Yep! And I found a lot of it!!
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A somewhat related issue. Is there a concern with only two poles being used on this 3-pole CB? Does the CB need to be rated for this? What other considerations? Thanks.
Bottom left
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No issue. Is this a 3 phase panel or did they wire it as only single phase?
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Ha, let me introduce you to my next-level situation. I am unable to determine all the voltages or phases conclusively. Possibly a delta system where they either eliminated or avoided the high leg (which was not identified or labeled as such). Here is what I have. I do NOT use clamp meters etc. It’s all visual. (I was so cramped in this room I was unable to get one good full photo)
Any insight appreciated.
What a mess. It does appear to be a 3 phase, 4-wire Delta service. You would need to take voltage measurements to accurately determine what it is.
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Thanks Robert, I appreciate the feedback.
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You’re welcome. I’ve said it before you guys find some really interesting things out there in the field. 
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The next time you see an overhead service that you want to identify, try getting pictures of the transformer connections from a few different angles. It’s easy to identify the configuration by looking at the connections.
A center-tap isn’t something that is eliminated or avoided. It is an optional feature that is added. Center-tapped Delta arrangements have limited uses. They are only appropriate when the ratio of three-phase loads to single-phase loads is high. If the ratio were 50:50, for example, a center-tapped Delta would be a poor choice. On the other hand, if the ratio is 95:5, a center-tapped Delta could be the best choice. That’s why you most often see center-tapped Delta services in facilities that have a high ratio of three-phase to single-phase loads.
Delta primaries are more common than Delta secondaries for a variety of reasons. Wye secondary connections have become the de facto standard for most three-phase commercial applications because of Wye’s versatility. The number of Wye connected systems greatly outnumbers the much less versatile center-tapped Delta.
While we are on the subject of grounding, inspectors should be aware that transformers are most often solidly grounded. Resistance grounding is much less common. Delta transformers can also be corner grounded, but those are relatively, and increasingly, rare, especially among newer systems.
Neutrals can either be floating or solidly grounded. This is something than many electricians and even more home inspectors get wrong. Floating neutrals are extremely rare. Home inspectors often speak of floating neutrals in residences. Neutrals are always solidly grounded in residential electrical systems. Center-tapped Deltas are usually solidly grounded, but can be resistance grounded. In very rare circumstances, a center-tapped Delta with a floating neutral may be employed. It is very unlikely that you will ever see one outside of a textbook though.
Companies such as IBM and Unisys used to push for floating neutrals. I worked for Champion Spark Plug Company for a few years in the 1980s. The 1970s-1980s was probably a peak period in history for a push toward floating neutrals. We had a mainframe system being installed with a large number of terminals connected to it. The computer people were insisting on floating neutrals. After much debate, we chose not to accommodate them because the risk far outweighed any potential benefits. Today, there are more options for powering sensitive electronics than there were 40-50 years ago.
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I can’t see much in the picture. I can only see two transformers. Were there three? An open Delta only uses two transformers instead of three. An open Delta can still provide three-phase power, but at a reduced capacity. One benefit of Delta connections that I hadn’t previously mentioned is that a Delta three-phase system can continue to function at a reduced capacity if one transformer fails or is removed.
I am not 100% sure if it were two or three? I am leaning towards two from memory. I find a good bit of Delta systems in this area of AL, notably older properties such as this. This unlike my home base in Atlanta where I seldom see it.
That’s consistent with what I would expect. Delta systems were more popular in the past than they are now. They were also more popular in rural areas than in urban areas.
Utility companies might offer an Open Delta option in lieu of a smaller closed Delta because they buy standard 25kVA single-phase transformers in large enough quantities that the cost per kVA is probably less than buying smaller quantities of smaller transformers. When I had my electrical contracting business, it cost me less for 200A panels than for 125A or 150A because I’d buy the panels in large enough quantities that they cost less for each panel than the smaller panels. I can’t say with any certainty that that is why open Deltas may be popular in a particular area, but that’s my best guess.
Open Deltas present some challenges where single-phase is also needed though. Another transformer with a wye secondary could be placed downstream in order to derive a neutral. The pole mounted transformers might be owned by the utility company while the downstream transformer might be owned by the customer. That’s a fairly common thing to do. That could account for the lack of a high leg, but you probably would have seen the transformer while you were there. It could be a dry-type transformer hanging on a wall somewhere. It is possible to center-tap one of the two pole mounted transformers to create a neutral, but then there would be a high-leg. Another, but unlikely, option would be a corner grounded Open Delta. That wouldn’t be practical though.
Another possibility to consider is that two standard 25kVA transformers can be connected to create one 50kVA supply. In that case, you would see the tap between the secondaries of the two transformers. Here again, that might make more sense economically than a single 50kVA transformer for several reasons. One reason is that as transformers go up in size the cost per kVA goes up fast. A 50kVA transformer could cost three or four times what two 25kVA transformers cost. If a single transformer fails, another relatively low cost transformer can replace it.
As I mentioned earlier, the best thing to do (other than actually checking Voltages), would be to get good pictures of the connections.
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I see this often. Depending on the service and customer needs I may see two or a dozen, it varies wildly.
Moving forward, better photos will be my standard procedure.
I appreciate the information!
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