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This circuit diagram has a symbol I've been unable to identify, which I've indicated with a stylish green arrow. I'm guessing some sort of capacitor based on the uF measurement, but I haven't been able to confirm that in my search through general circuit symbol lists or for capacitor symbols. Can someone clue me in?

circuit diagram with unknown symbol

Brad Mace
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2 Answers2

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It's an electrolytic capacitor. These are polarized, as the + sign also indicates. This is a less common symbol. Below are the more common ones, European on the left, American on the right.

enter image description here

Compare to the symbol for a non-polarized capacitor:

enter image description here

Note: I think the American symbol for a non-polarized cap is a bad one; it suggests that there is some kind of asymmetry where in reality there isn't one.

edit
From the comments it appears that the supposedly American non-polarized symbol is less common than I thought. I can only speak from my experience, and like I also said in comment, it could be that I've been looking mostly at older schematics (not the tubes, I'm not that old).
I found this schematic within a minute:

enter image description here

C2 might be an electrolytic (it won't be, will have a too low capacitance), but look at variable capacitor C1.
Also this page.

edit 2
Browsing through more symbols encountered also this weirdo (the one on the right):
enter image description here

stevenvh
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    I have to admit, I have seen about 30 symbols for drawing capacitors. I am actually used to just drawing two straight lines. I only draw a curved line if it is polarized, I always thought of the curved mark as a sign for polarity. I probably never follow standard though. – Kortuk Jul 17 '11 at 05:30
  • I don't think one is better than the other. I typically use the European version for non-polarized and the American version for polarized. That way I never have to use +. Although sometimes I write the + for good measure.... – Origami Robot Jul 17 '11 at 05:33
  • @OrigamiRobot - that would be a problem for me. I live in Europe and use the European symbols. I wouldn't know which side was the + on the American symbol unless I looked it up. – stevenvh Jul 17 '11 at 05:40
  • @steventh - I understand. I'm just used to seeing it that way. I do agree that using the American version to represent a non-polarized capacitor seems bad. – Origami Robot Jul 17 '11 at 05:44
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    I'm American, and haven't ever seen the Straight/Curved line cap symbol for a non-polarized cap anywhere I have worked. I don't know why you think it's an American thing. Frankly, it's a terrible way to do the schematics. – Connor Wolf Jul 17 '11 at 06:56
  • @Fake - I've seen them more than other symbols. It's possible that they were more used in the past. – stevenvh Jul 17 '11 at 07:01
  • My electronics text book from college (published in the 70's) uses the 'european' style (I'm UK), however I learned originally on one of those spring covered electronics kits from radioshack (a US company) and it used the 'US' style (-)|- for electrolytic and -||- for ceramic). – Majenko Jul 17 '11 at 10:01
  • I'd like to add that, as an American, afaik the general consensus here is that the curved plate symbol is used to indicate an electrolytic (or other polarized) capacitor, and the parallel lines symbols is preferred for non-polarized caps. – JustJeff Jul 17 '11 at 12:52
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    The straight/curved cap symbol, without polarization, was common on Radio Shack schematics I saw in the 70's and 80's. Nowadays, we mostly use the two-parallel-lines symbol, not the two-filled-rectangles symbol that Europeans use. At work, we require polarity markings ('+' in the case of capacitors) on schematics. Curved/straight lines don't count since a lot of the people who read the things don't remember which is positive. – Mike DeSimone Jul 17 '11 at 13:34
  • The relevant standard in the US is IEEE STD 315: "IEEE Standard American National Standard Canadian Standard Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters)". It's commonly referenced by other drawing standards. – Mike DeSimone Jul 17 '11 at 13:38
  • This site has an interesting explanation of the different symbols. – Dean Jul 17 '11 at 19:42
  • I wonder where the curved line originated. Here's a capacitor from 1901: http://i.stack.imgur.com/cSGJ1.png – endolith Jul 18 '11 at 00:12
  • @endolith - hey, that cap looks a bit like the weird one at the bottom of my answer! – stevenvh Jul 18 '11 at 14:28
  • Unpolarized caps aren't necessarily symmetric in physical structure. Some types have one electrode surrounding the other, and that's the one you want connected to ground, if the cap is going to be connected to ground at all, to reduce EMI. – DarenW Jul 18 '11 at 19:48
  • @endolith: In some contexts it's common to indicate normally-open contacts with two parallel lines, and normally-closed contacts with two parallel lines and a slash; using a different symbol for a cap would seem logical. That having been said, the fact that only one line is curved is a little curious. Perhaps that's because it's easier for right-handed people to draw a curve in one direction than the other? – supercat Aug 09 '12 at 17:45
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Regarding the non-polarized symbol with one curved side, the curved side represents the OUTER foil in a rolled foil capacitor. In a grounded capacitor, one would want the outer foil grounded.

Les Borean
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