Size of DC ground wire question

[rbk]

Originally Posted by gscriba

Just for the record rbk, I did not take your post as being "critical", nor was I telling you to "screw off". Just letting people in general know that I am interested in solutions. Thanks for your input!

None meant and none taken. Sounds like you’ve got a good plan. It had sounded like you were just running 4/0 around your boat as I’ve encountered others doing just that; buy a wad of heavy gauge and wire the whole boat in it. This can cost a lot more, harder to install and is not necessarily a ‘better’ system. Only thing I would add is every connection and bus bar you add, ads resistance, voltage drop and points for corrosion and failure (finding loose connections), not that VD will be an issue with 4/0 on a short run but something to consider if you go crazy with them. I have a similar setup but opted to eliminate/relocate a few bb’s to clean things up.

You don’t have to buy an expensive program for diagrams. Publisher does a good job (in most MS office suites) you can even drop pictures of your components into it to make it look real fancy.

[tarian]

Originally Posted by Wotname

There are no electrical issues with having larger sizes than necessary. The only downsides are cost, weight and inconvenience in fitting/terminating/routing etc.

Agreed
When re wiring my boat I upsized everything , a little more expensive but better in the knowledge of no real issues with the wire

[hzcruiser]

Originally Posted by gscriba

I just have to laugh. Thanks to all who didn't answer the question. Good entertainment. You funny.

Oh well, they all tried to help, as far as I was reading the replies. If you openly think that's funny they might not make that mistake again.

Wish I had one of those fancy dancy programs where I could show a wire diagram. Not willing to pay for one.

Try OpenOffice, it's free. Oh, no, I don't want to make you laugh again, sorry.

Just letting people in general know that I am interested in solutions. Thanks for your input!

Could've fooled me.

But bonus points for using LFP, hence here is my bit for your entertainment:


You seem to have a good understanding of DC, hence you're able to figure out what current is really going through that wire and size it accordingly.
And no, the negative wire doesn't _have_ to be the same length as the positive, trust me, the electrons are not going to complain if one is three times longer (just fuse it correctly, for your own sake).

[gscriba]

Thanks for your input.
I received the answer to my question a while ago.

[gscriba]

(People very often pontificate rather than answer THE question nor do they probe deeper to find out what is trying to be understood, which is a common problem on the forum...it gets tiring, sometimes to the point I just have to laugh; on a rare occasion, I react. Shouldn't have. Your response reminded me of that.)

I do have some understanding for sure. Here's what I don't understand and what nobody has really answered. I'll try to ask more clearly to get to the root.

Pos and Neg to complete a DC circuit. Then in addition, on a boat I believe we are supposed to ground or have a pathway or some other correct way of stating a wire from negative to a point on the engine. That last wire should not be carrying current. Correct? So if that is correct, is the purpose of that last wire stated above to assist with "grounding" to decrease electrical noise. If that is its purpose, why would it need to be sized the same as the larger wire within the boats 12 volt DC system.

Obviously not my area of expertise, just would like a clear answer to the above without all the "noise". If I haven't provided enough or correct info, then please ask.
Thanks.

[Wotname]

Originally Posted by gscriba

(People very often pontificate rather than answer THE question nor do they probe deeper to find out what is trying to be understood, which is a common problem on the forum...it gets tiring, sometimes to the point I just have to laugh; on a rare occasion, I react. Shouldn't have. Your response reminded me of that.)

I do have some understanding for sure. Here's what I don't understand and what nobody has really answered. I'll try to ask more clearly to get to the root.

Pos and Neg to complete a DC circuit. Then in addition, on a boat I believe we are supposed to ground or have a pathway or some other correct way of stating a wire from negative to a point on the engine. That last wire should not be carrying current. Correct? So if that is correct, is the purpose of that last wire stated above to assist with "grounding" to decrease electrical noise. If that is its purpose, why would it need to be sized the same as the larger wire within the boats 12 volt DC system.

Obviously not my area of expertise, just would like a clear answer to the above without all the "noise". If I haven't provided enough or correct info, then please ask.
Thanks.

Not correct.

As far as DC system is concerned there is no reason to have a non current carrying wire from the engine to the battery negative.

The reason almost all boats have a negative wire from the engine to battery negative is because almost all engines use the engine block as a current carrying conductor for the starter motor, the alternator and the various electrical sensors mounted on the engine (oil pressure, water temperature sensors etc). These engines clearly need a current carrying conductor to complete the circuit from the engine block back to the battery negative.

If the starter motor, alternator, sensors etc have their own negative returns, the block need not be connected to the battery.

This arrangement is popular with aluminium hulled boats.

[john61ct]

Ground really means Earth, and really is not needed wrt DC circuits.

Negative Return is just the other half of the circuit from the positive.

Circuit, get it? the electrons flow around in a circle (actually not literally, the physics gets mystical).

You want all the DC negatives to "reference" the same "common", as in chassis, framing, engine blocks, all at the same potential difference.

A certain gauge and quality wire will have a certain resistance, so thicker is good, less resistance.

It is normal to use the same wire type for both halves of the circuit, but no not important, so long as the resistance under max current loads doesn't cause too much voltage drop, or dog forbid hot spots, dangerous overtemp, melting insulation fire risk.

However the xPyS layout of a bank, those intra-bank connections between cells, strings etc should be well matched to prevent imbalance issues, especially in the series connections, paralleling is more forgiving, long as you don't lay out too many strings.

Now AC/shore connections, galvanic corrosion issues and EMI "noise" are all separate and a lot more complex, above is just DC electrickery basics.

[rbk]

Originally Posted by gscriba

(People very often pontificate rather than answer THE question nor do they probe deeper to find out what is trying to be understood, which is a common problem on the forum...it gets tiring, sometimes to the point I just have to laugh; on a rare occasion, I react. Shouldn't have. Your response reminded me of that.)

I do have some understanding for sure. Here's what I don't understand and what nobody has really answered. I'll try to ask more clearly to get to the root.

Pos and Neg to complete a DC circuit. Then in addition, on a boat I believe we are supposed to ground or have a pathway or some other correct way of stating a wire from negative to a point on the engine. That last wire should not be carrying current. Correct? So if that is correct, is the purpose of that last wire stated above to assist with "grounding" to decrease electrical noise. If that is its purpose, why would it need to be sized the same as the larger wire within the boats 12 volt DC system.

Obviously not my area of expertise, just would like a clear answer to the above without all the "noise". If I haven't provided enough or correct info, then please ask.
Thanks.

As you indicate you should have one (say 4/0) pos to your starter and one neg (matching 4/0) from your block back to your start battery, these carry current. The other wire your discussing seems to be a mix of a bonding system and counterpoise. Neither need to match the above mentioned 4/0. Most bonding systems are 4-6awg and the CP usually cooper foil/mesh/dynaplate etc. I’ll leave it to you to decide on the later two, use the google to learn about each system, then the search function here to really open Pandora’s box.

[Wotname]

Originally Posted by john61ct

Ground really means Earth, and really is not needed wrt DC circuits.

Normally no ground or earth can be found on board cruising boats unless they have run aground. I don't consider a dusty bilge to be ground.

Originally Posted by john61ct

Negative Return is just the other half of the circuit from the positive.

You mean the positive outgoing. And just what do you called the conductor interconnecting series loads???

Originally Posted by john61ct

Circuit, get it? the electrons flow around in a circle (actually not literally, the physics gets mystical).

Let's not forget the square, rectangular, oval, eclipse, polygon and many other configurations around in the average circuit.

[gscriba]

(FYI. I just had 3 "old way" Mai Tai"s at Trader Vic's in Emeryville, so keep that in mind. I'm feeling especially grateful) I so appreciate the specific responses to the (attempted) specific question. Thank you! Fo' real. We need that today. Concrete and to the point. No egos. Just answer THE question. Cheers.

If you don't want to be called out...don't waver, don't pontificate. Don't go beyond the question. I've PM'd you before. Just stick to the question. You know who you are.

Thank you. Helpful and that, despite the chafe, is why I continue to post/ask/help when I can.

[seabreez]

[QUOTE=gscriba;3011332]Rewiring for my LiFePO4s. There is 2/0 throughout the boat now and I am replacing that. Could go 3/0, but have a deal on yellow and red 4/0. I have a Xantrex SW3012 that calls for 4/0 and it's just 6 ft further to the panel. Alway open to suggestions. Thanks.[/QUOTEJ

Just to clear some facts... there is a big difference between a 2 gauge wire and a 2/0 cable, make sure you know the difference. Also you mention a 3/0... there is no 3/0 cable it only goes even numbers. Google marine wire sizes and you will find a chart with wire sizes and amperage chart for all wire sizes. My 2 cents...

[GordMay]

... Also you mention a 3/0... there is no 3/0 cable it only goes even numbers. ...

There certainly is a 3/0 cable size, and American Wire Gauge typically uses both even & odd numbers.

[john61ct]

https://www.overtons.com/ancor-marin...50-351741.html

https://www.amazon.com/Ancor-Red-AWG.../dp/B01HJTFB8A

[Frankly]

A-20 and A-25 contain specific installation directions that are not described in E-11.

2. Install the AC wiring to the charger or inverter including an AC grounding conductor of a size equal to the current carrying conductors unless the circuit exceeds 30A, in which case the grounding conductor may be one size smaller (E11.16.1.3.8.2). This is the typical grounding conductor that you would see with any AC appliance and returns with the other AC conductors to the power distribution panel.

3. Install a DC grounding conductor sized not less than one size smaller than the DC positive conductor and have a capacity such that the DC positive fuse has an amperage rating not greater than 135% of the current rating of this grounding wire. As a practical matter, this wire will be much larger than the AC grounding conductor. This requirement is the latest addition to the standards when it was discovered that faults in the DC side of an inverter or charger could provide sustained high currents that could start a fire from overheating the AC grounding conductor.


I lifted this from Blue Sea (they probably lifted it from ABYC). Kind of complicated to follow but suggests/ requires the conductor connecting the DC negative (which is almost always connected to the engine block) to the AC ground on inverter equipped yachts be sized same or slightly smaller as the wire size feeding the DC to the inverter (which is typically quite large).


My speculation (and mine only) is this requirement for this large current carrying ground conductor is what drove moving the zinc savers from this connection to being installed in series with the shore power ground. A decision I was never a big fan of. Because a failure in the zinc saver (think nearby lightning) creates a real and present electrical danger on the yacht. This is kind of hidden under the umbrella of the new series zinc savers must indicate if they have failed or"fail safe", another "can we really do that" item .


Just my $.02 worth,


Frankly

[Pelagic]

Since OP's question has been asked and answered,.....
I am curious about the DC wiring calculation for a Series/Parallel connection for the Series side?

Say you have 6 x 12v large capacity batteries wired Series/Parallel for 24v

The 3 Series connections are still a 12v connection...right?

If the max load was for both Bow Thruster and Anchor Windlass operating simultaneously was 400 amps @ 24v
.....what is the theoretical load on the 12v Series Cables?