Negative Bus-Bar

[fishnfire]

Working on isolating the grounds under my helm that are currently grounded to the aluminum dash/hull. Would like to ground everything back to the battery via a common terminal. What would be the best way to do this? Specifically: bus-bar type, amps, gauge of wire. The run will be 14'(28' round trip. The load will be: VHF, Sonar, Stereo, Nav/Anchor lights. I already have a fused/switched accessory bus, but it seems to be grounded to the dash.

 

[crab bait]

Re: Negative Bus-Bar

i made my own bus-bar..<br /><br />my local true value store was voted best in county..<br /><br />bought a piece-o-brass sheeting.. 4" x 8"x 1/8 ".. mounted that to a piece-o-wood.. but before i did,, i bored 20 or so 1/8 holes in sheet.. then mounted it to the wood..<br /><br />then mounted/screw the unit under dash in conveinant place.. ran # 4 gauge to neg post on battery.. then crimped an soldered a ring terminal to the other end an mounted it to brass bus with phil-head wood screw.. <br /><br />then every small circut ground with a ring term an screw..<br /><br />the '20' small 1/8 holes make the 'term screw' easier into the wood backing ..<br /><br />use aluminum wire compound or di-electric grease on the ring term - bus contact point surface.

 

[Texasmark]

Re: Negative Bus-Bar

Super idea Crab Bait. <br /><br />One thing to keep in mind Fishnfire is that the better grounds are "single point". You have chosen your batt. neg term as your point. Great. By using Crab Bait's suggestion, with the wood backing plate, you isolated the ground buss from the boats hull so that there are no "eddy" currents running thru the hull with can cause corrosion. Then with the engine's housing tied (grounded) to the engine's wiring harness and subsequently to the batt neg, you have your perfect setup.<br /><br />When you're all done, a quick sealer is to spray clear acrylic (polyurethane rattle can) all over the terminals, wire connections, and lugs.<br /><br />Mark

 

[Texasmark]

Re: Negative Bus-Bar

Super idea Crab Bait. <br /><br />One thing to keep in mind Fishnfire is that the better grounds are "single point". You have chosen your batt. neg term as your point. Great. By using Crab Bait's suggestion, with the wood backing plate, you isolated the ground buss from the boats hull so that there are no "eddy" currents running thru the hull with can cause corrosion. Then with the engine's housing tied (grounded) to the engine's wiring harness and subsequently to the batt neg, you have your perfect setup.<br /><br />When you're all done, a quick sealer is to spray clear acrylic (polyurethane rattle can) all over the terminals, wire connections, and lugs.<br /><br />Mark

 

[byacey]

Re: Negative Bus-Bar

There really isn't any eddy currents involved because this only occurs with AC current. However a "star" ground is good practice to follow, and this is essentially what you have done. The only thing I would do different is not relying on the wood screws to maintain a tight bond to the buss bar. This will eventually loosen up and cause high resistance connections due to wood swelling and shrinking as well as moisture. Better is to use stainless or nickel plate machine screws with a toothed lock washer and a nut to fasten the connections to the buss bar. Then use micarta or a couple of nylon blocks to isolate the buss bar from whatever you are fastening to. Micarta is good because it doesn't absorb water and is unaffected by higher temperatures, wheras the nylon could melt if the buss barr ever got hot from heavy currents due to shorts, etc.

 

[Texasmark]

Re: Negative Bus-Bar

Back the truck up Bill. <br /><br />DC is how you plate metals on metals. Polarity determines which goes to which. So with the hull corrosion, the dc will and can do it.<br /><br />Grant you that interferece that comes off the ground lead from other equipment operating has to be AC to be a problem.....45 years in the aircraft electronics industry. BTDT countless times.<br /><br />Mark

 

[byacey]

Re: Negative Bus-Bar

Oh, I'm not disagreeing about electrolytic action, but eddy currents are definitely not a factor here unless there is AC current involved. DC current does not produce eddy currents. Perhaps you meant ground loop current. Any time there is two ground paths for current, there will be a voltage difference created between point A and point B due to resistance. The whole point to using a star ground scheme is to eliminate any other possible ground current paths. I think the misunderstanding here is just one of nomenclature. I'm electronics technician and see various forms of this problem in equipment design as well as poor installation practices.

 

[Texasmark]

Re: Negative Bus-Bar

Ok Bill. Will give you the ground loop on DC. Most of the eddy currents I dealt with were in the cores of transformers and they were definitely AC.<br /><br />Also on grounding, we had to decide on the scheme to use; single point or random parallel. Sometimes one would work where others didn't.<br /><br />Enjoyed the exchange. Been retired for 14 months now and it feels good to dust off the noggin now and then.<br /><br />Mark

 

[Smig]

Re: Negative Bus-Bar

I'm getting ready to do some wiring and came across this thread - obviously there is a lot of good thoughtfull experience here, so I'll try to take advantage of it!!<br /><br />So to really "dust of the noggin" - just what is a "star ground?"<br /><br />Thanks<br />Shaun

 

[byacey]

Re: Negative Bus-Bar

A star ground is when all the ground leads from the various electric loads are brought back to one central ground connection. Automotives generally just ground the loads anywhere on the frame or sheetmetal body that is handy - and from the automotive perspective, this works fine. however with an aluminum or metal hull boat you don't want electric current from various loads in the boat traveling through the hull. It is better practice to make a central buss bar connection that all the ground leads run to and get connected to, and then have a nice heavy conductor from the buss bar to the negative battery terminal. This ensures that there is only one possible ground return path for the current from each individual load. The name star ground comes from the image of a central ground point with all the ground leads radiating from the center outwards to the various loads.

 

[Smig]

Re: Negative Bus-Bar

Thanks Bill, that makes perfect sense. <br /><br />As for each individual item on any given circuit, does this mean that each comes back to the bus (eg: in parrallel) or should multiple items on one circuit bring just one ground back to the bus (eg: in series.) I guess I am asking wheather each radiating arm in the 'star' corresponds to a circuit or an item?<br /><br />Shaun

 

[byacey]

Re: Negative Bus-Bar

Each arm would be an item, a light, a radio, can opener, whatever. you may have multiple lights on one circuit, but there should be a ground return wire from each light. This means there would be a seperate wire from the stern lamp, a seperate wire from the bow lamp, a seperate wire from the mooring lights etc. all going to the buss bar. As well, the ground wire going to the buss bar should be the only ground. This means that all lights, radios etc. should be isolated from the hull.

 

[Smig]

Re: Negative Bus-Bar

Thank you Bill

 

[byacey]

Re: Negative Bus-Bar

No Problem, glad to help any way I can.