Is it wrong to use a single (common) groundwire attaching accesories in series?

[madhtr]

... Or do I actually need a ground buss as well as a positive one?

The ground is 14 gauge wire ... I just got this boat, and the after-market wiring is all screwed up. whoever did it before me used a common in series on the bilge pump and the TWOLED flood lights. (the bilge pump was actually slaved to the bow floodlight, heh). It'll be a bit cheaper if I do it like the attached diagram, but I do not want to endanger my passengers, myself, or my accessories.

The boat is an 89 15' Bayliner Capri.

Thanks!

 

[glenn property of pam]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

the ground is carrying current over distance so 14g is to small with the stereo. everything else like the led lights and biege pump should be ok but the stereo realy needs its own ground or to go to a ground block thats running a larger gauge wire back to the battery

 

[Scott Danforth]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

yes you need a ground buss. your ground wires need to be the same size as the power wires. just like running too small of a power wire leads to failure and problems, same goes with ground wire. think of the ground as a return that carries the same current as the supply.

 

[fairbank56]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

This is not ground. It is DC negative. Yes, there should be a DC main negative bus located at the distribution panel. The method of negative wiring currently on your boat is called daisy-chaining and is inappropriate. Proper wire size for the feed from battery to distribution panel depends on total load (current) and length of cable run. You'll want to consider what would be required if you intend to add more accessories such as VHF, GPS, etc. in the future.

Eric

 

[madhtr]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

Thanks, all!

Looks like I'd better get some more wire

 

[NYBo]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

The usual practice is a pair of 8 or 10 gauge wires (10 is fine for your application unless you add a lot of additional devices) from the battery terminals to the fuse block and negative buss bar.

 

[MH Hawker]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

And it is a lot simpler to use a bigger gage wire to start off than to change it out later.

 

[Scott Danforth]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

i ran 4 gauge wire for accessories, however I have a 24' boat and plan on adding an amp, more electronics, etc. I do recommend you make a list of every possible item you want to add to the boat. lights, radio, GPS, depth finder, bilge pump, spot light, etc. add up all the current draws and multiply that by 2.5. then find the appropriate wire size for that load and run length. you may need 8 gauge, or 6 gauge.

the reason I mention 2.5 times, you want 50% overhead in the wire, and you will most likely be adding more than what is on your original list.

 

[madhtr]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

Thanks again all!

I turns out that the radio curcuit was factory so I didn't need to include it. I wound up using 12gauge wire from the batery to the busses (+ and -) and 18 guage for the subcircuits. my total amps were 3+3+7+15 = 28 and according to a chart I got, 12g was good for that total. (my chart said 41 amps) I may have to use heavier later, but the way I wired it, it wont be difficult. I also put a 30 amp fuse in the main positive (as well as an appropriate sized one on each sub-circuit), on the OFF chance that any of my wiring comes apart and shorts at the buses. I'm new to this, and I don't really know how water might affect copper wire. a link to the chart I used ... someone might find it useful ... http://www.powerstream.com/Wire_Size.htm I went with the chassis wiring column. Thanks again all!

 

[fairbank56]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

You must also take into account the voltage drop when sizing wiring for 12 volt circuits. The voltage drop is due to the resistance of the wire. For a 12 volt feeder from batteries to the distribution panel, you should keep the voltage drop to within 3%. In your case, 28 amps with 12 gauge wire will allow only about 3 feet (one way) of cable run to meet this requirement. For a one way distance of say 10 feet, you would need 8 gauge.

While 12 gauge is probably sufficient in your case to handle a max of 28 amps, the true ampacity rating depends on the temperature rating of the wire used, whether the conductors are bundled, sheathed, in conduit, and/or in engine spaces and how many other conductors there are.

You have a small boat with minimal requirements but to meet the voltage drop requirement (ABYC recommendation), 12 gauge is likely too small and leaves no room for additional load in the future.

The minimum subcircuit wire size is 16 gauge (ABYC).

Eric

 

[MH Hawker]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

You may want to look at and save this chart for 12 volts.

http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm

 

[JB]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

Your diagram shows your accessories connected in parallel, not series. Yes, a common negative lead is permissible, but remember that it carries the sum of all accessory currents and needs to be at least as big as the positive main lead.

 

[fairbank56]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

You may want to look at and save this chart for 12 volts.

http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm

That chart appears to be for anywhere from 5% to 10% voltage drop. Suggest you use either the tables in the ABYC standards or use an online voltage drop calculator that gives or allows you to input the percentage of drop, which should be 3% for distribution panel feed.

Eric

 

[Jlawsen]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

This is not ground. It is DC negative. Yes, there should be a DC main negative bus located at the distribution panel. The method of negative wiring currently on your boat is called daisy-chaining and is inappropriate. Proper wire size for the feed from battery to distribution panel depends on total load (current) and length of cable run. You'll want to consider what would be required if you intend to add more accessories such as VHF, GPS, etc. in the future.

Eric

Tickles my heart to hear it stated correctly.. Voltage and Curent flow from negative to positive in DC battery circuit. Essentially the bus creates a common termination point and is sized according to the combined requirements of all the circuits that connect to it. You can daisy chain if you steadily increase the diameter of the wire back to the battery. Often this is done in the opposite manner where someone ties something in and uses a smaller wire. This usually results in a smoke leak and once the smoke leaks out the circuit is shot.

 

[JB]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

Voltage does not flow. It is pressure. It can be measured at different levels at different points in a circuit, but does not move.

Current flows, but there are two theories about what direction. Electron flow theory has it moving from negative to positive (as you state) and hole flow theory has it moving from positive to negative. The fascinating thing is that both theories work. If one of them is the only correct version it has never been proven.

You have to use the - to + theory to explain vacuum tubes and the + to - theory to explain semiconductors. I spent 45 years doing mostly that.

 

[fairbank56]

Re: Is it wrong to use a single (common) groundwire attaching accesories in series?

If one of them is the only correct version it has never been proven.

They are both correct. The two ways to describe current flow are electron current flow and conventional current flow (hole theory). The most commonly used and widely taught is conventional current flow. Electron current flow is taught in the military which is where I learned it and have continued to use it for 37 years still repairing electronic equipment for the military as a civilian. Doesn't matter which method you use.

Eric