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Does anyone know the reason (historical, practical, etc) that polarized capacitors usually have the negative lead marked instead of the positive lead?

I would expect markings to indicate a positive potential. Since we commonly ground the negative lead and refer to "ground" as "zero" volts in reference to the rest of a circuit, the positive side would be the "hot" or "dangerous" side, so you would think that would be the marked side, especially on high voltage caps... We color positive wires red, we indicate the "hot" side of AC circuits, etc. Emphasizing the negative lead seems backward to me.

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    \$\begingroup\$ Be aware that most Tantalum capacitors have the Positive lead marked. This is opposite of most other capacitors. As is often said: "The wonderful thing about standards is that there are so many to choose from". \$\endgroup\$
    – Dwayne Reid
    Commented Sep 1, 2016 at 23:32

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Why are capacitors usually marked on the negative terminal, not positive?

Here some polarized capacitors: -

enter image description here

Now you tell me which is the dominant polarity marker?

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  • \$\begingroup\$ Yikes, I did not know that! I had only been exposed to ones marked on the negative side. I stupidly assumed all capacitors followed this standard. So is it just a coin toss to use the negative or positive side, or is something else at play? \$\endgroup\$
    – Ryan Griggs
    Commented Sep 1, 2016 at 23:36
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    \$\begingroup\$ For electrolytic capacitors, unless specifically designed to be insulated, the case (the metal surround) is usually connected to the negative terminal and somehow, through a conventional thought process, you could make an argument that marking the body (case) with the negative sign indicates that the case is negative as well as pointing to the terminal which is negative. That's my "long-shot" of the day! \$\endgroup\$
    – Andy aka
    Commented Sep 1, 2016 at 23:40
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    \$\begingroup\$ Radial electrolytic caps are conspicuously missing from the lineup. Those are predominantly marked on the negative side. [On that note, -1. No hard feelings.] \$\endgroup\$
    – Nick Alexeev
    Commented Sep 2, 2016 at 0:39
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    \$\begingroup\$ Of course I have hard feelings about your seemingly trivial down vote - the picture shows a selection that somewhat undermines the assumption in the question. Did you down vote the question for containing that questionable assumption? \$\endgroup\$
    – Andy aka
    Commented Sep 2, 2016 at 7:41
  • \$\begingroup\$ LOL @NickAlexeev, Andy is simply pointing out that there are myriad capacitor styles and types that mark the positive side. My limited exposure to capacitors had me thinking they were all marked on the negative side. Now I know better. :) Thanks Andy for clearing this up! When working with alternate types, I will be careful to check datasheets before assuming anything. \$\endgroup\$
    – Ryan Griggs
    Commented Sep 4, 2016 at 21:17

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