Red dot no top of a run capacitor indicate

Discussion in 'General Electronics Chat' started by bwd111, Aug 14, 2013.

  1. bwd111

    Thread Starter Member

    Jul 24, 2013
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    Know one seems to know what that dot represents? Is it chassis ground,load start terminal,run terminal or load common terminal? Ive googled and used other search engines with no luck. Why use the red dot then give no information on why the dot is used???
     
  2. #12

    Expert

    Nov 30, 2010
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    It is the terminal that is connected to the internal fuse.
     
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  3. bwd111

    Thread Starter Member

    Jul 24, 2013
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    What if there is no fuse
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There are occasions where non-polarized capacitors have one post marked as being the outer plate or nearest the can.
    But I don't ever remember seeing one on a run cap?
    On a normal run cap it should not matter anyway?
    Max.
     
  5. #12

    Expert

    Nov 30, 2010
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    Then the terminal that doesn't have a fuse won't be marked as having a fuse.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Pressure vent?
     
  7. #12

    Expert

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    Run caps don't have pressure vents. Start caps have vents.
     
  8. WBahn

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    Find one that has a dot and go to that manufacturer's website and look in their specs for the part to see if it is mentioned.
     
  9. THE_RB

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    Is it a red paint dot marker, or a little red rubber dot molded into the cap?
     
  10. #12

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    What? This is my day job. Did I accidentally put a question mark on my answer? It's a red paint mark or sometimes a red insulator on the terminal with the internal disconnect.

    Presto: Run caps with dots and start caps with vents.
     
    Last edited: Aug 15, 2013
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  11. WBahn

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    I've opted to not make any of the half dozen snarky retorts I've been pondering and simply state that my response was completely independent of and unrelated to yours and in no way indicated disagreement with anything you said.

    The OP indicated that their attempt to answer the question on their own was to use Google and other search engines. I merely suggested an approach that was more focused and might have been more fruitful.
     
  12. #12

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    Sorry to provoke the snarky in you, but I am baffled when people ask a question, receive the definitive answer, and then look for a different answer. It reminds me of the time I was asked to serve on a church administration board because of my qualifications in the construction industry. I told them the law required them to recharge the fire extinguishers in all buildings that are open to the public, and they had a public opinion poll printed up asking the parishioners if they wanted to refill the fire extinguishers.
     
  13. bwd111

    Thread Starter Member

    Jul 24, 2013
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    They are the old type of caps and the guys there have no idea what the red dont means
     
  14. bwd111

    Thread Starter Member

    Jul 24, 2013
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    YES that is the dont. If you had to choosebetween common terminal,run terminal,start terminal or chassis ground which one would a person connect to
     
  15. #12

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    A person generally does not connect to a capacitor, a wire does, but I think I am misunderstanding you.

    Maybe if I tell you the original intent?

    Most run capacitors are connected to the power line at one side and a motor winding at the other side. The fuse, or disconnect, is supposed to be connected to the power line so that it will fail if the capacitor shorts internally to its metal case. The metal case is usually strapped to sheet metal that is connected to "bond" (or Earth ground) and/or wired to bond with a 1/4 inch spade connector which is soldered to the case. This avoids using the circuit breakers (which might be 30 or 60 amps) to disconnect when the capacitor fails. Instead, the internal fuse disconnects the capacitor from the power line when it fails. The capacitor current can be calculated from its capacitance and voltage rating, and the internal fuse is usually less than 10 amps.

    I have described a 2 terminal capacitor that is marked on the fuse terminal. A multi-section capacitor has a "common" terminal which is common for all the capacitors in the can. It is usually not marked because it is the only logical place to put a fuse that protects all of the capacitors in the can.

    I think you have not said what you intend to connect to the capacitor, so I can't tell you which terminal to connect it to.
     
    Last edited: Aug 16, 2013
  16. THE_RB

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    Dilution. In a thread the OP asks a question, gets 20 answers, and sees (from a very cursory glance) that the "expert" people seem to be saying different things. It's normal for the OP to then ask more questions or get confused etc. :)

    That's just plain old "incompetence by committee". One man may be a great decision maker. A group of men will be lousy at making decisions even if one of them is a great decision maker. ;)
     
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  17. #12

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    Must keep reminding myself that public forums are a sort of committee.:D
     
  18. WBahn

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    For better or worse -- or, more accurately, for better AND worse.
     
  19. THE_RB

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    Well there's not much that is "better" in a committee. ;)

    Committees are a bit like plagues, you have to struggle to find something nice to say about them. :D
     
  20. bwd111

    Thread Starter Member

    Jul 24, 2013
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    The red dot is connected to the outer foil. Connecting this terminal to the lowest potential voltage source to ground will result in the minimal leakage of current and will provide a path to the fuse
     
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