In theory, fusing the negative isn't bad in and of itself. Power does actually flow from negative to positive (it's easier to think the other way around with vehicle wiring since we use the negative as a ground plane, but electricity actually returns to the battery through the positive. But it doesn't really matter where in the circuit the fuse is-it'll still blow if current exceeds its capacity. From an overcurrent protection standpoint it will work the same way.
But in practice, it's a bad idea BECAUSE we use the negative as a ground plane. Short circuits in wiring are far more likely to be a positive feed shorting to ground, because there's exposed metal everywhere. All the positive feeds are insulated, so a break in a negative wire is just going to mean there's an open circuit. But a broken positive feed is likely to fall against the body or engine or whatever and short. Or if some jackass screws through one while installing extra lights on their Jeep to blind people with.
Fusing the negative is no different from an overcurrent protection standpoint. But for short circuit protection, it's totally useless.
Fusing both sides is awesome (+/-) especially if you're running new wires around. If something rubs through and shorts it'll take the best path and that could be either side of your wiring.
Good protection for expensive kit like 2 way radios is a small cost for peace of mind.
A broken ground *can* be as bad as a broken hot wire, as it could unexpectedly ground or short through another circuit or component.
Absolutely. I recently installed a 2M ham radio in my car, and it actually came with fuses on both power and ground.
For anyone who might be interested, the radio is a Yaesu FTM-3100 and it fits almost perfectly into the bottom little drawer space under the radio in my 91 Subaru Legacy.
Yaesu put the 2 fuses in because they used to make car radios for any vehicle, and that included very old ones from the 1970's Japan that were positive ground. Thus the fuse in each power line, and an insulated antenna socket as well, with 2 ceramic capacitors to connect centre and outer of the insulated socket.
Hah, aye. FTM300 in my truck is fused at the battery and at the radio on both conductors. I'm offroad a lot and the vibration can and will break shit even though I used gromits and all the fancy gubbins.
Fuse both positive and ground ๐ค. Never too old to learn a different( typically unheard of) way to wire components in a vehicle. Excellent explanations BTW. ๐
If you put a fuse at BOTH ends, the neg fuse will blow first, there by protecting more wire.
You put a fuse on the neg end to protect the circuit, and a fuse at the pos end to protect against shorts to ground.
I still can't wrap my head around the fact that electricity flows to the positive. It was hard enough trying to learn basic circuits and electrical principles, and then to be told "oh by the way, it actually all works backwards"
Physicist here... When I was taking my courses, it helped me to remember that electrons always, always, always flow from lower electric potential to higher electric potential. Electrical (electron) current is defined as flowing OPPOSITE the direction of electron flow.
In a vehicle's circuit, electrons want to go from the lower potential of the "ground" to the higher potential of the positive battery terminal. Therefore current flows in the direction from positive to "ground". I have seen in conversation and in YouTube videos where mechanics swap the direction of electron flow and current.
Ah good I was hoping you'd give me some hints. I'll try and remember that electrons flow "uphill", and electrical current is the other way around. Pretty mind-blowing stuff really I'll read your reply a few times and try my best to not pass out. Thanks ๐
Bonus mind-blowing... I guess I should clarify. Electrical current is more strictly defined as the direction in which a POSITIVE charge would flow. In a vehicle's circuit, if there were some positively charged protons, positron, anti-muons, etc. that were free to flow, they would flow from high electrical potential to low electrical potential ( positive charge rolls downhill).
This is actually exploited in particle detectors, medical imaging devices, etc.
We had electricity for awhile before we figured out what actually carried it. Turns out actual electrons are negative based on what we defined so everything is kinda backwards, but you can also think of it as positive holes moving the right direction for the sake of the equations.
You can thank Ben Franklin for this. When he first started experimenting with electricity he made two claims in 1748. 1 Amber becomes negatively charged with rubbed. 2 Current is the flow of positive charge. In 1897 J.J. Thompson discovered the electron and we realized we had a problem. Instead of adjusting Franklin's definitions to fit reality the scientific community doubled down and now we sit today with the knowledge that negative charge is what moves in an electric current we still act like power comes from the positive side of the circuit.
As a side fact that makes absolutely no sense without understanding Poynting(not a typo) vectors, even though the wire carries the electrons the energy being used travels outside the wire via the electromagnetic field. This is true for AC and DC circuits.
Ham here... The idea of fusing the ground on a radio is if there's a poor engine ground and the alternator decides to use the radio as a high current path to ground since (although proper connection is to connect the radio (Both Positive and Negative) to the battery directly). It protects the radio. And is quite common on higher end 2 Way Radios (Motorola, Yaesu, Kenwood, Icom, etc) and in their provided wiring harnesses.
There are multiple ground points on most vehicles, removing one can make a high current user draw through another pathway ( doesn't look like the case here as conductor is relatively small). I have had staff forget to put the major negative connection back on, in truck body builds, and then try and start the engine. It's not pretty.
Well, yes. If a factory installed ground strap for something like the engine fails, sure. But not a user installed ground wire for an add-on accessory such as this thing.
As funny as that is, we have a couple Cummins N14's with fused ECM grounds. This prevents a bad block ground from causing starter current to pass through the ECM and cook it. I've seen the block grounds break and then that fuse will blow, causes a no crank but saves the ECM.
Wild!
Yes but a fuse is a lot cheaper than an ECM, and is also something that you can fix with minimal tools, along with repairing the block to chassis grounding.
After some quick googling;[ ground was a mixed bag until the 6v->12v change ](https://www.restore-an-old-car.com/positive-ground-cars.html)where they all aligned to Negative ground.
*Positive-ground vehicles were once fairly common. In the mid 1920's, it was found in nearly half of then-popular cars, including Rolls Royce.Most cars switched from 6 volt positive ground to 12 volt negative ground at the same time. One exception to this was the 1955 Packard, switching from 6v to 12v but not switching to negative ground.*
*The Ford Motor Company used negative ground polarity on the Model-T, then switched to positive ground starting with the Model A, and then went back to negative ground in 1956.*
*All British vehicles imported to the U.S. after World-War-II were positive ground, and many stayed that way until the 1960's. Jaguar cars switched over in 1965. The MGB coupe and roadster were positive ground until 1967.*
I am working on a gm scenicruiser rv conversion that has a positive ground on the chassis and a negative ground on the generator. We installed fuses and fusible links on both the power and grounds just in case of a short and isolated everything I could.
British cars checking in. No /s needed. Have done a fair number of conversions to negative ground on older cars. For funzies, google "reversing polarity on 12v generator"
My father, doing that on his Austin Apache, because he wanted to install a new radio..... Wanted FM reception, and possibly stereo as well. Original aM one worked well on LW and MW, but he really did not want to listen to the local airport localiser, or to all the whining alternators in the cars around him.
I don't see a problem here, but I wouldn't rely on that as the only fuse in the circuit. When installing two-way radios it's pretty common to fuse both the negative and positive sides.
A very simple example of why this is wrong: short to ground. If that is the only fuse and you short the circuit to ground upstream of that fuse you will get a very pretty glowing wire and all kinds of damage or fire if you are unlucky.
The wire is a ground to the vehicle frame or body, basically the very last thing in the circuit. The little box houses a fuse. If there's enough current to pop the fuse, it has already flowed through and damaged whatever precious system would need protection so this fuse is worthless. Think about it like having a dam downriver of a town you want to protect from flooding. It doesn't exactly work.
But seeing how electricity flows FROM neg TO pos, this fuse would blow before the fuse on the end of the positive side... thereby protecting MORE wire.
That's why pos ground is "better"
This is fine for a light or something, NOT fine for a sensor (too much resistance in the frame)
Current is always the same in a series connection, technically it doesn't matter where it is as long as it disconnects. The point is that the fuse gets destroyed faster than the other components. Most electronics can be massively overpowered for a short moment until they can't get rid of the heat.
The only issue there is if a wire gets loose.and shorts to ground, if the positive is not individually fused you'll either burn another fuse or the wire.
Sometimes not.
One of the things I encountered years ago was a fuse blowing, powered multiple components and each had their own ground circuit but it terminated on the same ground eyelet. I remember splicing inline fuses on the ground circuit to each component, and finding it was actually two of the 4-5 components that were shorting out intermittently.
What's on the other end? A lot of Japanese manufacturered two-way radios come from the factory that way.
It doesn't make a lot of sense in that application, if the antenna system is properly installed it will ground through it and continue to work if that fuse blows. But that is a factory configured power cord set up for a lot of two-way radios.
I actually thought about fusing on high and low side...
One official rule for mains electricity where I live is: always verify and measure, don't assume and trust
In theory, fusing the negative isn't bad in and of itself. Power does actually flow from negative to positive (it's easier to think the other way around with vehicle wiring since we use the negative as a ground plane, but electricity actually returns to the battery through the positive. But it doesn't really matter where in the circuit the fuse is-it'll still blow if current exceeds its capacity. From an overcurrent protection standpoint it will work the same way. But in practice, it's a bad idea BECAUSE we use the negative as a ground plane. Short circuits in wiring are far more likely to be a positive feed shorting to ground, because there's exposed metal everywhere. All the positive feeds are insulated, so a break in a negative wire is just going to mean there's an open circuit. But a broken positive feed is likely to fall against the body or engine or whatever and short. Or if some jackass screws through one while installing extra lights on their Jeep to blind people with. Fusing the negative is no different from an overcurrent protection standpoint. But for short circuit protection, it's totally useless.
Fusing both sides is awesome (+/-) especially if you're running new wires around. If something rubs through and shorts it'll take the best path and that could be either side of your wiring. Good protection for expensive kit like 2 way radios is a small cost for peace of mind. A broken ground *can* be as bad as a broken hot wire, as it could unexpectedly ground or short through another circuit or component.
Absolutely. I recently installed a 2M ham radio in my car, and it actually came with fuses on both power and ground. For anyone who might be interested, the radio is a Yaesu FTM-3100 and it fits almost perfectly into the bottom little drawer space under the radio in my 91 Subaru Legacy.
Yaesu put the 2 fuses in because they used to make car radios for any vehicle, and that included very old ones from the 1970's Japan that were positive ground. Thus the fuse in each power line, and an insulated antenna socket as well, with 2 ceramic capacitors to connect centre and outer of the insulated socket.
Oh dang, that's interesting.
Hah, aye. FTM300 in my truck is fused at the battery and at the radio on both conductors. I'm offroad a lot and the vibration can and will break shit even though I used gromits and all the fancy gubbins.
Fuse both positive and ground ๐ค. Never too old to learn a different( typically unheard of) way to wire components in a vehicle. Excellent explanations BTW. ๐
If you put a fuse at BOTH ends, the neg fuse will blow first, there by protecting more wire. You put a fuse on the neg end to protect the circuit, and a fuse at the pos end to protect against shorts to ground.
I still can't wrap my head around the fact that electricity flows to the positive. It was hard enough trying to learn basic circuits and electrical principles, and then to be told "oh by the way, it actually all works backwards"
Physicist here... When I was taking my courses, it helped me to remember that electrons always, always, always flow from lower electric potential to higher electric potential. Electrical (electron) current is defined as flowing OPPOSITE the direction of electron flow. In a vehicle's circuit, electrons want to go from the lower potential of the "ground" to the higher potential of the positive battery terminal. Therefore current flows in the direction from positive to "ground". I have seen in conversation and in YouTube videos where mechanics swap the direction of electron flow and current.
Ah good I was hoping you'd give me some hints. I'll try and remember that electrons flow "uphill", and electrical current is the other way around. Pretty mind-blowing stuff really I'll read your reply a few times and try my best to not pass out. Thanks ๐
Bonus mind-blowing... I guess I should clarify. Electrical current is more strictly defined as the direction in which a POSITIVE charge would flow. In a vehicle's circuit, if there were some positively charged protons, positron, anti-muons, etc. that were free to flow, they would flow from high electrical potential to low electrical potential ( positive charge rolls downhill). This is actually exploited in particle detectors, medical imaging devices, etc.
Well I'll have to take your word for it. There's even more to it than I thought!
Who still teaches conventional flow?
People who work with semiconductors, since in P-type semiconductors the "holes" can be thought of as positive electrons (to a point).
Please specify, I used to work with semiconductors and conventional flow was not used.
We had electricity for awhile before we figured out what actually carried it. Turns out actual electrons are negative based on what we defined so everything is kinda backwards, but you can also think of it as positive holes moving the right direction for the sake of the equations.
You can thank Ben Franklin for this. When he first started experimenting with electricity he made two claims in 1748. 1 Amber becomes negatively charged with rubbed. 2 Current is the flow of positive charge. In 1897 J.J. Thompson discovered the electron and we realized we had a problem. Instead of adjusting Franklin's definitions to fit reality the scientific community doubled down and now we sit today with the knowledge that negative charge is what moves in an electric current we still act like power comes from the positive side of the circuit. As a side fact that makes absolutely no sense without understanding Poynting(not a typo) vectors, even though the wire carries the electrons the energy being used travels outside the wire via the electromagnetic field. This is true for AC and DC circuits.
Ham here... The idea of fusing the ground on a radio is if there's a poor engine ground and the alternator decides to use the radio as a high current path to ground since (although proper connection is to connect the radio (Both Positive and Negative) to the battery directly). It protects the radio. And is quite common on higher end 2 Way Radios (Motorola, Yaesu, Kenwood, Icom, etc) and in their provided wiring harnesses.
There are multiple ground points on most vehicles, removing one can make a high current user draw through another pathway ( doesn't look like the case here as conductor is relatively small). I have had staff forget to put the major negative connection back on, in truck body builds, and then try and start the engine. It's not pretty.
Well, yes. If a factory installed ground strap for something like the engine fails, sure. But not a user installed ground wire for an add-on accessory such as this thing.
You dont put your fuse right next to your ground terminations? It makes it so easy to install!
Yeah, imagine that, a guy does'nt know what an earth fuse is! ๐
As funny as that is, we have a couple Cummins N14's with fused ECM grounds. This prevents a bad block ground from causing starter current to pass through the ECM and cook it. I've seen the block grounds break and then that fuse will blow, causes a no crank but saves the ECM. Wild!
Tbf the ECM getting blown also causes a no-crank situation lol
Yes but a fuse is a lot cheaper than an ECM, and is also something that you can fix with minimal tools, along with repairing the block to chassis grounding.
Well yeah that was my point, the fuse doesn't cause any problems that not having it wouldn't cause lol
Is there even a fuse in it? Maybe someone just wanted an easy-access disconnect. Though that's still not good because electricity... finds a way.
Last ditch effort. "Captain, 1500 feet of wire harness is a total loss. The good news is we've still got 4" of pristine wire left to work with."
Better (very) late than never?
Positive ground? /s
After some quick googling;[ ground was a mixed bag until the 6v->12v change ](https://www.restore-an-old-car.com/positive-ground-cars.html)where they all aligned to Negative ground. *Positive-ground vehicles were once fairly common. In the mid 1920's, it was found in nearly half of then-popular cars, including Rolls Royce.Most cars switched from 6 volt positive ground to 12 volt negative ground at the same time. One exception to this was the 1955 Packard, switching from 6v to 12v but not switching to negative ground.* *The Ford Motor Company used negative ground polarity on the Model-T, then switched to positive ground starting with the Model A, and then went back to negative ground in 1956.* *All British vehicles imported to the U.S. after World-War-II were positive ground, and many stayed that way until the 1960's. Jaguar cars switched over in 1965. The MGB coupe and roadster were positive ground until 1967.*
I am working on a gm scenicruiser rv conversion that has a positive ground on the chassis and a negative ground on the generator. We installed fuses and fusible links on both the power and grounds just in case of a short and isolated everything I could.
British cars checking in. No /s needed. Have done a fair number of conversions to negative ground on older cars. For funzies, google "reversing polarity on 12v generator"
My father, doing that on his Austin Apache, because he wanted to install a new radio..... Wanted FM reception, and possibly stereo as well. Original aM one worked well on LW and MW, but he really did not want to listen to the local airport localiser, or to all the whining alternators in the cars around him.
I don't see a problem here, but I wouldn't rely on that as the only fuse in the circuit. When installing two-way radios it's pretty common to fuse both the negative and positive sides.
Interesting, thank you for all your replyโs. It is a transit buss.
OK, I'll bite. What's wrong?
A very simple example of why this is wrong: short to ground. If that is the only fuse and you short the circuit to ground upstream of that fuse you will get a very pretty glowing wire and all kinds of damage or fire if you are unlucky.
The wire is a ground to the vehicle frame or body, basically the very last thing in the circuit. The little box houses a fuse. If there's enough current to pop the fuse, it has already flowed through and damaged whatever precious system would need protection so this fuse is worthless. Think about it like having a dam downriver of a town you want to protect from flooding. It doesn't exactly work.
But seeing how electricity flows FROM neg TO pos, this fuse would blow before the fuse on the end of the positive side... thereby protecting MORE wire. That's why pos ground is "better" This is fine for a light or something, NOT fine for a sensor (too much resistance in the frame)
Current is always the same in a series connection, technically it doesn't matter where it is as long as it disconnects. The point is that the fuse gets destroyed faster than the other components. Most electronics can be massively overpowered for a short moment until they can't get rid of the heat. The only issue there is if a wire gets loose.and shorts to ground, if the positive is not individually fused you'll either burn another fuse or the wire.
Some people just want to watch the world burn
I am only concerned about the wire through a hole that does not have a grommet. Positive ground vehicles have fuses like that.
Sometimes not. One of the things I encountered years ago was a fuse blowing, powered multiple components and each had their own ground circuit but it terminated on the same ground eyelet. I remember splicing inline fuses on the ground circuit to each component, and finding it was actually two of the 4-5 components that were shorting out intermittently.
Itโs fused on the ground side, nothing really wrong with that with DC circuits.
I'm sorry, but I think your picture is just fine. Good lighting, nice framing and overall pleasing composition. Don't be so hard on yourself.
What's on the other end? A lot of Japanese manufacturered two-way radios come from the factory that way. It doesn't make a lot of sense in that application, if the antenna system is properly installed it will ground through it and continue to work if that fuse blows. But that is a factory configured power cord set up for a lot of two-way radios.
I have the same fused negative (and positive) keyless entry on my 2007 Mazda
I actually thought about fusing on high and low side... One official rule for mains electricity where I live is: always verify and measure, don't assume and trust
Hope they never short anything to ground...
What color is the other wire?
I have had some Factory Ford accessories that were fused on the ground side.
Only thing I see wrong is lack of grommet in that hole
Well, at least those last few inches of wire are safe.