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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance > Electrical Systems
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Old 02-25-2011
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Is this wire corrosion?

A lot of the DC wiring on my boat is not tinned. Everything is working fine. However, I just replaced the wire in the picture for other reasons and wondered if the black area on this copper wire is corrosion. The picture is out of focus, but you can probably see that some of the strands are copper colored, while others are black. All the strands seem to be intact, simply two different colors. If it is corrosion, what are the implications? This section was mid span and encased in plastic, not an exposed end. I unwound the strands for the picture. Don Casey's book has a drawing of wire corrosion, but since the picture is drawn it's hard to see what it really looks like. Anyway...could this be a problem?
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Last edited by L124C; 02-25-2011 at 07:49 PM.
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Old 02-25-2011
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Yes it looks like corrosion. I usually cut back an end if there is extra length to get to clean copper when the wire is impossible to replace. If at the end it doesn't usually extend very far, but can extend throughout the wire in worse cases.If the wire was wet with salt water it will be a green color.
The implication is more resistance. Electricity travels on the outside of the strands, one reason why you are better off with more rather than less strands.
You say it was encased in plastic? The original wire covering or something else?
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Old 02-25-2011
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Yes it is corrosion. It's bad because it works from the outside in, it won't stay just on the surface, and additionally any crimping in contact with those corroded areas is going to have high resistance.

Electricity does not just travel on the outside of the strands, it most certainly travels on the inside. Resistance reduces as cross-sectional area increases, not as circumference increases. More strands are better because it's more flexible and resistant to breaking.
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Old 02-25-2011
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I looked it up, and DC current does travel throughout the wire's cross section. AC current travels on the outside of the strands much more readily than the center following the path of least reactance, the "skin effect".
I stand corrected.
Does electricity travel through the wire or on the outer surface? | Answerbag

And it will increase the resistance of any crimp connection.
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Old 02-25-2011
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The only way to re-use that wire is to clean each strand of it's black oxidation. This is not easy and often results in damaged strands. Acids do well but then they can degrade the wire if not properly neutralized. The also can NOT be allowed to wick under the wires jacket and ideally should never be used unless it's an emergency situation. Sometimes a Scotch-Brite pad in a pulling motion works but you'll never get it all and the new fitting will have higher resistance.

Best bet is to replace the wire or strip back to clean copper. It looks like lamp cord anyway so I doubt you'll even find clean copper..

Good Copper / Bad Copper


These wires were installed by a hack, never use wire nuts on a boat. The important point though is that both wires are the SAME age. One tinned and one cheap lamp cord.
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Last edited by Maine Sail; 02-25-2011 at 08:21 PM.
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Old 02-25-2011
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Quote:
Originally Posted by mitiempo View Post
You say it was encased in plastic? The original wire covering or something else?
The original plastic covering.
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[QUOTE=Maine Sail;702350]
It looks like lamp cord anyway so I doubt you'll even find clean copper..QUOTE]

Why is that (quality of the copper, casing, etc.)?
In any case, you are right. As I indicated, the corrosion in the picture was far away from the ends of the run, and therefore fully encased.
Do you think tinned wire is the only way to go on a boat, or is better quality copper wire OK?
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Any quality of bare copper will corrode if air and moisture gets to it. I think tinned wire should always be used on a boat. But not everybody agrees. You make the connections the best you can, properly crimped with a good crimper and sealed with adhesive heatshrink but the tinning is an added measure of protection in a moist, salty atmosphere.
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Old 02-25-2011
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[quote=L124C;702363]
Quote:
Originally Posted by Maine Sail View Post
It looks like lamp cord anyway so I doubt you'll even find clean copper..QUOTE]

Why is that (quality of the copper, casing, etc.)?
In any case, you are right. As I indicated, the corrosion in the picture was far away from the ends of the run, and therefore fully encased.
Do you think tinned wire is the only way to go on a boat, or is better quality copper wire OK?
Cheap wire insulation seems to let moisture in over the years. There is phenomenon called water treeing that I have read up on and I suspect that is what some of the cheaply jacketed wire is suffering from. Some think that chemicals in the jacket material may be the cause but either way when I see wire oxidized along it's entire length, and I know it is not from wicking, then I know that I need to buy high quality wire not the cheap stuff..

I have pulled two absolutely identical wire runs out which were side by side and terminated in the same dry spot on both ends yet the cheap lamp cord was completely oxidized along the entire length and the high quality wire with the PVC jacket was like new the entire length except for about 3/8" in from the ends.
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Old 02-25-2011
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uh oh, Maine Sail started using Wirenuts on his boat again...
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