Author Topic: 3 Phase Breaker Tripping  (Read 27111 times)

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Offline phmade

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3 Phase Breaker Tripping
« on: September 06, 2014, 08:32 AM »
I recently upgraded some equipment in the shop and now I'm troubleshooting an issue.  I have a 7.5HP 3 phase dust collector (Nederman) that continues to trip a breaker on the 3 phase panel.  The nameplate on the motor states a max draw of 21Amps so I put in a 30A breaker and #10 wire.  I should also mention that I'm using a rotary phase converter to generate my 3rd phase.

When I turn on the dust collector, the motor starts and turns but before it reaches full RPM, the breaker trips on my 3 phase panel.  I have very little experience with 3 phase power and I'm really stumped.

I did swap out circuit breakers with another 30A breaker (in the event that I may just have a bad breaker) but that did not resolve the problem.  Does anyone have any recommendations? 

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Offline tjbnwi

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Re: 3 Phase Breaker Tripping
« Reply #1 on: September 06, 2014, 09:13 AM »
New dust collector or purchased used? Can you tell if the unit is turning the proper direction? Do you have other 3 phase equipment that functions properly? Are the inlets to the dust collector open?

Tom










Offline Steve Rowe

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Re: 3 Phase Breaker Tripping
« Reply #2 on: September 06, 2014, 09:40 AM »
Does the breaker trip immediately or is there a delay?  If immediate, I would be looking for a short.


Offline tjbnwi

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Re: 3 Phase Breaker Tripping
« Reply #3 on: September 06, 2014, 10:14 AM »
Does the breaker trip immediately or is there a delay?  If immediate, I would be looking for a short.

"When I turn on the dust collector, the motor starts and turns but before it reaches full RPM, the breaker trips on my 3 phase panel.  I have very little experience with 3 phase power and I'm really stumped."

Above is the second line from the op. I read it as the unit starts to spin up then the breaker trips.

Tom

Offline Sparktrician

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Re: 3 Phase Breaker Tripping
« Reply #4 on: September 06, 2014, 11:43 AM »
On the surface, it sounds like high inrush current is tripping the breaker before it gets up to operating speed.  Might be a good idea to get a qualified electrician to check it out with proper instrumentation. 

- Willy -

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Offline Steve Rowe

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Re: 3 Phase Breaker Tripping
« Reply #5 on: September 06, 2014, 12:11 PM »
What Willy said.  Need more info on voltages, currents, length of wire run, etc. 

Offline Loren Woirhaye

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Re: 3 Phase Breaker Tripping
« Reply #6 on: September 06, 2014, 12:18 PM »
I have a little 7.5hp wide belt sander which I run off a 10hp rotary converter.  I can barely start it without tripping the 50 amp breaker the converter is wired into the single phase panel through.  It's the startup load. 

Assuming the motor is spinning in the correct direction on the DC (you can look through the grill on the back to observe the motor cooling fan direction),  I would think it's air resistance to spinning that big impeller.  Take the impeller off and that motor may fire up, no problem.  Then you'll know it's the load of pushing the air.  You could go to a 5hp motor, or  upgrade the system feeding the dust collector.
« Last Edit: September 06, 2014, 12:22 PM by Loren Woirhaye »

Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #7 on: September 06, 2014, 01:33 PM »
I should also mention that I'm using a rotary phase converter to generate my 3rd phase.


The most likely cause is with your phase converter. Check the phase voltages and see how far out of balance it is. The voltage from phase-A to Phase-B should be 240 volts, as that is line voltage. However, the voltages from A to C and B to C will be different from this. Even on a properly functioning rotary converter these will be above and/or below 240. If you find them significantly out of whack, then you probably lost a run capacitor on the phase converter, or worse, the converter's start capacitors are not disengaging.


Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #8 on: September 06, 2014, 02:06 PM »
Thanks for the replies.  I just picked up a clamp-on amp meter so I'll report back shortly. 

I purchased this dust collector used, and it was running fine when I disconnected it.  It was run on true 3 phase power in the previous shop - not a phase converter. 

I'm heading out to the shop to test now.  Thanks again.

Phil

Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #9 on: September 06, 2014, 02:28 PM »
Quote
Can you tell if the unit is turning the proper direction?
Yes, it wasn't initially, but we switched the 2 120V wires and now it is.

Quote
Do you have other 3 phase equipment that functions properly?
We have an Altendorf sliding tablesaw that appears to be working correctly.  It starts and continues to run without any problems.  We installed it at the same time as the Dust Collector (this week).

Quote
Are the inlets to the dust collector open?
Yes, the inlets are open.




Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #10 on: September 06, 2014, 02:34 PM »
Quote
it sounds like high inrush current is tripping the breaker before it gets up to operating speed
I doubt this is the problem; the breaker that powers the phase converter is not tripping.  It is a 100amp breaker with #2 wire so I don't think that's the problem.  My phase converter is a 10HP so it should be able to start a 7.5HP motor ok. 

Here are the results of my voltage testing (C is the manufactured leg):
Voltage from A to B Phase: 243.2
Voltage from A to C: 243.6
Voltage from B to C: 273.7

These measurements are taken when the DC is not running.  Should I measure this on startup? 
So there is definitely an imbalance but I'm not sure what is considered acceptable.

Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #11 on: September 06, 2014, 02:35 PM »
Quote
Are the inlets to the dust collector open?
Yes, the inlets are open.

Although not necessarily the primary problem, this can be a contributing factor. Granted, if the inlets are wide open and unrestricted, it could actually be the sole problem.

Dust collector impellers are under maximum load when there is no restriction to the inlets. On the face of it, that may sound counter intuitive compared to other tools such as saws. However, when there is no restriction to the inlet, there is maximum air movement through the impeller.

For initial testing, you should completely block the inlets so no air can enter the system, but make sure the outlet is unrestricted so that any air that is present in the system has an evacuation path.

Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #12 on: September 06, 2014, 02:46 PM »

Here are the results of my voltage testing (C is the manufactured leg):
Voltage from A to B Phase: 243.2
Voltage from A to C: 243.6
Voltage from B to C: 273.7

The 273.7 is a little high, but I don't believe this is causing your breaker to trip on startup. During startup that voltage will probably come down. It may be something to look at for the future, but for now it is probably fine.

I see that you have another 3-phase tool--tablesaw. You could recheck the voltages with the tablesaw running to see how close to balance you have with a tool motor running. Each additional motor you operate on a rotary phase converter will help bring the generated phase closer to the ideal value.

Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #13 on: September 06, 2014, 02:57 PM »
Quote
it sounds like high inrush current is tripping the breaker before it gets up to operating speed
I doubt this is the problem; the breaker that powers the phase converter is not tripping. 

To the contrary, inrush current is the root problem, but you need to discover what is causing it. No, the single phase breaker is not tripping nor should it be. The inrush current on the dust collector motor is tripping the 3-pole breaker feeding it.

The current through an induction motor will be at it highest when the motor is running at its slowest. When the motor is stalled, the windings appear as a near short-circuit with the only resistance being the resistance of the copper wire. As the motor begins to turn, the magnetic field in the motor creates additional resistance (called reactance) in the windings that is proportional to the speed of the shaft. So the faster the motor turns, the higher the resistance of the coils, and the lower the amperage. Yeah I know. That's more than you really needed to know.

Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #14 on: September 06, 2014, 03:21 PM »
We just closed off the dust collector to see if that made any difference and it did not.

Rick - when I start the tablesaw, the C Phase does come down in voltage.  I can't remember what it came down to, but I think it was about 230V from 273V.  I have tried starting the saw first and then the Dust Collector but that didn't make a difference. 

Here is another question:
Sometimes, the 3 phase breaker for the Dust Collector doesn't actually trip but the Thermal Overload protector is tripping.  I think that's called the Thermal overload protector? It's in the ON/OFF box of the Dust Collector.  I'll take a picture and post it.  Could that be the problem?

Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #15 on: September 06, 2014, 03:37 PM »
Here is the photo inside the ON/OFF box on the dust collector.


Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #16 on: September 06, 2014, 03:41 PM »
Here is another question:
Sometimes, the 3 phase breaker for the Dust Collector doesn't actually trip but the Thermal Overload protector is tripping.  I think that's called the Thermal overload protector? It's in the ON/OFF box of the Dust Collector.  I'll take a picture and post it.  Could that be the problem?

If it was only the breaker or only the thermal, it would be easier to say that that device was the problem. However, since both of them have tripped, it is more likely the motor (although still may be breaker/thermal).

How long does it take before the motor sounds like it is approaching full speed? With the inlets blocked, this should take just a couple of seconds. If it is coming up really slow, that would be why both of these devices are tripping.

Oh, I just thought of something. Since this is a new dust collector for you, have you checked to make sure it is not configured for 480 volts (460 on the nameplate)? You previously said you once ran the motor, but simply getting it to run does not guaranty that it isn't configured for the higher voltage. This of course assumes that it may be a dual voltage motor. Not all motors are dual voltage, but it is still pretty common.

If you are not sure, open up the junction box on the side of the motor and inspect how the wires are connected together. If it is a dual voltage motor, it will typically have a connection diagram printed on the inside or outside of the junction box. If you don't have a diagram, at least count how many wires are going into the motor (not counting the 3 supply wires entering the junction box). If my fuzzy memory serves me, it should be either 9 or 12 wires.

Your newest post came in while I was typing. I'll take a look at that picture in a minute.

Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #17 on: September 06, 2014, 03:51 PM »
Quote
How long does it take before the motor sounds like it is approaching full speed?
It doesn't sound like it ever gets up to full speed.  It sounds like it's accelerating for about 10 seconds and then the breaker and/or thermal overload trips. 

I checked to see if it was wired for 460 and it's not.  It is wired for 230.  I had the same exciting thought last night and then was sorely disappointed this morning...


Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #18 on: September 06, 2014, 03:58 PM »
It sounds like it's accelerating for about 10 seconds and then the breaker and/or thermal overload trips. 

I was in the middle of typing another post, but this is way more important. 10 seconds is way too long for a normal startup. This is why the breaker/thermal are both tripping.

Double check the wiring at the motor. I know you said it was set for 240 volts, but triple check it then.

Also, get your volt meter in there and check the voltages at the motor. You might have lost a phase. So check the voltages just like you did previously from A-B, A-C, and B-C.

Inspect the wire connections inside the motor junction box to ensure there isn't a loose wire under one of the wire nuts.

Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #19 on: September 06, 2014, 03:59 PM »
I found a troubleshooting guide for the Marathon Motor (the motor on the DC).  One of the listed problems is slow acceleration of the motor and the cause is too small of wire size.  I'm currently running #10, should I switch to #8 and see if that makes a difference?  It's a relatively short run (about 15').

Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #20 on: September 06, 2014, 04:02 PM »
No, the wire size would not cause this long of a startup time. A loose wirenut could, but I have a feeling you lost a phase somewhere.

Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #21 on: September 06, 2014, 04:11 PM »
I'm heading back to the shop now.  I'll report back shortly...

thanks

Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #22 on: September 06, 2014, 04:29 PM »
I looked at your picture. You have an Allen Bradley contactor (A26-30-10) and overload (TA25DU25). This is NOT your main problem, but the overload setting is a little low. Right now it is just slightly over 20 amps, but your motor is rated at 21 amps. Because it is a dust collector, it will be running close to full rated load.

After you diagnose the long, 10-second, startup, if the thermal overload trips under normal use, you could dial it up slightly. If it doesn't trip, then leave it where it is.

By the way, the other 2 dials appear to be set correctly, and they just control whether the thermal overload uses manual versus automatic reset.

P.S. When you are checking wirenut connections described previously, don't forget to inspect all of the terminal lugs on both the contactor and overload blocks.

Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #23 on: September 06, 2014, 04:51 PM »
This is really a huge stretch and not likely to be true, but it is worth asking simply because I have seen people do this.

Some people mistakenly think that a wye configured motor means that it is supposed to be connected to power in a wye configuration too. This is not correct. Motors should always be connected as Delta (just 3 wires) to the incoming power. They can get away with it if they have 3-phase wye (120/208) power, but you do not. So make sure the previous owner did not connect either the neutral or ground to any of the wires inside the motor. The ground should be going to the metal frame of the motor, but not to any of the motor leads.

Your phase converter is the equivalent of an open-delta, and the neutral point is not a center point. (See the image I posted earlier). If the neutral or ground are connected to the center of the motor's wye configuration, it will pull the generated C-phase down to a low value.


Offline Michael Kellough

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Re: 3 Phase Breaker Tripping
« Reply #24 on: September 06, 2014, 04:54 PM »
Quote
it sounds like high inrush current is tripping the breaker before it gets up to operating speed
I doubt this is the problem; the breaker that powers the phase converter is not tripping. 

To the contrary, inrush current is the root problem, but you need to discover what is causing it. No, the single phase breaker is not tripping nor should it be. The inrush current on the dust collector motor is tripping the 3-pole breaker feeding it.

The current through an induction motor will be at it highest when the motor is running at its slowest. When the motor is stalled, the windings appear as a near short-circuit with the only resistance being the resistance of the copper wire. As the motor begins to turn, the magnetic field in the motor creates additional resistance (called reactance) in the windings that is proportional to the speed of the shaft. So the faster the motor turns, the higher the resistance of the coils, and the lower the amperage. Yeah I know. That's more than you really needed to know.

Thanks for that explanation Rick. I've puzzled over that more than once.

Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #25 on: September 06, 2014, 05:02 PM »

Thanks for that explanation Rick. I've puzzled over that more than once.

You're not alone, Michael. A lot of people assume that motors don't conform to Ohm's Law because current and voltage appear to be inversely proportional during an under-voltage condition. They don't realize that resistance is not a constant in a motor, and it is what is changing that makes it appear that current and voltage are inversely proportional.

Motors still follow Ohm's Law, but resistance is a mathematical function of frequency.

Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #26 on: September 06, 2014, 08:23 PM »
ok - partial success.  I connected another 3 phase machine (edgebander) and it runs perfectly at the same time as the tablesaw.  So I focused my attention on the dust collector wiring.

All wire nuts and connections are secure and correct at the motor.  After inspecting the overload, I noticed that the reset button was "sticky" and inconsistent.  I decided to bypass the thermal overload as a quick test.  The dust collector starts within 5 seconds and the 3 phase breaker does not trip!  I'm going to pick up a new thermal overload on Monday morning and confirm that's the problem. 

Rick - I know you said that's not the main problem.  Please let me know if you think there is something else incorrect here.  I really just cannot figure out what else could be wrong.  Especially since (2) other machines are running perfectly...

Thanks again to everyone.  I'll post another update on Monday.

Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #27 on: September 06, 2014, 08:27 PM »
Rick - I will review the motor wiring tomorrow to confirm.  I don't think the ground or neutral are connected to any motor leads but I will double check.  Thanks so much for your assistance.  I really like a thorough explanation and you've given me one!

Offline Rick Christopherson

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Re: 3 Phase Breaker Tripping
« Reply #28 on: September 06, 2014, 09:18 PM »
Not enough is known here. Previously you said you had a 10 second startup and now it is 5 seconds. Is this a change, or were you just not specific on the previous time?

If it is a "change", then what changed in your system to account for it? You implied that removing the overload may have caused this change. However, this thermal overload is not a circuit breaker. It does not open any circuits feeding the motor. What this overload does is tells the contactor (a motor relay) that the contactor should open. In even simpler terms, the overload block just senses the current flowing through the wires, and if the current gets too high, then the overload tells the contactor to turn off the circuit. However, the wires passing through the overload block do not get disconnected. It simply acts as a signalling device.

So if removing the contact block is the only thing you changed to go from a 10 second startup to a 5 second startup, then you probably just had a poor connection somewhere between the contactor output and the motor input. If that's the case, you should be able to reinstall the overload block and still see the 5 second startup time, because what you corrected by removing it was a poor connection.



Now on the other hand, if you were mistaken about the 10 to 5 second decrease, then the setpoint on the overload does come into play and was more significant than I suggested in my previous posting. The setpoint of the overload should be increased. Start by setting it to maximum and see if the motor runs like it did with the overload removed. If it does, then dial it down to determine where it results in a trip. Normally you could reliably set this to the motor amperage rating of 21 amps, but because you are powering the motor from a phase converter, you may have one phase with a higher than typical amperage. This overload will sense that single phase and trip prematurely.


Offline phmade

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Re: 3 Phase Breaker Tripping
« Reply #29 on: September 07, 2014, 07:05 PM »
Ok - here's an update:

Firstly - Rick, you're correct.  The problem was not solved by removing the thermal overload.  When I started the dust collector today, it tripped the 30A breaker in my 3 phase panel.  So, I reviewed all of the wiring in the motor junction box.  Everything was secure and consistent with the diagram on the nameplate.  I did not actually check the wiring inside the motor - should I?  In the junction box, there are 9 leads coming out.  Three (T4,T5,T6) of the leads are are wired together and the remaining 6 leads are wired in 3 pairs.  These pairs are consistent with the nameplate label on the side of the motor.

Regarding the startup time, I never accurately measured the startup time until today; therefore, I believe that it did not change; it was only my hopeful imagination.  Today, I measured the startup time at 9 seconds before the breaker trips.  I believe that the motor is still not up to full RPM at 9 seconds. 

I also checked the current draw near the breaker and it is over 100amps for that entire startup period.  On one startup attempt, the breaker did not trip and the current draw was between 12-13amps. 

So now I feel that I'm back to square one.  I'm trying to be methodical now to diagnose the problem.  Could it be with the phase converter?  Would the other 3 phase machines run correctly if that were so?  My plan is to contact the phase converter company in the morning for recommendations.  They are local and have been very helpful in the past.

I am not a professional electrician but I have done a fair amount of wiring including several homes and all other machines in my shop.  I had an electrician here today (family friend) and he is equally as perplexed as I am.  He has never worked with a phase converter though... My confidence is running pretty low at this point.