# Question on proper ladder diagram procedures



## MDShunk (Jan 7, 2007)

In series with the existing nc stop push button.


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## jza (Oct 31, 2009)

MDShunk said:


> In series with the existing nc stop push button.


I figured you'd be the one to answer. Thanks.


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## jza (Oct 31, 2009)

What if I wanted to add a light to be on only when the motor runs, and off in the event that the overloads were to trip, as well as a second light to be on when the motor is off?


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## MDShunk (Jan 7, 2007)

That's typically done with aux contacts snapped on the sides of the coil or with extra contacts sometimes featured on certain overload units.


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## jza (Oct 31, 2009)

MDShunk said:


> That's typically done with aux contacts snapped on the sides of the coil or with extra contacts sometimes featured on certain overload units.


That much I know. But I'm not sure how to draw it out.


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## MDShunk (Jan 7, 2007)

I'm just on my phone. Someone else will need to jump in


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## jza (Oct 31, 2009)

Could I place the overloads before the motor instead of after it, and put the light in parallel with the motor? I would however prefer to leave the overloads "after" the motor.


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## jza (Oct 31, 2009)

Does this make sense?


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## jza (Oct 31, 2009)

Meant to mark R1 next to the N/O and N/C contacts, rungs 2 and 3.


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## bigdan1 (Jun 16, 2013)

I would just have two new rungs from L1 to L2. One with a normal open contact and the run light. The other with a normally closed contact and the stop light.


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## dronai (Apr 11, 2011)

Your last drawing looks right on post 10


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## jza (Oct 31, 2009)

dronai said:


> Your last drawing looks right on post 10


Thanks guys. Got a few more of these to work on. May need more insight.


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## don_resqcapt19 (Jul 18, 2010)

None of the drawings tell you if the overloads are tripped. Many overloads have a NO contact that closes when they trip that you can use to indicate a tripped overload. If you don't have that you can make something with a relay and an additional NC contact on the starter. 

One side of the relay coil would be connected to the left side of the starter coil, the other side of the relay coil would be connected to the neutral. You would use a NO open contact on the relay to "seal-in" the relay. This contact would get its power from the wire between the start and stop buttons and connect to the relay coil. This will keep the relay pulled in when the starter coil drops out because the overload has tripped.

Power would be taken through NO contact on the relay and through a NC contact on the starter and then to the light. This light would only be on if the starter was being told to be on and the overload was tripped.


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## lefleuron (May 22, 2010)

Put your green light in parallel around your M coil, just like you did the "holding" or "latching" cantact around your start button.

Your red light is fine.

In other words, the green light is wired between A1 and A2. Save you a set of contacts.


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## jza (Oct 31, 2009)

If I wanted to change this to having no voltage protection, aka if there's loss of utility supply the motor would return to whatever state it was in once it is re-energized, would it be as simple as replacing the pushbuttons with switches?


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## pudge565 (Dec 8, 2007)

jza said:


> If I wanted to change this to having no voltage protection, aka if there's loss of utility supply the motor would return to whatever state it was in once it is re-energized, would it be as simple as replacing the pushbuttons with switches?


Yes you would use a two wire control vs a three wire. A manual motor starter would serve that purpose.

ETA: the two wire control could be anything though, a float switch, pressure switch, limit switch, etc.


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## jza (Oct 31, 2009)

pudge565 said:


> Yes you would use a two wire control vs a three wire. A manual motor starter would serve that purpose.


Don't quite understand what you mean.


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## pudge565 (Dec 8, 2007)

jza said:


> Don't quite understand what you mean.


http://support.automation.siemens.c...objaction=csview&extranet=standard&viewreg=IT


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## jza (Oct 31, 2009)

Thank you.


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## don_resqcapt19 (Jul 18, 2010)

You have to be careful with auto-restart equipment if the unexpected restart could be a safety hazard.

This SquareD book has lots of control circuit information.


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## Handasee (Dec 18, 2009)

Your original title or thread was: "Question on proper ladder diagram procedures"
Ladder diagrams usually refer to PLC controls.
What you are showing is a schematic diagram.


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## EBFD6 (Aug 17, 2008)

Handasee said:


> Your original title or thread was: "Question on proper ladder diagram procedures"
> Ladder diagrams usually refer to PLC controls.
> What you are showing is a schematic diagram.


What he is showing is a ladder diagram. You are correct that ladder diagrams are also used in plc controls, but ladder diagrams were around long before plc's were invented. A schematic diagram is different than a ladder diagram in that all the components are shown "in order" in the circuit. Basically, a schematic diagram essentially allows you to physically follow the circuit on paper.


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## Handasee (Dec 18, 2009)

EBFD6 said:


> What he is showing is a ladder diagram. You are correct that ladder diagrams are also used in plc controls, but ladder diagrams were around long before plc's were invented. A schematic diagram is different than a ladder diagram in that all the components are shown "in order" in the circuit. Basically, a schematic diagram essentially allows you to physically follow the circuit on paper.


I stand corrected. Made the distinction with my first PLC (Westinghouse PC-1100) and changed my vocabulary, but you are right.


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## oldtimer (Jun 10, 2010)

don_resqcapt19 said:


> You have to be careful with auto-restart equipment if the unexpected restart could be a safety hazard.
> 
> This SquareD book has lots of control circuit information.


 
Is a hard copy of The Square D Book available ?

Where ?


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## don_resqcapt19 (Jul 18, 2010)

oldtimer said:


> Is a hard copy of The Square D Book available ?
> 
> Where ?


I had one years ago, but have not seen it in a long time. Not sure if they still have hard copies.


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## JRaef (Mar 23, 2009)

Handasee said:


> I stand corrected. Made the distinction with my first PLC (Westinghouse PC-1100) and changed my vocabulary, but you are right.


Man, do I feel older now...

When I first got into PLCs, they did NOT program in "ladder", it was something more akin to Boolean Logic statement programming done not on a "personal computer" because they did not yet exist, but rather on a relatively gigantic "Programming Terminal". A program looked sort of like this:

Sequence 01
Not I01
Or Not I02
And I03
Or Q01
And Not I04
Equals Q01

Sequence 02
Not M01 
Equals Q02

Sequence 03
And M01
Equals Q03

This by the way is the above ladder diagram, with the addition of the OL relay aux contact (I04), in Boolean.

But because most electricians were NOT trained in Boolean logic, there were problems with expecting them to maintain equipment. So about 9-10 years AFTER the initial release of what became PLCs (PLC was specific to Allen Bradley originally), a couple of smart guys released programming SOFTWARE that allowed the programs to be DISPLAYED and later created in ladder format. That way when the guy trouble shooting it would look at a printout, it made sense to him based on his previous experience with relay ladder logic. If I recall correctly, Ladder Logic programming was not available or reliable intil maybe around 1979 or 1980, whereas the first "Sequential Machine Controller" from Modicon came out in I think 1970, and the first A-B PLC came out in 1973 or so. Don't quote me on the dates though, it's just coming out of my head.


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