Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Switch pole/throw naming

  1. Jan 7, 2015 #1
    http://www.allaboutcircuits.com/videos/15.html
    5:50

    Why does the double pole single throw picture only throw one circuit?

    Doesn't it throw two circuits since there are two lines on the right side of the picture?

    "throw refers to how many circuits are opened or closed" <- looks like my question hinges on this. Graphically what does it look like for a circuit to be open or closed?
     
  2. jcsd
  3. Jan 7, 2015 #2

    Doug Huffman

    User Avatar
    Gold Member

    Following the rules for the particular schematic schema, a closed circuit can be traced without lifting the pen.
     
  4. Jan 7, 2015 #3
    Where am I tracing my pen?

    http://www.allaboutcircuits.com/videos/15.html

    So double poel single throw has evidently 1 circuit opened or closed during operation. So why aren't there 2 circuits?

    upload_2015-1-7_13-12-41.png
     
  5. Jan 9, 2015 #4

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    There are two circuits. I don't understand why you think there is only one shown?

    Here is an example showing how a DPST can control two electrically separate circuits...

    DPST.jpg

    Both poles are mechanically linked so if one switch is ON they are both ON. They are shown in the OFF position (aka "open circuit").
     
  6. Jan 9, 2015 #5

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    When you come across this sort of confusion, because you don't like the particular phrasing that's used, it's a good idea to look elsewhere (Google) with the term that confuses you and look at other examples. Personally, I think that what he says on that video is fine and not at all confusing. It just might have helped if he had explicitly pointed out that the words "throw" and "position" mean the same thing.
     
  7. Jan 15, 2015 #6
    Why is this single throw

    upload_2015-1-15_16-43-50.png

    upload_2015-1-15_16-44-5.png


    So if the above picture is single throw then there should be one circuit opened or closed. Aren't there two?

    upload_2015-1-15_16-45-7.png
     
  8. Jan 15, 2015 #7

    berkeman

    User Avatar

    Staff: Mentor

    It is Single Throw because both switches are mechanically linked (as has been said several times already). When you close the switches, they both close at the same time. The upper pole closes the circuit for the upper pair of contacts, and the lower pole closes the circuit connected to the lower terminals.
     
  9. Jan 15, 2015 #8
    " Both poles are mechanically linked so if one switch is ON they are both ON. They are shown in the OFF position (aka "open circuit")."

    Is it the dotted line here that means mechanically linked?

    upload_2015-1-15_17-9-42.png
     
  10. Jan 15, 2015 #9

    berkeman

    User Avatar

    Staff: Mentor

    Yep, that's what that dotted line means. :-)
     
  11. Jan 15, 2015 #10

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    If it were a wire it would be drawn as a continuous line, like all other wires. Sometimes it helps if one tries to come to terms with a system instead of just complaining about it. The examples quoted in this thread are comprehensive enough to give a clue about the system. There are many examples of circuit diagrams all over the web. A few minutes looking at a sample would be more useful than a good winge on PF, imo.
    BTW, what would be the point of designing such a switch if it worked as you seem to think it does? Two input wires, joined together? Whatever for?
     
  12. Jan 16, 2015 #11

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    Might also help if I redraw it like this..

    upload_2015-1-15_16-43-50.png

    The two switches are usually physically close together but could be any physical distance apart. There is no electrical connection between AB and AD.

    On these circuit breakers you can see the mechanical link on the Double and Triple pole versions..

    https://akirajunto.files.wordpress.com/2011/08/mcb.jpg

    On this relay (which is a Double Pole, Double Throw) the mechanical link is the brown bar at the top made from an insulating material..

    http://4.bp.blogspot.com/-ElkCEsbdJ...images_a04_vm_ug_dpdt-relay-work_-800x800.jpg

    On this knife switch it's the black plastic handle..
    http://www.globalspec.com/ImageRepository/LearnMore/20123/sk3940c869b55196cb48ddb50bf45657a24dfd.png
     
  13. Jan 19, 2015 #12
    So it looks like from the quote above bolded that there are two circuits opened/closed ^

    upload_2015-1-15_16-44-5-png.77712.png <- Green box

    So is this green box wrong? Green box says throw refers to how many circuits are opened or closed and the quote berkeman above says there are two circuits. Berkeman says its single throw because the switches are linked but green box doesn't talk about switches- green box talks about how many circuits opened or closed.

    upload_2015-1-19_10-7-25.png

    Thank you all for your help.
     
  14. Jan 19, 2015 #13

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    I also thought the green box was a bit confusing if not outright wrong. The term pole to me means that there are several isolated circuits that can be switched. A 2 pole switch is two simpler switches in one package that all operate together. The term throw to me means how many different directions we can 'steer' the current.
     
  15. Jan 19, 2015 #14

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Yes, I agree. When one comes to a confusing figure on the Web, the first thing to do is look at several others for resolution. The person who published it may or may not know what he's talking about. This is another instance of classification being chased, rather than understanding.
     
  16. Jan 19, 2015 #15

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    I agree. Green box is confusing. Perhaps better if it said..

    "The term throw refers to how many circuits PER POLE are opened or closed during the switching operation."

    ..even then it's not perfect.
     
  17. Jan 19, 2015 #16

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    A circuit diagram is always needed and it says nearly everything about the functionality of the switch. The only time when you could feel forced to use the terms poles and ways would be when you are looking through a catalogue. But even catalogues tend to have exemplar diagrams. Haven't we done this to death yet?
     
  18. Jan 19, 2015 #17

    OmCheeto

    User Avatar
    Gold Member
    2016 Award

    I would say, based on CWatters diagram in post #4, that the green box is wrong. I think it could have been worded better.
    I just found an old post of mine where I quoted wiki about a year ago:

    November 20, 2013
    The number of "throws" is the number of separate positions that the switch can adopt.

    I accused myself of being drunk that day, as I could imagine "2 separate positions", but not "1 separate position". It didn't make linguistic sense to me.

    But, it has since been revised, to my satisfaction:

    January 19, 2015
    Switch Contact Terminology
    The number of "throws" is the number of separate wiring path choices other than "open" that the switch can adopt for each pole.

    I would focus on the phrase; "choices other than open" = "number of throws"
    And then repeat it 100 times.
    I don't think I ever did, and is why I always have to look it up.

    No! I've been working on this for 45 minutes!
     
  19. Jan 19, 2015 #18

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    Apparently not based on post #12.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Switch pole/throw naming
  1. Double pole switches (Replies: 1)

  2. Poles and Filters (Replies: 1)

Loading...