Originally Posted by Canibul
This is confusing me a little. I thought that the actual flow of electrons was from negative to positive, ( hence the very terms themselves) and that would make the positive wiring
the "dc return".
If the "dc return" (negative) is not a ground, but is connected to ground at the engine
...then it definitely IS a ground....
this is kinda why I asked the question....
Yep, electickey can be confusing and when terms like ground returns, earth loops, single
ground points, RF grounds, ac ground, dc ground, shield grounds , isolated circuits, floating voltages, current flow, bonding, equipotential earths and so on get tossed around in the conversation, even well qualified practitioners of this dark art can get confused so really the lay person has no chance of staying abreast of the conversation, let alone fully understanding it.
But help is on it's way Canibul
with my simple to follow explanation.
When discussing or thinking about low voltage (12 or 24 volt) DC boat circuits, disregard and don't use any term that contains ground or earth. I would go so far as to remove the word "return" as well. Leave these terms for the others to use. There are only two wires to consider, the positive one and the negative one.
Now remember that all DC electrical
devices require current flow in order to operate and this flow must have a path to flow along. Interrupt the path and the item stops working. In this simple explanation, it really doesn't matter which way this current flows or what the current is (more below on that).
The source of the current will be a battery
or a solar
panel or a alternator
and these items have two terminals - one marked positive (+ve) and the other negative (-ve). Conventional flow is considered that the current flows from the +ve to the -ve external to the source. Of course, you can see that internal to the source, this same current must be flowing from the -ve to the +ve but mostly we don't care about where the current flows inside the battery or solar
panel or what have you.
So we have a +ve lead taking the current to your desired device or load (light, anchor winch
, radio etc) and a -ve lead taking this current back to the source (battery etc). The load has two terminals, a +ve one and a -ve .We connect the source to the load using +ve to +ve and -ve to -ve. That's it in a nutshell.
We usually stick the circuit protection devices (circuit breakers / fuses) in the +ve lead along with controls (switches) and distribution items (switchboard, bus, panel etc) and then lump all the -ve leads together and take them back to the battery.
We could do it differently, we could put say the switch in the -ve side or even everything in the -ve wire but we normally just don't, we stick with the conventional way.
We now have the DC device working and no mention of ground, earth or whatever. These terms do have uses and do mean things, it is just they are not relevant to understanding how low voltage DC circuits work.
Now about the direction of current flow; this keeps changing as the conventions change but really at the end of the day, they are merely conventions. If current is to be considered as the movement of electrons, then they move from the -ve terminal to the +ve terminal (exterior of the source); if current flow is considered to be "holes" or the absence of electrons, then it flows the other way. So you see it really is just convention and the current convention (no pun intended) is that it flows from +ve to -ve which is kinda easy to follow. It goes from where there is plenty (+ve) to where is none (-ve).
Now please, no complicated replies pointing out theoretical inconsistencies of the above, it is just a basic DC primer to point out how to understand a boat DC circuit without resorting to confusing terms like grounds etc. for the uninitiated.
By all means point out gross inadequacies of my explanation.
Originally Posted by btrayfors
Nice article Bill, clear and concise, thanks for osting it.