# motor overload quesion



## htneighbors (Jan 23, 2009)

What exactly is supposed to shut down at 200A?
OL probably should be set at 115% of FLA = 195.5A
You mention an AMP meter...Is the AUTO circuit wired thru the current reading somewhere and this is what should somehow be opening the coil?


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## jw0445 (Oct 9, 2009)

htneighbors said:


> What exactly is supposed to shut down at 200A?
> OL probably should be set at 115% of FLA = 195.5A
> You mention an AMP meter...Is the AUTO circuit wired thru the current reading somewhere and this is what should somehow be opening the coil?


The feed auger is suppose to shut down until the amperage drops, then start up again to feed the hammer mill. There is a visual amp meter for monitoring the motor.

Is the AUTO circuit wired thru the current reading somewhere and this is what should somehow be opening the coil? I believe it is.


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## John Valdes (May 17, 2007)

You have a current meter with a pointer or setting mechanism that can be set/adjusted. It might have a set of contacts that are intiated when the current exceeds or falls below your set point.
This would be an analog measuring device, with contacts/output.
Does this sound like what you have?

If you are having to manually accomplish what this set point meter does, you need to look at the meter itself.


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## jw0445 (Oct 9, 2009)

John,

That does sound like what I have. I thought the meter was passive only indicating the amperage as it's about 10 ft. off the deck. I'll look for the location of the leads. Guess I'm looking for welded contacts, yes?


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## Wirenuting (Sep 12, 2010)

Take a look at all items in the start circuit. 
It could be a stuck push button for start.
If its an old Square D push button that is mechanically tied to the off button, insure that that rocker linkage isn't dirty and hanging up. 
Some times the old ones would hang or become slow at returning to the open position. 

Other then that I go with what John said. 

The safety part if the circuit is probably ok. But check them all anyway.


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## htneighbors (Jan 23, 2009)

Very possible - the dirty contact suggestion. Especially on a hammer mill at a feed store.


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## John Valdes (May 17, 2007)

jw0445 said:


> John,
> 
> That does sound like what I have. I thought the meter was passive only indicating the amperage as it's about 10 ft. off the deck. I'll look for the location of the leads. Guess I'm looking for welded contacts, yes?


Does the meter have an adjustable set point?
Some have a knob and a pointer/needle on the face, for setting the set point.

In the back, look for the connection diagram. You should have a set of contacts or even two sets of contacts that open and close when the meters set point is achieved. 
These contacts can facilitate anything you want.

If this meter is what I think it is, you might need to replace it or send it out for repair.
I am certain they make something more up to date in a digital/electronic format you could exchange it with.

This analog type was very common and seems there are still some in service even today.

Here is one of the old type. The red pointer is adjustable by turning the knob in the middle. 
When the current reaches the pointer (set point) it actuates the relay or relays within.

Note: If you're relay is not located where personnel can readily address it, it very well might just be a meter and nothing more?


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## jw0445 (Oct 9, 2009)

John,

This meter looks like a poco meter enclosed in glass and doesn't have a set pointer, it just sweeps to the amps in use. I'm thinking it's just a meter.


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## CYoung (Apr 19, 2013)

I worked in a lumber mill that had a similar set up to this with a hammer hog and a shaker bed. In our control circuit we had CT's that monitored the the 'hogs' current draw. When the current went above the set point it would open a relay and in turn de-energize the shaker beds coil until the current fell. Not sure if this helps at all but may be worth looking to see if CT's are present in your circuit.


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## Introyble (Jul 10, 2010)

I wonder if it's a solid state starter that somebody crammed larger heaters into to prevent shut down while overloading the motor.


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## SteveBayshore (Apr 7, 2013)

Does it have to be manually restarted, or does it restart itself after turning off on high current? If it restarts itself, it will need some type of timing or material sensing circuit to cause the restart.
I don,t think that they had electronic starters in 1954.


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## John Valdes (May 17, 2007)

jw0445 said:


> John,
> 
> This meter looks like a poco meter enclosed in glass and doesn't have a set pointer, it just sweeps to the amps in use. I'm thinking it's just a meter.


Then I have no idea jw. You will need to pull the prints if you have any and see exactly how this thing is supposed to work.
If you have no prints, make sure you have one after you get done figuring this out.
Make a drawing is what I mean.
Let us know what you come up with!


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## micromind (Aug 11, 2007)

jw0445 said:


> John,
> 
> This meter looks like a poco meter enclosed in glass and doesn't have a set pointer, it just sweeps to the amps in use. I'm thinking it's just a meter.


I've worked with tons of those meters, mostly differential current or ground current. 

They certainly can have contacts inside that open or close when the dial reaches a certain position. They can wear out, weld closed, or the cam on the dial shaft can wear out. 

A note when working with CTs; never open the CT secondary circuit when current is flowing in the primary. To do so will destroy the CT instantly, and very likely shock the sam-hill out of you. Many thousand volts can be present in an open CT secondary with even a slight current flowing in the primary.


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## Big John (May 23, 2010)

JW, are you talking about one of these:


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## micromind (Aug 11, 2007)

Big John said:


> JW, are you talking about one of these:


That's the kind I'm familiar with. Most of them have contacts inside, the ones I usually work with will cause a breaker to trip when the setpoint is exceeded. 

This type of meter could easily be used to stop a feed conveyer when the motor current got too high, and it would start it back up when the current is lower. 

All you'd need is a CT around one of the phases to the motor, and connect the feed starter in series with the meter contact. 

Don't be surprised if the CT has the motor wire through the hole plus one or more turns of the secondary wire as well. This is to trim the output current to the exact level the meter wants to see.


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## JRaef (Mar 23, 2009)

The meter might just be a meter, but there may be a Current Sensing Relay (CSR) buried in the controls somewhere that has ceased functioning.

CSRs usually look something like this:










Regardless of what type it is, the common thing is that somewhere, the motor current is being sensed, so it will be going through a small CT somewhere that is either attached to the relay, or the CT secondary wires will lead to it. Find the CT and you can find the CSR to replace it. It might be using the same CT as the meter, in which case you just need to follow those secondary leads.


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## Introyble (Jul 10, 2010)

For once I'm not trying to be a smart a$$ but the reason I asked if it were just a heater issue is because of this statement:



> The auger feeding the line is suppose to shut down automatically at 200 amps to let the mill process what it has to bring the amps down.


I have many issues with that phrase


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## Introyble (Jul 10, 2010)

75HP @ 460 suggests FLA's are most likely under 100
75 HP @ 230 3 phase seems unlikely but also doesn't fit the model of a guess 185 FLA range


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## Introyble (Jul 10, 2010)

Not to mention all the automation problems I have with that phrase, nobody controls that way. They were smarter than that even in 1950 :laughing:


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## SteveBayshore (Apr 7, 2013)

I misread problem the first time. The overcurent on the 75hp motor is not shutting down the 75hp motor, it is shutting down the screw conveyor feeding the 75hp hammer mill. Operation makes more sense now. The current monitoring unit needs have some sort of dead band that is adjustable, so the feed conveyor does not restart until some lower setpoint is reached. If the off point is 200 amps the restart point needs to be set for the 75hp nameplate FLA, or there abouts. Modern crushers work this way except with analogue circuits controlling variable speed conveyors feeding the crushers.


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## Introyble (Jul 10, 2010)

SteveBayshore said:


> I misread problem the first time. The overcurent on the 75hp motor is not shutting down the 75hp motor, it is shutting down the screw conveyor feeding the 75hp hammer mill. Operation makes more sense now. The current monitoring unit needs have some sort of dead band that is adjustable, so the feed conveyor does not restart until some lower setpoint is reached. If the off point is 200 amps the restart point needs to be set for the 75hp nameplate FLA, or there abouts. Modern crushers work this way except with analogue circuits controlling variable speed conveyors feeding the crushers.


 
I was thinking deadband is the ability to equalize the non responsiveness in a pot. But we are getting closer.


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## Introyble (Jul 10, 2010)

First, I really need you to explain the Nema name plate information of the motor because I refute the statement that a 75HP motor overloads at 200 AMPs.


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## JRaef (Mar 23, 2009)

Introyble said:


> First, I really need you to explain the Nema name plate information of the motor because I refute the statement that a 75HP motor overloads at 200 AMPs.


He said in the beginning that it's 240V, 170A FLC. Wer'e so far from the OP now its easy to miss. 200A would be well within a 1.15SF, but you would want to reduce it at that point. This sort of process control is very common.


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## SteveBayshore (Apr 7, 2013)

Introyble said:


> I was thinking deadband is the ability to equalize the non responsiveness in a pot. But we are getting closer.


Easiest way to explain deadband is a common heating thermostat, set to keep temperature at 70 degrees. Circuit closes at say 66 degrees, and opens circuit at 70 degrees, deadband of 4 degrees. This keeps the unit from short cycling between 69 and 70. Many process controllers have a user programmable set point and password protected programmable dead band instead of two separate setpoints. That way the user would only have to adjust the final required setpoint. The dead band will follow the user's setpoint up and down the scale.


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## Introyble (Jul 10, 2010)

You are correct, I did completely miss that point. Having said that, who the hell would ever design a process that ran in the SF?

You and I both know the consequences of that. LOL I just palm deleted again, I hate laptops sometimes, I'll have to edit.


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## Introyble (Jul 10, 2010)

Introyble said:


> You are correct, I did completely miss that point. Having said that, who the hell would ever design a process that ran in the SF?
> 
> You and I both know the consequences of that. LOL I just palm deleted again, I hate laptops sometimes, I'll have to edit.


This sort of process control is common? Gayest response ever. Nobody in their correct mind would start and stop a 10+ HP anymore than they had to. I was under the impression that motors of this size should be integrated with the respect towards limited start cycles as they significantly reduce motor life. To even think they would start and stop the motor in response to load is absurd.


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## Introyble (Jul 10, 2010)

Something this and other sites have taught me is their is almost always some obscure exception to a general statement. Disregard that, without being cute, name a VFD set list that doesn't require a HID response to clear an over current.


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## SteveBayshore (Apr 7, 2013)

Depending on the parameters installed, a VFD in a continuous process won't trip while running up in the SF, maybe only issue a warning. Running up into service factor is not generally considered overcurrent in quite a few processes that I work on. Yes they will need to be manually reset once tripped by overcurrent. Generally, electronic motor controls need to have the service factor entered into the parameters so it can be used formulate trip curves. I'm pretty sure that newer thermal type overload charts take SF into consideration also.
It was never mentioned how many times the mill actually gets overloaded, maybe it is only a couple of times a day? That is why newer processes usually varry the speed of the input to maintain a constant current to the crushers. Don't forget, this controller is from the '50s.


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## Introyble (Jul 10, 2010)

The FLA's are clearly stated on the plate and the SF is never a consideration when in context of over current. Yes, the autotune requires the input of the nameplate data including the SF. If you are sizing your protection with the SF built in, your going to be replacing that motor soon.

So what is your secret formula? FLA x SF x 1.25 :laughing:


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## SteveBayshore (Apr 7, 2013)

Manufacturers thermal OL selection tables take the FLA, ambient temperature, service factor and time curves into consideration for overload heater selection. Not quite your formula , but close.
Using class 30 overloads as opposed to class 10 or 20 gives a longer time/current trip curve to allow running at maximum current for optimal production and reduce OL tripping in the SF and on short duration overloads during operation. The programmable controllers that I have worked with have had the trip class as a selectable parameter.
Yes, some customers have a 3 year rotation on all motors. Motors are removed and serviced every three years during winter maintenance to assure optimal run time during the production seasons.


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