Working on a schematic meant for the documentation of a system I'm building (an airsoft prop as a strongpoint for the game).

Since I am using this as a learning experience, I want to really do it as good as possible, even though it's not really needed. I'm working with inkscape designing my own library (originally wanted to use the Wikipedia lib, but I found it lacking in some places, so I pretty much started from scratch).

In schematics in my textbooks, I've run across a few different symbols for rails. I was wondering if there is any difference between these symbols. If so, what does each mean, and what others should I consider. If not, which is preferred? Most of my textbook use the middle symbol (black line with voltage written on top/under it. Positive voltages are labeled as seen here, negative voltages are mirrored horizontally, so the text is under the symbol.)

Voltage Rail Symbol

As a followup question - what is the preferred way to mark bus names in schematics?

I have a bus that is my LCD data, and I would like to label it as such for clarity, but I don't really know what the proper way to do this is. Just write the name above the bus like this?

enter image description here


1 Answer 1


Really, there is no difference between those symbols. All of them mean the same thing. Any engineer reading the schematic will recognise what each one means. I know sometimes different software gives you different symbols, but I don't think it really matters.

The majority of the time, it is the middle symbol. It is the most common and the one I tend to use. I tend to use the arrows or 'pin' for different nets that aren't a voltage rail, but I am sure other people do it differently.

So to answer your question, use either of them, but if you want to use the one that is used most often, go for that middle one.

For your follow-up question, that is the way I do mine as well. For a bus name, just have it written along the top. Just make sure you have it in a place where you can tell definitely which bus the text belongs to (so don't put it right at a point where 2 separate bus lines run close to each other for example).

I hope this helps!

  • 1
    \$\begingroup\$ I suggest putting a thick black dot at the interjection of the middle symbol to make it different from the ground symbol. Not placing the dot will lead to misunderstandings and mistakes. \$\endgroup\$
    – Janka
    Apr 10, 2017 at 11:38
  • \$\begingroup\$ Thanks for the reply! I wasn't sure, and I saw that some people are almost religious when it comes to symbols so I wanted to make sure I got it right. @Janka - I've never seen that symbol used as a ground! Didn't know that was done. When you say a thick black dot, you mean where the thick line crosses the thin "wire"? \$\endgroup\$
    – Joren Vaes
    Apr 10, 2017 at 11:42
  • \$\begingroup\$ No worries. Janka makes a good point but I usually have the 3 lines symbol for my GND so don't get them mixed up! Always better to ask if you are not sure :) \$\endgroup\$
    – MCG
    Apr 10, 2017 at 11:44
  • \$\begingroup\$ Most circuits only have one "rail", and that is used for GND. It became so common it's even used without the GND label attached to it. Look at the example circuits in datasheets. It's everywhere. So, using a rail symbol elsewhere, one might mistake it for that "GND symbol". Putting a connection dot to it helps people understanding it's the original rail symbol. \$\endgroup\$
    – Janka
    Apr 10, 2017 at 12:04

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