When would the Auto reset on motor starter be used?

Status
Not open for further replies.
hockeyoligist2 said:
I opened the panel on a new machine with multiple motors this morning. I noticed that all of the motor starters were set on auto reset. Why would they do this?
Click to expand...

Because they want the overloads to reset after a fault so the machine will start running again.

I am not a huge fan of it in general, but there are some cases where having the tripped overload automatically reset makes some sense (like for a sump pump).
 
This will be done where access is not quickly available or you don't have he necessary personnel to quickly go to it. In a supervised situation, I don't recommend it since you can easily blow up a motor. But the overloads don't reset until an appropriate cooling time has passed so there is some protection. A good example is sumps of lift pumps where they are started by local controls and you don't have any supervision. You want them to run to failure so you don't flood the ground with crap (literally).
 
hockeyoligist2 said:
I have never put one on auto, but I have been tempted. I have been out many dark and stormy nights resetting starters because of a power blip!
Click to expand...

The auto reset only affects the overloads, and will do nothing if the starter drops out due to power sags.

And you have to carefully consider the use of auto reset..in applications like conveyors or other machinery where an unexpected motor restart can cause injury or death if you change manual reset to auto reset you leave yourself open to severe liability.
 
mxslick said:
The auto reset only affects the overloads, and will do nothing if the starter drops out due to power sags.

And you have to carefully consider the use of auto reset..in applications like conveyors or other machinery where an unexpected motor restart can cause injury or death if you change manual reset to auto reset you leave yourself open to severe liability.
Click to expand...

Many conveyor applications I have worked on the things start and stop a lot on their own anyway.

Since they are suppsoed to be guarded to prevent accidentally getting maimed by one anyway, how would an unexpected start of the conveyor add any additional risk??
 
design

design

design dictates the use of the auto reset it should be a no volt restart circuit so that the sequence is restarted by human element or critical nature of application where the motor is expendable,usually for remote locations like rock crushers in a quarry , conveyer plant applications and vent fans in hazardous loctions ,if left unattended and motor keeps tripping on load fault, line fault protection will eventually trip the circuit and you will be looking to rewind or get a new motor
 
hockeyoligist2 said:
I opened the panel on a new machine with multiple motors this morning. I noticed that all of the motor starters were set on auto reset. Why would they do this?
Click to expand...

Its a great way for the manufacturer to make follow-up sales of new replacement motors after the originals burn up from constant restarting without proper troubleshooting. :)
 
hockeyoligist2 said:
Sorry, but I disagree. A motor cycling on and off due to power blips will cause the overloads to trip.
Click to expand...

Possibly, but having the overloads auto-reset will NOT automatically re-engage the contactor, unless the control input is a maintained contact. In that case of course the motor would restart when power is re-applied. Which is still a possible serious safety hazard, if someone was trying to figure out why the motor had stopped in the first place.

petersonra said:
Many conveyor applications I have worked on the things start and stop a lot on their own anyway.

Since they are suppsoed to be guarded to prevent accidentally getting maimed by one anyway, how would an unexpected start of the conveyor add any additional risk??
Click to expand...

Depends on the application. I make that statement based on a recommendation from a motor application guide, which mentioned a conveyor as one possible type of load that an unexpected restart would be dangerous.

Even in an application where a conveyor started on its own, what do think would happen if someone was working on that conveyor because it wasn't starting at all, when the motor overload suddenly re-engages?

There are literally millions of possible motor applications, and thus millions of reasons why/why not to use auto reset. Are we really gonna try to discuss them all in this thread? :roll::grin:
 
mxslick said:
Possibly, but having the overloads auto-reset will NOT automatically re-engage the contactor, unless the control input is a maintained contact. In that case of course the motor would restart when power is re-applied. Which is still a possible serious safety hazard, if someone was trying to figure out why the motor had stopped in the first place.



Depends on the application. I make that statement based on a recommendation from a motor application guide, which mentioned a conveyor as one possible type of load that an unexpected restart would be dangerous.

Even in an application where a conveyor started on its own, what do think would happen if someone was working on that conveyor because it wasn't starting at all, when the motor overload suddenly re-engages?

There are literally millions of possible motor applications, and thus millions of reasons why/why not to use auto reset. Are we really gonna try to discuss them all in this thread? :roll::grin:
Click to expand...


That is why we have LOTA!

I appreciate your input, so don't get me wrong, OK?

What about an unmanned sewer plant? It seems that they have more power blips during storms ETC. than other facility's. I am on call 24/7/365. One of our worst plants is 40 miles from home. Computer/PLC controlled.

Beeper goes off 2 AM. I drag out of bed, log on and try to restart the pump or whatever isn't running. Won't restart. Drive 40 miles, check every thing out and everything is OK. Reset the starter, everything is cool. Drive 40 miles back, storm still raging, beeper goes off again........

Would that qualify for auto restart?
 
petersonra said:
Many conveyor applications I have worked on the things start and stop a lot on their own anyway.

Since they are suppsoed to be guarded to prevent accidentally getting maimed by one anyway, how would an unexpected start of the conveyor add any additional risk??
Click to expand...




With all due respect, this is a really bad way of pondering this. There's a big difference in a photo eye starting and stopping a conveyor through a PLC, and a motor starter that's gonna cool down and start up automatically about the time that someone starts looking at why it won't run.
Very dangerous and I agree with MX slick
 
mcclary's electrical said:
With all due respect, this is a really bad way of pondering this. There's a big difference in a photo eye starting and stopping a conveyor through a PLC, and a motor starter that's gonna cool down and start up automatically about the time that someone starts looking at why it won't run.
Very dangerous and I agree with MX slick
Click to expand...

Again it would only restart if the control is maintained contact.

If it is maintained contact the 'problem' is no worse than when a circuit trips or there is a power failure, as soon as power is restored the unit will start without notice. That is why we do LOTO before troubleshooting not after a lost arm.
 
iwire said:
Again it would only restart if the control is maintained contact.

If it is maintained contact the 'problem' is no worse than when a circuit trips or there is a power failure, as soon as power is restored the unit will start without notice. That is why we do LOTO before troubleshooting not after a lost arm.
Click to expand...



I agree,,,but I would not use that as a reason to use this feature. True, a normal start/stop station would not restart, but there are huge amounts of on/off selector switches out there in production:D. In my 25 years of working stuff, I've only set a starter to auto reset ONE TIME,,,,,and that was for a submerged pump supplying cooling water to a 600 hp boiler, which ran a 6000 rpm turbine, which truned a 1,000,000 watt 4160 volt generator.
 
hockeyoligist2 said:
That is why we have LOTA!

I appreciate your input, so don't get me wrong, OK?

What about an unmanned sewer plant? It seems that they have more power blips during storms ETC. than other facility's. I am on call 24/7/365. One of our worst plants is 40 miles from home. Computer/PLC controlled.

Beeper goes off 2 AM. I drag out of bed, log on and try to restart the pump or whatever isn't running. Won't restart. Drive 40 miles, check every thing out and everything is OK. Reset the starter, everything is cool. Drive 40 miles back, storm still raging, beeper goes off again........

Would that qualify for auto restart?
Click to expand...

Yes it would as you're talking about an unmanned facility and who would want to deal with the mess when the ca-ca hits the fan?:D

However, as the service tech, (I am presuming) it would be unwise for you to take on the decision to change those starters to auto-reset. Only the designer/engineer should make that decision.

Besides, if you get paid extra to respond to those calls, why cut yourself out of a nice cash cow? :grin:
 
mxslick said:
Possibly, but having the overloads auto-reset will NOT automatically re-engage the contactor, unless the control input is a maintained contact. In that case of course the motor would restart when power is re-applied. Which is still a possible serious safety hazard, if someone was trying to figure out why the motor had stopped in the first place.



Depends on the application. I make that statement based on a recommendation from a motor application guide, which mentioned a conveyor as one possible type of load that an unexpected restart would be dangerous.

Even in an application where a conveyor started on its own, what do think would happen if someone was working on that conveyor because it wasn't starting at all, when the motor overload suddenly re-engages?

There are literally millions of possible motor applications, and thus millions of reasons why/why not to use auto reset. Are we really gonna try to discuss them all in this thread? :roll::grin:
Click to expand...

Of course we will have you read and of the ground up / ground down threads?:D
 
hockeyoligist2 said:
What about an unmanned sewer plant? It seems that they have more power blips during storms ETC. than other facility's. I am on call 24/7/365. One of our worst plants is 40 miles from home. Computer/PLC controlled.

Beeper goes off 2 AM. I drag out of bed, log on and try to restart the pump or whatever isn't running. Won't restart. Drive 40 miles, check every thing out and everything is OK. Reset the starter, everything is cool. Drive 40 miles back, storm still raging, beeper goes off again........

Would that qualify for auto restart?
Click to expand...
I assume you mean auto reset rather than auto restart - they are two distinct and different functions.
Anyway, I don't think so. I'd want to know why the overload protection keeps tripping.
If it is, as you have suggested, a result of frequent loss and restoration of power, then maybe the control system needs to be reviewed. With the PLC control you mention it would be a fairly simple matter to limit the number of starts per hour. On larger machines we normally make this twice consecutively from cold with a maximum of four starts per hour.
Even at local level, you could implement a re-start delay using a pneumatic delay on de-energise timer.
I just don't think using an auto reset feature is really the best option for the scenario you mention. The auto reset might work but it requires the motor to be thermally stressed beyond its normal rating. Taking steps to prevent that happening in the first place would be a better solution in my opinion.
 
petersonra said:
Many conveyor applications I have worked on the things start and stop a lot on their own anyway.

Since they are suppsoed to be guarded to prevent accidentally getting maimed by one anyway, how would an unexpected start of the conveyor add any additional risk??
Click to expand...

The guy that got swept off the sweep chain 15 ft in the air could probably tell you. He was laid up for several months .
 
One-eyed Jack said:
The guy that got swept off the sweep chain 15 ft in the air could probably tell you. He was laid up for several months .
Click to expand...

Why in the world did he go up on the conveyor without locking the thing out in the first place? LOTO is not just about something that might start up on its own. Its also about the guy who walks by from a downstream department to see why there is no product coming to him and sees the conveyor is stopped and restarts it not realizing his buddy was on the conveyor.

Its a little different with a PLC controlled system because presumably you have some fault detection and decision logic built in, and can alert someone what actually happened. Hopefully the logic realized it tripped and reset, and thats OK for now but it needs to be flagged so someone can go check on why it tripped.

I would not ever trust my life to pushing the stop button and hoping that the thing stays stopped while I climb on it, nor am I going to be climbing on something that mysteriously stopped for no obvious reason. Its not nice to say so, but the guy that gets himself hurt because he did not follow the proper LOTO procedure is the problem (or maybe the company is for letting him be so stupid), not a control system that restarted itself after a legitimate fault recovery procedure.
 
Status
Not open for further replies.
Top