Direct current symbol: What does it represent?

June 21, 2011 2:39 PM

Direct current symbol (solid line above three dashes): What does it represent?

My best random guess is "constant voltage above ground", but I couldn't find any evidence to actually back this up; i.e. does the symbol specifically mean one leg of DC referenced to ground, or is there any history of using a dashed line to represent ground?

posted by trevyn to Technology (10 answers total)

I think it really just represents the flow of the electrical charge. As in it is not alternating.
posted by zephyr_words at 2:43 PM on June 21, 2011

Response by poster: Right, this makes sense in light of the sine-wave-shaped AC symbol, but what is the dashed line doing there?

(This has definitely confused me a few times, thinking the DC symbol represents AC, because look! The symbol has an intermittent appearance! etc.)
posted by trevyn at 2:50 PM on June 21, 2011

It's been a while since I've worked with this kind of thing, but doesn't a dashed or two-color wire represent ground (assuming you don't have a black wire)? If you only have one color to work with, it seems to make sense to me that + is solid and - is dashed.
posted by WasabiFlux at 2:55 PM on June 21, 2011

I believe it essential represents what WasabiFlux said. For a DC system, you have two wires. One is held at a constant voltage potential while the other is (usually) referenced to ground. The solid line indicates a wire with relative voltage and the dashed line indicates a ground or reference point.
posted by mungaman at 3:00 PM on June 21, 2011

Best answer: Conceptually, it's an image from an oscilloscope. The AC symbol shows a sine wave, so that part's fine. The DC symbol shows a flat line which is above the center of the graticule. The solid line in the icon is the oscilloscope trace and the dashed line is the zero point of the graticule.
posted by Chocolate Pickle at 3:01 PM on June 21, 2011 [5 favorites]

Given that most folks wouldn't have operated an oscilloscope, they're not obvious symbols.

I can't think of better ones.
posted by Homemade Interossiter at 3:07 PM on June 21, 2011

If you're dealing with electrical circuit diagrams, you've used an oscilloscope. Well, until the last few years maybe. It's not like capacitors only have one flat side.
posted by GuyZero at 3:31 PM on June 21, 2011

A dashed line indicates shielding on circuit diagrams. So "solid above dashed" probably means a single conductor with shielding around it.
posted by exphysicist345 at 8:11 PM on June 21, 2011

ExPhysicist345, did you read the filename that was linked to in the question?

"200px-Direct_current_symbol.svg.png"
posted by Chocolate Pickle at 11:13 PM on June 21, 2011

Oh. It's not part of a circuit diagram, it's a symbol used on a circuit diagram. Nevermind!
posted by exphysicist345 at 11:04 AM on June 22, 2011