Why Have a Fuse Box Ground Bar?

[Larry Fine]

Ah, c'mon Larry! Now you have brought me back to square one- why have an additional ground bar?

It's optional to use and still up to the installer to decide. In some cases, the terminal strip may be easier to access than a suitable ground point. Also, the current usage of the accessory in question matters. Several high-current devices may overload a single wire between the fuse-block ground bus and the point where it's grounded.

I believe the real answer is to make it easier than having to stack several ring terminals on the battery's negative terminal, possibly requiring a longer terminal bolt, the same way the fuse block eliminates the need to do the same thing on the positive terminal and using several in-line fuse holders, which is what many people have done.

 

[rjs987]

I can't help but think of all the cars I've torn into to add something or fix something. I have ALWAYS found, when I have looked for it, that someplace on every individual metal body part that may need a ground path has someplace on it a bolt that connects to a ground wire that daisy chains all the way back to the primary ground point in the engine compartment connecting each individual metal panel or frame member by wire all the way back to the battery ground as needed (though I will admit that I haven't been under the panels of my newest Rav4). That primary grounding point is either on the engine or a nearby body/frame member that the battery Neg terminal is tied to and branches off to all other points that need a reliable ground path. Even if that ground wire is connected at one end of a metal part with the lamp ground connected (for example) at the other end where you don't see an obvious wire connecting all the way to the battery. So there is no relying on frame part to frame part contact for ground but a wire bolted on to provide a reliable ground connection. Same is on every bike I've taken apart for the purpose to add electrical stuff. There is, if you search for it, a bolt on the engine or frame/engine mount someplace for the battery neg cable to connect for ground and from there other wires branch off to other parts of the bike where a ground is needed or on that same individual chunk of metal there is another wire. It is not likely where you can easily find it. At least this is what I've found in all modern vehicles.

btw- the engine must have a reliable ground or there may be degraded or no spark from the plugs so there IS a ground wire from the engine to a primary ground bolt with a heavy wire that leads back to the battery (or the primary ground bolt is directly on the engine).

So go ahead and use frame for ground. But unless you are certain that individual frame part is wired back to battery ground you may be subject to unexplained issues due to corrosion between frame parts that may or may not be grounded by a wire bolted on.

 

[Andrew Shadow]

In my experience Bob you are correct in that in most vehicles the negative battery cable goes directly to the engine and then there will be one or more ground straps connected from the engine to the body and frame to ensure that they also have a complete ground path. The correct functioning of any accessory will depend on that complete circuit. Every other electrical device on the vehicle is dependant on this same ground path and they all seem to function barring the connection issues that can crop up anywhere. I find it interesting that there is this opinion that it is not prudent to trust our added on accessories to the reliability of the same ground path that the rest of the bike's electrical system uses. I find that curious and was wondering why that is.

Interesting discussion in that I have become aware of a few things I hadn't thought about before I asked this question.

 

[rjs987]

Just another thought not related... or maybe really a side thought but somewhat related... or maybe not.

I just completed adding a heater/fan/light in the master bathroom. I do my own wiring and I do it to the current electrical code. 50-60 years ago it was common for a 2-wire cable to run in metallic conduit from the fuse or breaker panel to each and every metal electrical box or device in a home. That metal conduit was relied on for the ground connection back to the panel. That was found to be unreliable since conduit couplers were prone to oxidation and other corrosion breaking the ground path. Now house wiring includes a dedicated ground wire within the sheath (Romex usually) to provide a dedicated ground path all the way back to the breaker panel. The neutral (white) wire is also tied to earth ground but ONLY in the breaker panel and no place else. These 2 wires provide a redundant path to ground in your home and the panel is the ONLY place where they are tied together to ground. Kind of the similar thing with a dedicated ground wire to the battery on a bike only we really don't provide redundant paths. Of course you don't see metal conduit in most applications that are otherwise enclosed in a wall or ceiling now. They are all plastic or Bakelite composite except for the fixtures themselves. Metallic conduit is still used and is grounded like before but there is always also a dedicated ground wire in there now.

 

[spiderman302]

If you tie to the FRAME of the bike you are fine.
There is only one wire from the alternator going to the positive side of the battery, it's negative return is through the frame/engine. The same is true with the starter motor.

But if you tie to the forks or swing arm you will have current going through your greased bearings. Or if you tie to a painted rack or brace the "connection" might be through a small bur or edge.
Since you are running the positive wire to the fuse anyway, the ground block makes for a convenient place to hook your cluster of ground wires in one place that should be a known low resistance connection to the frame. This assumes that your hooked the ground block up to the frame or - battery with a heavy gauge wire......... (See first statement)

By the way all the power that is running your farkels is coming from the alternator not the battery hence the need to be tied to the frame.... this assumes that you are actually riding the bike.....

 

[Al Gully]

To me, the engine is not the best place for a ground termination. Most engines reside on isolators made of rubber.
If you do ground to the engine, make sure your ground strap is in excellent condition.

 

[Andrew Shadow]

To me, the engine is not the best place for a ground termination. Most engines reside on isolators made of rubber.
If you do ground to the engine, make sure your ground strap is in excellent condition.

Because the engine is rubber mounted this makes it the best place to ground to. The cable from the negative battery terminal is solidly bolted directly to the engine. Using the engine as a ground plane offers a lot more conductive mass, and therefore much less resistance than any size cable that you could add, and a direct ground path back to the battery. This assumes of course that the negative battery cable can handle the capacity that you are adding which I believe it can.

 

[Andrew Shadow]

I wanted an accessory system which doesn't rely on the bike's own system as I have no idea about the route that my components will then take to ground and the capacity of the connectors and cables to take my additional load. The cable to the battery looks thick enough, but I'm not one to make assumptions.

In the scenario I have laid out for the purpose of this discussion no additional capacity is being added to any of the existing ground connectors or ground wires that are already there. The accessory would be grounded directly the the engine/frame (preferably engine) through its own ground connection. The ground path would be through the mass of the engine back to the negative battery cable.

I wanted my accessories to be easily isolated from the bike's electrics so that if I ever have an electrical issue, I can eliminate my add-ons as the cause by disconnecting one connector.

This is the one advantage that I see to date about having a ground bar- the convenience factor of one connection if troubleshooting becomes necessary. In my scenario I am ignoring the convenience factor for the purpose of this discussion. This is because I am trying to learn/determine if there is a technical or theoretical advantage. i.e. Does having this additional ground bar make the electrical circuit deliver the current in a superior manner, barring any defects, than does using the engine/frame?

However, the question I would ask you is could isolating your added accessories not be accomplished by simply disconnecting the +ve to your accessory fuse block? I don't understand the need for a seperate ground bar to accomplish this.

I didn't want a number of connections stacked up at any single point. So I have one +ve connection and one -ve connection - both to the battery. Everything else comes from my own connectors built into my own wiring harness which is properly fused and relayed as appropriate

Agreed but again the convenience factor that I am not disputing.

If my accessory wiring fails I don't want it to affect the bikes normal electrics.

As I am suggesting that all accessories be grounded through their own separate ground wires and connectors apart from the bikes existing ground wires and connectors, a failure in the ground path of any accessory should only affect that accessory.

But it looks as though I have made an assumption after all. As @spiderman302 pointed out, when the bike is running, the power is coming from the alternator, not from the battery. So in connecting to that battery post, it looks as though I may be adding to the current being put along the main battery leads to the alternator and to ground.

The technical training that I received as a GM technician was that a ground connection is always to be made to a solid attaching point on the engine first and foremost whenever possible because of this reason. Grounding to the frame was always to be considered as a second choice. If a student asked about grounding directly to the battery a definite no response is what the instructor would give to that question but I can't remember if there was a specific reason. Because I was already aware of what Spiderman pointed out this is one of the primary reasons why I initially asked this question. Adding an additional ground bar makes sense to me. But I didn't know the logic behind grounding it separately from the vehicle electrical system and directly to the battery. I thought that maybe there is something different about motorcycle electrical systems that I am not aware of.

The very thing that I was trying to avoid. I'll be trying to check that out now, but fairly content in the knowledge that the power would then be coming through the main 60 Amp fuse, and that has never blown.

You previously questioned my assumption that there is more than sufficient unused capacity available in the negative battery cable. This is another reason why I am confident that the negative battery cable can easily handle the added capacity- because this fuse does not blow. The negative battery cable can carry the same load as the positive cable does. If the positive side of the circuit can handle the additional load that is being added without blowing a fuse that is rated at less than what the cable can carry, why wouldn't the negative cable also be able to handle it.

Good discussion- still has me thinking.

 

[spiderman302]

Let me muddy the water here a little more......

The alternator creates AC power. Within the alternator is a full bridge rectifier that turns the AC into pulsating DC. This pulsating DC current flows into the battery. The battery is a filter that smooths the current flow. If you have sensitive electronics like an audio amplifier or radio and you connect its ground directly to the alternator frame you might hear a slight buzzing sound. If you move the ground wire to the negative side of the battery the buzzing will disappear. So it would be cleaner to just connect to the battery terminals. Your lights will not be affected either way.

The wire from the battery to the alternator has to be able to handle the starter current which could be as high as 100 amps. There is no fuse in the starter circuit. The short heavy wire from the battery to the alternator is about 1 milli-ohm so the voltage lost at 10 amps is about 10 milli-volts ( 0.01 volts). So we are splitting hairs here.
However if you have a cannabis bike that monitors the bikes accessory current, I can see the need for an isolated power and ground to add farkels.
This is a good discussion.

 

[ST Gui]

However if you have a cannabis bike

You can now have those for recreational use in CA. Previously you needed an MJ1 medical endorsement on your license.

 

[spiderman302]

You caught my engineering humor.... Someone was smoking something when they developed that interface.....

 

[st11ray]

You could have already wired up lights, heated gear and other stuff with two wires running back to a fuse box in the time it's taking for this electrical engineering thread to play out!

 

[Andrew Shadow]

If you have sensitive electronics like an audio amplifier or radio and you connect its ground directly to the alternator frame you might hear a slight buzzing sound. If you move the ground wire to the negative side of the battery the buzzing will disappear. So it would be cleaner to just connect to the battery terminals

Just for clarification purposes for anyone reading this, I do not not suggest ever grounding to the alternator frame. This was always considered a bad idea for the reason you mention. When I write grounding to the engine/frame I am referring to frame of the bike not the alternator frame, with the engine being preferred as mentioned earlier.

I never dabbled much with audio systems in cars so want to ask- would grounding an audio system to the engine at a location not close to the alternator cause the same interference? Car OEM stereo systems are grounded through thebody and don't exhibit this problem so does distance from the alternator provide a sufficient buffer?

The wire from the battery to the alternator has to be able to handle the starter current which could be as high as 100 amps. There is no fuse in the starter circuit.

Not sure I follow you on this. The alternator wire does join up to the positive battery cable on the battery side of the starter relay switch to feed current to the battery and is fused at 65 amps. This wire does not feed the starter motor however. The positive battery cable connects directly to the starter motor through the starter relay switch.

 

[Andrew Shadow]

You could have already wired up lights, heated gear and other stuff with two wires running back to a fuse box in the time it's taking for this electrical engineering thread to play out!

Yes, but it is still winter here and unseasonably cold. My garage is not heated so I can't work on my bike so I'm bored.

 

[T_C]

For audio purposes, copper conducts better the aluminum or steel. You want issues, create multiple paths for the electrons with varying levels of resistance.

For me, it makes more sense to run a separate negative wire (if we are discussing audio use then need to seperate ground from negative, definetly not the same thing as there is no ground on a bike or a train) for each farkle. I don't like too rely on spade connectors or ring terminals and their potential difference with their attachment point. Wire to wire and a bus bar connection is a known and easily diagnosed path.

 

[spiderman302]

To clarify. Your concern was the Ground side of the circuits.
The ground wire from the battery to the alternator/frame has to be able to handle the starter current which could be as high as 100 amps.....

The audio system is a hypothetical example that could be susceptible to pulse noise generated by the alternator, which was used to help your understanding.
The best tool would be to use an oscilloscope with a current probe..... but now we are splitting hairs, just wire your farkels to the battery and it will filter out the noise.....

 

[thekaz]

Just for clarification purposes for anyone reading this, I do not not suggest ever grounding to the alternator frame. This was always considered a bad idea for the reason you mention. When I write grounding to the engine/frame I am referring to frame of the bike not the alternator frame, with the engine being preferred as mentioned earlier.

I never dabbled much with audio systems in cars so want to ask- would grounding an audio system to the engine at a location not close to the alternator cause the same interference? Car OEM stereo systems are grounded through thebody and don't exhibit this problem so does distance from the alternator provide a sufficient buffer?


Not sure I follow you on this. The alternator wire does join up to the positive battery cable on the battery side of the starter relay switch to feed current to the battery and is fused at 65 amps. This wire does not feed the starter motor however. The positive battery cable connects directly to the starter motor through the starter relay switch.

ground loops, poor resistance to ground really come into play when trying to create a signal and transmit like comms or pa. The cleanest power will always be directly attached to the battery through some kind of twisted pair which also helps with inducted noise too ....... lots of vehicles have suppression capacitors all over the place to keep in coming radio signal quiet as the alt is not the only noise maker on a vehicle,many devices can create "noisey power"

 

[thekaz]

You caught my engineering humor.... Someone was smoking something when they developed that interface.....

actually I am pretty sure satan himself developed canbus .......

 

[SMSW]

All this talk about ground loops, resistance, volts, and wires makes my head spin. How about a good ole oil thread?

And here I thought a ground loop was something P-41 Mustangs were prone to do....

 

[mello dude]

All this talk about ground loops, resistance, volts, and wires makes my head spin. How about a good ole oil thread?

Funny, you just beat me to it - I was thinking to write - jeez this thread is kinda nutzo interesting fun, what about an oil thread?