Electrical: use extra switch as main to power all rocker switches?

[Idiotfool]

Howdy! For Christmas, I was given a rocker switch panel with battery voltage display, usb and 12 volt receptacle. The battery voltage ran down my battery in the month and a half that the boat sat idle.

I'm going to be installing a mains switch, but I looked at the ticket switch panel and realized that I could use a spare switch to toggle power to the rest of the panel. I don't need the cabin lights, usb, etc. on most daysails, so this would be a secondary behind the mains switch.





Is there any reason I shouldn't do this?

[Russ]

I'm not sure what you are trying to do.

Are you using one of the switches to be a "MAIN" on/off switch to the panel?

I suppose that's possible if the "main" is fused/breakered to carry the load of the rest.

The main panel still needs to be fused close to the battery. So this seems unnecessary.

[Jimmyt]

Howdy! For Christmas, I was given a rocker switch panel with battery voltage display, usb and 12 volt receptacle. The battery voltage ran down my battery in the month and a half that the boat sat idle.

I'm going to be installing a mains switch, but I looked at the ticket switch panel and realized that I could use a spare switch to toggle power to the rest of the panel. I don't need the cabin lights, usb, etc. on most daysails, so this would be a secondary behind the mains switch.





Is there any reason I shouldn't do this?

No.

All of my loads are downstream of my battery A/B switch, which is where I shut my power down. If you aren't wired that way, a switch to shut down your loads is a good idea (as you discovered ). Agree with Russ's comments regarding circuit rating and fusing.

[Idiotfool]

I'm adding an A/B switch to completely depower everything*. I have only the standard wiring in the boat (cabin, running, and masthead lights) with a spare auxiliary switch. All switches are back-lit and the voltage display is always on.

I want to be able to run my motor and, basically, depower the cabin during a daysail. I thought about getting another cutoff switch to mount near the panel but, once I realized I had a spare switch, it made sense to use it for this purpose. That switch still has the backlight, but that draw is low, especially since the volt meter is off.

It seems stupid, since I'm feeding a bunch of breakers and switches from a twin, but if I wire this up regular, the positive and negative just pigtail to all the breakers. Not altogether different, except the current goes through the switch, I suppose, but the lights don't draw much power...

I may still get another main cutoff, but I'd rather not cut into the boat more...

I say everything*, by the way, because I just mean everything in the cabin. I still want to have power go to the pedestal for the outboard and such.

[Starscream]

There are fusing concerns, as others have said.

Maybe the cheapest, safest, and quickest way to do what (I think) you want is to add one of these:

https://www.amazon.ca/Jeemiter-Circuit- ... HJ1ZQ&th=1

For 30$ CDN and a tiny bit of extra wiring, you can add simple on/off control, and put this breaker near the battery so that everything downstream has a certain amount of protection. These breakers are available in pretty much any amperage you want; I have two 100A breakers like this for my ACR.

Doing what you suggest is certainly feasible, and may work just fine, but there are several reasons not to do it. Like Electrical Codes, best practices, safety for future owners of your boat, overcurrent protection, and so on.

[Russ]

There are fusing concerns, as others have said.

I have one of these between my house battery and my main switch panel. I "could" cut power to the panel. But I see no real reason to do so as long as everything is off.

Other boats I've owned had a "main dc off" switch which I assume just cut power to the panel.

[Be Free]

Whether or not you can repurpose the spare switch as a master is going to depend on how your panel is wired. Some have a single 12v lead going to a small internal bus bar that the individual switches are powered from. You can probably do it, but is it worth the trouble? How more likely are you to remember to turn off the master switch than you are to turn off the other three switches in the same panel?

On a related note: even that LED backlight can kill your battery "graveyard dead" if you leave it on long enough. It's the devices that will continue to work when the battery is well below 12v that will take the battery down so low that it won't recover. I had the backlight in a meter destroy a pair of 12v batteries because I left it on for a couple of weeks. One of them came back enough to sometimes start the engine. The other would never even take a charge again.

[OverEasy]

Hi IdiotFool!

Just my 2 cents…..
I agree with the others in that what you “can do” and what you “should do” are two different animals.

You “should” have a close to the batteries fuse or breaker. Guidance is something like within 6 to 12 inches (or less which is where things like the fuses mounted directly to the positive battery terminal posts come into play). That way if any portion of the wiring anywhere resulting in a dead short were to occur the fuse or circuit breaker pops off.

You “should” have separate circuit switches with dedicated fuses or circuit breakers for each ‘point of use’ distribution such as cabin lights that are going to limit the current to the requirements of the ‘use’ AND the wire gauge AND switch capability (generally whichever is lower. That way if something on the individual ‘point of use” goes awry that particular circuit is protected. When that circuit goes down the problem is limited to just that circuit. For example we have our two cabin lights on two separate circuits so that if there was a problem with one of them we aren’t leaving ourselves totally in the dark.

Same goes for our Navigation light circuits, our DC utility outlets, each of the bilge pumps, & etc….

Now back to your original question… ‘Can you use one of the switches on your new panel as a sub main for the rest of the circuits going through your new panel?” The answer is it depends on the rated capability of the particular switch, the system wire used and the limiting current of the associated fuse or breaker. Too much current through the switch will cook the switch. Too much current through the wiring feeding the other circuits will cook the wires. Too large a sub-main fuse or breaker will allow the system to cook off (which could cause a fire or damage) and too low a sub-main fuse or breaker will prematurely drop out everything on all the other circuits all at once (which could be rather annoying).

An adequate understanding of what circuits are involved, the electrical loads involved, the actual gauge/condition/lengths of wire involved, the rated capabilities of the switches involved and the proper fusing or breaker capabilities are all required knowledge before an actual appropriate answer to your question can be given.

Hope this helps some….

Best Regards,
Over Easy

[Idiotfool]

Hi IdiotFool!

Just my 2 cents…..
I agree with the others in that what you “can do” and what you “should do” are two different animals.

You “should” have a close to the batteries fuse or breaker. Guidance is something like within 6 to 12 inches (or less which is where things like the fuses mounted directly to the positive battery terminal posts come into play). That way if any portion of the wiring anywhere resulting in a dead short were to occur the fuse or circuit breaker pops off.

You “should” have separate circuit switches with dedicated fuses or circuit breakers for each ‘point of use’ distribution such as cabin lights that are going to limit the current to the requirements of the ‘use’ AND the wire gauge AND switch capability (generally whichever is lower. That way if something on the individual ‘point of use” goes awry that particular circuit is protected. When that circuit goes down the problem is limited to just that circuit. For example we have our two cabin lights on two separate circuits so that if there was a problem with one of them we aren’t leaving ourselves totally in the dark.

Same goes for our Navigation light circuits, our DC utility outlets, each of the bilge pumps, & etc….

Now back to your original question… ‘Can you use one of the switches on your new panel as a sub main for the rest of the circuits going through your new panel?” The answer is it depends on the rated capability of the particular switch, the system wire used and the limiting current of the associated fuse or breaker. Too much current through the switch will cook the switch. Too much current through the wiring feeding the other circuits will cook the wires. Too large a sub-main fuse or breaker will allow the system to cook off (which could cause a fire or damage) and too low a sub-main fuse or breaker will prematurely drop out everything on all the other circuits all at once (which could be rather annoying).

An adequate understanding of what circuits are involved, the electrical loads involved, the actual gauge/condition/lengths of wire involved, the rated capabilities of the switches involved and the proper fusing or breaker capabilities are all required knowledge before an actual appropriate answer to your question can be given.

Hope this helps some….

Best Regards,
Over Easy

Thanks. I figure there's a risk of overloading the circuit, but the gauge of the wire from the battery to the switch panel is the same as the wiring on the panel itself. In the original, the supply wires were connected to a bar to feed power to all the fuses and in this, the power daisy chains from one breaker to each of the others. I hadn't considered for through the switch, as I'd expected the breaker would protect against that.

Genuinely curious how the wiring could be a problem if it's all the same gauge, though.

I've seen some sailboat retrofit videos, before, with a main switch to completely depower all cabin DC systems, but I don't see anything commercially available out there.

I'm still puttering around with this. I will be installing an A/B switch this weekend (I hope) and I'll probably undo the switch panel idiosyncrasies. Thanks for all the responses.

[OverEasy]

Hi IdiotFool
Here is a helpful links related to 12 VDC wire load capacity.

https://www.engineeringtoolbox.com/amps ... 205%20amps.

https://www.rpc.com.au/pdf/Wire_Chart.pdf

Typical rule of thumb is to avoid overloading by limiting peak current to no more than 50% of wire capacity.
Fuses and breakers are circuit protective devices and are typically based on what is the anticipated load requirement but not to exceed the 50% wire load capacity. Same for switches.
The last thing one wants to do is overload current in wires (especially in a boat).

Best Regards
Over Easy

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