Rotary Phase Converter and Equalizing Voltage Output

[Bertsbolts]

In my shop, we have a rotary phase converter (15 HP Idler RPC).to bring our 240VAC 1Ph to 460VAC 3 Phase, The voltage is first stepped up from 240V to 460V through a single phase transformer. Then it is passed through a fused disconnect to a rotary phase converter. This same Disconnect is also where we tap the 3 phase with a cable to test run 460V 3Ph Condensers. The problem I am having is that I have a very high leg on the manufactured line. With some of the new equipment, electronic monitors/controls exist, and I am suspicious that the uneven voltage is a cause of loss of phase trips on, say, a Scroll Compressor monitor or phase monitor. On typical machine motors we experience little problem.
Currently I have the transformer tapped to boost from 240V to 464V (single phase). After the rotary phase converter, my voltage readings are as follows-
L1 - L3 = 462V, L1 - L2= 515V, L2 - L3= 532V. (Though not a common measurement, to Ground L1=242V, L2=385V, L3=242V ) Amperage readings on a served motor from the converter usually shows around 1/2 the amps on L2.
The Rotary phase converter does contain a start capacitor (50mfd) and a run capacitor (80mfd).
Questions: Is the solution to better equalizing the voltage a matter of placing capacitors across L1-L2 and L2-L3?
Can someone point me to the proper equation for figuring the mfd sizing, if so?
Aside from purchasing an expensive control attachment from the OEM, I am trying to just utilize this piece of equipment as best possible, until we upgrade our facility electric service and go to digital converters. All suggestions considered. Thanks in advance for the help.
I do have one other question concerning transformers and phase converters.
Can a three phase step up transformer be used safely/effectively fed from the outputs of a digital phase converter? 240VAC output stepped to 460VAC.(For single point load)
Thanks again

 

[tom baker]

I would suggest you split this into 2 posts.
Welcome to the forum

 

[LarryFine]

Can a three phase step up transformer be used safely/effectively fed from the outputs of a digital phase converter? 240VAC output stepped to 460VAC.(For single point load)

Welcome to the forum.

I was thinking of suggesting a 3ph transformer for the first question.

I have wired 3ph RPCs, but not for loads with electronic drives.

 

[MTW]

To reduce voltage on the output of the RPC, you need to reduce the run capacitance. To achieve better voltage balance, split the run capacitance between both supply legs and the generated leg. One leg should have slightly bigger capacitance than the other, not both the same size.

The likely reason that your output is high is that your RPC was designed and built for a larger load than you are running on it. Tune the capacitors for the largest connected load, with a lesser load connected the voltage will rise. You need to find a happy medium for the loads that you run and how you cycle them.

If your new solid state converters will be phase perfect units, you can run a transformer off of its output, you might want to consider using multiple units if your connected loads are vastly different in their current requirements.

 

[Bertsbolts]

I would suggest you split this into 2 posts.
Welcome to the forum

Thank You

 

[Bertsbolts]

Welcome to the forum.

I was thinking of suggesting a 3ph transformer for the first question.

I have wired 3ph RPCs, but not for loads with electronic drives.

Thank You. I had considered such. But was unsure (over cautious) on fit. These new monitors throw us old aged dudes for a loop at times. LOL

 

[synchro]

I agree with MTW's approach. Your excess voltages are likely caused by getting too close to parallel resonance between the running cap and the inductive reactance of the motor.

 

[kwired]

To reduce voltage on the output of the RPC, you need to reduce the run capacitance. To achieve better voltage balance, split the run capacitance between both supply legs and the generated leg. One leg should have slightly bigger capacitance than the other, not both the same size.

The likely reason that your output is high is that your RPC was designed and built for a larger load than you are running on it. Tune the capacitors for the largest connected load, with a lesser load connected the voltage will rise. You need to find a happy medium for the loads that you run and how you cycle them.

If your new solid state converters will be phase perfect units, you can run a transformer off of its output, you might want to consider using multiple units if your connected loads are vastly different in their current requirements.

Problem is the intended use is not for any one specific item, so he will end up needing to tune it to every different load utilized. Even then probably won't get as even of voltages very easily as you get with a true three phase source, These are kind of a crude conversion that gets the job done and is suitable for a motor that isn't going to draw full rated load for long time periods. The unbalanced voltages will result in unbalanced currents in the motors, and you probably would not want such converter as a permanent part of the supply to that motor in this sort of equipment.

Most these crude phase conversion setups I seen particularly on a long run duration load has the motor derated from what would likely be used if it were fed from a true three phase supply. Loads that have significant variance in current drawn also kind of need oversized motors on them if they are to last on this sort of setup.

Had someone else fit a static converter (just capacitors only, not a rotary converter) on a used air compressor they purchased. Asked me to look into it, it would kick out overloads when they used it hard enough. I was able to tune it to get close to right balance voltage/current but then it would vary according to actual pressure in the storage tank, so you can only tune it to a particular load level - I think they would have been better off to use a VFD on this setup, or even change to a single phase motor as it was only 10 HP, though it also was somewhat an OEM motor and not easy to find a general purpose motor that would been a simple swap.

 

[MTW]

Kwired, I agree with your post, to get it to work at all, it has to be tuned to a range not a specific fixed load.

Bert already acknowledged that some of his equipment runs fine as is, but newer loads are having issues. More sensitive and likely much lighter loads, that don’t pull down the generated voltage as much. He didn’t give any specific load data, so all we can do is speculate at this point. But generalities do apply.

Phase converters are a get buy solution and usually always require tuning to the loads. If he had a 230V converter and then a delta to wye transformer with some adjustment taps, that would give him some additional adjustments, and additional stability, but that is not what he has.

A static phase converter paired with an air compressor is about the worst combination setup you could install. If load motors were oversized for their loads, that would help. But that is not how equipment is normally designed and built.

 

[kwired]

Kwired, I agree with your post, to get it to work at all, it has to be tuned to a range not a specific fixed load.

Bert already acknowledged that some of his equipment runs fine as is, but newer loads are having issues. More sensitive and likely much lighter loads, that don’t pull down the generated voltage as much. He didn’t give any specific load data, so all we can do is speculate at this point. But generalities do apply.

Phase converters are a get buy solution and usually always require tuning to the loads. If he had a 230V converter and then a delta to wye transformer with some adjustment taps, that would give him some additional adjustments, and additional stability, but that is not what he has.

A static phase converter paired with an air compressor is about the worst combination setup you could install. If load motors were oversized for their loads, that would help. But that is not how equipment is normally designed and built.

Have customer with a crop drying fan, I helped install it when I worked for someone else 25-30 years ago. Single phase supply, static phase converter. 25 Hp motor on a fan that likely would be driven by maybe 15 Hp if it were direct connected to a regular three phase supply.

Back then you didn't see single phase motors that big, unless air over rated which this was not. Now I see 15 HP single phase motors quite often, probably would have used that back then if they would been as common as they are now.

That phase converter maybe needed a capacitor or two replaced over the years but is still going.

 

[Bertsbolts]

To reduce voltage on the output of the RPC, you need to reduce the run capacitance. To achieve better voltage balance, split the run capacitance between both supply legs and the generated leg. One leg should have slightly bigger capacitance than the other, not both the same size.

The likely reason that your output is high is that your RPC was designed and built for a larger load than you are running on it. Tune the capacitors for the largest connected load, with a lesser load connected the voltage will rise. You need to find a happy medium for the loads that you run and how you cycle them.

If your new solid state converters will be phase perfect units, you can run a transformer off of its output, you might want to consider using multiple units if your connected loads are vastly different in their current requirements.

Thank you for that advice. I had wondered if the sole run capacitor was a possible issue. I will definitely see about splitting the mfd acoss both poles in relation to the L2. I am of the mind, given the voltages, that a 40%/60% is a good place to start. Am I on the right track to begin?
Thanks for the advice on the "after" trans. Phase Perfect is who we are considering for a digital converter.

To reduce voltage on the output of the RPC, you need to reduce the run capacitance. To achieve better voltage balance, split the run capacitance between both supply legs and the generated leg. One leg should have slightly bigger capacitance than the other, not both the same size.

The likely reason that your output is high is that your RPC was designed and built for a larger load than you are running on it. Tune the capacitors for the largest connected load, with a lesser load connected the voltage will rise. You need to find a happy medium for the loads that you run and how you cycle them.

If your new solid state converters will be phase perfect units, you can run a transformer off of its output, you might want to consider using multiple units if your connected loads are vastly different in their current requirements.

For an update from today:
We managed to run and test the two pieces of equipment I was having trouble with. Just FYI, they are refrigeration compressors with Copeland Scroll compressors and a Core Sense Monitor. I had a tech rep (senior person) from the manufacturer come down to help us out. So, it seems to make these units run with a high leg (Copeland quirk) is to put the high leg on L3, and keep the rest of the phases in order. (In this case on my TB for L!, 2, and 3 I have run from the panel L3 to L1, L1 to L2 and L2 to L3.) Ran good for us to test. Typically we test these units after installing Direct Exchange Shell and Tube Evaporators for water, rather than air coils. These particular units require a different wiring from any kind of high leg "Y" source, as opposed to Delta. Seems the core sense monitor only monitors the high leg through phase monitor L3 and no where else. If it is L2 (as per my source phase sequence) it will think something is wrong and trip on a loss of phase. So, besides my "dirty" power, we learned a valuable manufacturer quirk which is only in comparison to our other four manufacturers we use.
I thank all of you for the advice, suggestions, etc. you have provided. We are still definitely doing a power upgrade and going to digital converters. I have a Dig Conv 230V that I am going to try the step up transformer with taps, for now.

 

[kwired]

motors won't care which leg is the high leg, controls and monitoring equipment very well might though.

Bertsbolts, high legs do not exist in normal wye systems, they are on delta systems when you ground the midpoint of one phase. Motors still won't care which leg it is on either as they won't have a neutral connection and only care about line to line voltages

 

[Bertsbolts]

motors won't care which leg is the high leg, controls and monitoring equipment very well might though.

Bertsbolts, high legs do not exist in normal wye systems, they are on delta systems when you ground the midpoint of one phase. Motors still won't care which leg it is on either as they won't have a neutral connection and only care about line to line voltages

According to an electrician and the tech rep (knowledgeable about these things), my current configuration is a "Y" with a high leg. I am not even sure how that has occurred. It is a contraption I have been complaining about for over 5 years. Mad scientist stuff. So, I suppose we just have to treat it as such. Apparently Copeland Core Sense Monitors care. Emersons could give a crap. It has a short life expectancy in my eyes. We need to clean this situation up. The whole thing was added to test small motor systems. Now the company wants to do bigger motor loads with more amps needed, and more electronic monitoring systems. This thing is lucky it can do 42 without popping a fuse.

 

[hbiss]

Seems as you are getting bigger and bigger, ever consider installing a 3 phase service just for this? Is 3 phase available where you are?

-Hal

 

[MTW]

Bert, glad to hear that you got some help and got your two units tested. Part of what you learned is correct and part of it is incorrect. Let's see what we can do to give you a better understanding of the mad scientist part, that your confused about. I'm going to drop the brand trade names and wiring nomenclature and use generic terms to try and simplify things, for you and others that may come across this. Buckle up...

3Φ Electrical system types and phase converters. For 3Φ as supplied by any normal utility (your customers systems) you have delta and wye type systems as standard. Your end customers will be running one of these type systems. Phase converter outputs are similar but slightly different to standard utility delta supplied system, that's the part that seems black magic to you at this time.

Phase converters are supplied from single phase 240V utility systems and always produce a delta 3Φ center tapped delta output (high leg system), whether it's a rotary or electronic unit. This is due to the 1Φ center tapped input that they are supplied with, not because of the type or brand your using.

Most modern utility systems are typically supplied today as a wye system in two main voltages 208/120V and 480/277V. There are some areas that supply a center tapped delta (high leg) 240/120V system similar to a phase converter output, but these are not as prevalent today as they once were. As you have become aware, these different systems are not universally interchangeable, and the differences need to be understood and dealt with accordingly, to have success in deploying new equipment loads.

Equipment loads can have similar differences as to what type supply system they require or prefer. It's not just 3Φ power at a specific voltage. Most new 3Φ equipment today prefers or demands a wye system, it is designed and built for that, the whole world basically uses only wye systems, only North America still uses, in places, a delta system, typically older districts where they are grandfathered in. So this is where your frustration basically results from, you have a center tapped delta (high leg) testing source (RPC output) and most of the equipment you are testing is designed to run from a wye system.

As kwired stated earlier, plain motor only loads will run on either type system, as long as the voltage matches the motor tag. But, you almost never have just a plain motor, there are always controls that require power to function. Control systems are wide and varied, but the vast majority of them don't perform well or become damaged when connected to a delta high leg, because one phase leg voltage to ground is higher than the other two legs to ground. If the control system is powered by a internal control transformer, this will normally correct for the high leg voltage. However it's still bad practice to use the high leg to power control systems, especially on a RPC output, the generated leg. This generated high leg voltage varies with load, a good amount dependent on the connected equipment load, you don't want your control voltage wandering all over the place while your equipment load is cycling. That will lead to faulty operation, hiccups, and instability.

To help you, and warn others, the high leg on any system should be marked with orange tape, to readily indicate that it is the higher voltage to ground, and to not use it for control power. This is also a code requirement. Seeing a orange marker tape or wire color is much easier to identify in the equipment when connecting and testing, than trying to remember which terminal over there, or over here at the equipment is actually the wild leg. A simple roll of orange tape can save you from burning up controls, mistakes in connections, and erratic control operation. Dispense with the L1, L2, and L3 markings and use the orange tape on every wire that is the high leg. While on the high leg subject, it is also a code requirement to place the high leg on the center terminal of all distribution equipment and disconnect switches. This may need to change at equipment terminations, as the tech support showed you on your compressor phase monitor, but it should still have that orange marker to be clear what voltage it is. Whenever you need to change equipment rotation, never move the high leg to a different terminal, once you have determined where it belongs. Always interchange the other two phase legs, never the high leg.

I will attach some drawings showing the different type standard distribution system types and voltages for you to study for an overview. When I can find some more time we can continue the discussion, but in the mean time you can digest this first installment. All others, feel free to jump in and add information or comments or error corrections as you see fit.

Supply system to your phase converter, before your 1Φ step up transformer.

This is a typical low volt utility supplied wye system. Note all phase leg voltages are the same referenced to ground.


This is a typical high volt utility supplied wye system. Note all phase leg voltages are the same referenced to ground.


This is a typical 240V low voltage utility supplied delta system. Note that the top A phase is a higher voltage to ground than the others.


Then this is the 480V high voltage RPC output supplied delta system, from your RPC. Your actual measured voltages are slightly different due to your input voltage is lower, and you have an excess capacitance in your RPC.

 

[kwired]

According to an electrician and the tech rep (knowledgeable about these things), my current configuration is a "Y" with a high leg. I am not even sure how that has occurred. It is a contraption I have been complaining about for over 5 years. Mad scientist stuff. So, I suppose we just have to treat it as such. Apparently Copeland Core Sense Monitors care. Emersons could give a crap. It has a short life expectancy in my eyes. We need to clean this situation up. The whole thing was added to test small motor systems. Now the company wants to do bigger motor loads with more amps needed, and more electronic monitoring systems. This thing is lucky it can do 42 without popping a fuse.

Not possible with standardized systems, if you have some sort of crude conversion equipment, maybe.

Real wye system will look like the one in drawing MTW provided, all the phase conductors are equal distant from the mid point of the wye, they will always all be same voltage to mid point (neutral).

Most that crude conversion equipment is supplied by single phase with a center tapped neutral. The neutral isn't a part of the conversion equipment itself, but that single phase supply is one side of the delta that ultimately gets created in such conversion equipment. But unlike a delta transformer arrangement which will have pretty stable voltage on that third leg the conversion equipment third leg voltage does vary with loading conditions, not just voltage to the neutral but to the other two phase conductors as well. There is a phase shift that is sufficient to create rotation in motor windings, but is not as stable as in more conventional delta sources which will lead to unbalanced current in the motor windings, which if running at or near full load rating will shorten life of the windings also.

If control volts is tied to this, whether directly or via a control transformer - the controls end up seeing voltages not designed for, could end up being high or low depending on loading conditions again.

Phase monitor - may not hurt it much, but yes it will see the imbalance and will lock out whatever it is set up to control. A phase monitor on equipment that doesn't utilize a neutral conductor typically won't have a neutral connection and won't care if there is a high leg, all they monitor is line to line to line voltages, that will be equal on normal delta supply that wasn't derived from said phase conversion equipment.

The other thing you run into particularly on VFD controllers is surge protectors on the drive input - those are usually connected from each line to ground. Many them designed to be used on wye systems with equal voltage to ground and if you use them on any delta system they may not have high enough design rating for the voltage to ground that may be present on at least one of those input lines.

You mentioned certain units that will work properly with high leg on a certain position, it may be possible they are designed specifically to accept non wye systems, but things like voltage/phase monitoring or surge protection likely won't have as tight of acceptable tolerance allowances as other units designed around a wye system being the input.

 

[zbang]

I think something that's missing here (unless I've missed it myself) is the simple statement that most/many rotary phase "converters" are not actual 3-phase generators; they use the back-EMF of a motor to derive the third phase. While it has the correct phase displacement from the other leads, it can't supply nearly as much energy as they and that derived lead may have a wildly-different magnitude (voltage) than the others.

Strangely , the wikipedia article does a decent job of explaining things- https://en.wikipedia.org/wiki/Rotary_phase_converter.

 

[Bertsbolts]

Bert, glad to hear that you got some help and got your two units tested. Part of what you learned is correct and part of it is incorrect. Let's see what we can do to give you a better understanding of the mad scientist part, that your confused about. I'm going to drop the brand trade names and wiring nomenclature and use generic terms to try and simplify things, for you and others that may come across this. Buckle up...

3Φ Electrical system types and phase converters. For 3Φ as supplied by any normal utility (your customers systems) you have delta and wye type systems as standard. Your end customers will be running one of these type systems. Phase converter outputs are similar but slightly different to standard utility delta supplied system, that's the part that seems black magic to you at this time.

Phase converters are supplied from single phase 240V utility systems and always produce a delta 3Φ center tapped delta output (high leg system), whether it's a rotary or electronic unit. This is due to the 1Φ center tapped input that they are supplied with, not because of the type or brand your using.

Most modern utility systems are typically supplied today as a wye system in two main voltages 208/120V and 480/277V. There are some areas that supply a center tapped delta (high leg) 240/120V system similar to a phase converter output, but these are not as prevalent today as they once were. As you have become aware, these different systems are not universally interchangeable, and the differences need to be understood and dealt with accordingly, to have success in deploying new equipment loads.

Equipment loads can have similar differences as to what type supply system they require or prefer. It's not just 3Φ power at a specific voltage. Most new 3Φ equipment today prefers or demands a wye system, it is designed and built for that, the whole world basically uses only wye systems, only North America still uses, in places, a delta system, typically older districts where they are grandfathered in. So this is where your frustration basically results from, you have a center tapped delta (high leg) testing source (RPC output) and most of the equipment you are testing is designed to run from a wye system.

As kwired stated earlier, plain motor only loads will run on either type system, as long as the voltage matches the motor tag. But, you almost never have just a plain motor, there are always controls that require power to function. Control systems are wide and varied, but the vast majority of them don't perform well or become damaged when connected to a delta high leg, because one phase leg voltage to ground is higher than the other two legs to ground. If the control system is powered by a internal control transformer, this will normally correct for the high leg voltage. However it's still bad practice to use the high leg to power control systems, especially on a RPC output, the generated leg. This generated high leg voltage varies with load, a good amount dependent on the connected equipment load, you don't want your control voltage wandering all over the place while your equipment load is cycling. That will lead to faulty operation, hiccups, and instability.

To help you, and warn others, the high leg on any system should be marked with orange tape, to readily indicate that it is the higher voltage to ground, and to not use it for control power. This is also a code requirement. Seeing a orange marker tape or wire color is much easier to identify in the equipment when connecting and testing, than trying to remember which terminal over there, or over here at the equipment is actually the wild leg. A simple roll of orange tape can save you from burning up controls, mistakes in connections, and erratic control operation. Dispense with the L1, L2, and L3 markings and use the orange tape on every wire that is the high leg. While on the high leg subject, it is also a code requirement to place the high leg on the center terminal of all distribution equipment and disconnect switches. This may need to change at equipment terminations, as the tech support showed you on your compressor phase monitor, but it should still have that orange marker to be clear what voltage it is. Whenever you need to change equipment rotation, never move the high leg to a different terminal, once you have determined where it belongs. Always interchange the other two phase legs, never the high leg.

I will attach some drawings showing the different type standard distribution system types and voltages for you to study for an overview. When I can find some more time we can continue the discussion, but in the mean time you can digest this first installment. All others, feel free to jump in and add information or comments or error corrections as you see fit.

Supply system to your phase converter, before your 1Φ step up transformer.
View attachment 2560674
This is a typical low volt utility supplied wye system. Note all phase leg voltages are the same referenced to ground.
View attachment 2560675

This is a typical high volt utility supplied wye system. Note all phase leg voltages are the same referenced to ground.
View attachment 2560676

This is a typical 240V low voltage utility supplied delta system. Note that the top A phase is a higher voltage to ground than the others.
View attachment 2560677

Then this is the 480V high voltage RPC output supplied delta system, from your RPC. Your actual measured voltages are slightly different due to your input voltage is lower, and you have an excess capacitance in your RPC.
View attachment 2560678

Thank You for all of that information. Very helpful. I have been telling the boss for a few years that it is the wrong thing to be using for these applications. In this case the other issue is that it is a 10HP idler, (if I said 15 prior I misspoke) and the units they want to run are also 10HP. The company originally got this to run 3 phase motor loads with no electronic monitors ( under 5HP). I had been forced (reluctantly) to find ways to make the system do more, but when I speak of more money, they want to shoot it down and still try to get a Ford Escort to perform like an F350. The tech was there again, today. He and I went through all of the system and components. It's just plain wrong for the application. I asked him to go through it with me, because though I am the only electrical tech in the building, I have to argue with and Industrial Engineer. He confirmed a lot of my suspicions, and we proved it. He went in and spoke to the boss with me just being a fly on the wall. Hey, no argument. Questions, but answered. He also told him about the wye and delta systems in the US, and since he does go all over the country and elsewhere plus does UL testing. Boss has to listen. Now he has heard it three times. So, we are now going to upgrade and get the right equipment to do the testing we want to do. Finally.
Having let all in on that. I do very much appreciate all of the knowledge imparted to me from any of you on this thread. It does keep me fresh ( have been basically building control panel type equipment for the last 12 years), and it also provides me with info I seem to need to bolster my arguments against substandard and wrong equipment. So please keep the info coming. And yes, I will keep and understand the info imparted. I thank you again very much.

 

[Bertsbolts]

Seems as you are getting bigger and bigger, ever consider installing a 3 phase service just for this? Is 3 phase available where you are?

-Hal

I have raised that issue. Our electric company would have to run the three phase up our road from a main highway. Our road only has single 240. We were given a price a few years ago of a bit over $30K. To me, with the direction they want to go in, it's worth the investment. Then we have a bean counter who will say we can rent a generator over 100 times for less money. (Not considering the hook up, take down, delivery and etc.) I have also suggested higher amp/output phase perfect converters, and because the end result is half the price of utility upgrade, the bean counter comes up with a similar comparison. So, we paddle without an oar a bit longer.

 

[Bertsbolts]

Not possible with standardized systems, if you have some sort of crude conversion equipment, maybe.

Real wye system will look like the one in drawing MTW provided, all the phase conductors are equal distant from the mid point of the wye, they will always all be same voltage to mid point (neutral).

Most that crude conversion equipment is supplied by single phase with a center tapped neutral. The neutral isn't a part of the conversion equipment itself, but that single phase supply is one side of the delta that ultimately gets created in such conversion equipment. But unlike a delta transformer arrangement which will have pretty stable voltage on that third leg the conversion equipment third leg voltage does vary with loading conditions, not just voltage to the neutral but to the other two phase conductors as well. There is a phase shift that is sufficient to create rotation in motor windings, but is not as stable as in more conventional delta sources which will lead to unbalanced current in the motor windings, which if running at or near full load rating will shorten life of the windings also.

If control volts is tied to this, whether directly or via a control transformer - the controls end up seeing voltages not designed for, could end up being high or low depending on loading conditions again.

Phase monitor - may not hurt it much, but yes it will see the imbalance and will lock out whatever it is set up to control. A phase monitor on equipment that doesn't utilize a neutral conductor typically won't have a neutral connection and won't care if there is a high leg, all they monitor is line to line to line voltages, that will be equal on normal delta supply that wasn't derived from said phase conversion equipment.

The other thing you run into particularly on VFD controllers is surge protectors on the drive input - those are usually connected from each line to ground. Many them designed to be used on wye systems with equal voltage to ground and if you use them on any delta system they may not have high enough design rating for the voltage to ground that may be present on at least one of those input lines.

You mentioned certain units that will work properly with high leg on a certain position, it may be possible they are designed specifically to accept non wye systems, but things like voltage/phase monitoring or surge protection likely won't have as tight of acceptable tolerance allowances as other units designed around a wye system being the input.

Thanks for all of that. See my reply to MTW.