# Motor load



## Service Call (Jul 9, 2011)

I replaced a 460V 3P motor with a nameplate of 12.2 amps. Voltage available was 480. Motor was only drawing 6 amps under load. Thought this was too little. Found out this is the sixth motor replacement in 5 yrs. I figured that at 480 the draw would be about 10 amps or so. 

Any thoughts on what the draw should be.


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## Service Call (Jul 9, 2011)

This is for an exhaust fan.


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## McClary’s Electrical (Feb 21, 2009)

Service Call said:


> I replaced a 460V 3P motor with a nameplate of 12.2 amps. Voltage available was 480. Motor was only drawing 6 amps under load. Thought this was too little. Found out this is the sixth motor replacement in 5 yrs. I figured that at 480 the draw would be about 10 amps or so.
> 
> Any thoughts on what the draw should be.


 
Was the 12.2 FLC?


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## Service Call (Jul 9, 2011)

Yes as per nameplate.


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## SteveO. (Oct 17, 2011)

If the motor isn't fully loaded it won't draw FLC. Do you think it's loaded right up or oversized?


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## Service Call (Jul 9, 2011)

We adjusted the pulleys to increase the load and that's the best we could get. I'm thinking it's oversized. It's about a 30" squirrel cage fan for a restaurant exhaust. The last motor was installed in Nov. of 2011.


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## Wirenuting (Sep 12, 2010)

Service Call said:


> This is for an exhaust fan.


Is this a direct drive or belt driven? Is it in the airstream or outside of it? Besides being over sized in the past, is it aligned correctly, proper shive and belt's? Are be fan bearings over greased and worn out?

Are the belts A or B sized and do they match the shives? VX seem to last a little longer for kitchen exhaust. 

After you do all this, I would install overloads just shy of FLA, save the motor and return on a service call to see what caused the tripping.


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## Service Call (Jul 9, 2011)

It's belt driven (dual) on the roof. Nothing was tripped, the old motor ( and previous ones ) burned up or shorted to ground. I'm suggesting installation of a phase loss monitor and low / high voltage protection. But was wondering if damage was also a result of under loading. Requirements called for a 1 1/2 - 10 hp for this install and I was not involved in the previous motor changes. So I don't know what we started with. This is in a large hotel and no other systems seem to have any problems.


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## millelec (Nov 20, 2010)

Wirenuting said:


> Is this a direct drive or belt driven? Is it in the airstream or outside of it? Besides being over sized in the past, is it aligned correctly, proper shive and belt's? Are be fan bearings over greased and worn out?
> 
> Are the belts A or B sized and do they match the shives? VX seem to last a little longer for kitchen exhaust.
> 
> After you do all this, I would install overloads just shy of FLA, save the motor and return on a service call to see what caused the tripping.


everything Wirenuting just said, plus is it a totally enclosed or an open motor?


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## acro (May 3, 2011)

I was not aware that there is ever a problem with under-loading a motor.


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## McClary’s Electrical (Feb 21, 2009)

acro said:


> I was not aware that there is ever a problem with under-loading a motor.


 

I don't think there's such a problem.


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## wdestar (Jul 19, 2008)

acro said:


> I was not aware that there is ever a problem with under-loading a motor.


There isn't.


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## wdestar (Jul 19, 2008)

Service Call said:


> We adjusted the pulleys to increase the load and that's the best we could get. I'm thinking it's oversized. It's about a 30" squirrel cage fan for a restaurant exhaust. The last motor was installed in Nov. of 2011.


Huh???:no:


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## wdestar (Jul 19, 2008)

Is this motor vertically or horizontally mounted? Does the establishment have a maintenance person over-greasing the bearings?


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## Service Call (Jul 9, 2011)

Horizontal mount. Enclosed motor. Over greasing the bearing?


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## Service Call (Jul 9, 2011)

I just thought the current draw was too far below the nameplate.


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## Wirenuting (Sep 12, 2010)

Service Call said:


> Horizontal mount. Enclosed motor. Over greasing the bearing?


Over greasing will cause bearing wear and failure. Same as using the wrong or mixed grease. I clean the bearings on the air jandlers I work on. Seems that the younger guys don't want to get dirty.. 
If the motor is enclosed, is it in the exhause air stream? If so sealed bearings would work well for the motor. Don't let Mr Maintanceman pump it full every month.. 
If it's a dual belt shive check for wear, grooving on them. 
Matched belts will save the motor also. You get less jerking on start up and a smoother run, no slapping. Your supplier will know what matching is. 
If you use Opti-belts, that brand stinks, IMHO. 

Phase loss protection is a great idea.


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## muck (Jun 30, 2008)

Are the hood system being steam cleaned prior to motor failure?


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## Service Call (Jul 9, 2011)

New belts and pulleys. Don't know about the steam cleaning tho. Besides its 2 floors away. 

I was mostly curious about the low amp draw. Again I'm trying to determine why so many motor failures on this one piece of equipment. The last one was in Nov.


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## garfield (Jul 30, 2009)

Disassemble the motor and look at the windings... You can usually make a close guess as to what caused the failure.


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## John Valdes (May 17, 2007)

The motor is not pulling much current because its not doing much work. Are you restricting the air flow in any way? If so, you could allow for more air flow and thus increase current. Low current is good for the motor. But it is inefficient. Waste of dollars in operating cost. Maybe someone put a larger frame in that spot. Maybe a smaller motor goes there?
The current is not the reason for premature failure. The root cause has not been found.
I would check the breaker and the starter for a high resistance connection. And see if the motor is the right HP for the application. Fan blade pitch is something else you can look at. Maybe someone put on a fan blade that is not original. 

Are you using roller or ball bearings. Bearing failure leads to electrical failure. If the belts are to tight that could shorten the life of the bearings.


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## JRaef (Mar 23, 2009)

Service Call said:


> New belts and pulleys. Don't know about the steam cleaning tho. Besides its 2 floors away.
> 
> I was mostly curious about the low amp draw. Again I'm trying to determine why so many motor failures on this one piece of equipment. The last one was in Nov.


No issues with under loading a motor, other than some wasted energy. But are you sure it is under loaded? If the dampers are closed when you check the current, there will be virtually no load on it, but with the dampers fully open, that's when the load couples (air flow = load on a centrifugal fan or blower). But even in this situation, the overload relay should protect the motor from damage. Did you check the overloads? If they are set or selected too high, that's an indication that the motor is under sized and someone tried to "solve" the nuisance tripping problem by tweaking the overload, which allows the motor to cook itself. This is the easiest thing to check.

If it's not that and the OL is set to trip at 12.2A, then the next thing I would suspect is moisture / condensation. Even if the motor is far away from the cleaning process, there will still be a lot of moisture going through the air system and if it comes in contact with the motor, it can condense on and inside of it when the power is off for a while, like after hours. The motor should have space heaters to protect against that, but sometimes when the original one goes bad, they don't realize or think to order the replacement motor with heaters, so the next one dies faster, etc. etc.

Next would be severely unbalanced current. Current imbalance causes excess motor heating that is highly disproportionate to motor current. So you can be running well under the OL setting, but still over heat the motor because the unbalanced current is making the motor fight itself, heating the rotor far faster than it should.

Like John Valdes said, you haven't found the problem yet, you need to check more things and get off of the underloaded idea, that isn't it.


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## garfield (Jul 30, 2009)

How much imbalance is acceptable?


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## Service Call (Jul 9, 2011)

Here we go again. Resturant called and the new motor is "shooting sparks". He's got someone bringing in a new motor so I have to wait till I'm called to go out. I installed the phase monitor at the disconnect to the motor. At install FLA were within 1/2 amp of each other. Couldn't check overload settings at the time they were too busy to get in there. Will post what I find.


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## JRaef (Mar 23, 2009)

I'm going to call it as moisture.


Put in a space heater so that when it is off, it doesn't get internal condensation. There are also what are called "Motor Winding Heaters" but they are expensive. Still, if you don't have a circuit at this motor to tap off power for a heater, a motor winding heater may be cheaper than running conduit.


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## RIVETER (Sep 26, 2009)

Service Call said:


> I replaced a 460V 3P motor with a nameplate of 12.2 amps. Voltage available was 480. Motor was only drawing 6 amps under load. Thought this was too little. Found out this is the sixth motor replacement in 5 yrs. I figured that at 480 the draw would be about 10 amps or so.
> 
> Any thoughts on what the draw should be.


How did you arrive at your figures?


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## frenchelectrican (Mar 15, 2007)

Is any chance this is a 5 or 7.5 CV( HP ) motour?

The reason why you mention 12 amp so I am kinda figureing that is pretty big motour and you say 30 inch fan but squrell cage type but will like to know what the width of the wheel.

I am thinking either you have some restriction on suction side either been throttled back alot or alot of restriction on ductwork.

What the motour speed at 1750 or 3500 T/min and fan pulley size as well.

Once you post the number one of us in this fourm can crush the number to see if that is correct appaction of the motour / blower housing.


The other thing you should done is run the recording on triphase supply to see if the supply is steady voltage/ amparage reading if get wonky then you have to find what cause it to affect the performace of the unit.

The other thing I know you say enclosed motour but this is TEFC or TEAO ? if latter that will cause issue.

Merci,
Marc


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## nitro71 (Sep 17, 2009)

New motor is blowing sparks? You guys buying the harbor frieight special edition motors? I would check everything mentioned then change the motor to a different brand and probably something weather proof.


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## Service Call (Jul 9, 2011)

Was expecting the call today to go over but nothing yet. I'm meeting with them tomorrow so they might just be waiting till then.


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## nolabama (Oct 3, 2007)

What about a spray/washdown rated motor. One with the screw top peckerkead?


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## Service Call (Jul 9, 2011)

Motor is covered and protected. The last one and the replacement motor are Dayton. The owner purchases them and has them installed.


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## Service Call (Jul 9, 2011)

This exhaust motor is on the roof. Actually 3 floors away. And out of the airstream.


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## jontar (Oct 11, 2009)

hi the low amp draw is about right, 460 or 480 is about 1.1 to 1 so a 10hp motor will draw alittle over 11.0amps 3phase of course. so 3hp would be about 3.5-4.0 amps, I'd re-read the name plate is it 230/460 motor I think the 12.2amps is for 230v.


As far as burning out, it maybe a open dripproof motor and needs to be tefc. Dust will be a huge factor.


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## nitro71 (Sep 17, 2009)

Who's installing them? Have you checked line voltage? Have you checked make up in the peckerhead?


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## frenchelectrican (Mar 15, 2007)

Service Call said:


> This exhaust motor is on the roof. Actually 3 floors away. And out of the airstream.


That the issue if you use the TEAO motor but with TEFC you should not have the issue sound like you have unbalanced voltage.

Did you or other guys ever megger the conductors yet if not that will be a good time due something causing the motour go early death that quick.

As other guys mention it as well that should be checked out as well.

BTW what size conductor you have in the conduit. ( just stop and think for a second due the voltage drop and you may have wrong conductor size if not sized properly for the motour useage.)

Merci,
Marc


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## Service Call (Jul 9, 2011)

Will post more, but for the moment, which wiring diagram would you use to hook up this motor to 480v 3ph. It is via an across the line starter.


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## Service Call (Jul 9, 2011)

Here's the nameplate.


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## MDShunk (Jan 7, 2007)

You want to start it across the line in two stages or one? One stage, use the top right. Two stages (wye-delta) use the bottom right.


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## MDShunk (Jan 7, 2007)

What's it driving? That might influence the decision. Feeder breaker and service size makes a difference too.


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## Service Call (Jul 9, 2011)

MDShunk said:


> You want to start it across the line in two stages or one? One stage, use the top right. Two stages (wye-delta) use the bottom right.


As of now it's one stage. At the moment it pulls 6 amps.


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## MDShunk (Jan 7, 2007)

Service Call said:


> As of now it's one stage. At the moment it pulls 6 amps.


It's already hooked up and running? What's the question? I'm confused.


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## Service Call (Jul 9, 2011)

This is the 7th motor in 4 yrs. 3rd in 4 months. Trying to determine the problem. Read the beginning posts as they start describing the issues.


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## JRaef (Mar 23, 2009)

Service Call said:


> Will post more, but for the moment, which wiring diagram would you use to hook up this motor to 480v 3ph. It is via an across the line starter.


The one on the upper right. High voltage.


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## Service Call (Jul 9, 2011)

This is a 10 hp motor. The name plate on the control cabinet and exhaust frame assembly all say 7.5 HP max. I've installed a phase / voltage monitor. The overloads in the control cabinet are adjustable and were set for 11.5A (max setting). So since its only pulling 6A I set the O/L at 8A (lowest setting). 

The last time it blew a 10A fuse. This motor drives a 30" squirrel cage fan. I've checked voltage and amperage at the motor and there is less than 1% difference. 

During checking the control cabinet I found a bad contactor for the supply fan. So that hasn't been working for who knows how long.


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## Service Call (Jul 9, 2011)

It's wired as per the top and bottom right drawings. They're the same. But I needed to make sure.


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## JRaef (Mar 23, 2009)

Service Call said:


> It's wired as per the top and bottom right drawings. They're the same. But I needed to make sure.


Well, the RUN condition wiring is the same on the lower right, but the lower diagrams are supposed to be for Wye-Delta starting. You would not use that with an across the line starter, so don't get yourself confused here.

So the motor _*is*_ properly connected, it _*is*_ definitely over sized because it had replaced a motor that was not over 11.5A (probably a 7-1/2HP motor originally), yet you are still losing them rapidly and you don't know why.

Now you say the fuse blows? Did you know this before? That is a *totally* different situation. Fuses blow in a motor starter only because the instantaneous current is too high. The Overload Relay will take it out long before you reach the thermal current rating of the fuses. Blowing fuses in a motor starter is one of only two things:

1) You have a short circuit somewhere
2) You have the wrong fuses.

When you went from a 7.5HP motor to a 10HP motor, did you change the fuses to be the right ones for a 10HP motor? If you used the fuses for the 7.5HP motor, well, pardon my vernacular but... duh! By the way now that we know the motor is bigger than the original, did you check to make sure that the contactor is rated for 10HP at 480V? That will be the next weak link most likely.

Assuming though that you know what you are doing and you have a 10HP starter and fuses for a 10HP motor, and the fuses are blowing, then it's back to #1, you have a short. So troubleshoot that further:

A) You have a bad motor. 6 bad motors in a row though? Highly unlikely.

B) You have a bad motor lead(s), i.e. a nick in the insulation. Did you megger the motor leads? That's something that probably hasn't changed in all those motor swap outs so it fits the scenario.

C) You have moisture ingress into the motor winding insulation. When this *outdoor motor* is running warm and is turned off in a cool environment, say *winter time*, the motor cools down and condensation forms on the warm metal surfaces, then makes its way into the motor insulation. Most standard motor winding insulation is "hygroscopic" meaning it absorbs moisture. Even if it is not getting directly hosed, outdoor motors can still get too much moisture if not protected with heaters. That's why they offer them.

Oh wait, did someone say that already?


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## Service Call (Jul 9, 2011)

I should clarify here, we never changed any motor. I am the last in this chain of events. I have not even wired a motor here. The owner is buying the motors and calling in an A/C company to install them. I was pulled into this via the A/C company to help solve this issue. I thought this was a simple lost phase issue. I did not see the last motor so I don't know what it looked like. I've adjusted the O/L to the lowest setting and the fuses are 15 Amp T/D. The phase / voltage monitor is installed between the disconnect and the motor. 

I was also wanting to double check thoughts on the proper terminations. I know the high volt but was curious about the wye and delta hookup.


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## frenchelectrican (Mar 15, 2007)

I have see what is going on so far.,

I know you replyed that you have it hooked up in delta. Ok there are only three conductors from control panel to the motour ? > need to know this.

IMO after I look at the photo of the motour the ODP is not really a correct appaction for outdoor the moisture will kill it as I say before just get a TEFC ( total encosed fan cooled ) motour this will useally slove most the issue what you are having now due the ODP is cheaper than TEFC is that one reason why you are going thru alot of motour.

Third I know you say bad contractor take care of that right now otherwise it will fry more motours down the road.

Service Call., If I were you ., I will suggest to tell the owner not to buy any more motour until you get the rest of the issue fixed first and also I think I did mention the conductor size as well so check it out to see if that is correct size for this motour.

I know you mention 10 amp fuse that is complety wrong size fuse for this motour size c'est too small for this. you should have at least 20 amp fuse on this one and check the overload to see if that is sized properly as well.

For the Wye-Delta hook up if you are starting across the line aka direct starting no soft start just hook up in delta fashion on top right on wiring diagram the reason for Y-D is use for reduced current during start up once you get up to running speed it should be on delta connection never leave it on Wye otherwise you will burn up windings ( they can get overheat pretty fast ) 

The infomation above this is for 10 CV ( HP ) motour so tell the owner to get correct motour size and double check everything again use the TEFC not the ODP.

Hope the info will give you more answer with it.

Merci,
Marc


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## Service Call (Jul 9, 2011)

frenchelectrican said:


> I have see what is going on so far.,
> 
> I know you replyed that you have it hooked up in delta. Ok there are only three conductors from control panel to the motour ? > need to know this.
> 
> ...


Thanks for the info Marc. Also what I found were 7.5 hp starters on the 10 hp motor. The conductors to the motor are #12. I don't know if they will change out the motor or not so I'll present them with upgrading the controls to the 10 hp rating. You think even with the shroud covering the motor, moisture is still getting in and ruining the motor?

Thanks again.


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## JRaef (Mar 23, 2009)

Service Call said:


> Thanks for the info Marc. Also what I found were 7.5 hp starters on the 10 hp motor. The conductors to the motor are #12. I don't know if they will change out the motor or not so I'll present them with upgrading the controls to the 10 hp rating. You think even with the shroud covering the motor, moisture is still getting in and ruining the motor?
> 
> Thanks again.


If air can get to it, moisture can get to it. The issue of condensation building up on the metal surfaces as a motor cools down has nothing to do with falling water. Think of this analogy: a glass of ice water sidding on your table, you pick it up and there is a ring of moisture left behind on the table top, but the glass isn't leaking. Where do you think that moisture came from? It condensed out of the air because the surface of the glass was changing temperature. Same concept.

If you change out the starters to 10HP and they reinstall 7.5HP motors later, chances are that you can adjust a 10HP motor overload relay down to 7.5HP, but not the other way around.


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