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me too, regardless of type of power supply , 3 phase is 3 phase right? Definitely a phase reversal in running mode is a no no , this sounds different, and on inspection one leg high amps , after switching 2 all ok? stan?
Originally Posted by wolfdog Don't make anything out of my statement beyond what I said. The transformer is grounded at "B" phase and IF "standards are maintained", every "B" phase throughout the system will have ZERO potential to ground. If you change the load wires at the motor contactor\ starter to change rotation - no harm, no foul. If you swap the grounded "B" phase somewhere else in the system, you have created a hazard for the next poor shmuck that has to work on this thing, because ZERO potential to ground on a live phase is now where it is not supposed to be. (assuming the poor shmuck understands what he is dealing with to start with) So, you were saying that A B and C should be kept in their expected positions? I agree with that. I'm still curious about the connection being made in this thread between the presence of a grounded B and a fried motor due to a phase reversal using two wires to achieve a change in rotation.
Originally Posted by timebuilder I'm not sure what you are trying to say by "maintain that standard." The B phase is only grounded at the transformer. Are you saying that the B phase is always in second position? I would agree with that. What I don't get in the thread is the assertion that a motor was fried because motor leads were swapped where one lead was for the B phase. Electricity has taught me nothing that says the B phase lead cannot be swapped with the A or C phase for motor reversal. So, some piece of this situation is still missing. Don't make anything out of my statement beyond what I said. The transformer is grounded at "B" phase and IF "standards are maintained", every "B" phase throughout the system will have ZERO potential to ground. If you change the load wires at the motor contactor\ starter to change rotation - no harm, no foul. If you swap the grounded "B" phase somewhere else in the system, you have created a hazard for the next poor shmuck that has to work on this thing, because ZERO potential to ground on a live phase is now where it is not supposed to be. (assuming the poor shmuck understands what he is dealing with to start with)
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Originally Posted by VTP99 Yes pole mounted with 3 high voltage wires and no ground wire. Getting pictures is no problem. My problem is knowing how to post them here. How many transformers in the group? To post a pic: Store the pic on your computer. Open the "post reply" box Click on the "Manage Attachments" button below the reply box. Click "browse" and find the file name on your computer. Click "upload" When the file is uploaded, the file name will appear below the second white box. To post a large version of the pic, click on that file name, and a new browser window will open showing your picture. Right click on that picture, and click "copy." Now, click in your already opened reply box and click "paste." Now you will have a large picture and a thumbnail version when you finish your post.
Originally Posted by bobboan Are the transformers pole mounted? If so, can you post some pics of them clearly showing their wiring? Yes pole mounted with 3 high voltage wires and no ground wire. Getting pictures is no problem. My problem is knowing how to post them here.
Originally Posted by bobboan Interesting. I don't think I've ever seen a corner grounded secondary Delta used at a shopping center. The obvious reason being that a grounded neutral would be necessary for 120v loads and it would not seem make sense to have a separate corner grounded system to supply relatively small to medium hvac loads. But, I haven't seen everything either. Are you certain it was corner grounded or could there have been a fault in a phase? Could someone have changed something not realizing the type of system it was? I doubt if the poco would have changed phasing. They are very careful about that and one of their standard tools is a phase rotation meter. The tenant spaces have two electric meters. One for three phase and one for single phase. It's easy to identify the grounded B phase because you will get no voltage to ground on that phase.
Corner grounded Delta Service Are the transformers pole mounted? If so, can you post some pics of them clearly showing their wiring?
Corner grounded Delta Service
Originally Posted by VTP99 The wiring appeared to be in it's original position. Wires on load side of contactor were marked left to right 1/2/3. I switched 1&2 around and the amps leveled out. My only theory is that the electric co. switched two phases around. Be a reciprocating compressor rotation was not a concern. On a side note. Yesterday i got a no cooling call on a Heil dry unit i installed last year. This is at the same shopping center where i had the blower motor problem that started this thread. Get this i check the unit and found the phase monitor flashing. Panal cover says phase problem. I reversed two phases and the light stops flashing. Runs a few seconds and shuts down. I then switch it back and same thing again. I can not get the board to reset. I call tech support and explan. He tells me it will not work with this B phase ground and has me install a Carrier CLO ( compressor lockout ) Yet it ran all last summer no problem. Interesting. I don't think I've ever seen a corner grounded secondary Delta used at a shopping center. The obvious reason being that a grounded neutral would be necessary for 120v loads and it would not seem make sense to have a separate corner grounded system to supply relatively small to medium hvac loads. But, I haven't seen everything either. Are you certain it was corner grounded or could there have been a fault in a phase? Could someone have changed something not realizing the type of system it was? I doubt if the poco would have changed phasing. They are very careful about that and one of their standard tools is a phase rotation meter.
Originally Posted by bobboan Did you meg the windings? How long had the compressor been installed and running? Has anyone recently changed any wiring or controls? I have to agree with "timebuilder" that the motor only "sees" the 3 phases at 120* apart. It doesn't recognize whether one phase is grounded or high leg to ground; it only "sees" the potential between the phases - unless a winding is shorted. Please, I would really like more info. Can you check it out and get some answers to these questions? The wiring appeared to be in it's original position. Wires on load side of contactor were marked left to right 1/2/3. I switched 1&2 around and the amps leveled out. My only theory is that the electric co. switched two phases around. Be a reciprocating compressor rotation was not a concern. On a side note. Yesterday i got a no cooling call on a Heil dry unit i installed last year. This is at the same shopping center where i had the blower motor problem that started this thread. Get this i check the unit and found the phase monitor flashing. Panal cover says phase problem. I reversed two phases and the light stops flashing. Runs a few seconds and shuts down. I then switch it back and same thing again. I can not get the board to reset. I call tech support and explan. He tells me it will not work with this B phase ground and has me install a Carrier CLO ( compressor lockout ) Yet it ran all last summer no problem.
Originally Posted by VTP99 came across a k body copeland tripping it's overload. Amped out the 3 phases and got 18/7/7 reversed phases and got 7/7/7 rounded off. Once again a B phase Corner Grounded Delta system. Did you meg the windings? How long had the compressor been installed and running? Has anyone recently changed any wiring or controls? I have to agree with "timebuilder" that the motor only "sees" the 3 phases at 120* apart. It doesn't recognize whether one phase is grounded or high leg to ground; it only "sees" the potential between the phases - unless a winding is shorted. Please, I would really like more info. Can you check it out and get some answers to these questions?
Here we go again came across a k body copeland tripping it's overload. Amped out the 3 phases and got 18/7/7 reversed phases and got 7/7/7 rounded off. Once again a B phase Corner Grounded Delta system.
Here we go again
I'd have to say that it sounds as though the real culprit is the power quality rather than the existence of a grounded B phase, because all three phases will behave identically at the motor regardless of the B being tied to ground, or a high B where the voltage to ground exceeds that of the other two phases. I wish I was there to look into this further.
Originally Posted by timebuilder In order to explain what happened after the switch, we would have to know what was happening BEFORE the switch. We just don't have enough info. If there is no problem with the starter, I have to think there was a defect in the first motor. A coincidence can lead to incorrect conclusions. The first motor was cooked and the story goes from a single phase scenario(brown out) . This is what i was told. I installed the same motor and reversed two phases to get the correct rotation. At that time i did not check the amps on each phase. I also did not install a motor starter at that time. The next day the call came again that the blower was off. The new motor was cooked the same as the first motor. I installed a second new motor and a motor starter to protect this second motor. Wiring was not changed for this second motor as rotation was correct. When i started the motor the overload tripped so i amped my phases and found them way unbalanced. Like 5 amps 2.5amps & allmost 0 amps. It was then that i realized i had used the grounded B phase to reverse rotation the last time. So i moved the B phase back and reversed A with C phase and the amps evened out and the overload did not trip. Now my guess is that the first motor did get cooked from a true single phase condition. That motor was a little over a year old and had no protection. My first motor got cooked i believe because i did not check amps and did not install a motor overload. Had i installed a motor overload at that time i think my first motor would still be good. The overload would have tripped and i would have been alerted at that time.
Originally Posted by VTP99 I here what your saying timebuilder. Before this i was with the same thinking. I will try to get the motor & overload #'s for us. How does one explain the amps leveling out after the switch ? Same motor start. In order to explain what happened after the switch, we would have to know what was happening BEFORE the switch. We just don't have enough info. If there is no problem with the starter, I have to think there was a defect in the first motor. A coincidence can lead to incorrect conclusions.
Is it possible that there is a ground fault somewhere else in the building causing some sort of ground loop? This may not be what caused the motor to burn but may be the cause of your limited choices of phasing or it may be both. We had an issue where strange things were happening and it turned out it was being caused by a motor with a shorted winding to ground in a completely different part of the building. It was off of the same substation which had an ungrounded delta secondary, which is an important fact. It didn't exhibit the problem when the motor was off, when the motor would start the shorted winding to ground would actually corner ground the system and we would see this in another area of the building as an intermittent thing causing some unusual things to happen. Zero current to ground on that phase means no tripping of the overcurrent device and the motor continued to cycle on and off. My point is, strange and unusual things can happen in systems like these. I would investigate the power system of this building and its loads (if possible) and see if anything raises any eyebrows.
Originally Posted by timebuilder What I don't get in the thread is the assertion that a motor was fried because motor leads were swapped where one lead was for the B phase. Electricity has taught me nothing that says the B phase lead cannot be swapped with the A or C phase for motor reversal. So, some piece of this situation is still missing. I here what your saying timebuilder. Before this i was with the same thinking. I will try to get the motor & overload #'s for us. How does one explain the amps leveling out after the switch ? Same motor start.
Originally Posted by wolfdog It makes no difference. the motor sees 3 phase and the line voltage is where the grounded phase is. The significance of my statement is that the "B" phase is grounded and should maintain that standard on all line side disconnects, starters, and contactors. As ling as you are just swapping the load side, standards are maintained and the next poor shmuck may not get fried. I'm not sure what you are trying to say by "maintain that standard." The B phase is only grounded at the transformer. Are you saying that the B phase is always in second position? I would agree with that. What I don't get in the thread is the assertion that a motor was fried because motor leads were swapped where one lead was for the B phase. Electricity has taught me nothing that says the B phase lead cannot be swapped with the A or C phase for motor reversal. So, some piece of this situation is still missing.
Originally Posted by timebuilder Unless the motor is grounded where it shouldn't be, a grounded B phase should behave just like the A and C phases. That's why I am asking. It makes no difference. the motor sees 3 phase and the line voltage is where the grounded phase is. The significance of my statement is that the "B" phase is grounded and should maintain that standard on all line side disconnects, starters, and contactors. As ling as you are just swapping the load side, standards are maintained and the next poor shmuck may not get fried.
Switching Phases "I don't see a lot of grounded B. High B, yes. There's a bunch of that in Philly. It used to be that way for most three phase services. I guess my point is that it should make no difference to the motor if the B phase is grounded, and the practice of switching any two phases to reverse the rotation should work just fine. That said, there may be some issue involving the motor starter, and how it is wired, since a control circuit is often derived from two of the phase legs for a single phase control for the starter. You wouldn't have a schematic to post, would you?" Timebuilder, You're right on this. The motor only responds to 3 phases that are of equal potential 120* apart. It does not matter that one of them is grounded because the potential is the same between any two of them. There is either a short in the motor winding or the wiring that ceases to cause a fault when connected to the grounded phase or something in the control wiring.
Switching Phases
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