# Voltage Fluctuation



## telsa (May 22, 2015)

Any chance that it's single-phasing ?


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## Mr.Awesome (Nov 27, 2015)

telsa,

I could be wrong in my understanding, but if it were single phasing wouldn't I be seeing random voltages on the two connected phases and not a steady 80-130v on all three?
I've only seen a couple of RTU motors single phase due to bad fuses, but they also made some troubling noise. This motor is purring like a kitten.


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## telsa (May 22, 2015)

Let's take a wild guess that you have other 3-phase motors tied in to your MCC.

They can 'manufacture' the missing leg and bounce it back through the MCC... or any other cross connection. 

Feeble connections can drive you crazy -- as they read decent voltage to a DMM while the actual ampacity is screwy -- choked. 

The feeble connection could be inside a contactor -- across some heaters -- pitted faces -- on and on the failure modes go.

When this happens you're left with a low power 3-phase motor. It won't be as 'sick' as a single-phasing machine.

So, you need to make sure that your target motor is totally isolated, off-line...

Then test everything up from zero... 

I'd meg the puppy straight off... with some concern that you've got internal damage.

A fall of potential test may be necessary across your contactor if the easy stuff doesn't pan out.


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## Mr.Awesome (Nov 27, 2015)

Well hopefully its as easy as a fried contactor.
Long story on my current work situation, but I have no access to a megger or any fancy gear. I would put money down that there is some internal damage. Something in the motor's mcc section blows up, then the motor runs for who knows how long on low voltage.


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## Corysan (Jan 20, 2017)

The CT might be part of an overload control feature to monitor power usage, could be for a current relay, etc. Hard to tell without more information. With damaged contact faces you will see a higher impedance that may fluctuate with arcing, and result in a fluctuating voltage drop, hence the fall of potential test Telsa referred to. Visual inspection will do well too, and will show carbon debris in the contactor which would prevent solenoid seating. Any significant damage will be noticeable. You may have a high impedance ground fault in the conduit as well. This is where an insulation test of the conductors would be helpful. Don't exclude the pump itself as a problem, it may be the root cause of anything electrical. Odds are, if the electrical system is properly designed and installed, it will not fail unless there are external factors contributing a problem- system age notwithstanding. I recommend checking another MCC bucket for power fluctuations to ensure that your system integrity is good from the outset. The bucket connection to the buss may also be the failure point. Any connection will be a potential problem. I have seen starters that lasted in service for years with a loose connection between the overload relay and the contactor which came from the starter manufacturer. Also, the starter coil maybe compromised. What is the system voltage?


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## varmit (Apr 19, 2009)

Check voltage phase to phase, not phase to ground.
Do a "fall of potential" test across the starter contacts and the overload relay.
Verify the the pump impeller is turning.
Check all fuses or breakers.
CHECK PUMP MOTOR FOR PROPER ROTATION.

You will need proper tools to go further:
Tach the motor shaft RPMs.
Megger the motor and motor leads.
Check amp draw on each phase. 

Possibilities:
Motor running wrong direction.
Starter or overload failure.
Phase loss due to- bad fuse or breaker, high resistance at contactor, overload relay failure, broken wire, one winding open in motor.
Pump or bearing failure causing mechanical overload.


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## JRaef (Mar 23, 2009)

Can't be a total phase loss or the motor would not start. 3 phase motors can RUN AFTER losing a phase, but will not re-start because there is not longer a phase "rotation" with only two phases. So they sit there and shake back and forth making a nasty sound that generally makes people freak out and hit the Stop button, or trips the breaker/blows a fuse if allowed to continue. Rule that out.**

But if you have high resistance on one phase, the lower torque on the third phase may be enough to get it to BEGIN rotating, then from that point on it is spinning, but has severely unbalanced currents. Current imbalance causes what's called "negative sequence current" to flow in the rotor, which in turn creates negative torque, meaning torque in OPPOSITION to the running torque. So now the motor consumes more current, but performs less actual work and is thereby unable to develop full torque at the shaft. In a centrifugal pump, this results in a loss of pressure and a "static" pipe fill; no more flow once the head pressure in the pipe equals the decreased pressure capacity of the pump. I've seen that happen when an ME missed a decimal point and undersized 3 x 600HP pumps, resulting in the water only getting to within 5 feet of the outfall into a tank. We could see the freaking water, but it couldn't make it to the top, even with 1,800HP trying to push it. The laws of physics cannot be violated.

So yes, I'd say it's a good bet that your previous single phasing event took place WHILE this motor was running, so the increased current caused the contact in the starter to burn. Now it has higher than normal resistance, resulting in a voltage drop on the phases connected to that pole. Since you lack the tools to perform better tests in the field, I would just start with replacing that starter. It's might be something else, but I'd give this a 75-80% chance of being the culprit given your explanation of the history and symptoms.

**OK, one possible way it MIGHT still be a complete phase loss, but it will depend on the piping system. IF you have what's called a "pump control valve" that opens on COMMANDING the pump to run (instead of relying on it ACTUALLY putting out pressure), then what can happen is that the pump is turned on and the valve is opened, but because the pump isn't actually spinning, the back-pressure flows through the pump control valve and spins the pump BACKWARD. Then because it STARTED spinning backward, the single phase power KEEPS it spinning backward, but you don't know that because you can't see it, you just know there is no flow.


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## nolabama (Oct 3, 2007)

*OK, one possible way it MIGHT still be a complete phase loss, but it will depend on the piping system. IF you have what's called a "pump control valve" that opens on COMMANDING the pump to run (instead of relying on it ACTUALLY putting out pressure), then what can happen is that the pump is turned on and the valve is opened, but because the pump isn't actually spinning, the back-pressure flows through the pump control valve and spins the pump BACKWARD. Then because it STARTED spinning backward, the single phase power KEEPS it spinning backward, but you don't know that because you can't see it, you just know there is no flow.
Post Edited

Trick $?|+. 
Check frequency to see if this is happening.


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## Corysan (Jan 20, 2017)

> So they sit there and shake back and forth making a nasty sound that generally makes people freak out and hit the Stop button, or trips the breaker/blows a fuse if allowed to continue.


-The lighter side of JRaef 

I agree that it is probably not (I'm trying to not be definitive) a total phase loss. I am going to go back to the fluctuating voltage. We need to establish that there is proper voltage from the source to the line side starter terminals before anything else. Once that base is established, and the output of the starter is bad, the starter can be isolated. I don't necessarily think this is a mechanical issue, but it is a possible root cause for a prior phase loss, etc.

1. Using a good flashlight, and your nose, carefully make a visual inspection of the bucket's components. Literally sniff the components inside the bucket for any signs of a burning odor. Sounds silly, but it can be very helpful.

2. Test incoming power at the line side of the bucket's OCPD, if possible. If not possible, test it at the load side of the bucket's OCPD. If either test fails, the problem is further upstream.

3. If test #1 passes, test voltage sequentially at every point from the OCPD in order to find the current problem component. Do this before checking any terminations.

4. After the problem component has been isolated, tighten any suspect terminations and then re-test voltages. If they are better, it is simple. If not continue troubleshooting.

5. Inspect the starter carefully. Open it and inspect the mechanism for damaged contacts, debris (carbonaceous debris is a sign of failure, i.e. something burned), peening of the armature, delaminated armature, discolored coil windings, cracked bakelite, etc. Check every connection whether it is a field connection or manufacturer's connection. Copper that is a dull red, or brassy looking is a sign of excessive heating. Any soot or frosting is a sign of excessive heating. Bakelite plastic that is eroded looking or soft and whitish is a sign of excessive heating. Tip: if it doesn't look like it is normal, it probably is not.

6. Visually inspect the load conductors where they are accessible. Lower voltage on one phase is usually a sign of higher current on that phase, which means higher than normal heating of that conductors insulation. One caveat, signs of overheated insulation are usually visible only near the source of the problem, but not always.

7. If the starter passes your visual inspection, disconnect the load and energize the starter. Test voltage at the line side, load side, and across each phase (testing one phase from line to load). 

8. Check the nameplate data against the OCPD and overload size in the bucket. Check the wire for proper size, but be careful. There are times when the NEC allows conductors to be fused differently than the general rule from Art. 240. If anything is amiss that could be the root cause.

9. What kind of pump is it? If it is a centrifugal pump (non-positive displacement pump- there is nothing to keep the outlet physically separated from the inlet) how do you now correct rotation? Some have a volute shape like a seashell. If this is the case, the impeller should turn with the volute towards the outlet. If it is not volute shaped, the pump may be bi-directional. Check for an arrow cast into the pump. Remove the fan cover and try to manually sin the motor shaft to ensure it turns freely (this is probably the case as you said the motor was running).

10. Since you do not have access to a megger, test the motor windings with your ohm meter. This is always a preliminary test to meggering anyway. If it fails this test, there is no point in testing further. There shoud be no appreciable difference in reisistance between any of the sets of windings.

12. What kind of water is being pumped? Is it clean? If it is, you can rule this out as a problem. If it is dirty or contains debris, this may be the root cause as large debris can damage a pump's impeller. 

13. Is there a valve after the pump outlet? Check to see that it is open. If it is a check valve, it may be clogged with sediment or stuck shut or partially shut. Is there a strainer before the pump inlet Remove the screen to see that it is clean. 

Bottom line, you need to really invest yourself in this to find the root cause. It may be electrical, or it may be mechanical. My bet is on the bucket connection to its source. This is why I recommended testing power at another bucket in my earlier post. If the same issue exists at more than one bucket, the problem goes further upstream. Okay, so there was a prior single phase event. Good to know, but what caused that. Odds are, the real problem didn't go away by replacing parts.

Troubleshooting is always to isolate and correct the root cause. It must always be done from our field of expertise as a starting point, be absolutely must be done systemically. It must also always be done systematically as evidence leads.

Good luck Mr.Awesome. Let us no how it turns out.


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## Corysan (Jan 20, 2017)

> Current imbalance causes what's called "negative sequence current" to flow in the rotor, which in turn creates negative torque, meaning torque in OPPOSITION to the running torque.


JRaef, thanks for this post. Something I didn't know. Cheers!


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## JRaef (Mar 23, 2009)

LOL, the old "sniff test" is something I've used for years, never failed me. That acrid smell of burnt insulation (or lack thereof) can tell you a lot.

But in this day and age, sticking your head into an MCC bucket without having the entire MCC shut own can't happen any more. So to be clear, REMOVE the bucket, close the door or replace the starter, THEN sniff it when the bad starter is on the bench....


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## Mike_kilroy (Sep 2, 2016)

Worth REPEATING Just IN case: VARMIT SAID Check VOLTAGES PHASE TO phase, NOT PHASE TO ground. You might want to confirm to us that is where you see 80...v

Sent from my SM-G900V using Tapatalk


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## frenchelectrican (Mar 15, 2007)

There something else along the way .,,

Do you have any heavy cycling loads on the MMC ?? that may affect the reading of voltage and if you are on Wye or Delta system that may affect the voltage reading some. 

But as other guys posted alot of very good points for troubleshooting. 

As they posted that is well proven methold of trobleshooting and I have done simuair way as they posted.


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## Mr.Awesome (Nov 27, 2015)

Thank you guys very much! For a guy with little motor experience, this thread is a treasure trove of information! I've been through alot of what has been said so it is nice to know I was on the right track. You have also given me some useful new information.
I'll address Corysan's thread as it covers some of the other points made...

1. Sounds silly yes but I was told in my first year by a wise old grouchy jman on service calls that your nose can save you time troubleshooting. I've since embedded it in my brain to smell things. No funk in this mcc section though.

2 - 4. I had tested the line and load side of the fuses yesterday. 347/600V respectively across the board there. I was able to get back to measurements today and will get to that in a moment...

5. Should the starter end up being replaced I fully intend to tear it apart and see what it looks like inside. I have replaced old panels that had rainbow coloring (red blue white you name it) from overheating and being leaked on over the years so I have also made a mental note to look for such things.

6. The load side conductors were all replaced after the initial explosion. They all look good.

7. Yesterday my tests were done at this location with the motor disconnected. 347/600V across the board.

8. Not done but will do. I assumed the repair guys sized everything accordingly but will check on this to be sure.

9/12/13. The impeller being part of the original problem causing something to blow has not been ruled out. The boss is thinking of tearing it apart (it is one of two pumps for the system so the other can run for now) to inspect it before they fire the system up in a couple of months. I think it is a pump for a water loop feeding their chiller unit and some coils around the building. That being said, would rotation really matter? Would it not just push water through the loop in the other direction just fine? I did consider that maybe two phases were flipped somewhere (ie: not in the order of red black blue) before the explosion and were not wired back up that way (new wires follow red black blue all the way through), but when we bumped the motor the boss claimed the rotation was correct. He could be wrong though. There is also no arrow on the shell nor any arrow stickers anywhere. Taking the pump apart will also allow for water inspection.
*Unrelated note: Wires should be orange brown yellow for the 600V system, but I have only seen this practice done a couple of times. Not sure why it isn't followed more often commercially.

10. I metered out the coils yesterday as well. I do not remember the resistance reading offhand but it was the same number across the board. It is a permanent wye connection with T1 T2 and T3 accessible. Meter also did not pick up on any shorts to ground.

I would love to vest more time into it and reinforce troubleshooting techniques while getting my hands on equipment I haven't used before, but it is up to the boss how much troubleshooting he wants to do vs. just replacing parts and hoping it works out. Even if the motor works fine from here on, I am very very curious as to why something blew up to begin with.

J,
I didn't know the "buckets" could be removed! The one mcc I touched during my apprenticeship was completely pre-wired, pre-fused, ol's set, everything. We just had to run our wires to the load side of the contacts (and did verify ol settings and such). I'm going to look up how these things are assembled.

Mike,
The 80-130V was phase to ground. I do not recall the phase to phase reading but it was off as well. 

SO.... today's progress:
I went back to metering out the mcc section, motor still disconnected. 347/600V line and load side of fuses like yesterday. 347/600V line and load side of contactor I was not expecting. I feel puzzled, go back to the motor, 347/600V at the freakin' motor!
So the plan now is to leave it be until they are ready to prepare the loop for service. Then it will be turned on, rotation checked. If there is any other issues I told the boss to call up one of the contractors he rubs shoulders with to come by with a megger and tachometer to perform tests. I expressed that I would personally put money down on the contactor being pooched (that is the only thing I could see causing all three phases to act erratically at the same time and at the same voltage fluctuation when we know the supply is good) and if the motor checks out ok under the tests it will be replaced.
So it seems to be a waiting game! Unfortunately I am on a month long contract so I may not get to see the outcome of this.


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## Mr.Awesome (Nov 27, 2015)

frenchelectrican said:


> There something else along the way .,,
> 
> Do you have any heavy cycling loads on the MMC ?? that may affect the reading of voltage and if you are on Wye or Delta system that may affect the voltage reading some.
> 
> ...


I don't think so. It is a small office tower. There are no monster air handling units or anything, all the equipment is relatively small.


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## Corysan (Jan 20, 2017)

Rotation matters with some centrifugal pumps, which it sounds like this is. In the "volute" style, it will pump very little backwards. In the bi-directional style, it does not matter. Glad your stoked about the help. JRaef is right about safety, I guess I depend on the PPE between my ears too much...or not enough. Your choice! 

Nice to know about the fuses as opposed to a circuit breaker. Do you have access to the blown fuses? If you cut the ends off the fuses and pull out the insides, it can tell you more or less what category of fault occurred. If the spring loaded section is open it was a sustained overload type of fault. This could be single phasing, mechanical overload, or a high impedance fault. If the short circuit section was open it was a low impedance, high amplitude fault. FYI


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## Mr.Awesome (Nov 27, 2015)

The old fuses are long gone but I will keep in mind what you said for the future.


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## B-Nabs (Jun 4, 2014)

Mr.Awesome said:


> 9/12/13. The impeller being part of the original problem causing something to blow has not been ruled out. The boss is thinking of tearing it apart (it is one of two pumps for the system so the other can run for now) to inspect it before they fire the system up in a couple of months. I think it is a pump for a water loop feeding their chiller unit and some coils around the building. That being said, would rotation really matter? Would it not just push water through the loop in the other direction just fine? I did consider that maybe two phases were flipped somewhere (ie: not in the order of red black blue) before the explosion and were not wired back up that way (new wires follow red black blue all the way through), but when we bumped the motor the boss claimed the rotation was correct. He could be wrong though. There is also no arrow on the shell nor any arrow stickers anywhere. Taking the pump apart will also allow for water inspection.
> *Unrelated note: *Wires should be orange brown yellow for the 600V system*, but I have only seen this practice done a couple of times. Not sure why it isn't followed more often commercially.


Is that a Saskatchewan amendment? Because it's not in the CEC.


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## MechanicalDVR (Dec 29, 2007)

varmit said:


> Check voltage phase to phase, not phase to ground.
> Do a "fall of potential" test across the starter contacts and the overload relay.
> *Verify the the pump impeller is turning.*
> Check all fuses or breakers.
> ...


Don't put the cart before the horse, know that the pump is actually pumping and running in the proper direction. Then move on to further electrical troubleshooting.

Saying it is running smoothly and not pumping leads me to think of a simple problem being over looked.


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## scotch (Oct 17, 2013)

I'm sorry for this....but it sounds like his boss and him have little understanding ....even as an apprentice he should ....some folks did a p*ss poor job of his electrical skills ! I'd have some concerns about giving advice from afar about dealing with 600 vac power on this .It's pretty basic stuff ....if it was 12v I'd say "go to it " ....but this power.....you need someone else !


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## Mr.Awesome (Nov 27, 2015)

B-nabs,
I don't believe it is electrical code, but the company I started with did large jobs and I was taught that it was good practice to color code your 347V system differently from your 120V. Easy visual identification and less chance of a screw up from an apprentice. I endorse this practice.
Random story related to this: One job I worked on last year, the jman in charge ran 12/2 bx out of 4x4s for both power and the DC heads. No labels on the wires or cables, no remarking of the white in the DC runs, no labels on boxes. He then had several different not so smart apprentices and even a jman come and go from doing joints instead of having one person complete the task (could have, was a small office). This recipe led to frying 6 grand worth of emergency LED lighting and a couple of days labor for 2 jmen to troubleshoot.

Mechanical,
I'm with you on that 100%. The first thing I did was bump the motor but there is no arrows on anything so I took my boss' word for it that it was spinning in its usual direction. He could be wrong though and it very well might be backwards.
The voltage fluctuation and the initial explosion at the MCC have yet to be explained though.

scotch,
My current boss isn't an electrician. General maintenance. As stated before, long story. I willfully admitted right off the bat that I didn't possess much experience with motors and have a commercial construction background consisting mainly of "run that pipe and put up those lights". If you read my posts carefully you will see that I had attempted much of the steps given to me already. I'm here because I need advice from someone with more experience than me as to why I got such a strange reading. I figured thats what this forum is about. I'm by no means a cocky person and am fully aware of my lack of experience in certain areas. Instead of making a statement about p*ss poor skills, your expertise on the subject to enhance those skills would be more effective.


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## scotch (Oct 17, 2013)

My comment is that there is some duty of care to make sure you as an apprentice understood and could safely troubleshoot electrical equipment ...even in Sask commercial bldgs have Fans and Pumps and Air Handlers ...so troubleshooting shouldn't be so much of a problem .If it is....and you don't understand Motor/Generator theory ...600vac voltage isn't a wise place to start . Any mistakes are FINAL !
I sure hope you have voltage gloves and eye protection on when you try to gain experience here !


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## Mike_kilroy (Sep 2, 2016)

I have to concur with scotch. 600 volts systems should be handled by very experienced electricians only.

Now to my point. I asked if you're 80 volts was perhaps phase to ground for a reason. Phase to ground voltage at this point has no meaning. Phase to phase voltage is all that matters until you find some reason to suspect a short to ground. In other words your 80 volt reading is and was totally meaningless and misleading to everyone here.

Sent from my SM-G900V using Tapatalk


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## Mr.Awesome (Nov 27, 2015)

You guys have valid concerns on the safety aspect. My deal with the boss was that he order arc flash gear if he wanted me in panels and poking around 347.
I'm not going to nitpick details on what I hadn't done during my apprenticeship and why I lack motor experience, the point is I don't have it and I won't get it by shrugging my shoulders and passing it off immediately.



Mike_kilroy said:


> Now to my point. I asked if you're 80 volts was perhaps phase to ground for a reason. Phase to ground voltage at this point has no meaning. Phase to phase voltage is all that matters until you find some reason to suspect a short to ground. In other words your 80 volt reading is and was totally meaningless and misleading to everyone here.


Please elaborate on this. Phase to ground voltage jumps around from 80-130v, then seemingly resolves itself the next day. Sincerely, how is this meaningless?


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## telsa (May 22, 2015)

Mr.Awesome said:


> You guys have valid concerns on the safety aspect. My deal with the boss was that he order arc flash gear if he wanted me in panels and poking around 347.
> I'm not going to nitpick details on what I hadn't done during my apprenticeship and why I lack motor experience, the point is I don't have it and I won't get it by shrugging my shoulders and passing it off immediately.
> 
> 
> ...


With experience, you'll come to understand that this is a garbage reading.


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## JRaef (Mar 23, 2009)

Chances are that in your 600Y347V distribution system, the ground reference voltage is only stable at the service transformer, the point where the neutral is bonded and in any specific NEUTRAL conductors from that point on. In an MCC, the usual practice is to NOT run the neutral conductor out to it, because you would have to buy the neutral bus bar ($$) yet very few things fed from an MCC will require a neutral connection. Three phase motors use phase-to-phase voltages, in this case 600V (BTW, you keep referring to this as "347V", that will get you in trouble. THIS IS 600V!).

When you are 50, 500 or 5,000ft away from the service transformer at the MCC, there can and often is inconsistent ground potential due to a number of variable factors; soil chemistry / resistivity, corroded bonding jumpers, capacitance etc. This is what Tesla was warning you about; using phase to ground voltages on 3 phase systems such as MCCs is not going to serve you well because you can get meaningless readings. Always use phase-to-phase readings, especially for motors, because that's all that matters in a motor.


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## Mr.Awesome (Nov 27, 2015)

Thank you again J,

Your explanation of the ground reading makes perfect sense to me and is not something I considered. Funny part is I have never been fond of "using the pipe as a bond" with pipe runs as cheated couplings or pipe pulling apart somewhere breaks your bond. This is the same mindset as what you just said. Not thinking there. You will have to take my word for it in this situation though that I did do a phase to phase reading and while I didn't commit the exact reading to memory it was also wonky, and also resolved itself the next day.
I do know that this motor is living on 600V. When I say 347/600V I am referring to reading 347V phase to ground and 600V phase to phase while I was metering out the MCC. I will word it differently for future posts.


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## B-Nabs (Jun 4, 2014)

Mr.Awesome said:


> B-nabs,
> I don't believe it is electrical code, but the company I started with did large jobs and I was taught that it was good practice to color code your 347V system differently from your 120V. Easy visual identification and less chance of a screw up from an apprentice. I endorse this practice.
> Random story related to this: One job I worked on last year, the jman in charge ran 12/2 bx out of 4x4s for both power and the DC heads. No labels on the wires or cables, no remarking of the white in the DC runs, no labels on boxes. He then had several different not so smart apprentices and even a jman come and go from doing joints instead of having one person complete the task (could have, was a small office). This recipe led to frying 6 grand worth of emergency LED lighting and a couple of days labor for 2 jmen to troubleshoot.


I don't disagree with the rationale, and I believe that in the US it is common to colour code different voltage systems differently (someone correct me if I'm wrong). But if you read CEC Rule 4-038 (colour of conductors), you will find that a 3 phase system is supposed to be colour coded Phase A - Red, Phase B - Black, Phase C - Blue, and Neutral - White (if used). Full stop. There is no provision for using other colours for other voltages. Perhaps this is one reason why we are not allowed to put conductors from different systems in the same raceways, I don't know. Your example above is not, to me, an example of a reason why a different colour code should be used, but rather an example of why qualified people should do neatly labeled, meticulous work, and when that doesn't happen, problems arise. I do not think we should make up practices that are in fact code violations in order to try to make sure bad electricians don't blow things up.


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## Mike_kilroy (Sep 2, 2016)

Thank you Jraef for spending the time to write out the WHY to stop using phase to ground or phase to neutral as an everyday meaningful measurement! Painfully poking one letter at a time on a small phone as I was doing does not lend itself to detailed explanations.

Thank you too Jraef for stating what hit me as also painful: the continued speaking of phase to neutral voltages to identify the power source! It hurt to see each time!

M. awesome, it appears obvious you are going to stay in the electrician field. With that, we would all like to hear from you 30 years from now helping the new guys coming into the field, not hear of your funeral in 2 months from now instead. I think I can include others when I say we are not trying to call you a dumb arss, we are really concerned for your future and trying to be helpful. 

So please heed Jraef's advice and NEVER identify a power source singly by its phase to neutral voltage. Please change from phase to neutral measuring to phase to phase.

I suggest you go back and remeasure phase to phase (L-L) voltages once the motor is back turned on, and post them. And if you see them not balanced at the level expected, then go measure ACROSS any contactors or other devices in series with the supply to the motor. You should quickly then find the culprit in one session. Please do be careful... I get more and more scared of taking 460v and 600v measurements each day! It may be do to watching some of the videos on forums of unfortunate electricians being electrocuted by not heeding safety properly.


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## John Valdes (May 17, 2007)

High resistance connection in any device that has contacts. Breaker and starter come to mind first.
Check each leg with a load. This should narrow it down pretty easy.


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## Mr.Awesome (Nov 27, 2015)

Nabs,
You have a fair point about rationalizing code violations. It would also set a precedent to violate more rules. But here is a question to ponder... a couple of sites where I saw this implemented had that color scheme in the specs. American companies doing the prints in the states for a building in Canada. Do you feel the general should have been told that the color scheme is a code violation and we wouldn't be running it according to the specs?

Mike,
I do plan to stay in the field and work on my weak points. I take no offense to the concern, but find it frustrating that I am seeking advice and am met with calls to give up and walk away from the problem. I have no intention of tearing into the MCC while I do not know what is going on in there, I simply wish to possibly identify the problem and understand it better.
I'd like to be clear as it seems this was missed by a few people: I did take phase to phase readings. Always do. But after J's post I understand why it is redundant to discuss the phase to ground readings.
This may sit until they decide to put their loop in service sometime this spring. I will definitely be reporting back to this post if I end up dealing with this motor more. 

John,
After reading this thread I'm putting money on the contactor.


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## Mr.Awesome (Nov 27, 2015)

Let's entertain the high resistance in the contactor idea.
Would it be typical to watch the voltage on your meter move around in that situation? That is what I have never seen and what confused me.
And should that coil in the contact be fried a bit, would it be within the realm of possibility that the coil has permanent damage, yet it can still overcome that and everything falls into place to pass full voltage through to the motor?


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## glen1971 (Oct 10, 2012)

Mr.Awesome said:


> Nabs,
> You have a fair point about rationalizing code violations. It would also set a precedent to violate more rules. But here is a question to ponder... a couple of sites where I saw this implemented had that color scheme in the specs. American companies doing the prints in the states for a building in Canada. *Do you feel the general should have been told that the color scheme is a code violation and we wouldn't be running it according to the specs?*
> 
> Mike,
> ...


This wiring color scheme (Orange, Brown, Yellow) would be in the specs on the job.. The General Contractor wouldn't have an issue so long as the job is being built to code and to the specifications...

How do you know what you don't know??



Mr.Awesome said:


> Let's entertain the high resistance in the contactor idea.
> Would it be typical to watch the voltage on your meter move around in that situation? That is what I have never seen and what confused me.
> And should that coil in the contact be fried a bit, would it be within the realm of possibility that the coil has permanent damage, yet it can still overcome that and everything falls into place to pass full voltage through to the motor?


What are your phase to phase voltage readings? Where did you take them? Load side of the breakers? Line side of the contactor? Line side of the overloads? Load side of the overloads? Have you measured the voltage across the contactor? Across the overloads?


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## Bird dog (Oct 27, 2015)

If you measure voltage from L1 to T1, L2 to T2 & L3 to T3 on the contactor, you should only have a volt or two(?). You are measuring contact resistance. If you have more, the contacts are bad or going bad. You're measuring the voltage drop across the contacts.


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## Mike_kilroy (Sep 2, 2016)

Bird dog said:


> If you measure voltage from L1 to T1, L2 to T2 & L3 to T3 on the contactor, you should only have a volt or two(?). You are measuring contact resistance. If you have more, the contacts are bad or going bad. You're measuring the voltage drop across the contacts.


And, don't forget, of course if you have voltage drop under load, that is heat. So you can quickly find faulty contacts also by using your $ 20.00 IR temp gun to see if any of those devices are hotter than ambient around them...


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## Mr.Awesome (Nov 27, 2015)

glen,
The key phrase there is "to code". CEC states that 3 phase ac shall be colored as red black blue, with no mention of changing the color scheme for different voltages. Nabs figures it is a code violation to run a different color scheme (with fair reasoning) and I'm curious if in the situation described above he would have told the general he wouldn't run it that way and cause a stink through the chain of command all the way back to the owners in the states.

I couldn't stand there and tell you about every part and connection in that MCC, therefore it is a safe assumption that I don't entirely know what is going on inside of it and shouldn't be pulling anything apart inside of it. I'm comfortable measuring what is directly behind the door but thats about it.

I mean no disrespect when saying this, but the phrase "beating a dead horse" comes to mind on the subject of the measurements taken. I've stated numerous times in this thread what was measured. I did not however measure across the contacts but will in the future. I did not identify any overloads, I think Corysan may be right and that CT is an overload feature.

Bird and Mike,
More good advice, thank you! However my previous question remains unanswered:
Generally speaking, not pertaining to this exact situation, and in your personal experiences, would a damaged coil in a contactor cause a fluctuating voltage you could watch on your meter? I personally have only encountered a couple of small lighting contactors that fizzed out. One wouldn't snap in at all and the other was chattering but we did not see a fluctuating voltage at the lights.
Secondly, even with permanent damage to the coil is it still a possibility that it works as normal on occasion?


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## glen1971 (Oct 10, 2012)

Mr.Awesome said:


> glen,
> The key phrase there is "to code". CEC states that 3 phase ac shall be colored as red black blue, with no mention of changing the color scheme for different voltages. Nabs figures it is a code violation to run a different color scheme (with fair reasoning) and I'm curious if in the situation described above he would have told the general he wouldn't run it that way and cause a stink through the chain of command all the way back to the owners in the states.


There are many places that are wired to 347/600 volt and use Or/Br/Ye for colors with no issues.. One place I know of used Rd/Bk/Bl for 120/208 volt supply and Or/Br/Ye for switch legs AND Or/Br/Ye for 347/600 volt supply and Rd/Bk/Bl for switch legs in the same building..
My point being - none of them had to be rewired or failed an inspection.. In most areas, the site's specs accompany the drawing package to the inspector upon application of the electrical permit.


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## Mike_kilroy (Sep 2, 2016)

Mr.Awesome said:


> glen,
> The key phrase there is "to code". CEC states that 3 phase ac shall be colored as red black blue, with no mention of changing the color scheme for different voltages. Nabs figures it is a code violation to run a different color scheme (with fair reasoning) and I'm curious if in the situation described above he would have told the general he wouldn't run it that way and cause a stink through the chain of command all the way back to the owners in the states.
> 
> I couldn't stand there and tell you about every part and connection in that MCC, therefore it is a safe assumption that I don't entirely know what is going on inside of it and shouldn't be pulling anything apart inside of it. I'm comfortable measuring what is directly behind the door but thats about it.
> ...


I would put probability a contactor coil causing your varied volts at about 0.02%. 

Sent from my SM-G900V using Tapatalk


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## sparkiez (Aug 1, 2015)

Alright man, I'll take the time to throw my two cents out there. There is going to be a lot to this, so I will try to organize it as well as I can. Read the entire thing before you do anything!

First, I wanted to touch on color codes a bit. Most places in the US use Black Red Blue for 3-phase wires at less than 240V (considered low voltage by most plant's procedures). Brown Orange Yellow is the code for "high voltage" which is greater than 240V 3 phase. Not sure where I read that, but it is a good rule of thumb though you should always check your source.

Motor circuits can have ALL KINDS of stuff in them. VFD, PLC Control, God knows what kinds of sensors for PLC monitoring, crazy hard-wired switching, you name it. What IS important here is to single out what part of the circuit you are dealing with.

Is your contactor pulling in and dropping out as it should? You are dealing with a power circuit issue.

Is your contactor not behaving as it should? You are dealing with a control circuit issue.

You MUST learn to determine what side of the circuit you are dealing with. Sometimes it can be both, but in order to effectively troubleshoot you MUST be able to segment these two sides of the circuit. I would say that next to safety this is the single most important part of troubleshooting a motor circuit.

Is this motor (by any chance) being fed from a VFD? If so, that would explain why you are getting these "strange" voltages. VFD's synthesize a sin wave and because F = 1/V when the frequency is changed to alter the speed of the motor, and the meter reads an RMS value, you will see what you are describing. I would make sure no one has installed a VFD somewhere and ran the wiring through the MCC to the motor contactor. I have done this before at a local plant at the customer's request (though I did label the wires and write a note on the bucket door).I'm going to make the assumption it doesn't, but please verify.

Now, lets move on to troubleshooting steps. Get you a note pad and write these down, you may want to post here if you have trouble interpreting the results. I'm seeing nominal voltage is 347 per leg for your switchgear. Is that correct? If not, where I say "347" just use your nominal voltage.

Lets talk about rotation, it is an easy question to answer. Most impeller pumps rotate clockwise when looking from the back, or fan side of the motor. Actually, I have never seen one that doesn't, but that doesn't mean they don't exist. If the motor is not rotating this direction, leave it for now until you can verify. You will want to try and find manufacturer information on the casing of the pump (get you a rag and some degreaser if necessary and clean it up). Try to get ahold of them and find out. Remember, when dealing with specialized equipment, if you don't know then you need to find out. Running some pumps backwards even for a second can destroy them (most likely the case with vacuum pumps though). Learning to find the correct information rather than assume is critical when dealing with systems like this one.

Now, lets move on to the electrical side. Next to safety, what was the most important part of troubleshooting motor circuits? Figuring out if your problem resides in the power or control section of the motor. You said the contactor is pulling in when you start the pump and dropping out when you shut it off. This is good. It means that if there is an electrical problem, it resides in the power portion of the circuit (most likely, without actually being there I cannot give a definitive answer). Lets start there.

You have been poking and prodding around with your meter. Proper procedure is this:

Put on proper PPE

Check meter against known source --> check a receptacle or something you know works with your meter or verify you get a correct result --> check voltage in question --> Check known source again to make sure meter is functioning properly. Always do this before and after you check for the power to be off on motor circuits THEY CAN EASILY KILL YOU AT 600V!

Once you know your meter is working properly, we can move on.

Shut off motor
Take a voltage reading on line side of contactor. Lets delve more into this. Take your reading from phase to phase. 1 to 3, 1 to 2, 2 to 3. This is how you read a 3-phase voltage. If reading to ground you can get backfeed from the transformer and still read nominal phase voltage even if you had a phase drop out. This is how you read 3-phase voltage, period. Write down your results.

This part is dangerous, please use PPE. I'm not sure of the classification of the bucket, but at the least you need hot gloves, ear plugs and safety glasses. Does the motor have a local disconnect? It damn well should. Shut it off and lock it out at the local disconnect to prevent the circuit from loading and minimize the risk of arc flash.

Start the motor circuit. Read the voltages from Line 1 at the line side to line 1 at the TOP of the heater section (also called overload). Line 2 at the top of the line side to line 2 at the top of the heater section. Line 3 at the line side to line 3 at the top of the overload. Write down each result as you go. This is measuring the voltage drop. Voltage, often called "potential difference" is just that. The difference in voltage at 2 points. Since there should be continuity across this part of the circuit, anything above zero is bad, and it should be less than 1 volt for sure. Anything more and you have worn components in the starter.

Now, leave the circuit as it is, and we will repeat the above process, but check across the heater section. Check line 1 at the top of the heater section to line 1 at the bottom of the heater section. Check line 2 at the top of the heater section to line 2 at the bottom of the heater section. Check line 3 at the top of the heater section to line 3 at the bottom of the heater section. You will expect to see less than 1 volt across. Any more, the heaters or the starter wheels are worn and you are not getting a solid connection. Make sure to write down these results.

Finally, take a reading at the incoming side of the local disconnect. THIS SHOULD BE THE TOP BUT NEVER ASSUME THAT IT IS. ALWAYS CHECK AND MAKE SURE THE LINE SIDE IS IN FACT LANDED TO THE TOP OF THE DISCONNECT. Remember to read phase to phase, 1-3, 1-2, 2-3. Write down the results.

Now, leave the local disconnect locked out and shut the bucket off. This is overkill, but I don't want you to get hurt. Take a known voltage reading with your meter, take a phase-phase reading at the local disconnect then read the known voltage again. All phases should read zero. This tells you that it is now safe to open the peckerhead. Take your ohm readings on the motor legs 1-2, 1-3, 2-3. They should all read the same +/- 5%. Any more variance in them and you at the very least have a weak leg. Do you have a megohmmeter? This is the part where you want to meg the motor windings and see how they perform under a load. If it fails the resistance test with a meter, you know the winding is bad. If it passes, you need to meg it. Quite often a motor will pass with a meter but fail under load. Make sure you marked your wires as you took them apart so you don't mix up your rotation. This is especially important when dealing with pumps. I'm guessing you don't have a megger, so you can't know for sure.

I am not going into taking amp readings on the motor, which is a very important step to spot a weak leg or mechanical issue with the motor just yet as I want to know if you have the proper PPE to perform the test. LOADED CIRCUITS CAN EASILY ARC AND KILL YOU!

Post your readings back here for the voltage and voltage drop test. All of this instruction is overkill for your problem, but I want to illustrate how much knowledge and skill is involved in something like this. You want to call someone more experienced in this type of work and work beside them on it. Watch and learn. These things are particularly DANGEROUS and I reiterate because it is important to know what you are dealing with. I also wanted to give you an idea of how you segment circuits when you are troubleshooting to identify a problem. During all of this, the pump may have also been damaged or may have been worn to start with, but the mechanical side is an entirely different issue.


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## glen1971 (Oct 10, 2012)

sparkiez - awesome write up for troubleshooting! The only thing I'd add, would be to megger, or at least minimum ohmmeter, the wiring from the starter straight through to the motor.. That proves the integrity of the power wiring. Most times, I'd disconnect in the cubicle and megger from there out without unhooking the motor.. If there was an issue, I'd open the motor and check again to determine a feeder issue or motor...


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## Mr.Awesome (Nov 27, 2015)

sparkiez,

Fantastic post!!! Your explanation needs to go into the modules at every school for motor courses.
The boss has decided to let it be until they are ready to commission their loop for the summer. If I get to poke around some more I will report back here.
Seriously awesome post, I envy your apprentices!


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## John Valdes (May 17, 2007)

Mr.Awesome said:


> sparkiez,
> 
> Fantastic post!!! Your explanation needs to go into the modules at every school for motor courses.
> The boss has decided to let it be until they are ready to commission their loop for the summer. If I get to poke around some more I will report back here.
> Seriously awesome post, I envy your apprentices!


I did not read sparkiez post, but will, when I have some spare time. 
Seriously, are we still working on this?
An amp meter (clamp) would have narrowed this down for you.
Have you not checked the *current* on each leg with the motor running?
This will tell you what you want to know.

This is very common and is not always easy to find. I'm going to give you a hint. The leg that is drawing 0 (zero *current*) is your problem.
Then its just a matter of locating the bad contact or bad connection.
This part will be harder......LOL


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## telsa (May 22, 2015)

John Valdes said:


> I did not read sparkiez post, but will, when I have some spare time.
> Seriously, are we still working on this?
> An amp meter (clamp) would have narrowed this down for you.
> Have you not checked the *current* on each leg with the motor running?
> ...


Even off kilter current means pure trouble. 100A; 100A; 50A -- that's one sick puppy.


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## MechanicalDVR (Dec 29, 2007)

telsa said:


> Even off kilter current means pure trouble. 100A; 100A; 50A -- that's one sick puppy.


Typically any more variance than 10% is a big issue.


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## sparkiez (Aug 1, 2015)

You guys are right, there were a few things left out. I specifically didn't give instructions for taking the amp readings because there is some safety concerns for me with a loaded circuit.

Also checking the wiring from the bottom of the starter to the top of the disconnect and from the disconnect to the motor, or even megging the motor from the bottom of the disconnect works quite well, but once again I have some safety concerns (I don't know his skill level).

Also, I'm an apprentice myself. I just started in the industrial sector so my first year was just distribution and troubleshooting while the next two were PLC and instrumentation / controls for the plant as I was the only guy there that could actually do that work, I kinda got the job without experience and by default.


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