# Motor Overloads



## TheRick (Apr 13, 2008)

Where are your motor OL contacts wired in?

At the last plant I worked in we moved all of our motor OL block contacts from the neutral, to the "hot" side of the control circuit. The hard-wired functionality was the same, we wired the OL contacts in series with the secondary fuse of the control transformer. The big advantage was that we then took this point back to the PLC as an input. 

The PLC input serves 2 functions; first it opens the rung in the logic in the event of an OL, and it provides indication to the control room operator as to why a motor has shut down. The second feature greatly reduces troubleshooting time and errors, especially on the night shift when the most competent help is not always in the plant. 

Does anyone else do this?


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## wirenut1110 (Feb 12, 2008)

Don't do it but it's a great idea.:thumbsup: I've only done something similar for phase monitors.


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## InControl (Mar 20, 2007)

Opening the hot seems to be the trend as machinery gets 'smarter'. Then again, I hardly see any new macines with contactors anymore. All the new stuff I see have VFD's.

When I see a contactor with the OL's opening the neutral, I think "old school". :rockon:


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## TheRick (Apr 13, 2008)

InControl said:


> When I see a contactor with the OL's opening the neutral, I think "old school". :rockon:


 
:laughing: 
Yeah...my thought exactly, I just wasn't sure what everyone else was doing.


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## randomkiller (Sep 28, 2007)

The only time we would run ol's and a control fuse to a PLC input is when it's a low voltage control circuit.


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## TheRick (Apr 13, 2008)

We bring everything back to the PLC; Control Power, OL, Test Switch position, Local Disconnect Auxilliary Contact, and Auxilliary Contact of the Motor Starter.

This gives our control room operator great feedback as to what is going on out in the plant, and reduces downtime. When something shuts down the operator knows why instantly. :thumbsup:


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## randomkiller (Sep 28, 2007)

TheRick said:


> We bring everything back to the PLC; Control Power, OL, Test Switch position, Local Disconnect Auxilliary Contact, and Auxilliary Contact of the Motor Starter.
> 
> This gives our control room operator great feedback as to what is going on out in the plant, and reduces downtime. When something shuts down the operator knows why instantly. :thumbsup:


 
I don't see why you would bring a local disconnect aux. contact into the PLC, unless the PLC has a seperate power source which is rarely the case in any we install. I don't like the thought of any power coming back in that is higher than 24v either, you could give someone troubleshooting a nice surprise.


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## TheRick (Apr 13, 2008)

randomkiller said:


> I don't see why you would bring a local disconnect aux. contact into the PLC, unless the PLC has a seperate power source which is rarely the case in any we install. I don't like the thought of any power coming back in that is higher than 24v either, you could give someone troubleshooting a nice surprise.


Actually anyone troubleshooting our system would be more surprised by a 24V input.

ALL of our I/O is 120VAC. Inputs such as the local disconnect are fed from the control power, along with motion sensing, limit switches etc. and all come back to the PLC as 120VAC inputs. Our PLCs are fed with "Clean Power" from an isolation transformer.

A local disconnect input can save time...when attempting to start a motor or process, the control room operator knows just by viewing his RsView control screen if a local disconect is open. With the 1,000+ motors and acres of plant, indications like this are very valuable.


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## 5volts (Jan 11, 2008)

TheRick said:


> Where are your motor OL contacts wired in?
> 
> At the last plant I worked in we moved all of our motor OL block contacts from the neutral, to the "hot" side of the control circuit. The hard-wired functionality was the same, we wired the OL contacts in series with the secondary fuse of the control transformer. The big advantage was that we then took this point back to the PLC as an input.
> 
> ...


 
"New School way"
For are new installations the overload contact is wired as a hot and we do send a input back from a aux contact to the PLC for a Alarm at the HMI and it will read _motor overload faulted with a detailed description_. Not many though pretty much everythings on a VFD now. 

"The Old School way"
In the PLC we programmed Motor start check Logic. We program a Timer and wire a Aux contact back to the PLC. Even though the overloads still open the neutral we will still get a alarm. If the aux contact didn't change states when the PLC gave the mag a output to run and the timer times out. We get a Alarm _motor failed to start with a detailed description._

In our plant we have large "scoreboards" mounted all over the production floor. The current alarms are listed by priority and area. We also have HMIs mounted to every machine listing the alarms as well. 


.


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## eddy current (Feb 28, 2009)

In Canada it's code to put the O/L on the hot if the control voltage is obtained from a grounded system so that an accidental ground in the control wiring will not start the motor or prevent it from stopping.
CEC 28-506


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## machasman (Mar 10, 2009)

we wire our overloads across the neutral, we use the NO contact with PLC voltage across it, starter drops out, contacts close=alarm 

Until I started at the plant however I was never in favor of opening the neutral


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