuse in the center phase, which has been the case in about half of the services that I have seen. It seems that one person explained that these service came about when 3 phase became needed for shop equipment, but the old equipment needed single phase 240v. I can understand that, but why not just use a 240 Delta?
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The three phase set up is delta, corner grounded delta.
 
I ran into something similar I think in Mexico back in the early 80's. I was told it was a 2 phase 5 wire system. Which was service for both resi and commercial. As I recall 1 neutral did not detect voltage from 2 of the hot legs. Very weird!!!
 
Yes you can and you would be correct. it used four ct's, two for the single phase and two on the three phase, the grounded leg is not measured. I do have one of these services still in use on a building we take care of. If anyone has specific questions I can go look at it if I do not know/remember the answer. I searched online and have not found anything like these. The poco claims that they will not restore power to them because they do not have the meters, I have been told by others that the older linemen that understand and know these systems have retired.
 
scottam99 said:
I ran into something similar I think in Mexico back in the early 80's. I was told it was a 2 phase 5 wire system. Which was service for both resi and commercial. As I recall 1 neutral did not detect voltage from 2 of the hot legs. Very weird!!!
Click to expand...

A client of mine has something like this ... I think ... 240VAC, 2ph open delta with one side having a center tapped neutral.

Jason
 
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