Which wire is generally switched, hot or ground?

[Blue Chips]

Not nearly to this stage as yet but it popped into my mind that the ground wire is switched, say to a trim motor or navigation lights. Did do some searching but found nothing stating.

Thanks
Ken

[WLIU]

In the western hemisphere the "hot" is + voltage and is switched. Most amateur built airplanes are +12V DC.

If you live in another hemisphere or a third world nation, your mileage may vary.

Past results are no guarantee of future performance. Do not try at home.

Best of luck,

Wes

[Blue Chips]

Thanks Wes, found a few schematics and they agree with your answer.
Not sure where I got the switch negative wire from, still seems right in my head but not on paper. :)

[1600vw]

Electricity flows from + to - or positive to negative. So we want to cut the power source. If you cut the ground and something goes to ground you still have power. But if you cut the power and something is still going to ground you have no power.

Tony

[Blue Chips]

That makes sense!

Thanks
Ken

[WLIU]

"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

[Bob Dingley]

I always wondered about the origin of "Lucas invented darkness" then I got an MG.

[rwanttaja]

Electricity flows from + to - or positive to negative.

The irony is that the actual physical flow is negative to positive (the electron flow). They just retained the "definition" that "current" flowed from positive to negative.

Some applications do switch the ground side. I had a 1946 Willys Jeep as a kid, and most of the buttons actually grounded things, rather than applied power to them. If you're running a long wire back from the device, it can be safer to make that the ground wire. If it shorts out, the device comes on, rather than producing a dead short to the battery. For a 16-year-old kid with cheap hardware-store wire, an ignorance of grommets, and a lack of hard-won understanding on how sharp edges of metal will saw through insulation, it was DEFINITELY a safer way to go.

Ron "Why is my horn honking?" Wanttaja

[WLIU]

If you owned an MG then you know that Lucas invented the intermittent windshield wiper also.

Best of luck,

Wes
N78PS

[Dave Stadt]

Electricity flows from + to - or positive to negative. So we want to cut the power source. If you cut the ground and something goes to ground you still have power. But if you cut the power and something is still going to ground you have no power.

Tony

I was taught lo so many years ago and made a living in electronics for decades believing those electrons leave the negative side and travel to the positive. I just checked and physics has not done a 180. Typically, the positive side is switched but as Ron says there are legit reasons to switch the negative side. Don't know if AC 43.13 has anything to say about the matter but it might be worth a look.

[skeeter_ca]

As they say current does flow - to +. I think the biggest reason they "usually" switch the postive side is in case the component or wire shorts to ground it will not work if it is interrupted on the positive side. If you had a vehicle with a positive ground you would want to switch the negative side of the circuit. It's all relative. Alot of computers and such usually ground the negative side of the circuit to turn on a component to keep arcing to a minimum.

skeeter

[rleffler]

As they say current does flow - to +. I think the biggest reason they "usually" switch the postive side is in case the component or wire shorts to ground it will not work if it is interrupted on the positive side. If you had a vehicle with a positive ground you would want to switch the negative side of the circuit. It's all relative. Alot of computers and such usually ground the negative side of the circuit to turn on a component to keep arcing to a minimum.

skeeter

As Skeeter mentioned, there are always exceptions. For example, in the Vertical Products product line, most of the switches are logic switches and all the switch does is provide a path to ground. The signals the controller to enable and apply power to that specified circuit.

[vaflier]

Have I been misinformed in electronics 101. ????. I was taught that current in a DC system flows from positive to negative, due to the fact that the + or positive battery terminal has an excess of electrons and the - or negative terminal has a deficit of electrons. In other words the flow would be from excess to deficit. Was this not correct ??????.

[rwanttaja]

Have I been misinformed in electronics 101. ????. I was taught that current in a DC system flows from positive to negative, due to the fact that the + or positive battery terminal has an excess of electrons and the - or negative terminal has a deficit of electrons. In other words the flow would be from excess to deficit. Was this not correct ??????.

Yep. Remember, electrons have a NEGATIVE charge. Having a lot of them doesn't produce a positive terminal.

Ron Wanttaja

[Dave Stadt]

Have I been misinformed in electronics 101. ????. I was taught that current in a DC system flows from positive to negative, due to the fact that the + or positive battery terminal has an excess of electrons and the - or negative terminal has a deficit of electrons. In other words the flow would be from excess to deficit. Was this not correct ??????.

You were misinformed. Gazillions of negativity charged electrons hang around the negative terminal looking for a way to get to the positive side. The positive terminal has the deficit.

[Neil]

You may have been thrown off track by someone talking about how to wire the master solenoid. As a rule the master solenoid is mounted as close to the battery as possible. The battery cable to the solenoid is kept very short this way. Also a jumper wire goes from the battery post on the solenoid to one of the trigger post. The other trigger post goes to the master switch and then to ground. This is done so that a minimum amount of wire in the airplane is hot when the master is off. All the master switch does is ground the trigger post to engage the solenoid.

[1600vw]

I could have gone into the the theory that the flow from a battery is from - to + but we do not practice this theory. If I would have said electricity flows from - to + everyone would have said I am wrong. But in theory this is correct.

But we switch the + just like I said and why. To kill the power and not to switch or kill the ground. If anything goes to ground you still have an closed circuit. But if you switch the + or the positive and something goes to ground you still have an open circuit. Simple. The flow of electrons is a complete different subject in itself.

But here in America we practice that electricity flows from + to - or positive to negative.

Tony

[1600vw]

Yep. Remember, electrons have a NEGATIVE charge. Having a lot of them doesn't produce a positive terminal.

Ron Wanttaja

Also remember its not the negative charge that will bite you but the positive charge that will bite you. This is why when you go to unhook a battery terminal you unhook the negative first.

Tony

[njones]

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

[Matt Gonitzke]

Also remember its not the negative charge that will bite you but the positive charge that will bite you. This is why when you go to unhook a battery terminal you unhook the negative first.

Tony

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).

[1600vw]

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

[Puertoricoflyer]

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. :cool:

[Puertoricoflyer]

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. :cool:

[Frank Giger]

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.

[1600vw]

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

[Jeff Boatright]

"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.

[Dave Stadt]

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.

[Frank Giger]

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.

[1600vw]

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

[jwzumwalt]

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 (http://en.wikipedia.org/wiki/Charge_carrier) 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! Engineers 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.

[MEdwards]

Thanks, Jan. Great first post! Very interesting. I never thought much about it, but now that you mention it, my electrical engineering education in the late '60s was just as you said. The first time I encountered "electrons and holes," different currents flowing both ways, was when we first studied semiconductors my junior year. As I recall, it didn't clarify much!

Of course all this interesting academic stuff is auxiliary to the OP's original question, which also is the title of the thread. He never mentioned +/-, he asked about hot/ground. That question was answered within the first hour, in the second message.

[Al Burgemeister]

As I recall some Fords also had a positive ground, i.e., the positive terminal was tied to the frame. Until those vehicles were no longer around some accessories had to be made to work either way. The norm now is to switch the positive side and to ground the negative side to the frame.

Al B12

[FlyingRon]

In my experience you can find switches both on the ground side or the ungrounded side in aviation and automative applications.
In the case of the Navion, there's one place where there's both. The gear horn circuit goes like this:

+ BUS --- breaker (share with starter) --- throttle switch --- horn --- gear_down_locked switches --- frame


If the throttle switch indicates the throttle is below a certain MP setting and the gear is not down the horn sounds. I found this out because the guy who installed my XM Radio had three active high and three active low inputs to mute the audio that he could connect things to. However neither side of the horn itself will provide a signal that is active high or low with it sounding. If hooked to one side it mutes the radio (or not) with the throttle position and on the other side with the gear being down. It took me a while to figure out why the radio only played when the gear was down.