3 Phase Breaker Tripping

[phmade]

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? 

 

[tjbnwi]

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

 

[stvrowe]

Does the breaker trip immediately or is there a delay?  If immediate, I would be looking for a short.

 

[tjbnwi]

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

 

[Sparktrician]

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. 

 

[stvrowe]

What Willy said.  Need more info on voltages, currents, length of wire run, etc. 

 

[Loren Woirhaye]

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.

 

[Rick Christopherson]

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.

 

[phmade]

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

 

[phmade]

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.

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).

Are the inlets to the dust collector open?

Yes, the inlets are open.

 

[phmade]

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.

 

[Rick Christopherson]

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.

 

[Rick Christopherson]

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.

 

[Rick Christopherson]

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.

 

[phmade]

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?

 

[phmade]

Here is the photo inside the ON/OFF box on the dust collector.

 

[Rick Christopherson]

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.

 

[phmade]

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...

 

[Rick Christopherson]

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.

 

[phmade]

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').