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Thread: Which wire is generally switched, hot or ground?

  1. #21

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    Quote Originally Posted by Matt Gonitzke View Post
    Only true for negative ground. If it is a positive ground system then you'd remove the positive cable first. The ground is removed first so that you can't short the positive terminal to ground with the wrench (on a negative ground system).
    Let me think, the last time I saw a positive ground system was, to long ago to remember.

    Tony

  2. #22
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    Current flows from positive to negative and from negative to positive at the same time. It is all about difference in charges and what makes more sense to you. If there are too many electrons then the charge is negative. Not enough electrons and there are "spaces" where the electrons should be resulting in a positive charge. Electrons get pushed out of the negative side (too many) and are attracted to the positive side (not enough). At the same time the "spaces" go from the positive side to the negative side. Remember; "Opposites Attract". So it really doesn't matter which way you look at this they are both right and are both wrong. The reason EE's say current flows positive to negative (look at the arrow on a Diode) is so the math doesn't wind up with lots of negative numbers, and for no other reason. In any electrical setup, you can't be bitten until you are touching both sides of the voltage source. So you can be bitten by touching and ungrounded negative side of a circuit even if it is the "ground" wire. If you don't believe this, how do you think birds can stand on one exposed high voltage wires and not get shocked? But if they touch both wires at the same time then ZZZZAAAPPPP! Fried bird meat.
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  3. #23
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    Quote Originally Posted by njones View Post
    Guys, direction of current flow is not the issue - there is no reason tied to any laws of physics that defines which wire should be switched. Safety, standardized design methods and ease of debugging are the main factors that drive why things are done a certain way.

    We commonly call the power supply (battery) terminal that is connected to the frame "Ground" (but in fact "Chassis" or "Circuit Common" is a better term since it isn't actually connected to the earth). And we commonly call the call the power supply (battery) terminal that is connected via fuses and switches to various loads "Hot" or "Supply".

    Because many systems use (-) common, it's common to hear people calling (+) "Hot" and (-) "Common" or "Ground" - while this is true on (-) common systems, it's very good idea to NOT get into this habit because it can lead to mistakes if you ever work on a (+) common system.

    There is no practical difference between a system with (-) "common" with (+) fused/switched and (+) "common" with (-) fused/switched. As some have already posted both types of systems are out there. That being said, there are a few cases where there is a good (electronic) reason for using either (+) or (-) common.

    The vast majority of North American systems use (-) common, and unless you have a particular piece of equipment (rectifier/regulator for example) that needs to be (+) common, then it's probably better to stay with (-) common because that's what most people expect to see.

    $0.02
    VERY well stated.
    Galin
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  4. #24

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    Okay, I think I'm now lost in all of that. For simple guys like me, I think all of that says:


    (+) ------------ switch ---------thingie---------(-)

    The (+) being the post on the battery that has a (+) next to it.

    The thingie, naturally, is whatever is getting the juice.
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

  5. #25

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    Quote Originally Posted by Frank Giger View Post
    Okay, I think I'm now lost in all of that. For simple guys like me, I think all of that says:


    (+) ------------ switch ---------thingie---------(-)

    The (+) being the post on the battery that has a (+) next to it.

    The thingie, naturally, is whatever is getting the juice.
    I like this post...



    You have those that when asked what time it is will tell you how to make a watch. If you do give the time, you will be wrong for you did not explain how to build the watch and only when one understands how to built the watch can one then learn to use it.

    Tony

  6. #26
    Quote Originally Posted by WLIU View Post
    "Electricity flows from + to - or positive to negative"

    I have to ask whether you have ever owned a British car? The builders of the old MG's etc seem to have a different opinion as to the physics. Hence my poor attempt a humor in my post.

    Best of luck,

    Wes
    N78PS

    Ha! I was just going to make the same point, Wes. My Sprite would beg to differ about which way things flow. And I "got" your humour! (I think that's the correct spelling... ). BTW, I've have many fewer problems with my Lucas electrics than I ever had with VW and Ford electrics in cars of the same vintage. As they say, YMMV.

  7. #27

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    Quote Originally Posted by 1600vw View Post
    I like this post...



    You have those that when asked what time it is will tell you how to make a watch. If you do give the time, you will be wrong for you did not explain how to build the watch and only when one understands how to built the watch can one then learn to use it.

    Tony
    Except now days people put the battery in backwards then go buy a new watch because they figure the old one is broke.

  8. #28

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    Well, 1600, there's merit in both ways of discussing things.

    I always figured there were three paths to learning stuff:

    First is the "how it's done" path, which was my post - short on why and how on long. This is the simple nuts-and-bolts procedure, and critical to getting it done.

    Second is the "why it's done that way," which is the bulk of the thread and is actually critical in maintaining equipment and elevating from basic installation to complex ones. If the electrical system is acting wonky, we'll know to check the wiring schematic and make sure it's actually wired that way, with the switch on the right side.

    Third is the "except when it ain't," which are the exceptions and alternate ways to do the same thing - often with mixed results. But it's nice to know when standard practices can be deviated from safely - and the why and how it was done.

    I just wanted to make sure I got the first path understood correctly, as I'll be designing and putting in the electrics - all three circuits - myself.
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

  9. #29

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    Quote Originally Posted by frank giger View Post

    third is the "except when it ain't," which are the exceptions and alternate ways to do the same thing - often with mixed results. But it's nice to know when standard practices can be deviated from safely - and the why and how it was done.
    rotflmao

  10. #30
    http://en.wikipedia.org/wiki/Electric_current

    "A flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges, or both, a convention for the direction of current which is independent of the type of charge carriers is needed. The direction of conventional current is arbitrarily defined to be the same as the direction of the flow of positive charges."

    I am a retired electrical engineer and can testify that in the United States electronic technicians use "electron current" - the current is described as following the electrons from negative to positive. Electronic engineers use
    "conventional current"; a different set of formulas (opposite) that are based on using "positive" current flow - this is sometimes referred to as "hole theory" (the electrical pressure by the absence of electrons).

    When current was discovered it was assumed to flow from (+) a high potential to low (-) as we experience in the natural world. When the mistake was discovered technicians and lay people made the correction while the "educated" people never did! E
    ngineers continued to use "positive" current in the same way doctors use Latin descriptions. It is to impress people (as in appear smarter than you really are) with non conventional nomenclature and formulas that are somewhat unrecognizable!

    You can imagine the problems caused because
    engineers use "conventional current" theory to design circuits and technicians use "electron current" formulas to build and test the circuits. When a problem arises and they try to talk on the phone, it can get complicated. Many universities use "electron current" flow for the first year or two, then switch to "conventional current" formulas for the remainder of the engineer's degree.
    Last edited by jwzumwalt; 04-21-2014 at 10:01 AM.
    Jan Zumwalt - EAA #66327
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