Size of DC ground wire question

[gscriba]

Greetings all,
Does the DC negative ground need to be the same size as the DC negative wire?
So if the house bank to negative bus bar and DC panel is 4/0, does the DC ground to the engine block also need to be 4/0?
Thanks!
Gordon

[rbk]

Yes they should match.

[rbk]

You’re not using 4/0 for your house panel are you? Also just because you use 4/0 to your starter does not mean you need 4/0 for your house panel neg as well.

[gscriba]

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.

[Wotname]

Originally Posted by gscriba

Greetings all,
Does the DC negative ground need to be the same size as the DC negative wire?
So if the house bank to negative bus bar and DC panel is 4/0, does the DC ground to the engine block also need to be 4/0?
Thanks!
Gordon

Depends on your definitions of negative ground and negative wire but generally speaking no wire sizes have to match each other.

Wire size is determined by the current flow, voltage drop and circuit protection limitations.

If the wiring in question have the same parameters, then their minimum sizes will be the same but otherwise no.

[Wotname]

Originally Posted by gscriba

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.

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

[john61ct]

The round trip circuit from load to source generally match on both +/- sides.

Within a bank, wires connecting the component units should ** really** be not only same gauge but lengths (resistance).

The main "chassis ground" (not really earth ground but "common") wires, between engine block & frame, body sections etc can be much more robust than anything connecting load device chassis/covers, fuse / distribution boxes, chargers VSRs etc.

Using the frame/chassis ground for a circuit's return path can be risky, can deteriorate over time with corrosion, connection issues in general need checking / maintenance, can be hard to troubleshoot.

And note all this only pertains to the DC electrickery. AC ground issues, and "electrolysis" actually galvanic corrosion issues are a whole 'nother ball of wax.

[a64pilot]

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.

That’s the bottom line, if there is a question go larger until there is no question. Why finite analyze this, go stupid big, you’ll be glad you did.
There is no downside, just upsides, less voltage loss, and the capability to add circuits later.

[gscriba]

I asked and I received. DC ground wire to engine will be at least same size as the primary battery cables supplying boat loads. That for me will be 4/0 cable.
I believe I'm good to go.
Thanks!

[smac999]

There is no such thing as neg ground vs neg.

All dc negative cables are just that. Dc negative. Then you need to figure out what currents flow through each one. Only then can you pick a size. The location alone dies not mean anything

[gscriba]

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

[rbk]

Originally Posted by gscriba

I asked and I received. DC ground wire to engine will be at least same size as the primary battery cables supplying boat loads. That for me will be 4/0 cable.
I believe I'm good to go.
Thanks!

But your engine negative (from your block) is only the negative for your starter. Your panel will have its own unless for some reason you’re running all your negative circuits back through your block. Your panel negative will/ should match your panel positive which could be much smaller depending on your loads. With 4/0 you could run 200amps almost the length of your boat with minimal drop. Also look at your house panel connection and make sure there is room for 4/0 to connect both in terms of cable diameter/space and available lugs for attachment.

[Wotname]

Originally Posted by a64pilot

That’s the bottom line, ..... go stupid big, you’ll be glad you did.
........

I gotta remember this line ; hope you don't mind if I use it.

[gscriba]

Originally Posted by rbk

But your engine negative (from your block) is only the negative for your starter. Your panel will have its own unless for some reason you’re running all your negative circuits back through your block. Your panel negative will/ should match your panel positive which could be much smaller depending on your loads. With 4/0 you could run 200amps almost the length of your boat with minimal drop. Also look at your house panel connection and make sure there is room for 4/0 to connect both in terms of cable diameter/space and available lugs for attachment.

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

I'll try to explain my thoughts/system and plan.
A 4/0 short negative cable from my Perkins 4.236 block as well as the alternator negative will attach to a 4 post HD negative bus bar. I will have a negative 4/0 cable from that 4 post HD busbar adjacent to my Perkins 4.236 leading forward to a 4 post HD busbar adjacent to my Xantrex SW3012 (approx 12 foot run). The DC panel negative as well as the DC negative from the Xantrex (essentially all the DC negatives with the exception of the solar negatives, which will tie into the 4 post HD BB aft near the engine) will lead to and tie in at the busbar adjacent to the Xantrex. A 4/0 DC neg will go from the 4 post HD BB (next to the Xantrex) through my battery monitor shunt (Simarine) direct to the LiFePO4 neg.

Start bank will have its own DC negative direct to the start bank (AGMs).

That's the plan. Be constructive, not critical, or screw off. No need to get into a pissing contest with each other.
And with that...cause I have a sense or humor AND I'm a sucker for punishment, have at it.

[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!