Switched and fused at the ground connection!!

[byacey]

Re: Switched and fused at the ground connection!!

Originally posted by Bill Yacey:<br />

Originally posted by --GQ--:<br /> What the heck is "positive ground". I don't think the word positive should be used to describe a ground when dealing with electricity. <br /><br />Bill, I can give you so many scenarios why you should never switch on the ground side. I hink you trying to pull a fast one...lol. Explain youself.....

GQ, positive ground systems have been around for a hundred years or more in vehicles, communication electronics, modern day bipolar power supplies to name a few. Look at any old Chrysler Automotive product from the mid 1950's or older. <br />I totally agree that fusing and switching the ground lead is dangerous; everything I wrote in my last post explains why. Older Chrysler outboards ( and perhaps others I am unaware of) used a positive ground connection - yep believe it or not. The only difference is the common or ground return is now at a positive potential rather than negative. All wiring practices are identical though, no fuses or switching in the ground / return lead. I am not arguing your point about proper wiring practice of putting the fuse and load switching on the supply side of the load, and not the ground / return side.

 

[jtexas]

Re: Switched and fused at the ground connection!!

Originally posted by KaGee:<br /> JB,<br /><br />Technically, current does flow negative to positive. But I'm surprised at that set up.

I always thought current flow is pos to neg - electron flow is neg to pos, but current is the holes.

 

[byacey]

Re: Switched and fused at the ground connection!!

In semiconductor theory conventional current flow is positive to negative, or also called hole flow. Actual current flow, and the modern accepted theory is the electrons moving negative to positive. <br /><br />The average starter could care less what direction the current is going aside from the proper polarity of the field to ensure rotation in the right direction.<br /><br />This is beginning to wander way off topic from JB's original question. Perhaps if some members want to discuss practical and theoretical electronics / electrics we should start a different post. There appears to be a lot of misunderstanding how this pertains to watercraft. Paul Moir, Davef,myself and others have knowledge and experience in these areas and I am sure would be happy to help and shed some light.

 

[JB]

Re: Switched and fused at the ground connection!!

Show me an outboard that uses the positive lead as a common ground and I might. . . just might. . .retract the "DUMB" comment.<br /><br />Using a negative ground on your engine systems and a positive ground elsewhere is even DUMBER!!

 

[byacey]

Re: Switched and fused at the ground connection!!

As I mentioned, there are positive ground outboards and motor vehicles that use positive ground systems. <br />I don't think anyone has suggested having mixed ground potentials - this would be idiocy. However, if you have a positive ground system and some polarity sensitive loads such as radios, gps, etc. There are certain precautions that must be taken to prevent damage to the electronics. If you don't have a thorough understanding of this I would recommend getting someone who knows what they are doing to do the work. 'nuff said.

 

[byacey]

Re: Switched and fused at the ground connection!!

Originally posted by JB:<br /> Show me an outboard that uses the positive lead as a common ground and I might. . . just might. . .retract the "DUMB" comment.<br /><br />

Any Chrysler outboard in the 1960's, maybe in the 70's too, but I'm not 100% positive.<br />You might want to look at this: Schematic<br /><br />JB, It could well be that the fuseblock setup you bought was meant to be used with such a positive ground system as I have shown. If that's the case, you're fine to just swap the busses as marked polarity-wise like you mentioned in your initial post.There have been a lot of confused and mis-directed posts concerning your original question. Hope this helps answer your question.

 

[jtexas]

Re: Switched and fused at the ground connection!!

no offense, Bill, we all appreciate the value of your expertise, and I am unanimous in that. (really, no joke).<br /><br />Isn't this mostly just a general academic and theoretical electrical discussion - original question: "Anyone ever seen this sort of lashup before?" <br /><br />JB, I think he "gotcha" on the pos-ground O/B - but since it's a Chrysler my vote is, don't retract the "DUMB". <br /><br />I also think GQ misdirected his comment at "Bill" - looks like maybe it was intented for "swist"? or did I misread?

 

[byacey]

Re: Switched and fused at the ground connection!!

No offense taken, I was just attemting to clear up some mis-understandings among some of the members. The danger is if someone runs across one of these positive ground systems and is unaware, they could do some expensive damage in a split second upon powering up. If this saved anyone from making this type of mistake, it was a good exercise. It would be interesting to know if the company that made the distro block that JB bought offers a negative ground version as well.

 

[JB]

Re: Switched and fused at the ground connection!!

I started teaching basic electricity and electronics in 1958, Bill. A lot changed by the time I retired in 1997, but positive ground systems were still an anomaly, definitely not standard practice. I am not really surprised that Chrysler might have used a positive ground on their outboards. Must have been an electrician's nightmare to wire up a boat with that lash-up on it.<br /><br />Modern outboards use a negative common, or ground. Modern marine electronics are supplied with in-line fuses in the positive lead.<br /><br />I am still amazed that this supposedly high end panel was supplied set up for fusing and switching at the common, or ground end of the circuit. As you suggest, the "common" bus will become the +12V source and I will construct a ground bus for it.<br /><br />Thanks for your input and for the insights of others.

 

[byacey]

Re: Switched and fused at the ground connection!!

A lot of electronics in the 60's and 70's using PNP transistors used a positive ground reference until the engineers could get their heads screwed around to thinking in terms of emitters to the positive supply rail instead of ground. Perhaps this is why I don't find it too difficult to flip things around in my mind as far as what the reference is. I guess someone accustomed to the ground always being the most negative potential a positive ground would seem kind of strange. As far as interfacing negative ground equipment, the chassis has to be isolated from the hull or any other structural metal at ground potential and have the power supply polarity flipped. The antenna ground has to be isolated as well and coupled to the boat hull through a small capacitor if a ground plane is required. This is another tangent to the whole issue and probably isn't encountered much nowadays.

 

[--GQ--]

Re: Switched and fused at the ground connection!!

Jtex, my first comment was directed for Bill. the second comment wasn't intended for anyone. Just general note and notice the tone of my comment and the smiley faces . You may also notice Bill and I had many "posting" discussion on topics similar to this. I respect his knowlege/opinion dearly. (Now Bill don't be going around with a big head on us all the sudden. You still have to elaborate my question below).<br /><br />At time it is difficult to determine whether the person typing on the other end is angry. This is never the case with me. I just stir things up a little. In doing so I maybe guilty of an act I did not commit. At least to the other person reading my posts. <br /><br />And I still don't know what a "positive ground" is. There I go thinking again.......Happy posting!

 

[byacey]

Re: Switched and fused at the ground connection!!

I'm not angry at all and I'm sorry if someone construed my posts as such, I just try to get the facts out straight when it's something I understand. There are a lot of posts where I just sit quiet because there are many more knowledgable members that know better than I. However in this instance, electronics is my career, and I am a licensed technician. So if I can help someone with my experience and knowledge - I do. That's what these forums are all about, right?<br /><br />Anyways, a positive ground is a ground that has a more positive potential with respect to any other part of the circuit; exactly opposite to a negative ground system. Electrons don't really care what what we call common or ground - there sole purpose is to move tp where there is a lack of electrons when an opportunity of a conductive path is given. In a negative ground system that most people are familiar with the electron current moves from the ground or negative potential of the battery, through the load, through a switch,fuse and then ends at the positive terminal of the battery completing a circuit with current flow. <br /><br />In a positive ground the electrons leave the negative post of the battery, travel through the fuse and switch (hopefully they are provided) through the load and end up at the positive post of the battery which is also the common or ground in this case. Both circuits accomplish the same thing, only difference is which direction the electrons travel through the circuit. I guess the misleading thing is most people assume ground and negative are the same thing, but it doesn't have to be. I hope I described it well enough. <br /><br />Even with lightning bolts - sometimes they strike down from the clouds to the ground indicating that the clouds carry a negative charge with respect to the<br />ground (Earth). This is one huge positive ground circuit. Other times the lightning bolt moves from the ground up to the clouds, meaning that the clouds are carrying a positive charge with respect to the ground that is negative, this being a negative ground circuit. Most people believe lightning always strikes down to earth, but it happens at the speed of light, so it's pretty hard to determine by looking...net result is the same.

 

[Silvertip]

Re: Switched and fused at the ground connection!!

GQ -- buy an older Mac truck or Chrysler car and then try to install a modern stereo in it. The reason it doesn't work is both vehicles have a positive ground/positive earth/positive neutral or whatever else you wish to call it. To be as simple as possible, (and I'm "positive" about this) the positive battery cable is connected to the frame of the vehcile. Hence, ground in this scenario is the positive battery terminal. Do the electrons care which way they go? Heck no, but the electronics connected in that circit do! Reverse polarity on a diode sometime and watch the smoke escape. The same event happens when people reverse the battery cables when attaching them in their boats after storage. Pops the regulator/rectifier every time. Can we please let this topic die. It's getting old.

 

[JohnRuff]

Re: Switched and fused at the ground connection!!

The theory of HOLE FLOW in a boat scares me. Any hole in my boat with stuff FLOWING into it scares me!<br /><br />And there is no right answers when it comes to electricity. That is why it is called the ELECTRON THEORY -- they have never PROVED IT! All that you currently believe is just conjecture!<br /><br />There is one thing you can depend on in electronics. Always connect wires in such a way that they produce the minimum amount of smoke! The reason for this is evidenced as once the smoke gets out of an electronic device, you can't put the smoke back in. Nobody sells CANNED SMOKE for repairing electronic disasters.

 

[byacey]

Re: Switched and fused at the ground connection!!

You're correct John, It is theory, however the results of mis-applying the theory have been demonstrated and verified countless times. I would recommend to anyone to ask a few question if there is any uncertainty about how to correctly wire something, due to the amount of possible variables as shown in previous posts. Randomly connecting things to see which way produces the least smoke doesn't seem like a very cost effective way to determine correct polarity.

 

[swist]

Re: Switched and fused at the ground connection!!

Sorry, I stand by my statement.<br /><br />THEORETICALLY, it doesn't matter where the fuse goes. The current in all segments of any circuit is the same (Kirchoff's current law).<br /><br />The argument being offered is that if the supply side is not fused then a short to ground somewhere in the circuit will not blow a fuse in the return circuit. There are several problems with this statement:<br /><br />1) You are confusing polarity and ground. As someone pointed out, it is simply a convention that we ground the negative side of a DC system. There are many applications where the opposite is true. So did you short to "ground" or to some other circuit's return line?<br /><br />2) A short to "ground" is only a problem if a ground exists (that is, if there is some global surface to which one side, usually negative, of the battery is connected. If a circuit shorts to another circuit's return, that is NOT necessarily the same as it shorting to ground. <br /><br />3) It is perfectly possible for there to be no ground. This is particularly true in internal wiring of a fiberglass boat. I will grant that most engine frames are connected to battery negative hence they function as a real ground. But if you have a house battery which runs only internal devices in an enclosed non-conducting boat, it is likely you have no ground. <br /><br />In this case there is no such thing as a short to "ground" - if a supply lead shorts to some other circuit's return lead, then it is correct that the first circuit's return fuse will not blow, but the second circuit's will.

 

[byacey]

Re: Switched and fused at the ground connection!!

The most logical place in the circuit to place a fuse is where it offers ther most protection. In an aluminum or steel boat the ground or common side of the circuit is most abundant and the chances are greater than average that this is where damaged wiring or electric devices will short to. Placing the fuse just before the circuit returns to ground offers very little in the way of protection should the wire develop a short to the hull or any other device connected top ground. The whole length of wire will burn up from the positive buss connection up to where the short occurs. Further to that, if the wire burns up and it is contact with other wires in a harness, pretty soon all your wiring is burning up with no protection. All the $0.50 fuses in the ground return fortunately will likely not blow, and not require replacing saving you a few dollars. The rewiring job unfortunately will cost quite a bit more. Examine any auto wiring and you will see that return circuits are never fused for the above reason.<br /><br /> If you have a fibreglass boat, it doesn't matter which you fuse, the supply or return line, as long as they are ALL WIRED THE SAME. If one is wired different, then it increases the possibilty of burning wire harnesses again.<br />If it's your own boat wire it how you please

 

[--GQ--]

Re: Switched and fused at the ground connection!!

Originally posted by Upinsmoke:<br />[QB] GQ -- buy an older Mac truck or Chrysler car and then try to install a modern stereo in it. The reason it doesn't work is both vehicles have a positive ground/positive earth/positive neutral or whatever else you wish to call it. To be as simple as possible, (and I'm "positive" about this) the positive battery cable is connected to the frame of the vehicle. <br /><br /><br />Upinsmoke, I understand your point, I don't think we're debating how things were done in the pass. Rather the correct way it should be done with regard to safety. just because it was done doesn't mean it's acceptable in today standard. And as far as "positive battery cable is connected to the frame of the vehicle" thing. I have this to say. Can you image the potential hazard, head ache and heart ache to go along with that scenario? Should the frame of that car ever come in contact with any grounded object........well you see where I'm going. Not surprisingly such practice is not done today for a good reason. Again safety is my argument.<br /><br />JohnRuff you are correct, no one will ever prove which direction electrons flow. However all electronic goods are designed based on Electron Theory (from negative to positive). Based on this, it makes sense to fuse/switch on the positive side for many reasons stated above. You may also know this; the moving force behind any chemical reaction is the result of valence electrons jumping or sharing between atoms. Since they are negatively charged, is it safe to say electrons flow from negative to positive? And because electrons are negatively charged, is it possible for electrons to flow from positive to negative? Also in my opinion, the "Hole Flow" thing has more holes than the idea itself. A "Hole" is an absent of an electron. Its is not a physical matter. It is an empty space. It is a condition. An object (electron) has the ability to fill an empty space (hole) but not the other way around. Just my understanding<br /><br />And I wouldn't be too caught up on the term "Theory". It was a "theory" that oxygen content wasn't sufficient to sustain lives on the moon until Apollo 11 landed many decades ago and proved it. Some "theories" are more difficult to prove. In all theories are stepping stones to human advancement. <br /><br />You get the last word

 

[JohnRuff]

Re: Switched and fused at the ground connection!!

Next time I will toss a few smiles into my message to denote the humor <br /><br />And I do know which way the electrons flow. Last week they flowed from a 110v ac wire into my arm and out my foot.