# External overloads downstream from vfd?



## acro (May 3, 2011)

The thread on upstream disconnects prompted me to start this thread.


I have a 40hp vfd that was installed back in 2006. At that time, the electrician also installed an overload relay. Just like you would have with a "conventional" motor starter with the "run circuit" wired through the nc contacts.

I am replacing the drive and feel that the OL is redundant and not needed. At first glance, I thought redundant is fine since it is already there.

But the other thread got me thinking that it could actually be harmful if it would trip. So I am going to remove it.

agree?


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## nolabama (Oct 3, 2007)

Disagree


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## acro (May 3, 2011)

Could not be harmful, since the overloads don't actually open the load conductors?

But would you still remove it?


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## JRaef (Mar 23, 2009)

acro said:


> Could not be harmful, since the overloads don't actually open the load conductors?
> 
> But would you still remove it?


Depends. But assuming there is no Bypass, or possibility of a bypass, or multiple motors down stream of the VFD, then I would remove it. The problem with redundant protective devices like overloads is in not knowing which one tripped, and ending up with a "cry wolf" scenario some time in the future when Joe Blow gets tired of resetting nuisance trips (or what he PERCEIVES to be nuisance trips) and just turns them all up or off.

It's possible that your older VFD did not have UL listed motor thermal overload protection and so required an external OLR, it was more common than a lot of people realized. But for the last 10 years or so, UL has stopped allowing mfrs to list their VFDs as "Power Converters" as they used to allow in the past and began only listing them as "Motor Controllers" which means they MUST now have tested and listed motor thermal overload protection.


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## John Valdes (May 17, 2007)

Take it out. The less connections the better.


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## gesparky221 (Nov 30, 2007)

I still use the external overload. With the drives we are using now you cannot reset an overload condition without powering down the drive. Big problem in a cabinet with 20 drives. I don't like powering drives down and re-applying power many times. I feel like the power up is when most drives fail. I set the drive overload setting high enough, or even disable it in the program, where the external will trip first and turn off the run signal to the drive. The overload relay has a yellow trip indicator plus I wire the N.O. contacts to a plc input or external alarm to signal a problem.


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## John Valdes (May 17, 2007)

gesparky221 said:


> I still use the external overload. With the drives we are using now you cannot reset an overload condition without powering down the drive. Big problem in a cabinet with 20 drives. I don't like powering drives down and re-applying power many times. I feel like the power up is when most drives fail. I set the drive overload setting high enough, or even disable it in the program, where the external will trip first and turn off the run signal to the drive. The overload relay has a yellow trip indicator plus I wire the N.O. contacts to a plc input or external alarm to signal a problem.


What do you mean by " With the drives we are using now you cannot reset an overload condition without powering down the drive".

You must remove input power to reset the control? I have never met a control like this.


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## gesparky221 (Nov 30, 2007)

At my job we are forced to use our brand of drive. A couple years ago we changed from one supplier to another and the new drive has a lot of issues. I have not found any faults that the Reset button will clear as of yet. I think it is just a poor design. They basically took a good drive and ruined it with the changes. I have talked with factory reps about it a few times but get no help. To reset an overload condition you must first power the drive down, and then repower it. Then press the reset key which will allow the drive to start. Not to mention the programming is not very user friendly.


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## Big John (May 23, 2010)

What brand drive is that, so I know what not to buy? :no:

-John


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## JRaef (Mar 23, 2009)

Big John said:


> What brand drive is that, so I know what not to buy? :no:
> 
> -John


Judging from his handle, GE maybe?
:confused1:


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## John Valdes (May 17, 2007)

gesparky221 said:


> At my job we are forced to use our brand of drive. A couple years ago we changed from one supplier to another and the new drive has a lot of issues. I have not found any faults that the Reset button will clear as of yet. I think it is just a poor design. They basically took a good drive and ruined it with the changes. I have talked with factory reps about it a few times but get no help. To reset an overload condition you must first power the drive down, and then repower it. Then press the reset key which will allow the drive to start. Not to mention the programming is not very user friendly.


Please tell us which one it is. Model number too.


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