Battery disconnect switch

[Bahala]

I have graphs wired direct to the battery. I have had one come on when putting the protective cover on. I didn't know it for a while and it pulled my battery way down. I would now like to use a disconnect switch. I used the Blue Sea battery terminal fuse mount.



To make things easy, could I use their new terminal mount disconnect on the negative side of the accessory wires?
https://www.bluesea.com/products/599...d_Mount_Switch

[bobcoy]

If you want a switch it should be on the plus(Positive) wire.
Note: the link you supplied said it will be available in July 2018

[tweakjr]

If you want a switch it should be on the plus(Positive) wire.
Note: the link you supplied said it will be available in July 2018

The usual way to do it is as bobcoy says, but technically it would work on the negative side as well.

[bobcoy]

I would be more worried about someone thinking there was no power at the unit with the switch turned off in the future.

[Bob B]

One of the basic rules of electric wiring is that the ground wire is NEVER switched.....as bobcoy says switch the positive side.

[bassin_man]

I was looking at the same switch myself. Think I will give it a try.

[pfisher]

My installer never gets excited about much but he is happy to see that new switch. At $20 or so according to him they will be mandatory on every install they do.

That is a nice, simple switch idea. They will sell many!

[toofy]

One of the basic rules of electric wiring is that the ground wire is NEVER switched.....as bobcoy says switch the positive side.

For those of us that can barely change a light bulb, can you explain why?

[Bob B]

The primary reason is that it is a RULE for electrical wiring. The reason for this becomes more apparent when you consider higher voltages. If you switch the ground wire, the device your are switching off will go off ... unless there is another path to ground .... but the voltage will still be at the unit, just not the ground. If you touch the voltage assuming things are off, you become the path to ground and electrocution could result.
In the case of low voltage, electrocution isn't a risk, but often times another ground path can be present. for instance, if your unit has an Ethernet connection, there could be a ground path back thru it .... anything connected to the unit could supply another ground path or maybe a resistive ground path......plus anyone working with the circuit will assume the voltage has been switched off and even a low voltage can cause some major problems if shorted to ground inadvertently....It is just a BAD idea to ever switch the ground to turn something off. The hot wire should always be switched off.

[tweakjr]

It is a general rule to ensure a "zero energy state" mainly for safety when working on high voltage systems or when inadvertently activating a device could be dangerous.
In this case of a low voltage fish finder and an electrical system that isn't chassis grounded, it's not much of an issue to put the switch on the negative side of the battery.
I personally wouldn't do it that way, but if for some reason placing the switch there was a necessity, it would work just fine.

[bobcoy]

Do it anyway you want. I always try to do things the way they should be done. Speaking of common ground, It depends what your boat is made of. Standard metal boat wiring is there be only one ground on the hull at the motor ground . You are correct about not being high voltage. However most batteries will deliver hundreds of amps when shorted. Bad burns and fires can result. Some things are not wise to do the wrong way. "The general Rule" is not in the book! If it were it would say render the circuit safe.

[Bob B]

Do it anyway you want. I always try to do things the way they should be done. Speaking of common ground, It depends what your boat is made of. Standard metal boat wiring is there be only one ground on the hull at the motor ground . You are correct about not being high voltage. However most batteries will deliver hundreds of amps when shorted. Bad burns and fires can result. Some things are not wise to do the wrong way. "The general Rule" is not in the book! If it were it would say render the circuit safe.

[toofy]

Interesting. Why is the positive the "hot" wire since I thought both carry current?

[Bob B]

In a 12V DC circuit, the positive is the hot wire or the potential voltage .... the negative can be considered the ground, common, or return. While it is true that both wires have current flow, the ground wire will be common to many devices on a boat and possibly even the boat hull in an aluminum boat. The common wire will also be connected to the motor and therefore even the water will be a ground path. Since there are so many potential paths to ground, including you, that is why the positive or hot wire is switched so there is no possibility of undesired current flow in a circuit.

[toofy]

Awesome explanation. You dumbed it down enough that even I can understand that!

[ezfishn]

Good explanation Bob. It really starts getting complicated trying to explain current flow in terms of protons and electrons...LOL

[Bob B]

Good explanation Bob. It really starts getting complicated trying to explain current flow in terms of protons and electrons...LOL

And the whole thing can be blown away with a discussion of hole flow.

[ezfishn]

[Bahala]

Reckon I'll switch the positive. Thanks for all the input!

[Ches.]

I don't know about your boat, but I would hate to have to go into my battery compartment to switch off my locators every day. Looks like a nice switch, but I am too fat and lazy for that. I have thought about installing a second master switch just like my factory one for just my locators. Ethernet hub would stay on the original boat master. Not sure if the way I am thinking about doing it is the best, but I think it is the way I am headed.
Ches.