Single Phase service labeled as three phase

[acolella]

I am surveying a job site to install A/C equipment in a very old manufacturing facility. Approximately 1930s-1940s. When I was in the facility today I noticed something very strange.

What I see outside is a single phase of 7620 Volts and a neutral conductor going underground from the pole in to a transformer vault in the buildings basement.

I can absolutely confirm that there is only a single phase and a neutral going to the vault from the pole outside. However, the switchboard leaving the vault has "240 Volts Three Phase" labeled on it and on every disconnect downstream of that switchboard. The transformer vault is locked by the utility company so I can not get in there at this time. I had no tools or test equipment with me today but plan on returning with some within the next few days. Can somebody tell me if they have ever seen anything like this before? Or if it is even possible to derive three phase power from this type of connection.

I would like to fully understand this type of system before we start installing, or even purchasing for that matter, three phase equipment. This building has three services, two of which I have worked with before. (Today was my first day in the older section of the building) One service is 480V 600A Ungrounded Delta (which I have confirmed) fed from a pad mounted unit substation. The other service is 240V 400A Ungrounded Delta (which I have also confirmed) fed from three cans on a pole outside of the building. But the third (and oldest) service is labeled as "240V Three phase" which clearly only has a single phase and neutral going into the vault. We would prefer to utilize this three phase service (if it is in fact three phase) that is in question, due to its proximity to the location of where the A/C units need to be installed, rather than run some 400-500 feet of conduit/conductors to the confirmed 240V Three phase service.

Any help would be greatly appreciated. Thanks.

 

[Mike01]

Three Phase 240V

Three Phase 240V

Search for "wild leg", "high leg". and you might find your ansewer.

 

[acolella]

Search for "wild leg", "high leg". and you might find your ansewer.

I am familiar with "wild leg/high leg" but these don't apply to my particular problem. From my visual inspection, I only have a single phase primary coming into the vault. One hot wire, and one neutral wire. I will be returning to the job site tomorrow with tools and test equipment so I hopefully can narrow this issue down. I will post the results. Thanks very much.

 

[hurk27]

You cant derive 3-phase from just a phase and neutral, but who's to tell if the other one or two phases are running underground from somewhere else? you can have a 3-phase open delta or Y with only two phase conductors of a 3-phase system and neutral.

 

[broadgage]

Or perhaps the switchgear is listed for 3 phase 240 volt, but actually used on single phase 3 wire 120/240 ?
Or was formerly 3 phase 240 volt, and then re used without altering the lables.

If you are certain that this service is derived from a single phase MV source, then it cant be 3 phase.

Could it be 240 volt 3 phase delta, as you found this elswhere in the premises ? With the single phase MV service redundant or used for some other purpose.

 

[acolella]

Or perhaps the switchgear is listed for 3 phase 240 volt, but actually used on single phase 3 wire 120/240 ?
Or was formerly 3 phase 240 volt, and then re used without altering the lables.

If you are certain that this service is derived from a single phase MV source, then it cant be 3 phase.

Could it be 240 volt 3 phase delta, as you found this elswhere in the premises ? With the single phase MV service redundant or used for some other purpose.

I'm betting that is was formerly a three phase system now modified to single phase without changing the labels.

I can't guarantee that there are no other phases entering the vault from some other location, but I did some extensive investigation outside and I highly doubt that there are any other phases entering the vault. The main conduits entering this switchboard come right through the wall of where the transformer vault is located so, I'm pretty certain that this switchboard is not fed from another location on the premises. Having access to the vault would be a definite plus.

Thanks very much for the input. Hopefully I will be returning to the site later this afternoon. I will post my results/findings. I'll even try to get some photographs of this scenario. Thanks again.

 

[sgunsel]

I see quite a few 3 phase switches, disconnects, motor starters, and misc contactors used for single phase power. It confuses people who read the label but don't count the wires.

 

[tlaidman]

It could be a corner grounded delta in which you would have 2 ungrounded and one grounded phase.

 

[acolella]

I see quite a few 3 phase switches, disconnects, motor starters, and misc contactors used for single phase power. It confuses people who read the label but don't count the wires.

Many of the disconnects have less than three wires. Many of them have three or four. Knowing how many wires are in the disconnects still doesn't fully answer the question about what type of service is supplying that section of the building. These are labels made up by the maintenance shop personnel, not the nameplate on the equipment. I should have been more specific. I am unable to count wires in a switchboard that I have no tools to open up anyway, and that is the main piece of equipment in question, being it the service entrance.

 

[acolella]

I returned to the site today with tools and equipment and verified that it is in fact a run of the mill 120/240V Single Phase/Split Phase service. Entering the switchboard is L1, L2, and a neutral. L1-Gnd/Neut=119V L2-Gnd/Neut=118V L1-L2=238V. This section of the building may have had three phase service at one time, most of the distribution equipment is all three phase but it is definitely a single phase service. I re-labeled all of the equipment properly before I left. Looks like we'll have to see if we can get single phase chillers which is highly unlikely so we'll probably just run conduit/conductors to the 240V Three Phase service. Thank you all for your input.

 

[Jraef]

It could be a corner grounded delta in which you would have 2 ungrounded and one grounded phase.

Absolutely. I had my business in a very old (100year+) building in Seattle and that's exactly what we had. One transformer on the pole, 2 insulated wires entering the weatherhead, 3 phase 240V at the panel. It was Corner Grounded Delta system and the EGC was not run from the pole, it was done in the building. This was a legacy system of course, it would have never been done that way in my lifetime. My partner at the time was older and more experienced than me, he had fun teasing me because I had only read about it in textbooks, I had never seen how it was done. So I did the exact same thing, I insisted it was a single phase service. He had me running around in this old building looking for where the utility dropped a 3rd wire... Kind of like a Snipe hunt.

 

[Jraef]

I returned to the site today with tools and equipment and verified that it is in fact a run of the mill 120/240V Single Phase/Split Phase service. Entering the switchboard is L1, L2, and a neutral. L1-Gnd/Neut=119V L2-Gnd/Neut=118V L1-L2=238V. This section of the building may have had three phase service at one time, most of the distribution equipment is all three phase but it is definitely a single phase service. I re-labeled all of the equipment properly before I left. Looks like we'll have to see if we can get single phase chillers which is highly unlikely so we'll probably just run conduit/conductors to the 240V Three Phase service. Thank you all for your input.

A lot of legacy corner grounded delta systems were converted to 1 phase over the years because of someone getting a new permit for renovations and discovering that the legacy system could not be altered or added to. But the panels should have been redone at that time.

 

[acolella]

Also, I took some photos today.

Photos of the primary wires outside:

http://i1235.photobucket.com/albums/...a/DSC00055.jpg

http://i1235.photobucket.com/albums/...a/DSC00053.jpg

Photos of the switchboard: (before re-labeling)

http://i1235.photobucket.com/albums/...a/DSC00057.jpg

http://i1235.photobucket.com/albums/...a/DSC00060.jpg

http://i1235.photobucket.com/albums/...a/DSC00059.jpg

Looks like some pretty substantial flooding happened in that basement at one time, or multiple times for all I know. You can see the water line is right at the lugs.

 

[hurk27]

That looks like a grounded "B" of course if you took voltage mesurments between the top common bar and one of the phases and got 120 volts I has to be a single phase, but if you got 240 volts then it is a grounded "B" 3 phase

 

[LarryFine]

http://i1235.photobucket.com/albums/...a/DSC00059.jpg

That pic answers your question, and confirms your deduction.

 

[hurk27]

Whoops didn't see post 10 it is a single phase with those voltage readings

 

[hurk27]

I returned to the site today with tools and equipment and verified that it is in fact a run of the mill 120/240V Single Phase/Split Phase service. Entering the switchboard is L1, L2, and a neutral. L1-Gnd/Neut=119V L2-Gnd/Neut=118V L1-L2=238V. This section of the building may have had three phase service at one time, most of the distribution equipment is all three phase but it is definitely a single phase service. I re-labeled all of the equipment properly before I left. Looks like we'll have to see if we can get single phase chillers which is highly unlikely so we'll probably just run conduit/conductors to the 240V Three Phase service. Thank you all for your input.

How far is the 480 delta 600 amp service, as it might be more cost effective to run 480 over and then set a transformer sized for what you need?

 

[acolella]

How far is the 480 delta 600 amp service, as it might be more cost effective to run 480 over and then set a transformer sized for what you need?

I was checking the other services yesterday, I hadn't been over to that section in some time and must have been mistaken. It is actually a 480V 1200A Ungrounded Delta. I'm thinking this may be the solution because we can always order chillers rated for 460V. We'd need a pretty large transformer if we were to go the route you suggested using 230V chillers. We'll need to do some more investigation/planning and see which solution is going to be the most cost effective. The 480V service entrance is in a completely different building and I would say is roughly 1000-1100 feet away from the location of where the chillers need to be installed. The 240 is only about 500 feet but we'd have to use larger conductors. So, three options. 400-500 feet of 240V, 1000-1100 feet of 480V, or 1000-1100 feet of 480V to a transformer stepping down to 240V. I think the third option would be the most expensive, granted we'd be able to use smaller conductors. This will also depend on the price difference between chillers with 460V compressors and 230V compressors. Lots of variables to consider.

 

[LarryFine]

Lots of variables to consider.

Well, if this was easy, everybody would be doing it.

 

[Jraef]

The water marks and corrosion on those lugs is scary. Looks like they decided NOT to replace the lugs? I can see salvaging the switchboard if the water only got that high, but corrosion on those lugs is dangerous.

That's what I call cheap...