# Motor Controls for Dummies



## glen1971 (Oct 10, 2012)

The stops are in series because they are a normally closed switch. When you push the button, the switch opens, and the circuit is de-energized..

The starts are in parallel because they are a normally open switch. When you push the button, the switch closes and you complete the circuit. To draw it, typically at the bottom of all the start buttons is a set of contacts from the starter. These are referred to as "holding contacts" or "sealing contacts". Once the starter coil is energized from a start button, these contacts close and keep the circuit energized. If a stop button, or other control device, opens the circuit, the starter coil is de-energized and the motor stops. Once the stop button is released, the motor is still stopped because of there is nothing completing the circuit past the start switches.. On your starter, these contacts are on the right side..

The neutral has to end up at the other side of the coil. Older starters used to have the overload contact(s) between the coil and the neutral. Newer starters have the overload contact in the line side, before the control. On your starter, the overloads are ahead of the stop button. The upper left red wire goes to the common on the overload relay (second terminal from the left at the bottom). The overload then goes from the left most bottom terminal to the stop button. 

On your starter, you can just see the neutral in the back of the starter on the coil.


----------



## macmikeman (Jan 23, 2007)

glen1971 said:


> The stops are in series because they are a normally closed switch. When you push the button, the switch opens, and the circuit is de-energized..
> 
> The starts are in parallel because they are a normally open switch. When you push the button, the switch closes and you complete the circuit. To draw it, typically at the bottom of all the start buttons is a set of contacts from the starter. These are referred to as "holding contacts" or "sealing contacts". Once the starter coil is energized from a start button, these contacts close and keep the circuit energized. If a stop button, or other control device, opens the circuit, the starter coil is de-energized and the motor stops. Once the stop button is released, the motor is still stopped because of there is nothing completing the circuit past the start switches..
> 
> The neutral has to end up at the other side of the coil. *Older starters used to have the overload contact(s) between the coil and the neutral. Newer starters have the overload contact in the line side, before the control.*


They used to always tell us that was a bad idea. I don't remember why now.


----------



## glen1971 (Oct 10, 2012)

macmikeman said:


> They used to always tell us that was a bad idea. I don't remember why now.


I thought I heard it had to do with the older overload relays failing and the contacts being in the "closed" state. I've seen some older ones, from the "Vintage Equipment" era (1960's ish) fail and they have all failed open..


----------



## boot (Mar 1, 2013)

Okay, so what I'm mistakenly calling aux contacts are actually called sealing contacts. So, IIUC the red wire coming off the coil into the top of the sealing contacts has nothing to do with powering the sealing contacts, the sealing contacts turn on at the same time as the coil, that wire is just permitting power to run back in through the other direction to keep the coil on?


----------



## boot (Mar 1, 2013)

Is an overload relay the same thing as a heater? I think that function makes sense to me, when it's triggered its like someone pressed the stop button, right?


----------



## JRaef (Mar 23, 2009)

Here's an animated diagram of what's called "3 wire control" of a motor starter. A starter is just a contactor + OL relay. This might help you grasp the operating principal.









In this diagram, M is the contactor, Ma is the aux contact attached to the contactor, driven by the same armature as the main contacts. OL is the *O*ver *L*oad relay that is attached to the contactor, aka "heaters", because there really are little heaters inside (although a solid state version is getting more common) that react to the motor current in the same way as the motor does. So too much current would overheat the motor, but it also heats up the heaters and they "bend" to trip a latched mechanism and release the contact that drops out power to the coil.

Technically, Ma are "Auxiliary contacts", the way they are USED in this scheme is called a "Seal-In" circuit.

Yes, often times the neutral wire to the coil is out of sight on starters, it gets buried by other components but if you took it out of the can and moved it around in your hands you could see it and follow it.

Also note that in this example, they are using the Line voltage as the coil voltage, something that used to be common but not so much any more. It's now mostly 120V control and in smaller more dense cabinets, 24VDC is getting used a lot too.


----------



## JRaef (Mar 23, 2009)

macmikeman said:


> They used to always tell us that was a bad idea. I don't remember why now.


In the olden days, OL relays were three (or even just two if you go back far enough) SEPARATE devices, each with their own set of NC contacts. So the NC contacts had to be wired in series with the coil for it to function. You can still occasionally see it depicted that way in old drawing standards. 
Example:








That meant either running those extra wires in the field, or the factory doing it before it shipped. Starter mfrs began shipping them pre-wired from the factory, but because people in the field used them differently, meaning either line voltage or separate voltage source, the only common place to put them that made sense was between the coil and the second connection, be it another line or the neutral. That was the standard for decades and in the 80s when people started coming out with new OL relays that were all one piece with only one common NC contact, it was just left that way out of convention; it's just what people were used to in North America. 

But then in the 90s when IEC starters came flooding in, that concept was actually against IEC codes, which required to OL contact to be on the LINE side of the coil. They never had separate OL relays like we did, so they standardized on the easier approach from the outset. The way it stands now it, whatever floats your boat is OK.


----------



## Bird dog (Oct 27, 2015)

Do some motors still have thermo discs which are the two red wires in the motor J-box?


----------



## bill39 (Sep 4, 2009)

Many electricians’ biggest difficulty with motor controls is just being able to correlate the wiring diagram to the actual termination points on the motor starter. Can’t find the coil, OL’s, etc.


----------



## micromind (Aug 11, 2007)

Bird dog said:


> Do some motors still have thermo discs which are the two red wires in the motor J-box?


A lot of Lesson 3Ø steel frame do, 1HP - 10HP. I don't know of any others though. 

Some of their 3Ø fan and blower motors have built-in auto-reset O/Ls that break the lines, not just a pilot device.


----------



## glen1971 (Oct 10, 2012)

Bird dog said:


> Do some motors still have thermo discs which are the two red wires in the motor J-box?


Thermisters? I've seen lots with them and none connected... I'm sure they are some where, just no where I've been..


----------



## glen1971 (Oct 10, 2012)

boot said:


> Okay, so what I'm mistakenly calling aux contacts are actually called sealing contacts. So, IIUC the red wire coming off the coil into the top of the sealing contacts has nothing to do with powering the sealing contacts, the sealing contacts turn on at the same time as the coil, that wire is just permitting power to run back in through the other direction to keep the coil on?


Sorta, but not really.. They are auxiliary contacts on the starter and their purpose in the control scheme is as a sealing contact.

Yes you followed the wire correctly, but your "flow direction" is a little off.. Or maybe I'm reading it wrong.. If you were to follow it on JRaef's animated picture, the voltage would go thru the stop button(s), to the start switches and sealing contact. Once the start button is pushed and released, the flow would be thru the auxiliary contacts, which are now closed, and to the "red wire" you traced and to the coil.


----------



## splatz (May 23, 2015)

boot said:


> Google said wire remote stop switch in series , start switch in parallel. I'll save you the minutiea of what wire I hooked where, but doing this worked . I just wish I understood why !


Rather than give a really good answer like those above, I am going to cherry pick and speak to the easiest part of your questions. 

I think of a relay as a switch that's operated by a switch. You energize the coil rather than flicking the lever or pushing a button. In this way relays are like momentary switches - momentary switches only stay in position as long as you keep pushing the button, relays only stay in position as long as the coil is energized.* 

A contactor is just a bigger relay, and a motor starter is a contactor with overload protection. 

I associate "parallel" with "OR" and "series" with "AND" in my head. This is the fundamental principle of relay controls. It is also the basis of digital logic. 

If you wire a bunch of switches in series, the circuit is closed if switch one is closed, AND switch two is closed, AND switch three is closed, etc. This is how you want safety switches to work, if any one of them is opened, the circuit is opened. So you can hit any e-stop, it opens the circuit, and it stops. (Remember that the normal position for an e-stop is CLOSED.) 

If you wire a bunch of switches in parallel, the circuit is closed if switch one is closed, OR switch two is closed, OR switch three is closed, etc. This is how you want the start switches to work, if they are all open, and you close any one of them, the circuit is closed. So you can hit any start button and it starts. 

So if your stops are in series, and your starts are in parallel, then all the stops have to be closed and any one of the starts has to be closed to energize the coil of the starter. 

*This part isn't 100% accurate; there are latching relays, where when you send the coil a pulse, it toggles position, and stays there until the next pulse. There are also latching circuits, in which the relay is wired so the coil stays energized after momentarily closing a switch. When you get to it you can look at some start-stop-jog circuits. But one thing at a time.


----------



## paulengr (Oct 8, 2017)

glen1971 said:


> Thermisters? I've seen lots with them and none connected... I'm sure they are some where, just no where I've been..


There are thermal switches, centrifugal switches, RTDs, thermcouples, and heaters that you might find in even a small motor. Thermal switches are basically small sensors buried in the windings (and there can be multiples...the most I've seen is 12) that are either normally open or normally closed (normally closed is the most common variety because it's easy for control wiring) that trigger if the motor windings reach a critical temperature where damage can occur. This is VASTLYsuperior to the standard overload relay because an overload relay is attempting to simulate conditions inside the motor and prevent damage as opposed to directly measuring it. The downside of thermal switches is if one goes bad, there's nothing you can do to repair it short of rewinding the motor. They are relatively rugged though so its a good idea to use it if you have it. With a working thermal switch you can actually push a motor closer to its thermal limits without fear of damage.

RTD's are similar in nature except that it is an analog signal (a resistor that changes with temperature). They are extremely accurate but also extremely fragile. Their reliability is significantly less than the motor. Typically you see 6 or more because everyone knows that a lot of failures are going to happen and again...not much you can do once they fail, RTD readers frequently have short/open detection and best 2 out of 3 type logic to ignore when a few fail, so this is a little better option compared to thermal switches. RTDs are common on larger motors but for obvious reasons also commonly not hooked up. Many plants want the best protection that money can buy and quickly find with RTDs that protection is not the same as reliability so often they order the motor with them and then quickly abandon them.

Thermocouples are the same idea as RTD's but since it is literally two pieces of wire that are welded together, they are much more rugged. Thermcouples also often are sitting in thermowells that have the classic "cobrahead" terminal box on the outside and can be extracted and replaced even with a running motor. The tradeoff is that the output is nonlinear so accuracy is not quite as good as RTDs but most people don't need 0.01 degree measurement accuracy either, and the thermal well slows down the response speed to where they are best for long term overload conditions and detecting hot spots in the motor. These are comparatively rare of motors. Motor shops will fight you on trying to put in RTDs instead of thermocouples because they are rare and not typically used but if you must use thermal sensors, these are the way to go.

Heaters are just strip heaters inside the motor that keep moisture down when the motor is offline, particularly larger and higher voltage motors where this is critical. They are often 220 V but can be any voltage. Often they don't work all that well. A common trick on DC motors is simply to energize the fields at a reduced voltage and use the field windings as the heaters. Same thing is a common option on AC VFD"s and I've sen it in some AC starter circuits where they put say 120 V in series with a current limiting resistor on a 4160 V motor. Strip heaters are relatively rugged and usually installed in pairs or more, in series or parallel or a mix. Technically motor heating is important but it depends on the conditions in the plant and its another thing to troubleshoot/fail so again they rarely get hooked up, particularly if the plant uses the "motor as a heater" approach and no longer needs them. Mining companies often ignore them too for reliability reasons even though obviously their environments are what the heaters are meant for. Again they get ordered and then quickly removed when they cause more trouble than they save.

Centrifugal switches are on single phase motors. They are used in capacitor start/run circuits particularly integrated circuits. But they are notoriously unreliable. Modern starters use a voltage triggered relay (potential relay) that works off the motor counter EMF to disconnect the start capacitor often with a backup timer. These are more reliable so motors sometimes come with centrifugal switches but they don't get used. I don't remember the last time I saw one actually used. So this is a common set of leads on a single phase motor that gets ignored for good reason. They are often maybe the third or fourth item on a list of common troubleshooting items.

That's just a quick rundown of some of the "extra" wires you may see inside a motor. Obviously you don't "need" any of these to make the motor run but there are definitely cases where its more than a good idea. For example with submersible motors it is virtually impossible to protect the motor with overload relays because they have ports through them where they are water cooled. Under normal conditions they cool so well that an overload would have to be set up for some crazy condition that would never work for air cooled motors. But if something happens and the pump plugs up, the motor will be destroyed even under normal operating conditions. Thermal switches or temperature sensors in submersible motors are not just a good idea..they are the only proper way to protect the motor.

EASA publishes a book of what all the wiring numbers and symbols mean for identification, commonly called an "Uglies" book but its not the same as that book. Motor shops often buy them by the case and give them away. I use them myself when I'm wiring up a rare motor, and I keep a half dozen in the truck to give away.

Sent from my SM-T350 using Tapatalk


----------



## telsa (May 22, 2015)

bill39 said:


> Many electricians’ biggest difficulty with motor controls is just being able to correlate the wiring diagram to the actual termination points on the motor starter. Can’t find the coil, OL’s, etc.


This is the nub.

The schematics are drafted to be easy to logically comprehend what goes to what.

But, the mechanical linkages are omitted. 

So a noob tech is left scratching his head as why M and Ma have anything to do with each other. In fact, where is Ma in the first place ?

They also don't make it idiot obvious which control linkages have been wired by the factory -- with this or that lug// connection point right up, out in the open -- begging for your field connection.


----------



## boot (Mar 1, 2013)

Thanks for all the replies guys. Its really awesome having access to such a wealth of experienced and knowledged individuals. I admit, it's easier for me to follow some of the simpler responses, as they're triggering my memories of taking my old motor control class. 

Obviously some of these controllers can get pretty sophisticated, but I take it the one in my photo is pretty run of the mill? I feel like it's starting to make sense. Like the first time I figured out a 3 way switch, or simpler yet, a switch loop. Challenge yourself incrementally, it gets easier and easier. I'm just a little bummed that in my current job doing resi I won't get to Branch out and learn more, it's really interesting stuff.


----------



## paulengr (Oct 8, 2017)

boot said:


> Thanks for all the replies guys. Its really awesome having access to such a wealth of experienced and knowledged individuals. I admit, it's easier for me to follow some of the simpler responses, as they're triggering my memories of taking my old motor control class.
> 
> Obviously some of these controllers can get pretty sophisticated, but I take it the one in my photo is pretty run of the mill? I feel like it's starting to make sense. Like the first time I figured out a 3 way switch, or simpler yet, a switch loop. Challenge yourself incrementally, it gets easier and easier. I'm just a little bummed that in my current job doing resi I won't get to Branch out and learn more, it's really interesting stuff.


Industrial pays better but the hours suck. And because the major skill sets are more metalworking as far as installs and mire controls oriented like HVAC, they avoid hiring residential/commercial.

Splitting the middle is HVAC and pumps/wells. More controls but it's just simple starters and maybe a drive once in a while. So once you get past the learning curve which believe me is pretty steep, its worth it. No crawling under houses and in attics with pumps and wells but they are more dirty and if you do waste water, smell bad. Margins are way better too with both of them and since equipment costs are in the thousands instead of tens of dollars, charging 10-15% on materials is often more profit than you make on labor unlike residential electrical work where it's all in the labor, and it's more specialized so the labor rates you can charge are often 2-3 times higher but that's just icing on the cake.

Sent from my SM-T350 using Tapatalk


----------



## John Valdes (May 17, 2007)

boot said:


> Thanks for all the replies guys. Its really awesome having access to such a wealth of experienced and knowledged individuals. I admit, it's easier for me to follow some of the simpler responses, as they're triggering my memories of taking my old motor control class.
> 
> Obviously some of these controllers can get pretty sophisticated, but I take it the one in my photo is pretty run of the mill? I feel like it's starting to make sense. Like the first time I figured out a 3 way switch, or simpler yet, a switch loop. Challenge yourself incrementally, it gets easier and easier. I'm just a little bummed that in my current job doing resi I won't get to Branch out and learn more, it's really interesting stuff.


What helped me most was having to draw it out on paper. Then take the drawing to the task/job.
You mentioned start and stop. 

Here's your homework:

Draw a start, stop station using momentary contacts (push buttons) to start a simple motor. (you have already been given your drawing in this thread)
*Then add a jog function to that same scheme.*
Put a number on each wire as you will have to do this in the real world.


----------



## splatz (May 23, 2015)

John Valdes said:


> Here's your homework:
> 
> Draw a start, stop station using momentary contacts (push buttons) to start a simple motor. (you have already been given your drawing in this thread)
> *Then add a jog function to that same scheme.*
> Put a number on each wire as you will have to do this in the real world.


The start - stop - jog circuit is really great to learn, once you understand that you have a pretty good grasp of controls, but you might want to work up to that one


----------



## boot (Mar 1, 2013)

Actually , the moment I got out of work that day I was trying to draw up what I had done to make it work. 

I guess it makes sense that the commercial / resi guys don't see a lot of it. You'd have to be part of a really large outfit with multiple divisions I would imagine in order to be exposed to all types of electrical work within the same company . I've only ever worked for small companies. Submitted resumes to the big industrial contractors in the past, full disclosure that I didn't have industrial experience , but not even get a call back . I even considered working a lesser wage until I proved myself. 

I suppose the best thing I can do is challenge myself in a hobbyist fashion , so I'm always ready for the occasional foray into this scene. This encounter was happenstance , contractor we do resi for wanted work done in his large wood / cabinet building shop.

He's also interested in automating his dust collector at some point. So maybe current sensors are on the map, which means at some point I'll be back inside that control box !

We did a jog circuit in school, but I forget what it is. I'll look it up again


----------



## gnuuser (Jan 13, 2013)

it helps a lot if you understand that in an mcc cabinet no matter how many starter/contactors there are they are individual systems, an "e" stop system will control cr1 or the master control relay! this relay provides control power to the rest of the system (in some cases 110 volt but in most cases 24 volt ) (usually controlled by prox switches, photo eyes, limit switches, and plc/slc).

"e"stops are wired in series forming a complete loop if any switch is depressed it breaks the control circuit and equipment cannot be started because control voltage is not there, and can only be started when the switch is pulled out or reset.
you can have multiple "e" stops providing they are wired in series.
(they use the normally closed contacts)
wiring start switches are done in parallel and use the normally open contacts
so you can start from any button (if the equipment can be configured for it)


----------



## telsa (May 22, 2015)

Go to eBay and purchase second-hand #2 contactors and such -- especially stuff from different eras.

The key to #2 and larger contactors: too big for any non-industrial motor -- so they sell for a SONG.

The old ( 1950-1970 ) era contactors really go for peanuts.

They are actually fun to mess with. Everything is large -- but not huge.

Forget about actually using them to pass a load.

Instead use them as a study platform for how contactors are wired from a controls point of view.

BTW, expect the ancient ones to use L1--L2 as the coil voltage. 

So, limit yourself to 208/240 coil voltages.

Hint, 480VAC motors really didn't take off until the 1960s. ( Modest sizes )

That's why half-a-century ago contactors ended up being so huge. 

They were passing a LOT of amps to get the HP up.

( Many, many, customers were locked into 208Y120VAC or 240VAC delta Services. )

That really put the kibosh on 480VAC motors.

It took CONGRESS to really shift this. 

Congress pushed 480Y277VAC Services... part and parcel of the Energy Crisis -- all those years ago.

With the 'advice' of the NEMA players.


----------



## gnuuser (Jan 13, 2013)

boot said:


> Actually , the moment I got out of work that day I was trying to draw up what I had done to make it work.
> 
> I guess it makes sense that the commercial / resi guys don't see a lot of it. You'd have to be part of a really large outfit with multiple divisions I would imagine in order to be exposed to all types of electrical work within the same company . I've only ever worked for small companies. Submitted resumes to the big industrial contractors in the past, full disclosure that I didn't have industrial experience , but not even get a call back . I even considered working a lesser wage until I proved myself.
> 
> ...


you can build yourself a play board using some parts (switches, relays, lamps or buzzers and probably photo eyes, Its not hard to experiment with and an easy way to test your design before putting them into operation on production equipment.

a good thing to check into is the CIE bookstore Plc/Slc course with the hardware lab. you will learn to program a plc and will have a variety of parts to play with 

http://www.ciebookstore.com/search?q=plc

although its a bit pricey its worth it.


----------



## frenchelectrican (Mar 15, 2007)

John Valdes said:


> What helped me most was having to draw it out on paper. Then take the drawing to the task/job.
> You mentioned start and stop.
> 
> Here's your homework:
> ...


This is one of my favor subject I teach the greenhorns about the motor control circuits .,

But I add a addtional twist is have *forward jog and reverse jog * function and once a while I will throw something else in the mix is multi speed motors but I dont tell them what is the sequince so they have to give me two ways on that.,, 

That part they will learn it in hard way and once they understand it then rest will be pretty easy to figure it out in hurry.


----------

