10 HP single phase motor serving exhaust fan having trouble starting.

[11bgrunt]

Large paint booth using 10 HP exhaust fan. Booth is two years old.
First motor had trouble starting and was replaced.
This motor is having similar problems. Don't know the time frame but installer said it did work fine in the beginning.
Facility served by REA single phase 7.2kV through 37.5 kVA transformer, 240V secondary.
Short 4/0 al. triplex to the building to serve 400 amp main. Everything else in the facility works fine.
50 amp DP breaker serves approx. 80' run of # 8 cu stranded in conduit to starter and then up through the roof to the motor.
Have not seen motor data plate.
Motor will eventually start and run but seems to stall on the first couple attempts producing 190 amps. Push the stop button when it stalls and start again until motor runs at 29 amps.
Voltage measured at start of wire run on breaker and voltage falls from 245 to 235 during stall.
Make same test at starter during stall and voltage falls from 245 to 210.
When motor is running at 29 amps the voltage drop is 1%.
They are prepared to replace the motor again but looking for explanations of starting problems.
Voltage drop calculations using measured running amps work with the #8. They have replaced the two start capacitors hoping that would make a difference. Didn?t know if they were bad, just changed them.

Is there a design problem?
Option is to change to inverter, VFD and 3phase motor.

They have installed 10hp single phase motors in paint booths elsewhere and haven't seen this before?

 

[GoldDigger]

Large paint booth using 10 HP exhaust fan. Booth is two years old.
First motor had trouble starting and was replaced.
This motor is having similar problems. Don't know the time frame but installer said it did work fine in the beginning.
Facility served by REA single phase 7.2kV through 37.5 kVA transformer, 240V secondary.
Short 4/0 al. triplex to the building to serve 400 amp main. Everything else in the facility works fine.
50 amp DP breaker serves approx. 80' run of # 8 cu stranded in conduit to starter and then up through the roof to the motor.
Have not seen motor data plate.
Motor will eventually start and run but seems to stall on the first couple attempts producing 190 amps. Push the stop button when it stalls and start again until motor runs at 29 amps.
Voltage measured at start of wire run on breaker and voltage falls from 245 to 235 during stall.
Make same test at starter during stall and voltage falls from 245 to 210.
When motor is running at 29 amps the voltage drop is 1%.
They are prepared to replace the motor again but looking for explanations of starting problems.
Voltage drop calculations using measured running amps work with the #8. They have replaced the two start capacitors hoping that would make a difference. Didn?t know if they were bad, just changed them.

Is there a design problem?
Option is to change to inverter, VFD and 3phase motor.

They have installed 10hp single phase motors in paint booths elsewhere and haven't seen this before?

That large a voltage drop can cause problems starting if the motor is undersized or is under load when starting. I would not expect that of a fan motor unless there is a serious backdraft at the time it is being started.
It is possible that there is something wrong with the start winding or the centrifugal switch (if there is one) which is preventing the motor from developing much starting torque. Jogging the motor until the poles are in just the right orientation at the time voltage is applied might allow it to start despite that fault.

Are there conditions where the motor itself is mounted that might affect the contacts or mechanical parts of a centrifugal switch over time?
Do the terminals of the motor allow you to measure continuity of the start winding and centrifugal switch for confirmation of a problem?
The symptoms of an open or near open start winding will be very similar to the symptoms of a failed start capacitor.
Does the motor also have a run capacitor? If so the problem might be there.

 

[ActionDave]

Since you didn't say- has anybody checked connections at the starter, and/or the starter itself?
Same for the fan. Has anybody checked that nothing is binding it up or it is freewheeling in the wrong direction at startup?

 

[11bgrunt]

Since you didn't say- has anybody checked connections at the starter, and/or the starter itself?
Same for the fan. Has anybody checked that nothing is binding it up or it is freewheeling in the wrong direction at startup?

I was in the starter today and all looked good. They have developed a routine of start/stop, start/stop and usually the third time the motor will kick off. Left in stall for 5 seconds, heater trips out the starter.
The fan is belt driven. Motor is attached outside the exhaust tube where fan is mounted inside. Motor has sheet metal shroud for weather and none of these shrouds were removed today. I rocked the motor a little with the belts and nothing was obvious. I asked if they were willing to test motor windings in place and they said they would remove the motor and take it to a shop for testing. If they go through the trouble of removal, a new motor will be installed.

 

[augie47]

Something seems amiss here.
Is there a drive somewhere in the picture ? A roto-phase or some type inverter ?
You state single phase service and 10HP motor but 29 amps FLA.
a 10 HP singlephase motor would be more like 50 amps,m a 3 phase more like 29 amps.

 

[cadpoint]

Where's the motor specifications? Seems electrical but could be mechanical, and a damper or louvers (- +)
could not be working or signaled incorrectly. Frankly, I can beleive there's a open flute and back pressure on this application.(glad I re-read-who said what)

Is this one of those electrical inferences where the 10 (HP) Amps pits the bearings of the fan? no because it's belt driven!
I'm going to say you need and isolation bushing in your duct work. I beleive it's called an expansion fitting.

QA and address all of the motor circuit and seek out what meets each requirements accordingly.

Your into higher classification of motor because of the nature of the application at your equipment. Let me assume that it's inline

 

[GoldDigger]

Is this one of those electrical inferences where the 10 Amps pits the bearings of the fan? no because it's belt driven!
I'm going to say you need and isolation bushing in your duct work.

?
Where did the 10 Amps come into the picture?
Bearing pitting usually comes from the high dV/dt produced by a VFD and has no direct relationship to whether the motor is connected to the load via a shaft or a belt. (Although if there is a voltage problem and the motor itself has insulated bearings, you have a risk of just transferring the bearing current to other bearings on a common shaft.)

 

[cadpoint]

Gold:

And only VFD's can cause this?

Excuse me there Stomping Their System.

I'll Defer to a Stomping.

They don't know what they have, and I state a mis print...

Happy Holidays

 

[GoldDigger]

Gold:

And only VFD's can cause this?

Excuse me there Stomping Their System.

I'll Defer to a Stomping.

They don't know what they have, and I state a mis print...

Happy Holidays

Happy Thanksgivikah!

I have not heard of problems with bearing pitting from current other than either
1. High frequencies induced by a VFD or
2. Some sort of ground/EGC current coming into the motor from a fault in the load.

 

[11bgrunt]

Something seems amiss here.
Is there a drive somewhere in the picture ? A roto-phase or some type inverter ?
You state single phase service and 10HP motor but 29 amps FLA.
a 10 HP singlephase motor would be more like 50 amps,m a 3 phase more like 29 amps.

I wanted motor data plate info but couldn't get it.
Tech who changed last motor said FLRA was supposed be 40. We talked about the 29 for a while with no answer. Breaker serving #8 cu to 10 horsepower motor is a 50 and did not trip before the heater any time today. Starter was sized for 10HP single phase.
I followed conductors from starter to motor. Nothing in between.
I didn't see a damper hinge in the exhaust stack and think it is a straight shot from the filters to the stack to the fan and out.
This company only builds paint booths and does installs all over the country. This motor has worked right at some time in the past.
The red herring is they said that it usually happens in the morning. I thought about something dragging the fan and motor torque couldn't get through it. Motor starts eventually. I heard it has tripped out while running after about 5 minutes sometimes.

 

[GoldDigger]

The red herring is they said that it usually happens in the morning. I thought about something dragging the fan and motor torque couldn't get through it. Motor starts eventually. I heard it has tripped out while running after about 5 minutes sometimes.

I have seen a vaguely similar condition in bathroom fans (with impedance protected motors). The bearings have gotten so gummed up that they prevent the motor shaft from rotating until the motor has heated them up enough to soften the gunk or increase the clearances.
I have never heard of anything like that is a 10HP motor though.
It sounds like the bearings are free, since you did not find anything out of the ordinary when you rotated the system by hand.
If you can look at the belt and pulleys, do they move at all, however slowly, when it fails to start or does the motor just sit and hum (suggesting problems with the start winding?).

 

[Jraef]

The #1 issue I see with things like this:

The user(s) is under the mistaken belief that having the damper WIDE OPEN makes it EASIER for the motor to start, and if the damper was closed, the fan would be trying to "suck a vacuum" and stall.

The truth is, it is EXACTLY THE OPPOSITE. In a fan, flow = load. So no flow = no load, = EASIER to start. The fan motor was designed to accelerate the fan with the dampers CLOSED, then some smart Alec came along and thought that was wrong, opened the damper, and now the motor is overloaded trying to start up. The starter OLs likely kept tripping, so they increased the size to "fix it".

Evidence in support of my theory:

Booth is two years old.
First motor had trouble starting and was replaced.
This motor is having similar problems.

Motor will eventually start and run but seems to stall on the first couple attempts producing 190 amps. Push the stop button when it stalls and start again until motor runs at 29 amps.

Restarting while it is still spinning, "solves" immediate problem, but is seriously thermally stressing the motor, especially the Start caps.

I didn't see a damper hinge in the exhaust stack and think it is a straight shot from the filters to the stack to the fan and out.

So, no damper then?

The red herring is they said that it usually happens in the morning.

Cooler air is more dense, harder for the fan to move it.

 

[kwired]

Something seems amiss here.
Is there a drive somewhere in the picture ? A roto-phase or some type inverter ?
You state single phase service and 10HP motor but 29 amps FLA.
a 10 HP singlephase motor would be more like 50 amps,m a 3 phase more like 29 amps.

I bet they didn't change any start capacitors on a three phase motor.hmy:

Is this one of those electrical inferences where the 10 (HP) Amps pits the bearings of the fan? no because it's belt driven!
I'm going to say you need and isolation bushing in your duct work. I beleive it's called an expansion fitting.

Original motor could have had this issue, but replacement was brand new hope it didn't destroy bearings that fast.

The #1 issue I see with things like this:

The user(s) is under the mistaken belief that having the damper WIDE OPEN makes it EASIER for the motor to start, and if the damper was closed, the fan would be trying to "suck a vacuum" and stall.

The truth is, it is EXACTLY THE OPPOSITE. In a fan, flow = load. So no flow = no load, = EASIER to start. The fan motor was designed to accelerate the fan with the dampers CLOSED, then some smart Alec came along and thought that was wrong, opened the damper, and now the motor is overloaded trying to start up. The starter OLs likely kept tripping, so they increased the size to "fix it".

Evidence in support of my theory:




Restarting while it is still spinning, "solves" immediate problem, but is seriously thermally stressing the motor, especially the Start caps.


So, no damper then?

Cooler air is more dense, harder for the fan to move it.

Air flow is a possibility, but this motor was drawing 29 amps when it was at full speed which would be when the blower itself would be loaded the most, roughly only 75% of what OP said FLA was.



IMO 8AWG is too small of conductor for a 10 hp single phase motor. T430.248 says 10hp FLA is 50 amps.

Min conductor ampacity needs to be 125% of that so that gives us 62.5 amps minimum conductor which would be at least 6 AWG @ 75 deg C. Fixing that alone may help some with voltage drop. If this is a high inertia fan it will take time to accelerate it and voltage drop becomes a more critical factor in accelerating the motor. If you have long feed you may still need to consider larger conductors for voltage drop reasons.

I am really surprised a 50 amp breaker even holds during this starting attempt, I generally am installing 90 or 100 amp breakers for 10 hp single phase motors - especially if a high speed application that takes more acceleration time.

 

[ActionDave]

The red herring is they said that it usually happens in the morning. I thought about something dragging the fan and motor torque couldn't get through it. Motor starts eventually. I heard it has tripped out while running after about 5 minutes sometimes.

Two motors, similar problems leads me to think it is not the motor. How many hours were on these motors?

We check out a lot of motors because people think that is what is wrong. As often a not it is something mechanical or electrical to do with the motor, not the motor itself.

 

[Jraef]

Air flow is a possibility, but this motor was drawing 29 amps when it was at full speed which would be when the blower itself would be loaded the most, roughly only 75% of what OP said FLA was.

Motor would not drop down to Running Load Amps until it got to 80% speed or so. We don't know what the Starting Current was or how long it takes to accelerate.

IMO 8AWG is too small of conductor for a 10 hp single phase motor. T430.248 says 10hp FLA is 50 amps.

Min conductor ampacity needs to be 125% of that so that gives us 62.5 amps minimum conductor which would be at least 6 AWG @ 75 deg C. Fixing that alone may help some with voltage drop. If this is a high inertia fan it will take time to accelerate it and voltage drop becomes a more critical factor in accelerating the motor. If you have long feed you may still need to consider larger conductors for voltage drop reasons.

I am really surprised a 50 amp breaker even holds during this starting attempt, I generally am installing 90 or 100 amp breakers for 10 hp single phase motors - especially if a high speed application that takes more acceleration time.

Might be on to something there. VD caused by the undersized wire might be contributing to making the acceleration take too long.

 

[GoldDigger]

If you have long feed you may still need to consider larger conductors for voltage drop reasons.

Good point. So far we know the voltage drop at the starter, but we do not know the length of the conductors from there to the motor on the roof.

 

[StarCat]

Fan Drives

Fan Drives

Al lot of valid points being made.
I will second 2 motors, same issue....this drive is set up wrong from the start....most likely electrically and mechanically.
My motor reference says #6 AWG / 100A breaker.
As stated above starting the motor as it is being done is going to damage it because several things are not correct.
If the " replaced " motor is then compromised this may complicate troubleshooting the drive.
I would find out the HP that the drive is rated for by the MFG and also question the way it is sheaved and for the short term, reduce the RPM if at all possible until a comprehensive solution can be arrived at. I would have a recording Amp meter on it which can catch and show peak inrush, min and max like a Fluke 87. I have seen drives set up with the wrong RPM motors which is interesting to say the least. I have also seen drives set up with the wrong HP motors from the install, and or others that have been hacked.
Engineering support at the fan MFG should be able to answer some questions.

 

[kwired]

Al lot of valid points being made.
I will second 2 motors, same issue....this drive is set up wrong from the start....most likely electrically and mechanically.
My motor reference says #6 AWG / 100A breaker.
As stated above starting the motor as it is being done is going to damage it because several things are not correct.
If the " replaced " motor is then compromised this may complicate troubleshooting the drive.
I would find out the HP that the drive is rated for by the MFG and also question the way it is sheaved and for the short term, reduce the RPM if at all possible until a comprehensive solution can be arrived at. I would have a recording Amp meter on it which can catch and show peak inrush, min and max like a Fluke 87. I have seen drives set up with the wrong RPM motors which is interesting to say the least. I have also seen drives set up with the wrong HP motors from the install, and or others that have been hacked.
Engineering support at the fan MFG should be able to answer some questions.

from what we have been told there is no "drive" this is across the line and is a single phase motor.

I run into similar situations a lot, but they are crop drying fans on grain bins, 7.5 to 15hp are pretty common and they all have similar problems as the OP is having, if you don't provide enough conductor they will run fine but because they have a pretty heavy blower they have a long acceleration time, voltage drop only complicates starting problems, as it extends that acceleration time. 10 hp conveyor motor supplied from same system with same size conductor has no problems because it doesn't have a long acceleration time.

 

[StarCat]

Additional Comments

Additional Comments

By no drive I am assuming you mean fan splined directly on the motor output shaft, as in Direct Drive.

A note on the bathroom exhaust fan comment made above. I was involved in response to a structure fire that was started by a Nutone or Broan bath exhaust fan that was in the same state described above - mechanically locked rotor. There are similar recorded instances of these units causing fires as they will get very hot without overloading the circuit breaker.

 

[GoldDigger]

By no drive I am assuming you mean fan splined directly on the motor output shaft, as in Direct Drive.

Actually, I think that in this case no "drive"' means no variable frequency drive (VFD) which could make starting less stressful on the motor and also result is a lower startup surge current.
Since the motor is single phase and the wire runs directly from the starter to the motor on the roof, there does not appear to be an unnoticed VFD in the picture.
We are also assuming (with justification) that the starter and motor combination do not implement wye-delta switching, high-low voltage tap changing or other specialized ways of reducing starting current at the expense of starting torque.