How to use GND symbol on wiring diagram with both AC and DC circuits? - Page 1
Forum section: electronics / beginners

author: doublec4
author_rank: Regular Contributor
timestamp: December 02, 2020, 04:58:28 am
content: Let's say I am making a wiring diagram for a control panel.Inside of the enclosure there is AC 110 coming in and going to a AC-DC converter. I have drawn in my live, neutral and earth ground wires here. The earth ground wire has the GND symbol attached to it. Coming out of the AC-DC converter is my 12VDC positive and DC gnd connections. Both go to terminal blocks inside of the panel to distribute 12VDC power and gnd within the panel/enclosure. When I terminate a 12VDC gnd connection on the diagram with a terminal symbol, should I be using one with the gnd symbol attached to it?I feel like this is confusing as I am potentially suggesting to someone reading this that the DC GND is being connected to the AC earth gnd that is shown on the same sheet?.. How do you differentiate between the two as my understanding is that they may be at different potentials? Do I just leave out the GND symbol for the DC circuit?On that note... I believe some AC-DC converters have DC gnd connected to earth gnd while others have floating output. I am usinghttps://www.meanwell-web.com/en-gb/ac-dc-din-rail-single-output-power-supply-with-drc--100afor this project. Is there something I am missing in the datasheet that would indicate if the output is floating or not?Thank you

author: bdunham7
author_rank: Super Contributor
timestamp: December 02, 2020, 05:03:24 am
content: Believe it or not this has been a contested issue. Here is an article referencing IEC 60417. Do note that this reg is regarding the symbols placed on the equipment itself, not in the schematic. I can't cite any authority as to schematics.https://incompliancemag.com/article/the-grounding-symbols/

author: djnz
author_rank: Regular Contributor
timestamp: December 02, 2020, 05:44:42 am
content: I use different electrical symbols for both grounds; using the same symbol when the output is floating is confusing and misleading.Also, in the datasheet, on page 2, you can see the specification for isolation resistance. There, I/P = Input, O/P = Output and FG = Frame Ground = Grounded Chassis = connected to GND / Earth pin of the mains supply plug. As it shows a value for O/P - FG isolation, the output appears to be floating.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: December 02, 2020, 06:31:56 am
content: If you think about it, in schematics GND is often just shorthand for common connection. What can ground mean for a battery operated device that's isolated from the real-world ground? Nevertheless I still use them in my schematics knowing that there just means common. There are several GNDs available in my EDA. I don't know what standards would apply to diagrams on equipment.

author: doublec4
author_rank: Regular Contributor
timestamp: December 02, 2020, 03:03:11 pm
content: Thanks guys.The software I'm using only appears to have one type of GND symbol that automatically comes off of a terminal , I may have to create a custom symbol for the second gnd (like a signal gnd)

author: pvsage
author_rank: Contributor
timestamp: December 02, 2020, 05:59:53 pm
content: I'd follow the IEC standard in the InCompliance magazine referenced above - use the "protective earth" symbol for your Earth bond. That is, after all, why you have that extra wire in the power cord - to shunt fault currents away from the user and other sensitive components and hopefully trip a breaker or blow the fuse before any magic smoke is released.QuoteIf I had to make a separate mains ground symbol for my schematics, I'd probably make it as close to the IEC standard as I could for clarity, but are you sure your software doesn't already have such a power symbol? In eeschema, it's actually called Earth_Protective.