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Murphy8166

Master Power & Ground - What Awg?

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Murphy8166

I am planning to run a set of power and ground wire from the back my amp rack to drivers dash area. All my pos's and neg's for my stereo terminate on the back of my amp and I would be running the wire from the amp rack in the passenger side compartment to the underside of the drivers dash. I was not planning on going all the way around the front of the boat but was going to use the shorcut and run the wire along the back of the front ballast tank. So I am thinking 12 feet max.

I am planning on using a terminal strip under the dash to wire up an Audiocontrol Three.2, Ipod Charger Cable and a switch to turn the AC unit on and off.

Knowing that my distance is 12ft and I am going to be powering the three items list above...is a good 12 awg wire ok or do i need to get beefier?

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Pistol Pete

AWG will vary based on distance (which you know) and amount of current drawn.

What would be the max amount of amps running over the run? Then, I'll bust out my chart and tell you what AWG you need.

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Pistol Pete

Example.

One chart I have says 12AWG is only good for a 6' run pulling a max of 40 amps.

The other chart calls.. 12AWG is only good for a 7-10' run....... max of 20 amps.

Sheesh,

That's about 100% difference. I'd like to hear what the experts have to say and I'll toss which ever chart is not correct.

Edited by Pistol Pete

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my malibu

Both charts are correct

Depends on the percentage of voltage drop you are using

In general 12 awg is good to 45 amps max

10 awg is good to 60 amps max

Example 12 awg at 10 percent voltage drop is good at 40 amps up to 18 ft but that's round trip so you cut that in half 9 ft

At 3 percent voltage drop only 5 ft

Example.

One chart I have says 12AWG is only good for a 6' run pulling a max of 40 amps.

The other chart calls.. 12AWG is only good for a 7-10' run....... max of 20 amps.

Sheesh,

That's about 100% difference. I'd like to hear what the experts have to say and I'll toss which ever chart is not correct.

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Pistol Pete

Depends on the percentage of voltage drop you are using

How would you determine the voltage drop "you are using".

Ideally, wouldn't you want 0 voltage drop by using a slightly lower number AWG wire than, what you really need as far as a minimum?

I'm not being a smart azz, I know what voltage drop is and how to measure it, I've just never considered accounting for it as some sort of given amount in the beginning of wiring something.

Would it be safe to say go with option 2 with: 12AWG is only good for a 7-10' run....... max of 20 amps. To account for voltage drop?

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my malibu

How would you determine the voltage drop "you are using".

Ideally, wouldn't you want 0 voltage drop by using a slightly lower number AWG wire than, what you really need as far as a minimum?

I'm not being a smart azz, I know what voltage drop is and how to measure it, I've just never considered accounting for it as some sort of given amount in the beginning of wiring something.

Would it be safe to say go with option 2 with: 12AWG is only good for a 7-10' run....... max of 20 amps. To account for voltage drop?

yes you are right with going to a lower awg gauge

first to answer yes it would be safe to run 12awg for that run but you have to account for the return so 7-10 becomes 14-20ft on the chart at 20 amps but not at 40 amps

the 3% drop will happen at 7-10 ft but on a 12v system not a big deal most electronics are made to run from 14v -11v

so 14 v form source after drop 13.8v not a big deal

it is more important to add 30% as head room

also have to take into account running wires next to each other

or bundled the maximum amperage goes down by 40 % if i remember right

10 % and 3 % voltage drop charts are standard to determine which one to use depends on the load

you can calculate the voltage drop by using the following equation

Voltage drop = Current x length x Ohms per ft

I know you know this and most don't know the resistance of the wire they have choosen

I always jump to the next lower awg size when i wire

I'm also just starting my stereo install and am also adding a power and ground form the stereo bank to run the eq , stereo ,ipod, etc

I will be running across the front tank for a total of 8 ft

so total length 16ft at 40 amps

on 10% chart its 12 awg but i will be using 10 awg for my 30% head room

hopes this helps

tried to keep it short

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shawndoggy

anecdotally, I can confirm 12awg will work just fine for what you are proposing to do.

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Murphy8166

yes you are right with going to a lower awg gauge

first to answer yes it would be safe to run 12awg for that run but you have to account for the return so 7-10 becomes 14-20ft on the chart at 20 amps but not at 40 amps

the 3% drop will happen at 7-10 ft but on a 12v system not a big deal most electronics are made to run from 14v -11v

so 14 v form source after drop 13.8v not a big deal

it is more important to add 30% as head room

also have to take into account running wires next to each other

or bundled the maximum amperage goes down by 40 % if i remember right

10 % and 3 % voltage drop charts are standard to determine which one to use depends on the load

you can calculate the voltage drop by using the following equation

Voltage drop = Current x length x Ohms per ft

I know you know this and most don't know the resistance of the wire they have choosen

I always jump to the next lower awg size when i wire

I'm also just starting my stereo install and am also adding a power and ground form the stereo bank to run the eq , stereo ,ipod, etc

I will be running across the front tank for a total of 8 ft

so total length 16ft at 40 amps

on 10% chart its 12 awg but i will be using 10 awg for my 30% head room

hopes this helps

tried to keep it short

Where did you come up with 40 amps.

Most head units have a 10 amp fuse and most eq's have a 1 amp fuse. Your calculation seems REALLY high even when adding an ipod charger in the mix.

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Earmark Marine

Murphy,

Normally you are trying to avoid anymore than a .5 volt drop.

The gauge relates to both the distance and the current application.

Add the sum of both the positive and negative lengths in a boat if you are using a chart.

Remember that the recommended component fusing is for protection from a failure or event and not an indication of normal current draw in this case.

With the component description you are looking at having just a couple of amps draw so a 14 gauge wire would be fine but 12 gauge would probably be the maximum you could justify.

The quality of the connections will also impact the voltage drop just like the cable. There is no substitute for a Western Electric type connection that is soldered. Each crimp connector will add some resistance resulting in some voltage drop. As amperage is increased the resistance becomes more critical in how it impacts the voltage drop.

You can easily measure the voltage drop with a $10 volt/multimeter between the voltage source in the port locker and the collective terminals of the EQ and ipod at their junction on the starboard side while the components are actually in use. That totally removes any speculation.

David

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philwsailz

I will agree with David that a Western Electric connection, (aka lineman's splice?) is a best type connection and provides the least current drop. Soldering provides further electrical stability as your copper-to-copper connection is sealed inside the solder. However soldering can be a problem mechanically, as you introduce stress risers to the wire to solder joint union and run the potential of solder wicking outside the joint and creating brittle individual strands. . ABYC/NMMA forbid soldered joints for new boat production as a result of this and other issues including cold joints which are prone to start fires.

I still think it is a good or even best electrical connection with these two caveats Support the soldered joint well to prevent excessive wire movement on either side of the connection and in particular at the copper to solder transition area. Also make sure not to create a resistive cold solder joint.

A wire crimp connection prevents mechanical stress risers due to solder creep. With heat-shrink in-line crimp connections one can approach solder joint efficiency from an electrical standpoint and exceed a solder joint's resistance to mechanical failure, with the heat shrink providing corrosion resistance.

Either needs to be done properly though to work well for the long term. Poorly executed, either will let you down.

Short story from the long post: regardless your termination method, do it well and properly. Your amps and batteries will thank you for it!

Phil

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Earmark Marine

Yep, there is no connection that is worse than a cold solder joint so execution is everything and not everyone knows the right procedure. Its definitely not about dabbing on the solder.

Heat is a great indicator of resistance. And there is no better testing ground than DC lighting with allot of current draw as its much more taxing than the transient nature of an audio draw.

In a test when using crimp connectors on a 14-gauge wire supplying three 5-amp halogen lights (15 amps total) the crimp connection would get hot enough to burn you. When the crimp connection was replaced with a Western Electric type connection that was soldered the heat of the connection was reduced from hot to warm. Its a revealing test.

We use crimp connections such as blades, rings and forks but we always dispose of the insulating sleeve and then solder and heatshrink. Its just one way but not the only way. Certainly aviation (which is kind of a critical environment) uses crimps which are a different variety than the ones you would get from the auto supply.

David

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my malibu

For what ill be doing I will be pulling 35 amps or so

It going to run the stereo, eq, and a couple more surprises

Where did you come up with 40 amps.

Most head units have a 10 amp fuse and most eq's have a 1 amp fuse. Your calculation seems REALLY high even when adding an ipod charger in the mix.

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