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How to draw a 2-position selector switch and its contacts? (IEC world)
4

How to draw a 2-position selector switch and its contacts? (IEC world)

How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)
Hi,

I would like your opinion on how to correctly draw a 2-position selector-switch (Hand-Automatic) under "IEC world". Should I draw both contacts opened and the switch neither in "H" nor "A"?

Both contacts themselves should be purchased "normal open" (NO) but one must be placed in such a way that it closes when the selector switch is in "H" and the other that should close when it is in "A"

Please see attached example

Thanks!

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Can't say if this is IEC or not but it's the only easily understandable panel-twist-switch symbol I've ever seen. It's also easily extendable to multi-position and to more than 2 contacts. You can just keep stacking them up. Multiple positions (more than 3) are easily accommodated.

The dotted line shows the switch position associated with the contact that closes in that switch position. Note that you can actually have a drum switch where an operator position actuates several separate contacts at once by adding more "x"s where needed.




Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

The AutoCAD Electrical library has example IEC symbols that can be found here. Don't forget to add the second contact.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

In xnuke's link try an HSS122R above an HSS21.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)
Hi,

Keith: I agree, that drawing is easily understandable but i should use IEC symbols

xnuke & waross: The "problem" I am facing is that both contacts should be "normal open" BUT operates in different positions of the selector switch, that's what i do not know how to draw

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

How can both contacts be normally open on a two-position switch? If there is a toggle position where neither deck is closed, like in a hand-off-auto switch or in a raise/lower spring-return-to-center switch used in generator control, it's a three-position switch.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)
Hi xnuke,

Agree with you. In one position, one contact will be open while the other closed, and vice versa.

The thing is that a colleage argue me that if I draw one contact NO and the other NC, someone may purchase a "2 position stay put selector switch with 1NC+1NO", and he should purchase 2 NO contacts (See an example on the link below, where it says: "Contacts type and composition 2 NO")

Link: https://www.schneider-electric.com/en/product/down...

Thank you!

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Multipole selectors are one of the places where the IEC symbology is awful. I acknowledge that the IEC symbology is very comprehensive, with early and late break / make contacts being available, but the techs hate the symbols and struggle to follow them. A drawing which confuses people and leads to mistakes is not a successful drawing, even if it is technically correct.

I admit to using the older British Standard on drawings which otherwise follow the IEC convention because the IEC symbology is so confusing on complex switches. Example BS symbol shown below - a square indicates that the path is closed when the switch is in that position. The symbol readily expands to accommodate multiple switch positions and multiple poles, and easily accommodates contact closures in multiple positions.


RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)
Hi Scotty,

Quote (ScottyUK)

A drawing which confuses people and leads to mistakes is not a successful drawing, even if it is technically correct.
Agree with that.


I really like the way of drawing selector switches in the example that you showed but I confess that I'm still in the struggle of wanting to draw my schematics 100% according to IEC standard (Anyway, I feel that it is a meaningless struggle haha)

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Please note that the data sheet says "Operator position information: 3 positions +/- 45°. This is a three-position switch, and should be drawn as such. I'd recommend following Eaton's guidance in here at the bottom of page 4 in the right column. It shows the toggle selected to the center off position, with the contact in the corresponding center open position, and the two positions of both toggle and contacts where the switch will be shut as the selector toggle moves. You may want to consider adding the columns of the table shown there for clarification, but not the "Letter symbol" column - that's there for the NEMA symbol, not the IEC symbol.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)

Quote (xnuke)

This is a three-position switch, and should be drawn as such.

And how can I differentiate this from a 3-position-stay-put switch? (For a "Hand-Off-Automatic" application)

I also need to draw that on another drawing lol

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

ON-OFF-AUTO are ALWAYS ON1-OFF-ON2. That there are two N.O. switches is totally normal. One typically turns ON something like a PUMP directly and the other position turns ON a signal to a controller allowing it to turn ON the pump when needed.

All the double toggle switches are the same ON-OFF-ON with the center contact the common.

If it is truly a "2 position switch" and not the normal three position switch then nothing changes other than there is no 'middle' detent for the switch to 'maintain'.

But I digress..

Here sire, I believe, is the moronic symbol thy seeketh:


Dashed means 'ON Position'.
Dipping 'V's mean detent.

For a three position you add a vertical dashed line in the 'BIG V' then you add a third Dipping V for the third detent.
Majorly idiotic. Bunch of monkeys in a crayon factory I'm thinking.

Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)

Quote (itsmoked)

If it is truly a "2 position switch" and not the normal three position switch then nothing changes other than there is no 'middle' detent for the switch to 'maintain'

So.. I understand that all that matters is the number of "detents". Interesting

Quote (itsmoked)

But I digress..
That was the original idea of this thread

Quote (itsmoked)

Majorly idiotic. Bunch of monkeys in a crayon factory I'm thinking.
Haha agree. This symbol is completely awful

PS: Although I understand the meaning of drawing the second "NO" contact "mirroring" I find it completely shocking

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

I can well understand a lot of people being shocked, electrocuted too, with these lame symbols. IEC symbolism is so bad that I and several other engineers I know will simply exclude any and all integrated circuit offerings for our designs if they're provided in IEC. Texas Instruments has lost many of our component selections due to the vapid IEC symbols they use. I actually think they've dropped them for saner pastures.


Why "completely shocking"? Note they (freakishly) show the dashed side of their Vs as being the ON position and that mechanically associates with physically shoving the dashed-to-contact in that direction to physically operate it. You can't continue that symbolism without mirroring the contact. But, I only spent about two hours puzzling this mess out. I CADded three other symbols that all failed their byzantine machinations by various details which this did not.

Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)

Quote (itsmoked)

You can't continue that symbolism without mirroring the contact

Some schematics i've seen use a roman numeral next to each contact and next to each position of the selector switch to indicate which contact is associated to each position. Anyway, I think is simplier to mirror some contacts :P

Quote (itsmoked)

I only spent about two hours puzzling this mess out

I've spent like two weeks lol

Thank you for your time and for sharing your point of view!

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Well for many years in the NEMA world we use an operator with a single cam operating a double contact block. The contact block, when mounted to a push button had one set of normally open and one set of normally closed contacts and that is how either a hand/auto switch or a hand/off/auto switch would be drawn.
That was the standard for many years until Switch operators appeared with two normally open contact blocks mounted side by side. A convention that works is to draw the switch shown the first position and show the other one or two positions with dotted lines, Show the contacts in the first position as solid and in the other one or two positions as dotted.
Add a truth table to remove ambiguity.
In the NEMA convention we have, in addition to normally open and normally closed, symbols for "normally open, held closed" and "normally closed, held open"
.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)

Quote (waross)

That was the standard for many years until Switch operators appeared with two normally open contact blocks mounted side by side
Intresting pice of history

Quote (waross)

"normally open, held closed" and "normally closed, held open"
I've been trying to find something like this in IEC world and I couldn't. In fact, that's what I tried to draw in the first picture I attached.

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

On the selector symbol use curved arrows pointing from the held positions toward the position where the switch toggle returns. See the link in my first post for examples. If it returns from both left and right positions to center, draw arrows from left to center and right to center.

Now, it's time you attempt to draw it, then post it for feedback.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)

Quote (xnuke)

Now, it's time you attempt to draw it, then post it for feedback.
See attached. IMO, option "A" is the clearest of all

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

I like option E
I stated that the NO or NC designation applies to the contacts when on the shelf, but you have presented a special case.
While a contact block may be NO, if it is mated with an operator that holds it closed in the normal position, then the assembly of operator and contact block may be designated NC.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

A Is wrong as it shows incorrect physical movement. It's showing both contacts have to operate when the "operator" (the knob) is turned clockwise. (BTW That was my first failed drawing!)

E is also wrong as it clearly denotes a Normally Closed contact is involved which is not the case.

D is the correct one IF this is a two position switch.

C is the correct one IF this is a three position switch - EXCEPT! In this case the truth table is wrong. It needs a third center column showing the center position with NO 'X's.

Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)
Yep, I agree with Keith. Option E may lead to a bad purchase of equipment needed.

The selector switches being used have only two positions (Hand or Automatic - both "latched")

What I do not like about "option D" is that I am drawing the switch in neither position H nor A (see dashed line on the big "V"), and we are used to draw schematics in "pasive state"

Conclusion: fuc* IEC

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Exactly! Bothers me too, but the IEC weenies have no schematic symbol that shows a NO switch in a closed state so you're stuck.

Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)
Yes, and this is a pain in the ass for me as a OCD ahah

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

By itself the contact block is normally open but when assembled to the operator it becomes normally-open-held-closed, or functionally normally closed.
In the absence of a symbol for normally-open-held-closed we are faced with ambiguity.
Option D is correct for a three position switch but may be misleading for a two position switch.
The position that the contacts are in in D does not correspond to any entry in the truth table.
This is not to argue, but to point out the ambiguity and suggest the need for a descriptive footnote.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)
Bill, I agree with you on almost everything except the following:

Quote (waross)

suggest the need for a descriptive footnote

In my short experience in engineering I realized that most of the people (sadly) do not read notes on a schematic. I think although messy, it is better to direct write it next to the symbol (or at least use an asterisk)

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

The drawings that I most often see would have the words See Note #1 next to the symbol on the drawing. If that direction is not included, then I agree with your comment.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

That is showing a three position switch.
Again, possible confusion.
The two position switch does not have a position where both contacts are open as shown.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

A "two position switch" will need to be expressed as one or the other contacts closed. I would have it in the "Auto" position
and have what ever be it a contactor or another switch which completes the circuit in the open position to indicate a non-energize state.

Chuck

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Chuck that doesn't seem to be available in IEC land. You have to just consider the schematic symbol as being a snapshot of the switch while it's in-motion on its way to a position the final outcome being shown as the dashed lines of the "V" with a two position showing both as dashed possibilities of "ON" switches.

Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

I mean no offence however, logical clarity is lacking in this design a two position switch must be in one or the other positions while I am probing during troubleshooting the circuit. But I always come here for advice when I need help so possibly missing the point, forgive me for thinking binary. banghead

Chuck

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Quote (OP)

See attached. IMO, option "A" is the clearest of all
Link
I still think option "E" most clearly demonstrates the action of the switch as installed.
I think that a lot of our confusion has been caused by a misleading catalogue description.
I suggest that if we lack a symbol to show normaly-open-held-closed then a normaly closed symbol most clearly describes the action of the circuit.
Remember that one purpose of the diagram is to aid in troubleshooting.
Included in the note that we discussed may be a bill of material that calls up the switch with the confusing description. That way you get the switch that you wish to use and the field technician has a drawing that he can understand.

Two position switch versus a three position switch.
I can understand the use of a Hand/Automatic switch in an application where the designer does not want the possibility that a Hand/Off/Automatic switch may be forgotten in the off position.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Chuck,

You're not missing anything. It is simply a horrible symbol.

By a perverse twist of fate I'm actually drawing up circuit schematics myself this week to bail out another group who forgot to request any drawings from Engineering before sending a job to the installation team, who are now sending us variation notices for stoppage time. I am using the old British Standard symbol because we all understand it, even if IEC says otherwise.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

:) Bill..

The "E" left switch is precisely the IEC symbol for a N.C. switch. You cannot use that anywhere in Any Ville NEMA or IEC or ? without mass confusion ensuing. Right from the start you'll have people buying the N.C. switch blocks to jack onto the back of the ON-ON operator. Of course that would then make the switch be open when in that position. Then the rocket will launch while they're disconnecting the fuel hoses and... poor outcomes would be expected.

Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Hi Keith. You are inadvertently making my point.
Back in the day when I was doing a lot of control work, ordering parts, designing new circuits, repairing, troubleshooting etc., All of our selector switches used contact blocks with one set of normally open and one set of normally closed contacts.
Then came the contact blocks with only one set of contacts.
In some product lines the single contact blocks were interchangeable with the two contact blocks.
Our diagrams always showed the contacts in the as installed or as assembled position.
It was not unusual to have an operator which held a normally open contact closed in normal operation.
It was up to the person ordering the parts to determine whether an operator would reverse the action of the contact block.
If I go to a different brand and order a switch with two normally open contacts, I will many times get a switch with two normally open contacts, just as the drawing shows. Not going to work.
Also, to show two normally open contacts presupposes that an electrician working on the circuit has pre-knowledge that one of the normally open contacts is actually normally closed.
I have had to assemble selector switches that reversed the action of a set of contacts. The drawing always showed the action of the selector switch as assembled.
It is up to the person buying or assembling the selector switch to select the proper contacts so that the action is as needed, regardless of the configuration of the contact block before it is mated to the operator.
By the way, a common contact block offered by more than one manufacturer back in the day was stackable.
The second contact block could be mounted in tandem where it may be open in the normal position or mounted to the back of the first contact block where held closed in the normal position.
You MUST show the action of the devices AS ASSEMBLED.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Given the info of a 2-position switch using 2 x N/O contacts, A or D are the only possible correct drawing.

We use a drawing like Keith showed first, except the lines would be above the circles. We always use the line above the circles for a N/O contact block and the line below and touching the circles for a N/C contact block. We DO NOT draw the switch contacts as installed with the switch in one of the positions. We have tried it various ways and drawing the contacts as the type of block is the least confusing. The way we draw it, it shows the type of contact blocks and when the contact is closed. So, all the info you need about the switch is on the switch drawing.

Translating this to IEC world, the same logic applies meaning A or D are the only possible choices. Since I like to see the same symbol used for the same type of contact block, I would use drawing A over drawing D. Mirroring the contact symbol as in drawing D could be confusing to someone.

B and D show a center position so they are wrong. E shows a N/C contact so it is wrong. Sorry Bill, but E would only be right if a N/C contact block is being used on the switch operator and the OP specified that 2 x N/O contacts are being used.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

LH; With respect to my drawing you're exactly right. I should've drawn the bars above the circles for N.O. blocks. Dang. And thanks.

Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

My point is that That with some operators, two normally open contacts are used.
With some operators one normally open and one normally closed contact are used.
And with the operator in question, two normally closed contacts blocks could just as easily be used.
H would become A and A would become H.
When you check an assembled switch with a continuity checker it will show one N/O and one N/C.
I have seen a lot of operators that reverse the operation of one contact block. The drawing always shows the configuration of the complete operator, not the disassembled operator.
Keith, If you were trouble shooting a circuit with a diagram showing a closed contact shown as open, I am sure that I would hear your cry of outrage all the way up in Canada.
When I was buying a lot of operators, and contact blocks for a large lumber mill, my catalogues would list a complete switch assembly, with the contacts designated in the "as assembled" configuration, even though if you purchased the individual components, the action would be reversed.
When we had to assemble a control switch, we would consult the diagram to see if we needed N/O or N/C.
Then we would determine whether the switch operator reversed the action of the contacts. When assembled the switch matched the drawing.
In a lot of operators, just moving the contact block from one side of the operator to the other side would reverse the action.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

You're right Bill the opposite case that I described is also electrically valid - I agree.

However:

Quote (Bill)

It is up to the person buying or assembling the selector switch to select the proper contacts so that the action is as needed, regardless of the configuration of the contact block before it is mated to the operator.

Rarely is that ability natively available and regardless the purchaser the purchased stuff should match the switches depicted by the schematic. If one is OK with cross wired NC switch blocks to take the place of straight NO switches they need to be correctly depicted on the schematics or yes you will hear me screaming or rather swearing clear to Manitoba.

Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Bill, we understand. But, the OP posted the switch was to use 2 x N/O contact blocks.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

The way I see it the OP by his discription is mistakenly defining a three position switch as two position.
The switch will automaticly return to center whitch is position 1 turning it to the left from center would
be a second position and turning right from center would be a third position.

Chuck

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Yes, but I am explaining why the configuration of the contact block is of interest to only the purchaser.
He needs, and should show a device with one normally open and one normally closed contact.
However that is achieved with hardware, that is what should be shown.
If we take the Auto position as the normal position, then the drawing should show the contact closed in the auto position. No matter what physical device is used to achieve the normally closed contacts is immaterial. The contacts are closed, show them as closed. Anything else will cause confusion.
The proposed device achieves the desired end with the use of two normally open contact blocks.
That is interesting but not important.
What is important is the action of the switch as assembled.
When assembled, the switch has one NO and one NC.
That is what the circuit requires.
That is what the drawing should show.

Quote (itsmoked)

Rarely is that ability natively available and regardless the purchaser the purchased stuff should match the switches depicted by the schematic.
The answer to that is to specify the switch desired by part number.

Quote (Lionel)

But, the OP posted the switch was to use 2 x N/O contact blocks.
I say again; Interesting but not important. Deal with this by properly specifying the device, not by using a misleading drawing.
(BTW, I have gotten bit more than once by assuming that the purchaser knew what I needed. I Should have used a specific part number rather than a generic description.)
Don't use a misleading drawing for something that should be adequately cover in the bill of materials.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

At work we have provided customers with 100's of drawings that DID NOT show the contact opened or closed as they'd be in one of the switch positions. Not one customer has complained. So, I don't find much merit in any argument that the switch drawing has to show the contacts the way they are when the handle is in one of its positions. The table or lines and X's showing when the contacts are closed make it quite clear in what position the contacts are closed.

Honestly, if you're an electrician or technician and can't use the info marked on the drawing that tells you in what switch positions the contacts are closed or open when troubleshooting the circuit then you really should be looking for a new job.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Good morning Bill

I agree with you, our electrical drawings include a comprehensive parts insert which gives specific part numbers.
However, somehow not only do contact blocks get mixed up but also the switch blocks as well. A few weeks ago I found
two N/O, (auto/manual) blocks with a switch block that engaged both at the same time because the cam action was so different.

The mistakes that you discribe occur more often on the older equipment when parts become obsolete and someone determines
their own cross refferance simply by schematic drawing and no thought about how the circuit is supposed to operate.

Lionel, What I found out in this field is that Bad electricians get weeded out by consequences when
making bad decisions which can be quite dramatic, expensive, and humbling. It can also be quite humorous
at times. bomb

Chuck

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

I use a program called EasyEl when I need to do an occasional non-Electronic drawing. It has the following symbols:





A Cardinal rule is that ALL symbols are drawn in their non-actuated position. Relays without coil voltage, switches in their neutral position and limit switches non-actuated.

If that rule is followed, much of the confusion illustrated in this thread just goes away.
Sorry for the Swedish text. I could have switched to English, but haven't the guts to do so. That COULD affect my drawings that I do not want to be changed. Not the least.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

(OP)
Hi,

I am proud that this post has reached 47 replies. It is clear that everyone has a different opinion based on their experience and based on their needs (because, in conclusion, IEC is NOT clear in how to draw switches), but I think that the debate that was developed on such a simple subject is very interesting

Thank you everyone!

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Yes! Proof the IEC symbols are idiotic.

All of Gunnar's depictions fail to show something even close to the simple switch you needed.

And he gets a star for it!


Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Hi keith

I felt the LPS was earned because of the suggested software brand he utilized, the symbols are easily understood and most of all
due to his mention of the cardinal rule which adds clarity to the diagrams. The rule alone is significant!

As always no disrespect to you and Bill, your advice is really great and food for thought for sure. I did notice that there are
plenty of other comments on this post worthy of a LPS as well, someone is being a little stingy with the left click button on mouse.

smile

Chuck

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Quote (flexoprinting)

However, somehow not only do contact blocks get mixed up but also the switch blocks as well. A few weeks ago I found
two N/O, (auto/manual) blocks with a switch block that engaged both at the same time because the cam action was so different.
I've been there too and got the tee-shirt.
That is the condition that I am trying to describe
That is the condition that I am trying to avoid.

I have generally been able to follow a control drawing.
I agree that in some circuits, it is not feasible to show all contact positions in all operator positions.
Drum switches and drum sequencers are two examples that come readily to mind.
In such cases my preference is that the connections be described in some type of truth table.
Rather than showing the contact as two small circles with a bar in either the normally open or in the normally closed position, The two small circles are shown without any connecting bar. The technician is not misled by a contact shown in the wrong position. He sees and checks the truth table.
I have read drawings that were easy to read and I have read drawings that were confusing and misleading, but I was able to eventually understand them.

My first supervisory position was in a large automated mill.
The stated cost per minute of down time was equal to a days pay for a foreman. When the mill went down we were under extreme pressure to get it running again.
Fortunately our drawings were excellent.

I have tried to suggest the most understandable and least confusing method of depicting the switch from the point of view of the people who may be trying to repair a stopped machine under the pressure of lost production. Time is often of the essence and any confusion with a drawing is too much confusion.
Did we bother to complain about the confusing diagrams? No. The equipment had to be fixed within minutes or at the most hours. Once the equipment was back in operation we exchanged a few snide remarks about the designers and moved on.

Quote:

Not one customer has complained.
Why am I not surprised. It's not worth the time.

Actually I did ask for some information once and when I got the information I did complain. It turned out that the drawings being shipped with the gen-sets were not the same as the drawings being sent to the engineering sales office. Once we got that sorted out, the sales engineer and myself became good long distance friends and worked well together for quite a few years.

Lionel, I have a lot of respect for you and do not often find myself in disagreement with you.
I think that we must be on different pages.
I have no issue with a drawing which shows a contact block with no contact shown and the action described in an accompanying truth table.
I do get a little reactionary when a drawing clearly shows a contact as closed when the truth table shows the contact open.


Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Hi Bill,

Although I hadn't really thought of it that way before, the old BS symbol effectively is a truth table within the symbol itself. Thanks for making that connection.

I think the disagreement over NC or NO contacts and the bare contact block v's the assembled switch loses its way somewhat once we're talking about switches with more than two positions. For two-position switches I find myself agreeing with you in terms of how to depict them but I completely understand Lionel's option too and in almost every other situation I would agree with him.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)


Quote (LionelHutz)

At work we have provided customers with 100's of drawings that DID NOT show the contact opened or closed as they'd be in one of the switch positions. Not one customer has complained. So, I don't find much merit in any argument that the switch drawing has to show the contacts the way they are when the handle is in one of its positions. The table or lines and X's showing when the contacts are closed make it quite clear in what position the contacts are closed.

I can't imagin having little truth tables all over a diagram instead of switch displays, truth tables take up more room
which means more pages for a given machine increasing the size of the book creating a very bust schematic visualy.

In a production atmosphere simplicity and clarity are key. Possibly it's all perspective depending on what one is comfortable with.

Chuck

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

I have found that most drawings done by consulting firms are very clear and unambiguous.
If a drawing is confusing, that leads to mistakes by installers and extra costs to repair.
Extra costs cause push back and change.

Drawings supplied by OEMs fall into two classes.
1. Excellent. Clear and easily understandable.
2. Not quite so easy to read. This is not perceived as a problem because all the OM people are familiar with the product and know what the drawing really means even though it may be somewhat ambiguous or misleading.
Eventually the field people figure it out.
Does anyone complain?

Quote:

Honestly, if you're an electrician or technician and can't use the info marked on the drawing that tells you in what switch positions the contacts are closed or open when troubleshooting the circuit then you really should be looking for a new job.
Honestly.
With this attitude, I can't see even a valid comment being passed on and evaluated.
Is this what hubris looks like?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

May I, perhaps, remind you that the OP asked about IEC symbols?

The first example in the first row (from EasyEl) shows the closing contacts and the fourth example in the second row is an axtension (the opening contacts) that one just drops in place. The system then "fills in the X) so that a correct symbol with the right numbering is created.

To do the same, but creating an ON-0-ON symbol, you just use the first symbol in the last row and add the extension (third in the same row) to get what later appeared in the thread (the Auto-Off-Manual etc switch).

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

I agree completely Gunnar.
The issue as I understand it:
The selector switch, due to the shape of the operating cam, uses two normally open contact blocks.
Because of this, some are advocating showing the drawing with two normally open contacts.
The switch, as assembled and installed, has one set of open contacts and one set of closed contacts as shown by your suggestion.
Some seem to be suggesting showing both contacts as normally open.
Maybe I missed something.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

Schematics.. Of the machines I repair I get to see a schematic in about one out of 20 cases because they're either missing or the useless companies that "provided schematics" ALWAYS leave out the details someone needs to actually repair the machine, leaving only the unimportant stuff like 8 motors and their leads and contactors (like anyone needs that!).

Keith Cress
kcress - http://www.flaminsystems.com

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

2
Bill, we used to draw schematics with the contacts shown in one of the switch positions and fielded plenty of questions about it being drawn that way and how to interpret the schematic. Hell, we used to draw 2-position switches with the contacts shown in one position and the "handle" shown only going to the text for that position. That's would satisfy exactly what you are advocating yet it caused a lot of confusion and we'll never do it that way again. The confusion we were seeing stopped when we quit trying to be so literal on the drawings and let the "truth table" symbols indicate when the contacts operate. We're not drawing them the way we do now because we are a stupid OEM that doesn't listen or know any better.

flexoprinting, Since we don't do IEC drawings the switch symbols we use look very much like the one Keith posted in the first response. There is no logic table taking up any extra space on a drawing since the "logic table" is right in the schematic. We do that because we didn't like the old NEMA way of having a separate drawing sheet with the operators truth tables since anyone working with that type of drawing has to flip back and forth as they troubleshoot. We've done this a long time and heard plenty about what customers don't like. Frankly, I think a multiple position switch being drawn in a schematic without a logic table is a very bad idea. The logic being shown in some clear manner is required.

The IEC symbol does not indicate any particular switch position. The switch drawings both Keith and ScottyUK posted do not indicate any particular switch position. So, why should the switch symbol show the contacts in one of the switch positions when the same symbol doesn't indicate which position the switch is in?

Fundamentally, I believe not knowing the switch position was the reason behind customers questioning the drawings we used to make. They didn't understand the switch contacts were drawn in the "off" or "hand" position on the drawing so seeing some drawn as closed and others drawn as open simply didn't make sense to them. This more or less falls back to the rule Gunner posted - draw everything neutral.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

When attempting to draw complex switches such as ammeter and voltmeter selector switches which have four switch wafers on a common shaft with each wafer containing multiple switches and some switches being early make / late break elements, then the only sane way to approach these complex switches is a truth table approach or one of the symbols which incorporate the truth table. I can barely imagine how difficult one of these would be to decipher if it was drawn using IEC symbology.

RE: How to draw a 2-position selector switch and its contacts? (IEC world)

60 replies to this request. I'm glad that the request was not for a 3-position switch....

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

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