Sizing Main Battery Cables

[john61ct]

Originally Posted by rgleason

The 1both2 Switch would be put on #2 Reserve Battery for emergency starts. This would not involve the ACR. Therefore no problems with the ACR which is just for charging the Reserve battery.

I think John is talking about the high Starter cranking amps that would be drawing by starter, through the 1both2 switch, down to the House positive bus, through the "Emergency Switch" and from the House Battery. This switch needs to be rated for those loads. That might be an issue.

Yes my comment was wrt using an ACR momentary "join" switch rather than a 1-2-B for self-jumping.

If that allows you to eliminate that switch then that's what I recommend.

And yes, any wires/devices potentially carrying the starter cranking load must be sized to do so.

[rgleason]

Why would wiring the Start Isolation in the ACR Combiner be needed? I guess I don't understand that part.

[john61ct]

to protect sensitive electronics from sags and spikes

[mitiempo]

Originally Posted by rgleason

Why would wiring the Start Isolation in the ACR Combiner be needed? I guess I don't understand that part.

It is wired to the ignition and prevents combining during starting to accomplish the above. Also prevents starting current from travelling through the ACR wiring.

[rgleason]

John and mitiempo thanks, it sounds to me like it is well worth doing with no downside.

I've reading Mainesail's study, advice and experience with voltage drop at fuses and connections.
When a fuse size is doubled the voltage drop improves significantly. Also every fuse connection is actually several connections and this can add up.
I believe he also wrote that if a wire is in conduit, it does not need a fuse. If I have this correct, why not run the voltage sense wires in copper tubing with no fuse? Nutty idea maybe but I thought I'd ask.

As another approach perhaps, increase the sizes of the sense wires and double or triple the fuse sizes to get a better reading?

[john61ct]

Stuff's complex enough without adding to it. Most of the time the normal way is best.

For example sensor wire's gauge may be an essential part of its design.

[mitiempo]

Originally Posted by rgleason

I believe he also wrote that if a wire is in conduit, it does not need a fuse. If I have this correct, why not run the voltage sense wires in copper tubing with no fuse? Nutty idea maybe but I thought I'd ask.

As another approach perhaps, increase the sizes of the sense wires and double or triple the fuse sizes to get a better reading?

All wires going to a positive source need a fuse. For main battery cables within 7" of the post or if in a conduit this increases to 72" I recall. But a fuse is still needed. The only exception under ABYC is a dedicated starter battery doesn't have to be fused. But it should be. You do not have a dedicated start battery.

As far as sense wire and fuse sizes use a reasonable gauge wire. For example 14awg - it has an ampacity of 30 amps in an engine room so use a 20 or 25 amp fuse instead of a 5 or 10 amp fuse.

[rgleason]

John and mitiempo, thankyou. All of it is useful info. I had in mind using #14 but will check with manuf of devices.
Would the copper tubing want to be grounded? To what?

[Stu Jackson]

Originally Posted by rgleason

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Would the copper tubing want to be grounded? To what?

You wouldn't use CU tubing on a boat. Why? While it may not be called rust, it will turn green.


They make plastic wire looms, dontcha know?


AL is usually used on land.



I find placing wiring in conduits on a boat a PITA, hard to trace (I'd rather put the work in to individually support them). In your case, though, you're installing all of it, so you'll have it labeled well.


rg, we keep telling you to buy a book. Have you? If not, why not, it will answer all these unusual questions and tell you why your oddball ideas make little sense (unless you were joking about the copper, then use one of these - ). They are NOT the kind of thing normally answered in internet posts and/or website articles by Maine Sail, me, mitiempo, john or others, because it is in books. Books are very good at summarizing Codes and highlighting the applicable and pertinent portions. Calder's bible covers a lot of this, too, Wing's is very good.

[rgleason]

Thanks, I will wait to get to my Calder's which is in a house that is rented right now.