Inverter cabling question

[bud37]

Just the coles notes explanation.

It has to do with the DC fault currents...they can be quite high and the 120 wiring cannot handle that load....that is why the case ground needs to be the size they recommend and go to the appropriate ground point....eg...the engine block to dissipate is one example.

[Helmsman]

Source of the post Just the coles notes explanation.

It has to do with the DC fault currents...they can be quite high and the 120 wiring cannot handle that load....that is why the case ground needs to be the size they recommend and go to the appropriate ground point....eg...the engine block to dissipate is one example.

I wonder if the ABYC regs also changed since 2006 for the cables coming from an isolator to the batteries. All three of my OEM banks have 4 gauge cable between the two. The original isolator was a diode isolator which was a 2-3 configuration. The alternators as stated before are 70 amp OEM alternators. The round trip distances are about 12 feet for the house, and 18 feet for each engine battery.

The Blue Seas chart of the ABYC regs says there should be 2/0 cable for the combined 200 amps from the alternator. That is an extremely big difference from the OEM 4 gauge. Of course, the OEM battery cables are 4/0 so this is just the isolator feeds to the battery switches for each one.

[km1125]

Source of the post

Source of the post Just the coles notes explanation.

It has to do with the DC fault currents...they can be quite high and the 120 wiring cannot handle that load....that is why the case ground needs to be the size they recommend and go to the appropriate ground point....eg...the engine block to dissipate is one example.

I wonder if the ABYC regs also changed since 2006 for the cables coming from an isolator to the batteries. All three of my OEM banks have 4 gauge cable between the two. The original isolator was a diode isolator which was a 2-3 configuration. The alternators as stated before are 100 amp OEM alternators. The round trip distances are about 12 feet for the house, and 18 feet for each engine battery.

The Blue Seas chart of the ABYC regs says there should be 2/0 cable for the combined 200 amps from the alternator. That is an extremely big difference from the OEM 4 gauge. Of course, the OEM battery cables are 4/0 so this is just the isolator feeds to the battery switches for each one.

I have an older copy of the ABYC regs, so I can't speak exactly to what they might say now.

However, for charging circuits the cables are specified to two requirements, one being the actual max capacity (which is a safety issue) and the other being voltage drop to insure the device at the end can meet its operational requirements. On a battery charging circuit this gets a bit more complicated because the current draw of the device (the battery) actually goes down significantly as it charges. As long as the lead is suitably large enough to handle the max current of the source, then the wire is fine from a safety perspective. As the battery charges, it will always eventually come up to the same final voltage regardless of the wire size, it will just take a bit longer for a smaller wire.

If you complicate the battery charging by running continuous loads through that same wire, then you need to start making the calculations on how much voltage drop is happening and how much more that's going to affect the battery charging to see if that's still acceptable. With so many unknowns in that calculation, I'd have a hard time seeing how a standards agency could come up with a requirement that fits every application (or even the majority).

[Helmsman]

Source of the post

Source of the post

Source of the post Just the coles notes explanation.

It has to do with the DC fault currents...they can be quite high and the 120 wiring cannot handle that load....that is why the case ground needs to be the size they recommend and go to the appropriate ground point....eg...the engine block to dissipate is one example.

I wonder if the ABYC regs also changed since 2006 for the cables coming from an isolator to the batteries. All three of my OEM banks have 4 gauge cable between the two. The original isolator was a diode isolator which was a 2-3 configuration. The alternators as stated before are 70 amp OEM alternators. The round trip distances are about 12 feet for the house, and 18 feet for each engine battery.

The Blue Seas chart of the ABYC regs says there should be 2/0 cable for the combined 140 amps from the alternator. That is an extremely big difference from the OEM 4 gauge. Of course, the OEM battery cables are 4/0 so this is just the isolator feeds to the battery switches for each one.

I have an older copy of the ABYC regs, so I can't speak exactly to what they might say now.

However, for charging circuits the cables are specified to two requirements, one being the actual max capacity (which is a safety issue) and the other being voltage drop to insure the device at the end can meet its operational requirements. On a battery charging circuit this gets a bit more complicated because the current draw of the device (the battery) actually goes down significantly as it charges. As long as the lead is suitably large enough to handle the max current of the source, then the wire is fine from a safety perspective. As the battery charges, it will always eventually come up to the same final voltage regardless of the wire size, it will just take a bit longer for a smaller wire.

If you complicate the battery charging by running continuous loads through that same wire, then you need to start making the calculations on how much voltage drop is happening and how much more that's going to affect the battery charging to see if that's still acceptable. With so many unknowns in that calculation, I'd have a hard time seeing how a standards agency could come up with a requirement that fits every application (or even the majority).

Bud, KM, or others, the electrician put 2/0 cable from the inverter to the battery bank and back to the inverter. As a “closed” circuit (just powering the inverter), that is acceptable. I bought a 2-4 isolator for the express purpose of being able to make use of the alternators to charge this bank along with the three existing banks while underway. That avoids using the generator while underway and allows the batteries to be close to full charge while underway. Now, adding the isolator to the battery bank, he used 4 gauge (13.66 feet one way) which is the same as the OEM gauge to the other batteries (6 ft, 9 ft, and 9 ft one way respectively). Per all the previous discussions, we all agree that cable is too small for the combined 200 amp feed from the alternators.

Focusing on the inverter bank, and referencing a post by Viper in Vineyard’s inverter project, adding cable to a circuit is only as good as the lowest gauge wire in the circuit (big paraphrase so I hope I am accurate in “quoting him”), which is 2/0.

My question is this. Will replacing the 4 gauge with 3/0 (Called for on the ABYC blue sea chart you posted) be more “effective” than 2/0 since the battery bank/inverter is 2/0? Bear in mind, that in the full 31 to 32 foot charging circuit there is about 3.5 to 4.5 feet of 2/0 battery cabling involved. I guess this is almost a practical experience question. Or perhaps a “What would you do?” type question.

To replace the inverter circuit from 2/0 to 3/0 is a much bigger job due to where the batteries are in the boat. They are tough to get to where they are, though it could be done. I was really really hoping to avoid doing that.

[bud37]

Without me standing there looking at your instal or seeing a schematic of it ( batteries and all ), it is impossible to answer your question as it is. I guess what this comes down to is an analogy of building a minimum code house or going above and beyond, the codes are there to try to create safety and consistency in the industry.

Please, at no point am I saying all your cables are wrong, but you seem to think so........The following is just my opinion and probably the way I would do it....... I think the choice is to spend some more money on the proper cable , you will feel better and could upgrade later without too much drama, and at sales time there will be no awkward questions about the wiring from their surveyor.

Make your own cables as the lengths are nearly impossible to get right until you are down there.....1 inch the wrong way and she wont fit.....

Hope this helps even a little.

[Helmsman]

Source of the post Without me standing there looking at your instal or seeing a schematic of it ( batteries and all ), it is impossible to answer your question as it is. I guess what this comes down to is an analogy of building a minimum code house or going above and beyond, the codes are there to try to create safety and consistency in the industry.

Please, at no point am I saying all your cables are wrong, but you seem to think so........The following is just my opinion and probably the way I would do it....... I think the choice is to spend some more money on the proper cable , you will feel better and could upgrade later without too much drama, and at sales time there will be no awkward questions about the wiring from their surveyor.

Make your own cables as the lengths are nearly impossible to get right until you are down there.....1 inch the wrong way and she wont fit.....

Hope this helps even a little.

Thanks for the help. I will attempt to describe the circuit as it exists now with pictures. The only work done electrically to the boat outside of OEM is the inverter, the isolator, and adding AGM batteries.

The inverter circuit (DC side) has 2/0 cable installed throughout. The cables run from the batteries to the inverter. Here are pictures of the setup. Notice the smaller cable that runs to the switch. That is the 4 gauge 14 foot wire running from the isolator. Notice also that there is not a negative back to the engine or a buss bar rendering an incomplete circuit.

200DF4AC-4AA1-4F7D-82D8-7D95FBA11D42.jpeg

0B341DE3-D744-41C9-B81C-177014F79388.jpeg

FC70AA38-E4BD-4776-BC1E-391451B4F584.jpeg

9CBADDA8-6CA1-474D-B2DB-B42CE90F142F.jpeg

The last picture shows the case ground which goes to a starboard engine ground. Notice the 4 gauge wire coming from the inverter going into the battery switch.

910BE4A8-AF5A-45AA-B511-9C656E675399.jpeg

The starboard engine stud with case ground attached. The two yellow negative cables there are a starboard starter Battery negative (2 gauge) and a negative (2 gauge) that goes to a large negative buss bar in front of the port engine, which also has a house battery 4/0 negative connection attached to it amongst other cables. .

E372CA66-9E93-4A42-B970-F9319974C799.jpeg

The negative buss bar with the 2 gauge connections from both engines and the house battery amongst other wires.

So, if I replace the 14 foot 4 gauge isolator cable with 4/0 cable and then add a negative cable to the Victron shunt on the other side of the batteries and route it to the negative buss bar in front of the port engine 18 feet away, then I have a complete circuit for charging from the isolator. However, along that path, the charge will run through the 2/0 cables from the battery switch, through the batteries, to the shunt. My question is, does that mitigate the benefit of the 4/0 cables? Are their safety issues to consider? Should I just use 2/0 cable to run from the isolator to the battery switch and from the shunt to the buss bar?

[km1125]

A couple of quick thoughts... I might have to go back and re-read a couple times and think a bit to post some more:

Source of the post
Bud, KM, or others, the electrician put 2/0 cable from the inverter to the battery bank and back to the inverter. As a “closed” circuit (just powering the inverter), that is acceptable. I bought a 2-4 isolator for the express purpose of being able to make use of the alternators to charge this bank along with the three existing banks while underway. That avoids using the generator while underway and allows the batteries to be close to full charge while underway.

Do you anticipate using the inverter for significant periods while underway? That really dictates how large the wires need to be from the isolator. Do you want to be able to pull upwards of 180A (which would only really happen if your inverter batteries were very very low and you were still using the inverter at a high level)?

Source of the post
Now, adding the isolator to the battery bank, he used 4 gauge (13.66 feet one way) which is the same as the OEM gauge to the other batteries (6 ft, 9 ft, and 9 ft one way respectively). Per all the previous discussions, we all agree that cable is too small for the combined 200 amp feed from the alternators. (If it is too small for the inverter feed, then obviously it is too small for the shorter runs, which becomes another project.)

I would not say that's too small, unless you're trying to run the inverter directly from the alternators.

Source of the post
Focusing on the inverter bank, and referencing a post by Viper in Vineyard’s inverter project, adding cable to a circuit is only as good as the lowest gauge wire in the circuit (big paraphrase so I hope I am accurate in “quoting him”), which is 2/0.

This is not really true regarding voltage drop, but only for the overall capacity of the wire. The capacity (and fusing) should be related to the smallest wire gauge used. If sections of a circuit are made larger, you reduce the voltage drop in those sections. You could have all the negative leads as 4/0 and all the positive leads as 2AWG (if 2AWG could handle the current). It would just make the voltage drop calculations a bit more complicated.

Source of the post
My question is this. Will replacing the 4 gauge with 3/0 (Called for on the ABYC blue sea chart you posted) be more “effective” than 2/0 since the battery bank/inverter is 2/0? Bear in mind, that in the full 31 to 32 foot charging circuit there is about 3.5 to 4.5 feet of 2/0 battery cabling involved. I guess this is almost a practical experience question. Or perhaps a “What would you do?” type question.

To replace the inverter circuit from 2/0 to 3/0 is a much bigger job due to where the batteries are in the boat. They are tough to get to where they are, though it could be done. I was really really hoping to avoid doing that.

If your main goal is to have the inverter run from the inverter batteries and 2/0 is sufficient for the current and length, then there really isn't a reason to go to a larger size.

[km1125]

Also... I'm sure I mentioned this before, but that new "tie-in" for the negative cable from the inverter battery to the "negative buss" must be at least as large as the "safety ground" for the inverter needs to be, as it is included in that circuit path.

[Helmsman]

Source of the post A couple of quick thoughts... I might have to go back and re-read a couple times and think a bit to post some more:

Source of the post
Bud, KM, or others, the electrician put 2/0 cable from the inverter to the battery bank and back to the inverter. As a “closed” circuit (just powering the inverter), that is acceptable. I bought a 2-4 isolator for the express purpose of being able to make use of the alternators to charge this bank along with the three existing banks while underway. That avoids using the generator while underway and allows the batteries to be close to full charge while underway.

Do you anticipate using the inverter for significant periods while underway? That really dictates how large the wires need to be from the isolator. Do you want to be able to pull upwards of 180A (which would only really happen if your inverter batteries were very very low and you were still using the inverter at a high level)?

Source of the post
Now, adding the isolator to the battery bank, he used 4 gauge (13.66 feet one way) which is the same as the OEM gauge to the other batteries (6 ft, 9 ft, and 9 ft one way respectively). Per all the previous discussions, we all agree that cable is too small for the combined 200 amp feed from the alternators. (If it is too small for the inverter feed, then obviously it is too small for the shorter runs, which becomes another project.)

I would not say that's too small, unless you're trying to run the inverter directly from the alternators.

Source of the post
Focusing on the inverter bank, and referencing a post by Viper in Vineyard’s inverter project, adding cable to a circuit is only as good as the lowest gauge wire in the circuit (big paraphrase so I hope I am accurate in “quoting him”), which is 2/0.

This is not really true regarding voltage drop, but only for the overall capacity of the wire. The capacity (and fusing) should be related to the smallest wire gauge used. If sections of a circuit are made larger, you reduce the voltage drop in those sections. You could have all the negative leads as 4/0 and all the positive leads as 2AWG (if 2AWG could handle the current). It would just make the voltage drop calculations a bit more complicated.

Source of the post
My question is this. Will replacing the 4 gauge with 3/0 (Called for on the ABYC blue sea chart you posted) be more “effective” than 2/0 since the battery bank/inverter is 2/0? Bear in mind, that in the full 31 to 32 foot charging circuit there is about 3.5 to 4.5 feet of 2/0 battery cabling involved. I guess this is almost a practical experience question. Or perhaps a “What would you do?” type question.

To replace the inverter circuit from 2/0 to 3/0 is a much bigger job due to where the batteries are in the boat. They are tough to get to where they are, though it could be done. I was really really hoping to avoid doing that.

If your main goal is to have the inverter run from the inverter batteries and 2/0 is sufficient for the current and length, then there really isn't a reason to go to a larger size.

Thanks.

I saw your next post also. So. I will make that new negative a 2/0 and run it the 18 feet to the negative buss. I would connect it to the engine at the pictured stud instead, but the engine only has a 2 gauge negative feed to the buss from that engine stud.

I am not interested in running the inverter from the alternators. I would just like be able to charge the bank safely. So, do you think the 4 gauge is ok for charging 13.66 feet away one way, or should I increase the gauge to 2 gauge or 2/0 like the new 2/0 feed to the negative buss or 3/0 or.... Again, thanks very much for you guys help. I think we are close.

[km1125]

If you can, I would move the 2/0 "safety ground" to the negative buss and I would also connect the new 2/0 "tie in" negative to the inverter battery at the same place.

There's no reason your "safety ground" need to be on the engine block. It is just a convenient place on most boats that establishes a "negative buss", as there needs to be a rather large connection from the negative battery terminal to the engine block. Now that you've admitted that the engine only has a 2 AWG negative feed, that lead is actually now "non compliant" since it also needs to be just as large as the "safety ground" to complete the circuit back to the battery negative. So, if you can just move the 2/0 safety ground to the negative buss bar then you also eliminate the need to upgrade that engine negative as well.

In a bit I'll run some more calcs on the 4 AWG run and give my updated opinion on that. Also, please clarify where your shunt is in the circuit and how other stuff around it are connected. With your description I will try and update that diagram I made with as much information as I can ascertain from your posts and you can critique it so I can correct it. That will make it easy for all to understand and make sure we're all on the same page.