Sizing Main Battery Cables

[Stu Jackson]

Originally Posted by mitiempo

Stu

Catalina used to use 4 awg for main cables but over the years corrected this to much larger wire.

When I replaced my battery cables and the wire to the starter with larger wire my cranking time changed from 10 - 15 seconds to almost instantaneous. Motors do not like low voltage.

I use 1/0 or 2/0 for battery inter-connects and wiring to the switch and starter for both banks, never anything smaller. Virtually all boat builders do currently as well.

Yup, I know and understand. One thing I continue to forget to share is that I do NOT have any trouble starting my engine. I have never had a "10 - 15 seconds" problem. If I did, guess what??? That was part of my discussion with Maine Sail back then, too.


For those doing NEW wiring, I agree with mitiempo, make the wire bigger than my OEM #4.

[Terra Nova]

Originally Posted by Stu Jackson

...the HUGE 250A starter load requires a wire size bigger than my forearm is overkill...

This kind of nonsense discredits the rest of your post.

[redsky49]

Originally Posted by Zil

Remember. Proper sized switches and bus bars and fuses and cables, do not have that much voltage drop.

Respectfully, I disagree with this statement.


Every added connection will introduce some added resistance. In some cases it will be insignificant (though cumulative), and in others substantial. And this is in addition to the voltage drop due to wire gauge/distance/load.


A perfect example of this is VHF cable, where every added component further degrades performance.


With resistance being such a critical issue, let me echo what was stated in post#41 above, where the use of an anti-oxidant was mentioned.


This is my bottle of Penetrox, a copper-based anti-oxidant, that is used for terminals and busbars. It seals out air and moisture, reducing the formation of oxides (oxidation) on contact surfaces. Label is hard to read, but this is because this small container has lasted me many years. Highly recommended.

[redsky49]

Quote:
Originally Posted by Stu Jackson
...the HUGE 250A starter load requires a wire size bigger than my forearm is overkill...

This kind of nonsense discredits the rest of your post."


I think we are all allowed a little hyperbole from time to time, when done to make a point. I utilize some 350MCM cable on board. This is a cable 2 sizes up from 4/0. I have referred to this on occasion as fire hose size, though it actually measures only a bit over 1" dia. (27mm).


There is an added expense, weight increase and difficulty in routing a larger conductor. Performance though will always be improved, however there is a point of diminishing returns. If in doubt, go a size (or two) larger. Over time, your system will degrade, regardless of your best intentions, and the added mil capacity of the larger cables will worthwhile when the inevitable future challenge finally comes to call.

[Adelie]

Originally Posted by rgleason

Terra Nova I guess you're right about the sizing for the main run, but I already have AWG 1 for all the main wiring from + post to - post. And also AWG 1 for all the internal battery wiring.

Is this going to be acceptable for ABYC standards?

Depends on your loads.

I have a 1000w inverter (2kw surge), 50amp line (33amps max actual) for electric trolling motor plus normal house uses.

Let’s say I run a 700w microwave for 10min (60amps accounting for inverter losses) at the same time I’m running the trolling motor; that’s 93 amps plus house load. I assume there will be times I use the full capacity of 1000w which is 83amps.
I am electing to size for a steady 110a load which puts me at the limit of 4ga for a 13’ round trip battery to panel. I realize I need to be conscious of not running inverter at same time as trolling motor.

Whomever suggested 8ga didn’t take into account the possibility of specialized high loads. If you never install anything that would be high load like that then 8ga might work. If you install smaller now then you may need to upgrade later.

[john61ct]

If you're crimping your own, choose maybe three gauges you want to use, and round up never down.

This lets you buy your top-quality wire in 50' or better 100' spools, and terminal / fittings in bulk, and only buy a limited set of quality crimpers.

[rgleason]

Thanks guys, I've redrawn the schematic here. Any suggestions to improve or simplify will be most welcome!

[Stu Jackson]

Originally Posted by redsky49

Quote:
Originally Posted by Stu Jackson
...the HUGE 250A starter load requires a wire size bigger than my forearm is overkill...

This kind of nonsense discredits the rest of your post."


I think we are all allowed a little hyperbole from time to time, when done to make a point. I utilize some 350MCM cable on board. This is a cable 2 sizes up from 4/0. I have referred to this on occasion as fire hose size, though it actually measures only a bit over 1" dia. (27mm)........................

Thank you, redsky. Much appreciated.


The downside of how rg chose to break up the discussion of his new wiring diagrams on this forum into two or more separate discussions means lots of what's said on one thread doesn't get to the other one. It would be helpful if someone could merge these two 'cuz they are really the same subject.

[rgleason]

Adelie wrote:" it depends on your loads" to the question is awg 1 going to acceptable?

I do not have a 700w microwave or an inverter or a trolling motor. I have normal house loads, max 25amps.

Sources of power are a 30a-40a charger (future), an alternator (100a-120a future), and 280-300watts of solar.

The biggest load is the starter, which is wired to the "C" on the 1both2 switch using AWG 1 wire, with direct connections and no fuses.

It now appears that my only choices are a 200a or 250a fuse because bluesea has discontinued 225a Terminal and ANL fuses. I am not so sure I want to rewire with 2/0 wire. I think that is complete overkill.
I am likely to just stay with the AWG #1 at this point and insert a 200a fuse, since I don't have the instruments to measure starter inrush amps. Either it works or it doesn't.

[rgleason]

The reason I broke it up was to have the subject focused on sizing the main wires. The other thread is more system oriented.

[stormalong]

Originally Posted by rgleason

Adelie wrote:" it depends on your loads" to the question is awg 1 going to acceptable?

I do not have a 700w microwave or an inverter or a trolling motor. I have normal house loads, max 25amps.

Sources of power are a 30a-40a charger (future), an alternator (100a-120a future), and 280-300watts of solar.

The biggest load is the starter, which is wired to the "C" on the 1both2 switch using AWG 1 wire, with direct connections and no fuses.

It now appears that my only choices are a 200a or 250a fuse because bluesea has discontinued 225a Terminal and ANL fuses. I am not so sure I want to rewire with 2/0 wire. I think that is complete overkill.
I am likely to just stay with the AWG #1 at this point and insert a 200a fuse, since I don't have the instruments to measure starter inrush amps. Either it works or it doesn't.

Don't limit yourself to Blue Sea Systems. A fuse is a fuse is a fuse. You can even use an AC 110/220 volt fuse. The voltage rating does not matter, only the current rating. Just find or make a plastic housing to put the fuse holder in.

[john61ct]

I agree to only the first sentence in the post above. There are **some** other good vendors.

The rest is nonsense verging on dangerous, please ignore.

[stormalong]

Originally Posted by john61ct

I agree to only the first sentence in the post above. There are **some** other good vendors.

The rest is nonsense verging on dangerous, please ignore.

Why do you say that? The voltage drop across a fuse is, ideally zero. The voltage rating is the voltage that the fuse can safely interrupt.

[Zil]

The voltage drop across fuses switches and any other connection does add to the over all voltage drop. It should not be a large voltage drop. That is why I said; "not that much"

We are talking about battery cables, specifically starter cables. Not VHF cable.

[redsky49]

Be careful with your terminology:
"The biggest load is the starter, which is wired to the "C" on the 1both2 switch using AWG 1 wire, with direct connections and no fuses."

ABYC defines "direct connections" (for cranking motors) as:
"Cranking Motor Connections.
If the conductor is connected directly to the battery terminal..."


On a more practical level, for my 4 cyl. 54 hp Yanmar, I am using a 150 Amp breaker for OCPD on the alternator, and have had no issues in the 12 years since installed. Similar to starter conductor protection. I have located the device to be readily accessible when working on or around the alternator. You can get a big spark in these areas if being careless. [As an aside, always remove rings, watches, loose sleeves, etc. when working among machinery].


Most OCPD for marine use are "slow-blow" types which will allow the startup surge from stationary motors to pass safely without tripping. There is a big difference between rated load amps (RLA), full load amps (FLA), locked rotor amps (LRA), etc. Learn the difference and how they apply to you.


Blue Seas is just a middleman in the retail chain. They manufacture little, if any, of their products. You will find their circuit breakers, bus bars, etc., being sold elsewhere under different labels, or directly from the actual manufacturer. A few of their products appear to be proprietary at this time, such as the ganged fuse block shown above, though that will surely change if it hasn't already. They are also now part of a big marine conglomerate so that also affects their marketing.


And for my application, I am using #2 for alternator hookup (de-tuned from 110 A to 80 A), and 2/0 for starter connection. Determine your conductor sizes per ABYC, and your particular situation. If a future problem develops, it won't help that your engineering decisions were based on an anonymous internet source. Do it right, and be particularly critical about following forum "advice", including my own.

In commercial applications, a "fused disconnect" is the standard method to provide a service disconnect, as well as OCP. Here is a pic of mine, this one being adjacent to the alternator: