Size of negative return???

[YankeeRebel]

If i run 3 seperate positive wires, all 16 Gage, up the mast 28 feet, what gage of wire would i need for these three to share one negative return? I need to power Anchor, Steaming, and deck light. While i'm at it, should i run additional wire for something in the future? Do TV antennas require power? What else might i mount on the mast in the future that would require power?

Thanks!

[mastreb]

The ampacity of enclosed 16 gauge wire is 13 amps at 12 volts. That's far more that the amount of power you'll need for three lights or anything else that you would put at the top of your mast. In fact, 16 gauge is over specified for everything you'd do on a mast. You do not want any weight up the mast that you don't need. Look to 22 gauge wire, which gives you 5 amps of deliverable power, and you can just use a common return for all three lights.

Antennas do not require power and must be returned using a separate coax wire, usually RG-8 or RG-58. Any modern sensors you put on the top of the mast would require a NMEA 2000 cable, which you may want to go ahead and pull if you're pulling through the mast anyway. There's nothing else that should go up to the top of the mast.

Matt

[Boblee]

The size of the negative wire will depend firstly on the load of everything you want to run at the top of the mast and secondly whether anything up there is voltage sensitive as if the wire is too small you could get voltage drop for this consideration should be taken to the total length of all cables to the battery.
Yes would leave a draw wire in for future additions.

[Trouts Dream]

Based on the thread title....thought this was a 401K discussion...

Carry on.

[vizwhiz]

Based on the thread title....thought this was a 401K discussion...

LOL...I thought the IRS got 'em!

[mastreb]

The size of the negative wire will depend firstly on the load of everything you want to run at the top of the mast and secondly whether anything up there is voltage sensitive as if the wire is too small you could get voltage drop for this consideration should be taken to the total length of all cables to the battery.
Yes would leave a draw wire in for future additions.

You're looking at about 20 ohms of resistance due to cable length presuming that your draw is below 5 amps, which it certainly will be. That's not enough to cause significant voltage drop, and in any case incandescent lights can tolerate voltage drop very easily.

The total wattage you can drive on 22 gauge cable is 60 watts, which is well higher than the Nav lights would be. Typical nav lights are 10 watts. So you can drive everything you need to and do the negative return on a single wire.

No need for guessing, it's pretty simple math.

Matt

[Hamin' X]

There are many factors that go into calculating amperage ratings for wire and wire size needed for a given application. One mistake that I often see, is that the return path is often ignored. It not only must be calculated for the overall run, i.e., if you are running 22ga. wire 50 feet and a return of 50 feet, you must calculate the load for both wires. In actuality, you now have a load on 100 feet of wire.

Connections add to the overall circuit resistance, so keep them to a minimum and make them good mechanical connections, that are both weather and vibration proof.

Next, be aware that 90% of weird electrical problems are due to faulty grounds. Running a separate ground for each circuit will go a long way to eliminating gremlins in your electronics, such as ground loops. If you cannot run separate grounds, you must ground the single ground wire to a single point in the boat and terminate it to a single point at the top of the mast and run all ground wires to these single point grounds. Once you get a ground loop going, your trouble shooting time will multiply exponentially. And, DO NOT use the mast as a ground. Trust me on this one. Electrolysis is a terrible thing. Unless you have megabucks for a whole boat grounding system, leave the mast and shrouds out of it.

Matt is correct about 16 ga. being over rated, unless you are planning to mast-mount a radar, which will consume about 60 watts. However, for mechanical strength, I would not go below 18 Ga. JMHO

~Rich
~Rich

[mastreb]

Rich makes some good points:

Ground faults are very hard to troubleshoot and can largely be eliminated by running a separate ground for every connection--this also simplifies the return power calcs. There really is no such thing as "ground" on a boat excepting the negative terminal rail on your battery or battery bank. Make sure everything goes directly back to it. Grounding to rails or the mast and then trying to tie to it can easily cause floating grounds that will cause big variations in delivered voltage as well as promoting corrosion.

Also, he's right that 22ga is very thin for mechanical strength, especially inside a mast where there will be flex to deal with. You'd be wise to put physical loops about the size of a coffee cup's radius each time you make a 90 turn or any time you are pulling around a corner. A free moving loop will keep the wire from stretching tight against the corner when the mast flexes. Also, be a bit loose with tie straps--they need not be tight to hold things together, snug is good enough. Multi-wire cables are best for strength, so if you need four wires up the mast try to take them all in a single cable vice two cables or four wires.