Earth ground for simple DC circuit

Wendy

Joined Mar 24, 2008
23,415
By tieing one side of the battery to this and defining it as the common point, it does define polarity. If it had been on the other side of the battery the polarity would have been opposite. Think ± power supplies.

As with most low voltage circuits, the earth doesn't have anything to do with it, it merely defines the common point of measurement.
 

GetDeviceInfo

Joined Jun 7, 2009
2,192
By tieing one side of the battery to this and defining it as the common point, it does define polarity.
You are correct, my error. I was thinking a specific polarity.

As with most low voltage circuits, the earth doesn't have anything to do with it, it merely defines the common point of measurement.
What I don't understand, is for the sake of clarity, why you would insist on ambiguity. In all the work I've done from electrical to instrumentation to PLC/logic, the earth symbol means tied to earth. Can it be a common reference, of course. The most important consideration in using (or not) the earth symbol, is ones' relationship with the circuit and their surroundings. With any circuit that I engage I check for two things, that it's tied to earth, or that it is appropriately isolated. You can belittle the finer points, but God help anyone progressing to a circuit that can kill.
 

Wendy

Joined Mar 24, 2008
23,415
I basically agree with you on many points, but the issue is common usage. This is in and of itself a standard, though not a formal one.

If I look at the schematic of a small portable stereo, there will be ground throughout the circuit, and it will probably use the standard I illustrated and was shown several posts ago.

It is probably appropriate to acknowledge the two standards to beginners, then emphasize one is highly formalized and defined because of safety, while the other is a convention for low voltage battery circuits. If the subject turns to line voltages emphasize both the standards and safety.

Unfortunately it can be even more confusing when you talk about an appliance such as a portable stereo that is both AC/DC powered, as that low voltage ground symbol will still be there.

So when we are talking about high voltage line circuits we can emphasize the standards, as they are pretty well defined. When talking about low voltage stuff you have to adopt a different set of conventions.
 
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GetDeviceInfo

Joined Jun 7, 2009
2,192
I basically agree with you on many points, but the issue is common usage. This is in and of itself a standard, though not a formal one.

If I look at the schematic of a small portable stereo, there will be ground throughout the circuit, and it will probably use the standard I illustrated and was shown several posts ago.

It is probably appropriate to acknowledge the two standards to beginners, then emphasize one is highly formalized and defined because of safety, while the other is a convention for low voltage battery circuits. If the subject turns to line voltages emphasize both the standards and safety.

Unfortunately it can be even more confusing when you talk about an appliance such as a portable stereo that is both AC/DC powered, as that low voltage ground symbol will still be there.

So when we are talking about high voltage line circuits we can emphasize the standards, as they are pretty well defined. When talking about low voltage stuff you have to adopt a different set of conventions.
Well I certainly can't argue with that. I guess it comes down to designers/drafters utlizing what they feel is 'standard'. Just hoping that everyone playing with electricity is aware of the considerations, be it ground, earth, chasis, or whatever references are being made. For me, working with power, I clarify the references with those I work with, both from prints (schematic) and a physical perspective. I just hate when those big cables slap around in conduit when someone wasn't clear.
 
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