Beginner's wiring question

[epicmariner]

If I'm wiring a pump to a panel switch via a terminal/bus bar, what do I need to know? Here's what I'm getting at: I have the wires coming from the panel connected to a bar then the wires from the bar to the pump. To which screws on the bar do I connect the wires from the panel and pump so that when I close the panel switch the pump will run? Assume that the pump has only on and off positions. I have looked around and in several books and can't find the answer. Thanks in advance and sorry if this is a stupid question.

 

[tashasdaddy]

Re: Beginner's wiring question

you bring pos power to switch from pos side of fuse panel, from switch to pos on pump, neg on pump to neg on buss bar.

 

[epicmariner]

Re: Beginner's wiring question

OK, I think I did a bad job of explaining that. I apologize, that's twice now. The situation is this, I've got a wire coming from the switch to the buss bar then to the pump. If there are other accessories attached to the bar, how do I go about hooking the wire from the switch to the wire from the pump so that the pump is controlled by the switch?

 

[Silvertip]

Re: Beginner's wiring question

You have it backwards. Current flows FROM the +12V bus TO one terminal on the switch. FROM the other terminal on the switch TO the pump POSITIVE lead. The ground lead on the pump connects TO the ground bus. The positive lead on the pump does not connect to the bus as you indicate.

 

[epicmariner]

Re: Beginner's wiring question

Thanks to TD and ST for responding. I think I am confused about and am confusing everyone else. Especially regarding terminology. I'm sure that I am the source of the confusion.

Anyway, I looked around online and think this is what I am trying to ask: how should I connect a switch at the panel to a terminal block then to a pump. In my boat, the terminal block is mounted on the transom above the pump in question. The switch is at the panel in the console.

Sorry for not being clear and doubly sorry if I am just repeating myself, but I can't be sure. I'm sure I am the source of all the confusion though. Thanks in advance.

 

[Silvertip]

Re: Beginner's wiring question

You don't need to use that terminal block at all. If you have a switch on the console, you also have power there. The only wire you need is one that runs to the bilge pump from the switch. Then connect ground on the pump directly to the negative terminal of the battery. Post a picture of the "terminal block" and explain what else is connected to it and whether the connections are ground, +12V or both. Look at it this way. +12V flows from the POS terminal of the battery up to the console. How it gets there is not of significance. You know its there because you have other stuff on the console that requires it. +12V then flows to one terminal of the switch. If the switch is open it can't go any farther. Closing the switch causes +12V to flow out the other terminal down the wire to the pump. It then flows through the pump motor to ground (NEG terminal ont the battery).

 

[Silvertip]

Re: Beginner's wiring question

Here ya go -- I can't make it any simpler than this.

 

[alandchris]

Re: Beginner's wiring question

silvertip

in your last pic of the bilge pump wiring diagram you have the ground wire on the pump direct to the neg side of the battery.

can the ground wire on the pump go directly to the ground bus on the fuse panel instead of directly to the battery ?

 

[Woodnaut]

Re: Beginner's wiring question

Alandchris - In the diagram above note that the ground bus is connected to the battery though a single wire. As more devices are hung on the ground bus the current flow in this wire back to the battery will also increase. Anytime there is current flowing in a wire there is a voltage drop. Usually, this voltage drop is very small and the voltage difference between the "ground bus" and the negative terminal of the battery is very slight.

But I have two 2000 gph bilge pumps on my boat and if they were both running they would draw a lot of current which would produce a greater voltage drop through this wire. Then turn on the navigation lights and maybe some other interior lights. So as it turns out, if the wire between the ground bus and the battery is too small, that "very small" voltage drop that I mentioned above could turn out to be a lot more than you might expect. Usually this will be only a few tenths of a volt, but I've seen some systems where the voltage difference between "ground" in the console and "ground" at the battery exceeded 2 volts.

Bilge pumps contain DC motors which have brushes that create a lot of "electrical noise". If the ground of a bilge pump is taken directly to the negative terminal of the battery, that "noise" really doesn't affect the rest of the electrical system. If the bilge pump ground is taken to the ground bus, however, then it might cause problems if the return wire back to the battery is too small. The "noise" from the bilge pump is added to whatever small voltage is already on the ground bus and the noise then ripples through the entire electrical system. Navigation lights don't care if a little noise is present in the system, but the GPS and the radio might.

Also consider the engine. Note that there is usually a large cable going from the negative terminal of the battery to the engine block. Therefore the engine has a ground that is at (or very close to) 0.0 volts because of that big cable. If an electrical device was present that interfaced with the engine AND the rest of the electrical system - for example, maybe an external tachometer - then that device might be connected to both the engine ground and the ground buss. Since they are at slightly different voltages, then a "ground loop" can be set up which can be a real problem for some electronics.

The bottom line is that all devices need a good return to ground to help prevent ground loops and shield the electronics from noise. On my boat the bilge pumps ARE connected to the ground bus, but I also installed a ridiculously large wire from the negative battery terminal to the ground bus. I hope this has helped and not made things more confusing.

 

[alandchris]

Re: Beginner's wiring question

woodnaut...
excellent point on the direct ground...

i have a smaller boat - 16' aluminum bass boat - it has a bilge and livewell pump that return both the positive and negative(ground wire) back to the fuse panel. they appear to be either 14 or 16 gauge wire.

seems like an easier / better idea to just bang it right on the battery which is less than 2 feet away from these pumps.

do you agree ?

although I would assume since the factory did it, that the voltage drop would be insignificant - maybe given that these pumps are only turned on for a very limited timeframe. the pumps are relatively small - maybe a 300 or 500 gallon per minute unit...

as i think about your last post - would it also make sense to take the back anchor lite and just ground it directly to the battery as well ?

 

[Woodnaut]

Re: Beginner's wiring question

It's OK to bring everything back to the ground bus as long as the wire from the ground bus to the negative battery terminal is sized sufficiently. On a small system (nav lights, 1 bilge pump, maybe a depth sounder and a radio) a 10 gage wire running a few feet would probably be just fine. For example, a 10 gage wire 10 feet long has a THEORETICAL resistance of 0.0104 ohms. (That's 1.04 ohms per 1000 feet). If you had a total load of 20 amps on the entire circuit, that would mean a voltage drop of 0.208 volts in the return wire. No problem. A shorter wire would mean even less voltage drop.

In my boat I ran everything to the ground bus. I then ran an 8 gage wire about 4 feet to the negative terminal of the battery. (At 0.653 ohms per 1000', that's a voltage drop of 0.05 volts at 20 amps - which is essentially nothing.) This system works fine for me. I like to keep all of the wiring nice and tidy so running a single ground wire back to the battery appealed to me. That way I don't have a lot of connections at the battery terminals either.

Also note that the drawing that Silvertip posted is an excellent one. On something like a bilge pump that is a noisy, high-current device it makes good sense to bring it back the negative battery terminal. In your case, since your two pumps are very close to the battery, I would say bringing their ground wires back directly to the negative terminal of the battery is great. Either way is OK as long as the conductors are sized properly.

Here's a little info on theoretical wire resistance in OHMS per 1000 feet. Wire gage is the first number and resistance in OHMS is the second:

6 0.411
8 0.653
10 1.04
12 1.65
14 2.63
16 4.18
18 6.64

Beware, however, corrosion on terminals and connections increases resistance changes everything! I use dielectric grease (silicon) on all connections. It keeps the corrosion at bay and maintains the electrical integrity. Good stuff!