Auxiliary contacts

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liquidtite

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Ny
I'll be starting doing industrial work on a few weeks so my friend let me borrow a motor controll book.

Started to read about contractors and motor starters ,

It shows a pic of a contractor with auxiliary contacts on it and says auxiliary contacts

May be added to a contractor to form an electrical holding circuit .


In the line diagram it shows stop and start puch buttons

Controlling a starter , the aux contacts are in series with the start button

I don't understand what aux contacts do could someone explain some senerios were u would use

Aux contacts and are their only normally open or do they also make nc auxiliary contacts aswell


and say if you have a norm open push button when you manually puch it does it go back to norm open
when your finger comes off button
 
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Little Bill

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Tennessee NEC:2017
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Semi-Retired Electrician
Aux contacts are "dry" contacts and yes, they make both NO & NC contacts.

One application would be like your start & stop button. When you push the momentary start button the NO Aux contact will close and keep the circuit closed (on or functioning).
The circuit opens when you push the stop button. The Aux contact is connecting a latching relay. So as long as current is there (contact closed) the relay remains latched. As soon as you push the stop button the current stops and the NO contact goes back to the NO state.

I'm not a controls expert and may use the wrong terminology but I've worked on them plenty and hopefully explained it so you can understand.

Edit to add: I found a diagram that will help with my explanation.

In the top portion The "forward " would be the start button, the M1 is the aux contact, and the M2 is the stop button
When the "forward" button is pushed M1 aux latches in and the motor runs in forward. It will only stop when the stop button is pushed.
I won't go into the reverse function as you can figure that out.

04061.png
 
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iwire

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Location
Massachusetts
I don't understand what aux contacts do could someone explain some senerios were u would use

In this case once a person pushes the start button the contactor and the aux contact will close. Now when you let go of the start button the contactor and aux contact stay closed because the closed aux switch keeps power flowing until you hit the stop button.
 

Cow

Senior Member
Location
Eastern Oregon
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Electrician
One of the best things for you to do might be to grab a 6' appliance whip, a 2 hole pushbutton enclosure with a start and stop button, and a motor starter with a 120v coil. Wire it up and operate it until it makes sense in your mind. Then you can move onto timers, alternating relays, jogs, etc.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
I'll be starting doing industrial work on a few weeks so my friend let me borrow a motor controll book.

Started to read about contractors and motor starters ,

It shows a pic of a contractor with auxiliary contacts on it and says auxiliary contacts

May be added to a contractor to form an electrical holding circuit .


In the line diagram it shows stop and start puch buttons

Controlling a starter , the aux contacts are in series with the start button

I don't understand what aux contacts do could someone explain some senerios were u would use

Aux contacts and are their only normally open or do they also make nc auxiliary contacts aswell


and say if you have a norm open push button when you manually puch it does it go back to norm open
when your finger comes off button

Good luck. first and answer that was sort of answered above. Normally open only tells part of the picture. It is either a momentary, or a maintained contact. In the case of the motor circuit, all of the contacts are momentary.

My suggestion is to make sure you don't over complicate things. If you look at one step at a time you will eventually grasp the bigger picture. Bill's diagram is a good place to start. Look at it as a puzzle. Picture yourself as one electron, you get to start at the beginning, in a ladder schematic this is usually the left side and your goal is to end on the right side. You must stop and "solve" the problem when you come to a barricade. You solve for each rung of the ladder. So you start at L1, run down turn left at the first dot, and stop at "forward".(checking the other rungs, you are stopped at M1, reverse and M2) Now wait and solve. The solution is someone has to push either the forward or the reverse button. When they do, you run through to M2 and must ask, is it ok to run through. This is where it gets a little deeper. M2 is a contact that is controlled by the coil M2, (something you have to know as a convention of schematics) so if M2 is running, the contact is open and you have to wait. If M2 is not running, then you can proceed on through. Once through you run through the M1 coil, causing it to close (if and only if you can get back to L2) and continue. You then come to a point, You can't go right because that is back the way you came. You must go forward. You come to the last puzzle. OL which again you have to know or research to figure out. This is an overload contact that is operated by the overload assembly (either heaters or electronic) that open if the motor runs at too high an amperage for too long. It must be manually reset if it "trips" And now you are home free to L2.

Now you need to start at L1 as the next electron. You follow the same path, but now, the normally open M1 is not open, it is closed because we energized coil M1 on the last pass. so, we go through that rung. I think you should get the idea from here.

Now you get to do the same thing on the other ladder rung.

I love puzzles and I love to solve ladder diagrams. Over time you have to learn a lot, like whether switches are momentary or maintained. Operated by pressure, temperature, flow, etc. Often you start with something that isn't working, and my first step is usually to figure out how it is supposed to work, and then I can usually figure out what will cause it to act like it is currently acting.
 

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
The term "auxiliary" in this context means a set of smaller control rated contacts that change state WITH the main contacts of the contactor (or any switching device). So on a motor starter, the aux contacts on the contactor portion are driven by the same plunger as the main power contacts, but are intended only for control circuits, not the same power as the main contacts. That typically boils down to 10A. If all of the contacts have the same current rating and are intended for controls only, we call it a "relay", not a "contactor".

On a related side note, now that you are entering the industrial realm, you will need to "train" your spell check system to not auto-correct "contactor" to "contractor". Many of us had to do it at one point or another, the propeller-heads that write spell check software have no idea that there is such a thing as a contactor.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
I'll be starting doing industrial work on a few weeks so my friend let me borrow a motor controll book.

Started to read about contractors and motor starters ,

It shows a pic of a contractor with auxiliary contacts on it and says auxiliary contacts

think of it this way.....

there are two predominant forms of controlling things, static control, and dynamic control.

static controls are PLC's and logic boards.
devices controlled by other logic devices, inputs, and sending outputs to control
dynamic control devices, like motor starters, or output indicators, etc.

dynamic, or moving control, is magnetic relays, and contact switches.

so dynamic control is switches operating coils, and coils operating other switches.

an auxiliary is a switch operated by a magnetic coil of a motor controller.
it can do anything you want it to, and is an isolated contact, so when it opens
and closes, it can control something else, in an isolated fashion, so control voltage
does not backfeed thru a control circuit, and do unwanted things.

static logic on paper, looks similar to dynamic logic, in the form of a ladder diagram,
with one important difference.

rungs on a dynamic control diagram, are continuity paths for control circuit voltage
to flow thru, to operate things.

rungs on a static control diagram, are logic statements, and when everything on
a specific rung is true, you get an output. when it's not true, you don't.

the big advantage is that you can use the same contact out in the field do to or
control a number of things, all separate from each other, without there being
control voltage backfeeds all over the place.

the other big advantage with static logic, is that you assign all the inputs to an
address, and all the outputs to an address, and all the controls are done with
software. you can change and fiddle to your hearts content until you get the
system to do what you want it to do.
 

liquidtite

Senior Member
Location
Ny
Thanks for the knowledge .

so pretty much the aux contacts keep the motor runing in a case were

your using momentary pb and the start button goes back to its norm open state

after your finger is off of button .

so once the coil is energized the dry contacts close and the coil is being feed through the dry contacts witch is by passing the norm open pb


.Once you hit the stop button the coil is de energized with opens up the norm open dry contacts.

So in most cases the coil controlls the dry contacts once the coil is energized the dry contacts

open up.


And so do you have to put a jumper wire from the load of the dry contactor to the coil contact

So once the pb opens up you feed the coil through the dry contacts.
 
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