Symbols
Symbols
(OP)
I'm drawing a schematic for a multiple pump hydraulic control system I'm designing. It has the usual pesky front panel covered with a matrix of the typical, grossly expensive, 30mm type selector switches.
I will be using some of those switches with mind numbing contact specifications. Essentially a double throw(center off) triple pole, spring return to center.
Keep in mind in the spirit of all these switches they are ALL internally and externally purely single pole, single throws that you must actually jumper to make single pole-double throw.
The Old Schematics I am upgrading from show these in single pole. I find the symbol used to be horrible and unclear.

Can someone direct me to a "good" symbol or where I could forage for one.
I will be using some of those switches with mind numbing contact specifications. Essentially a double throw(center off) triple pole, spring return to center.
Keep in mind in the spirit of all these switches they are ALL internally and externally purely single pole, single throws that you must actually jumper to make single pole-double throw.
The Old Schematics I am upgrading from show these in single pole. I find the symbol used to be horrible and unclear.

Can someone direct me to a "good" symbol or where I could forage for one.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com





RE: Symbols
A picture would be worth a thousand words.
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RE: Symbols
http://home.houston.rr.com/electricpete/switch.ppt
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RE: Symbols
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Symbols
I think for this situation we just show a contact table.
For example
____Hand_Off_Auto
1-2__X___________
3-4____________X_
With note nearby "Spring return to Off"
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RE: Symbols
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RE: Symbols
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RE: Symbols
http:
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RE: Symbols
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RE: Symbols
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RE: Symbols
Here's some stabs at it I just did. (I'll admit some were in the dark) {{the open and close do not refer to the switch state!! just the function}}
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Symbols
Actually both conventions are correct but refer to different devices.
The original symbol refers to what used to be the oiltight line of pushbuttons and selector switches. There are a lot of newer designations for bushbutton lines now in use.
The symbol you are using is as you state, two single pole contact blocks mounted on a single operator (Selector switch or push button.) There is another variation that is a double throw. The symbol is similar, but only one horizontal line is shown to indicate the movable contact and the dots are shown closer together. In industrial control diagrams, the symbols you have shown are widely used and widely understood. You will find those symbols used in the motor starter wiring diagram booklets given out by most motor control manufacturers.
In my GE Control catalogue, 1995 issue, the convention is used for both the wiring diagrams of the motor starters and to describe the action of the various push buttons and selector switches.
A couple of hints, Keith. The contact blocks do not have to be shown in the drawing adjacent to each other. In the case of interlocked pushbuttons for a reversing starter or a two speed starter, the normally closed section of the switch can be shown in a different line and offset to one side or the other. The sections are joined by a dotted line. For selector switches with a lot of contacts, the contacts can be shown in seperate locations, threaded together with a dotted line. It is considered good form to keep the switch sections as close together as is consistent with the circuit. You can usually arrange your diagram to keep your dotted lines reasonably short and limit as much as possible lateral shifts in location.
For selector switches with a lot of contacts, a "Truth table" is often shown to indicate the connections in each position.
The convention suggested by electricpete is also familiar to me but it is a different device. The magnetic motor starters supplied for the HVAC industry used to commonly have a light duty "Hand-Off-Auto" switch mounted in the cover. The physical arrangement of the switch and the symbol are just as shown by electricpete.
I haven't used it for awhile, but I still have the old template with all those symbols on it.
The symbols you have, Keith, work quite well with horizontal ladder type schematic diagrams. Drawing in the jumpers is valuable as it leaves no ambiguity for either the panel assembler or the service technician.
I understand your dislike for a different standard from what you're used to. I feel the same way when I run up against something like a Carrier Container Unit and try to figurew out a control sequence from a schematic in an unfamiliar format.
Those symbols that you dislike used to be and probably still are CEMA standards for Industrial Control Systems. (CEMA is the Canadian eqivalent of NEMA and I understand is almost identical)
Respectfully
RE: Symbols
It is a good symbol. You better get used to it - and use it - if you want to have a good relation to the people in that particular branch of industry. I once tried a simplified and "better" way of drawing hydraulic symbols, more in the electronic diagram style. I ended up redrawing the whole thing to get my last 10 percent pay.
Gunnar Englund
www.gke.org
RE: Symbols
On slide 2 above you'll note
HS-0002 switch 1 is labeled "Auto/Open"
HS-0002 switch 2 is labeled "Closed"
HS-0002 switch 3 is labeled "Auto/Closed"
HS-0002 switch 4 is labeled "Open"
These labels tell you what switch positions cause the contact to close without even looking at the table.
I suspect that won't change your approach but I just wanted to mention it.
As far as original symbol I wasn't sure if that is pushbutton or rotary but the description "spring return to center" made it clear it was rotary. Out of curiosity waross, how do you get 3 positions on a pushbutton?
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RE: Symbols
The standard drawing convention is used for both bush buttons and selector switches, two position selector switches and three position selector switches.
I spent some time looking online for a good example of a diagram using the symbols but so far no luck.
I'll post something if I find it.
respectfully
RE: Symbols
Thanks for your efforts electricpete I actually think your:
Hand_Off_Auto
1-2__X___________
3-4____________X_
With note nearby "Spring return to Off"
has a lot going for it, especially with respect to my switches that have three times the contacts.. hmmmm I may still go that way instead.
This seems pretty clear to me a tabular/symbolic hybrid. scematics
----> <----
Off Auto Hand
___1 X 2___
___3 X 4___
___5 X 6___
___7 X 8___
___9 X 10__
__11 X 12__
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Symbols
I found the standards.
http://nema.org/stds/ics19.cfm#download
You may have to go to nema.org and log on.
I did a search on the site for control symbols and the download in question came up 1st on the list.
respectfully
RE: Symbols
I worked for a while for e German company who made switches (Moeller) and as most German Co.s do, they had a very organized and systematic way of indicating contact operations using a target chart similar to the one electricpete showed. After they "deprogrammed" me away from JIC symbology I actually liked their method, it made a lot more sense. Moeller cam switch link
Unfortunately not one US electrician understood it, nor did they want to take the time to try. I had to issue supplemental drawings with that standard JIC symbol on almost every project.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Symbols
Boy jraef, that Moeller symbol is certainly an acquired taste.. lolo
Okay guys I'll stick with a NEMA or a very slightly modified one :)
skogs your warning is haunting me. I don't need no sting-king hold backs....
Thanks one and all.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Symbols
In case you missed it:
The symbol you are using is as you state, two single pole contact blocks mounted on a single operator (Selector switch or push button.) One contact is normally open and the other is normally closed, held open.
There is another variation that is a double throw contact block. The symbol is similar, but only one horizontal line is shown to indicate the movable contact and the dots are shown closer together."
The double throw versian is usually used for H-A-O service.
However, the double throw version is limited to "Same polarity" switching. To comply with this requirement, the double throw version is almost always used with a common connection to one side of the switch block.
When two single throw contact blocks are used as is indicated in your original post, there is no such limitation.
One double throw contact block is cheaper than two single throw contact blocks.
There are different contact arrangements in an assembled selector switch depending on the shape of the cam.
1> A double throw contact block.
2> A normally open and a normally closed single throw contact blocks.
3> Two normally open single throw contact blocks.
4> Not common but possible, two normally closed contact blocks.
Whatever the contact arrangement, show it on the drawing as shown in your original post. The schematic should indicate the operation of the assembled selector switch rather than the operation of actual contact block.
I hope this helps.
Respectfully
RE: Symbols
There used to be a three position pushbutton on the market.
I used a pair of them on a small boat I had with twin outboard motors.
The buttons had mini mushroom heads. Pushing them down would activate one circuit and lifting them would activate the other circuit. I wired them so that pushing down would kill the engines and lifting them up would start the engines. They may have been made by Cutler Hammer.
respectfully
RE: Symbols
RE: Symbols
I am using AB selector switches and spent all of my last Saturday trying to understand their spastic catalog and online configurator. This is after drawing pictures of what I wanted faxing them to AB tech support and being given absolutely wrong advice as to what devices to order(this after the dealer couldn't answer me and sent me to tech sup).
It seems to me that you cannot get a three terminal device (SPDT) at all! Everything is based on the "Push Button" except when you want selector switches everything is turned 90 degrees and the 'push' becomes a cam lobe. I actually wanted SPDT in some cases but that requires two SPST jumpered together. Not a big problem, just required a different pradigm.(and a saturday and part of a thurs and fri. argh!)
stevenal; Thanks.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Symbols
I understand your frustration.
One big advantage of the paradigm used to be spares stocking. One or two basic double throw contact blocks could be used in virtually any selector switch or push button in the plant. Except of course for the exceptions. SquareD had a contact block with slightly different clearances that was only used with the lever operated selector switch. If you used a standard contact block, the switch operator would destroy it. They sold us a lot of the wrong contact blocks before we found that out.
Just to make your day, I bet you a cup of coffee that you miss at least one of the little jumpers on an spdt. Been there, done that.
Respectfully
RE: Symbols
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Symbols
Dashed lines represent a mechanical link.
Black triangles represent a momentary contact.
http://kontikilink.home.mindspring.com/Switch.tif
RE: Symbols
I don't think your symbol is all that bad, the only thing I might change is the word "HAND" to "MAN" instead.
I did spend about 45 min searching for something more definitive with no luck, this in mind your symbol is just about awesome. Other then using a toggle or rotary style switch it seems there are no options. That does seem like a very odd kind of switch normally a push/pull type is for E-stop operation.
Chuck
RE: Symbols
Thanks for the complement. I thought mine were pretty good for a first hack but finally just reverted to the the original one at the top since that was the NEMA symbol used on the customer's system I am replacing. I figured (after direction from others above) they could hardly complain if I duplicated what they had. Thanks for the effort and feedback.
You know, I absolutely hate the term "HAND" I think it is lame. I have in-fact never ever heard of it before this job. But this customer is infatuated with it and wants "HOA" (pronounced 'hoe ah') switches on everything and everywhere. So I can either switch to "manual" or again go with the flow. The only thing I can see going for it is H-A-N-D is the same length as A-U-T-O and hence allows better visual symmetry in panel labeling.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Symbols
HOA may have been chosen as a more descriptive abreviation than AOA.
Respectfully
RE: Symbols
???? You mean MOA? AOA??? I've actually seen MOA many times.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Symbols
I looked in a couple of catalogues and you can buy either nameplate. Hand-Off-Auto or Man-off-Auto. Make your choice and you will be correct.
The name plate for the three position push button would read "PUSH TO STOP PULL TO START" (GE) or "PULL TO START PUSH TO STOP" (SquareD). It is not the same device as the "PUSH TO STOP PULL TO RESET" push button. One is a two position, maintained position button and the other is a normally centered button with a spring return push and a spring return pull.
BTW, do spaces count as characters? They do have a character code.
lol
Respectfully.
RE: Symbols
I would get rid of the dashed vertical lines and the X's on the power & controls lines.
Then replace with something like this.
OFF
Hand Auto
---------------o o--------
X00
---------------o o--------
00X
Place the 0 & X's as close to their respective line and contact as possible. And, of course, include the operator & contacts.
Every plant electrician I've worked with would recognize this as denoting the contact state for each switch position. At least in the US.
Ed
RE: Symbols
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Symbols
http://lit
http:
search for Document No. 0140CT9201
The NEMA-ISA format allows for a lot of situations that would be hard to cover with any other drawing method. The "Push-Pull", Spring Return", "Pull to Lock" have a lot of posibilities. If you going to do a lot of work with with control switches get one of every type of operator and contact block and keep them in your desk.
Jaref is right about the DIN and European sybology. You can describe allmost any situation with it. By the time you understand you may wonder why you didn't become an Egyptologist or study Chinese.
RE: Symbols
Oh WOW!! That Snider doc is chock full!! Sweet. I bet those two took you a month to find the first time...
Many thanks.
Oh and foreshore you can bet, I was wishing, I had one or two switches in my desk when I started the switchtology effort.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Symbols
I have had hard copies for years. I sent the title pages to the local reps and asked them to find the links. Be kind to sales reps. They can help you a lot.
RE: Symbols
Star for you, Thanks
Chuck