Capacitor symbols - right or wrong?

Discussion in 'General Electronics Chat' started by KLillie, Feb 5, 2015.

  1. KLillie

    Thread Starter Member

    May 31, 2014
    I found this circuit diagram that someone had posted.
    I always thought that symbol for the capacitors was a polarized capacitor e.g. an electrolytic. Is anyone savy enough to tell me if they all are or just c1 and c2? What is .01? Is that pf or uf? Also .o1 pico or micro farad sounds like a small electrolytic.
  2. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    Since all caps are 0.01 (I'm assuming they're in µF, which are the most common units) their capacitance is way too small to be electrolytic, and I very much doubt they're tantalum either. Therefore they must be disk ceramic, which are unpolarized. Lots of people draw them as "-|(-" even though traditionally an unpolarized cap is drawn as "-||-" ... but since the designer has omitted the "+" sign, you can be almost certain that they're unpolarized... Anyway, that looks a lot like a Forrest Mims circuit to me!.
    KLillie likes this.
  3. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    that image is from the old "Engineering Notebooks" by Forrest Mims. Yes, all capacitors were drawn that way when the book was written.
  4. WBahn


    Mar 31, 2012
    They're non-polarized. You can bet that those caps are going to see both polarities, so they better be non-polarized.

    Electronic symbols have never been rock-solid-engraved-in-stone standardized, so you often have to infer what was meant. Sad, but that's just the way it is.
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    I still draw non-polar caps that way.

    Polarized caps get the + sign *always* on the non-curved side.

    It's clear to me though I admit there could be confusion. Old habbits die hard.
  6. MrChips


    Oct 2, 2009
    0.01μF non-polarized capacitors
  7. alfacliff

    Well-Known Member

    Dec 13, 2013
    back in the old days, the curved plate of a cap was the outside foil on non polarized caps helpfull when you were using paper caps as bypass or coupling caps, to cut down hum or noise pickup. yes, that is a .01 micro farad non polarized cap.
  8. BillB3857

    Senior Member

    Feb 28, 2009
    When I was first introduced to industrial controls in 1965, the individual training me laid out a large set of drawings he referred to as the "prints". Opening a page and pointing to a -||- symbol, he asked if I knew what that was. "It looks like a capacitor, but I've never seen them connected like that", I said. After a slight chuckle, he explained that those were representing normally open relay contacts and the drawing was known as a ladder diagram. He turned a couple of pages and was able to show that capacitors were drawn as -|(-.
    KLillie, ErnieM and shortbus like this.
  9. wayneh


    Sep 9, 2010
    It is. I have that booklet.
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Ahh, I forgot about that symbol, and I used it for about 10 years in a test department. They had wonderful racks of equipment with 200 or so switch points in a backplane very easy to access for any random job.

    My boss was a buster and ran down my first design as "costing too much money" because I drew the backplane switches as traditional relays. Guessing he did not know the -||- symbol as a switch I used it on the next schematic I presented him.

    My guess was correct, he did not understand what he was looking at. I don't know if his thinking was "caps are cheap" or "I just don't get his work" but he stopped questioning my designs after that.
  11. MaxHeadRoom


    Jul 18, 2013
    It depends on the environment you are working in, if working with electrical schematics or PLC prints, then you expect the -||- to be a N.O. contact, and capacitors, if present should be labeled as such.
    I agree with Alfcliff, I have always regarded the -|(- as a polarized capacitor as far as the ( side being connected to chassis in the case of decoupling capacitors etc, but now you will find all kinds of symbol charts that show them as being electrolytic.