# Random Rotation Reversal



## glen1971

Did the utility do any work on site overnight? Maintenance crew doing work overnight? Can't say that I've ever seen rotation change overnight with no other intervention..


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## MikeFL

Something changed. If it wasn't on site, it has to be POCO.


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## foothillselectrical

glen1971 said:


> Did the utility do any work on site overnight? Maintenance crew doing work overnight? Can't say that I've ever seen rotation change overnight with no other intervention..


Not that we can determine. We had the utility out today and he said they had no work orders in that area for struck poles or anything else that would have required replacing lines. I am the only electrician that works on the facility, and the only work I have done there is replace a metal halide wallpack with an LED, but that was on the 208V side that is still working. AND, I did that yesterday, so if someone else had been there working I would have seen them.

Thank you for your input.


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## foothillselectrical

MikeFL said:


> Something changed. If it wasn't on site, it has to be POCO.


I agree. But if it was POCO then I would have expected both units to have changed. Am I looking at something wrong?

Thank you for your input.


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## glen1971

foothillselectrical said:


> Hoping someone can help with this problem.
> 
> I got called to a customer site today. One building with two tenant spaces. Space 1 is supplied by a pole mounted transformer, 208V Y, 200A. The primary connected loads are bandsaws, lathes, drill presses, milling machines, etc. Nearly all are 3Ph loads, and everything in the building runs perfectly.
> 
> 
> Space 2 is fed with a 480V delta, 800A service, pole mounted utility transformer fed from the same primary as the 208V. I can see the primary conductors jumping from transformer to transformer. When the tenant left yesterday everything was running properly, when he returned this morning his 3Ph motors (air compressor, HVAC, and dust collector) were reversed rotation. I have checked voltage and rotation from the main lugs on the switch gear through every bucket and transformer I could find, and everything is phased properly.
> 
> They do have a 208V, 200A panel supplied by a 75kva transformer. *When the secondary conductors hit the main breaker, B and C phases are reversed. *This, to me, indicates that the original system was reverse rotation, and when the sub panel was installed they reversed rotation to correct it. The air compressor and HVAC system are fed from the 208V system, and the dust collector is fed from the 480V system.
> 
> Any idea what can cause this?
> 
> 
> *Additional note, there is another building on the property and another one down the street who are also customers of mine, and who are fed by the same utility branch circuit. I checked the line side power on those buildings and they are both correct.


What do you mean? Is the equipment actually running backwards? Or is it wrong on a phase rotation meter? If it is actually running backwards, someone switched 2 wires.. If it is on one panel, they did it in that panel. If it is the site or one service, the POCO must have been involved.


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## HertzHound

If I take a rotation meter and hook up all three leeds, it will show one direction. If I remove a leed, it shows the opposite direction. 

Is it possible you lost a phase? What happens on a Delta, does it go from a closed delta to an open delta and everything still runs, but backwards?

Since the power company was there, are all their cut outs closed?

How many transformers do you have on the delta bank?


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## joebanana

What did you do to correct the situation? Was it just those 3 machines running backwards? When the compressor runs backwards does it become a vacuum pump?


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## HertzHound

Did you take your readings with the main off so that your not reading through the loads. What was the voltage reading between all the combination of phases and phase to ground?


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## foothillselectrical

glen1971 said:


> What do you mean? Is the equipment actually running backwards? Or is it wrong on a phase rotation meter? If it is actually running backwards, someone switched 2 wires.. If it is on one panel, they did it in that panel. If it is the site or one service, the POCO must have been involved.


1. The equipment is actually running backwards.
2. In the 120/208V panel is phased BLK, BLU,RED (around here FWD is BLK, RED, BLU) IMO, I think this is because the original POCO phasing was reversed.
3. No one has done any electrical work in the building.
4. Two tenant spaces in the same building are supplied by the same POCO primary, as well as 2 other buildings known to be on the same POCO primary. POCO says they have done no work in the area.


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## foothillselectrical

HertzHound said:


> If I take a rotation meter and hook up all three leeds, it will show one direction. If I remove a leed, it shows the opposite direction.
> 
> Is it possible you lost a phase? What happens on a Delta, does it go from a closed delta to an open delta and everything still runs, but backwards?
> 
> Since the power company was there, are all their cut outs closed?
> 
> How many transformers do you have on the delta bank?


I have 487V A-B, B-C, A-C. There are no open fuses. On my phase rotation meter if I lose a phase it won't rotate. POCO checked their transformer and said it was good. I have a single pole mounted transformer. I can physically see the jumpers from the 208 transformer of to the 480v transformer.


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## foothillselectrical

joebanana said:


> What did you do to correct the situation? Was it just those 3 machines running backwards? When the compressor runs backwards does it become a vacuum pump?


I have not corrected it yet. We left power off to the 3 phase equipment and are calling the POCO engineer today.


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## 3DDesign

Is it possible that a panel feeding the reversed motors lost a phase and were back fed by one of the phases causing it to reverse?
Do the panels have Phase Loss Alarms?


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## JRaef

Phase rotation can't just randomly reverse. I have seen one case where the PoCo lost a transmission line and the crew, working in a storm, reconnected it wrong, causing an entire lumber mill to run backward for a few minutes, damaging a lot of equipment. Other times this happens when people plug in portable generators that are not phased correctly. But temporary changes in rotation are just not possible without someone having physically done it. So someone knows something and is keeping their mouth shut because they don't want to pay for any damage that was caused.


As to the lost phase theory, 3 phase motors will not _start _with single phase applied, they just vibrate back and forth. If they are ALREADY spinning, they may KEEP spinning with single phase. So with things like fans, as in the HVAC and Dust Collector that might be back-spinning because of air flow, that can happen. But an air compressor, I don't think so, unless MAYBE there is no check valve on the compressor and the tank pressure made it kick back when the phase was lost, so it then kept running backward. That's a stretch though. Could it be though that they just THOUGHT the compressor was running backward?


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## glen1971

JRaef said:


> But an air compressor, I don't think so, unless MAYBE there is no check valve on the compressor and the tank pressure made it kick back when the phase was lost, so it then kept running backward. That's a stretch though. Could it be though that they just THOUGHT the compressor was running backward?


Depending if the air compressor is a screw compressor, I've seen them REALLY not like going backwards.. Like destroyed itself by running backwards when the screw tried running through the case..


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## JRaef

glen1971 said:


> Depending if the air compressor is a screw compressor, I've seen them REALLY not like going backwards.. Like destroyed itself by running backwards when the screw tried running through the case..


Right, which is why a screw compressor always has a check valve.


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## frenchelectrican

glen1971 said:


> Depending if the air compressor is a screw compressor, I've seen them REALLY not like going backwards.. Like destroyed itself by running backwards when the screw tried running through the case..


I have see even pistion compressor go bad too when they ran backward due the oil pump only work on one direction so run it reverse can burn up the bearing if not getting any lube oil. 

to OP did you are aware of momentary power dropped and kicked back on real quick if so it may cause to lock in reverse rotation even a phase conductor get brownout while other two still good it may cause this issue.


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## foothillselectrical

I agree with every theory posed here, including that "random Phase reversals cannot just happen." But, I am the only one who does work in these facilities and, other than the light fixture replacement previously mentioned, I haven't done any work in these two particular buildings in months. And the only two men who can authorize work to be done, haven't had anything done.


I am truly stumped on this one. The POCO is sending out a couple of engineers Monday to see if they can determine if something has changed on their side, but, as stated earlier, I can physically see the primary jumpers from the 208V transformer to the 480V transformer. And the 208V side is running correctly. I have checked rotation on several motors in facilities fed from the same utility line, including a different building yesterday a half mile away, and all is well in those facilities. I do not believe that the utility has done any work on the lines.

As far as the air compressor running backwards, it is a 2 stage piston compressor. I do not believe there is a check valve leaking by as it has held pressure for the several days this issue has been going on. And, I don't think it could cause the motor to start backward if it was leaking because it should only compress the piston to the bottom of it's stroke.

Thank you to everyone who has provided input on this.


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## varmit

If one of the transformer delta secondaries has failed, you could still measure the correct voltage on all three phases. The failed winding could cause a phase shift that would cause reverse rotation.


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## varmit

If one of the transformer delta secondaries has failed, you could still measure the correct voltage on all three phases. The failed winding could cause a phase shift that would cause reverse rotation. 

Motor current would probably be higher also.


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## varmit

Thinking a little more: If you have one transformer, it is probably a wye secondary with no neutral connected. If so, a primary winding failure could cause a similar problem.

In either case, it would seem to be a transformer problem IF NOTHING ELSE HAS CHANGED.


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## gnuuser

varmit said:


> If one of the transformer delta secondaries has failed, you could still measure the correct voltage on all three phases. The failed winding could cause a phase shift that would cause reverse rotation.
> 
> Motor current would probably be higher also.


 motor temp would also be higher as well
If a motor lost a phase while running it would still keep on running but would get very hot
the op's situation is a bit conspicuous!
what he changed is a light and it should not have had any effect on the 3 phase power system.
seeing that nothing else has changed points out to a poco issue even if they stated hasn't been changed but who knows?
its possibly a transformer issue.


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## HertzHound

varmit said:


> If one of the transformer delta secondaries has failed, you could still measure the correct voltage on all three phases. The failed winding could cause a phase shift that would cause reverse rotation.


That’s what I was thinking. Looking back at my post I should have said lost a winding not lost a phase. I know a three phase motor won’t start if it lost a phase, but loosing a winding makes it go from closed delta to open delta. 

With an open delta you will still read 480 volts phase to phase. I thought phase to ground was different. Like 480 to ground on two phases and zero on the last phase? <edit: maybe I was thinking corner grounded>

That’s why I was wondering if her checked voltage with the main open, so he wasn’t reading a back feed through three phase loads. 

Only one delta transformer on the pole? That part I don’t get. So what are they doing there? Grabbing two of the transformers from the other bank? 

Wouldn’t you need at least two transformers for the delta bank (not borrowing any from another bank? It is common to see a single phase center tapped transformer to feed one customer 120/240 and the added transformers for the small three phase customer. Like a four unit apartment next to a tire shop.


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## splatz

How does the missing leg cause a phase shift? I don't see how phase rotation changes with the open delta. 

Say you have AB BC and CA windings. They are 120 degrees apart. Say you lose CA winding and AC is now coming from AB and BA. OK. The voltages are all the same. The grounded corner if any is the same. 

Aren't AB and BC still 120 degrees apart, and in the same direction, because that comes from upstream? I would think if BC was AB + 120 before, it must be the same after.


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## HertzHound

It will be interesting to here what the problem turns out to be. 

Reading this

https://www.electricalpereview.com/open-delta-transformer-connection/

It appears the Voltage phase angle doesn’t change but the phase current does. They are using a perfect power factor in their formulas though. 

To me though, if nothing changed on the utility side, my guess is a faulty winding. I’m leaning that way more than a phase reversal bandit!


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## varmit

splatz said:


> How does the missing leg cause a phase shift? I don't see how phase rotation changes with the open delta.
> 
> Say you have AB BC and CA windings. They are 120 degrees apart. Say you lose CA winding and AC is now coming from AB and BA. OK. The voltages are all the same. The grounded corner if any is the same.
> 
> Aren't AB and BC still 120 degrees apart, and in the same direction, because that comes from upstream? I would think if BC was AB + 120 before, it must be the same after.


It would be determined by where the open winding or winding jumper was located. Say you lost the incoming "C" portion of the AC winding, The jumper from "A" could still energize the AC winding, but would be in series through the "A" winding. This would reverse the polarity of the "C" winding.


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## emtnut

varmit said:


> If one of the transformer delta secondaries has failed, you could still measure the correct voltage on all three phases. The failed winding could cause a phase shift that would cause reverse rotation.


Sorry Varmit, but I don't see what you're talking about either.

I've never come across this in countless failures.


Keep it simple ... Poco usually comes clean when you call them out on it. Maintenance guy just hides in the corner till the heat cools down :biggrin:

They did some work ... now you're not an electrician, but a detective :vs_cool:


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## glen1971

foothillselectrical said:


> I agree with every theory posed here, including that "random Phase reversals cannot just happen." But, I am the only one who does work in these facilities and, other than the light fixture replacement previously mentioned, I haven't done any work in these two particular buildings in months. And the only two men who can authorize work to be done, haven't had anything done.
> 
> 
> I am truly stumped on this one. *The POCO is sending out a couple of engineers Monday* to see if they can determine if something has changed on their side, but, as stated earlier, I can physically see the primary jumpers from the 208V transformer to the 480V transformer. And the 208V side is running correctly. I have checked rotation on several motors in facilities fed from the same utility line, including a different building yesterday a half mile away, and all is well in those facilities. I do not believe that the utility has done any work on the lines.
> 
> As far as the air compressor running backwards, it is a 2 stage piston compressor. I do not believe there is a check valve leaking by as it has held pressure for the several days this issue has been going on. And, I don't think it could cause the motor to start backward if it was leaking because it should only compress the piston to the bottom of it's stroke.
> 
> Thank you to everyone who has provided input on this.


What did you/they come up with and find?


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## tmessner

joebanana said:


> What did you do to correct the situation? Was it just those 3 machines running backwards? When the compressor runs backwards does it become a vacuum pump?


When a piston type compressor runs backwards for to long it burns up because the cooling fan on the flywheel is going backwards. Don't ask how I know this. It pumps air like normal. I think the valves are timed at TDC.


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## 460 Delta

tmessner said:


> When a piston type compressor runs backwards for to long it burns up because the cooling fan on the flywheel is going backwards. Don't ask how I know this. It pumps air like normal. I think the valves are timed at TDC.


The valves are reed style so no timing, no camshaft. When the piston goes down the inlet opens, going up the exhaust opens. IR compressors turn the opposite direction of the rest of compressor world, and it trips up a lot of installers. Iv'e ran into numerous compressors rolling the wrong direction and while they were hotter, they generally survived the abuse.


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## gnuuser

460 Delta said:


> The valves are reed style so no timing, no camshaft. When the piston goes down the inlet opens, going up the exhaust opens. IR compressors turn the opposite direction of the rest of compressor world, and it trips up a lot of installers. Iv'e ran into numerous compressors rolling the wrong direction and while they were hotter, they generally survived the abuse.



reed valve pumps can run in reverse and still function, to counteract the heat issue building in air flow guides around the pump housing allows better control of airflow and heat transfer.
for a setup like that it wouldn't matter which direction the motor runs.
losing a winding on a motor thats running will continue to run but it will be hotter.
now if it had an interuption of power it would not rotate but just hum.
if this motor was on a loaded belt conveyor (elevator type) unless it was equipped with a brake motor the weight on the conveyor could rotate the motor backwards enough for the power to run it up.(Ive seen happen this on an old batch elevator that was not equipped with a brake motor)


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## joebanana

tmessner said:


> When a piston type compressor runs backwards for to long it burns up because the cooling fan on the flywheel is going backwards. Don't ask how I know this. It pumps air like normal. I think the valves are timed at TDC.


I was KIDDING. It doesn't do much good for scroll compressors either. How do they time reed valves? (Again, just kidding). When the flywheel fan runs backwards, does it create a negative pressure? jk.


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## BrettC

OP, did they ever figure it out?


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## 460 Delta

Bump here, but what was the resolution to the problem? Enquiring minds want to know.


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