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Old 04-14-2021, 08:53 PM   #1
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Brittle electrical wire

Hi all,

So, some may remember my earlier post about a ghost reverse polarity light. I got back on that boat this week, but to trouble shoot different issues that are a higher priority for the owner.
Initially, the port bow light quit working. Then the starboard bow light.

A 2-conductor 12vdc power cable ran from the panel forward where it forked off to the two lights via butt connectors that acted as 1:2 splitters.

The cable leading to the port bow light was seemingly of 1981 vintage, stranded, and untinned, but labelled as "boat" cable. The strands seemed brittle, dull, coated in a black border substance that tested as high resistance. Cutting back didn't help. It was all like that, even a foot in. I directed it be replaced.

I was called back the next day. Same symptoms, but this time the port starboard light. Same problem. The positive wire for the starboard branch had actually broken and the insulation around it stretched, leading to an invisible gap in the wire, I assume from being pulled at while the port wires were serviced. I directed that it be replaced and that the feed cable be replaced as soon as possible. I've been told the problem was resolved by replacing the starboard cable and that the replacement of the feed is on "the list".

For the curious, the boat is a 1981 C&C sailboat.

I, personally, don't think I've ever before seen a marine grade stranded wire get so brittle it broke inches from the end, and show brittleness feet in.

My question is this, how common is it for marine grade stranded wire, from the days before tinning, to get that bad along the whole length of the wire vs just near the ends?

(I hope to update the reverse polarity thread soon, when the owner let's me get back to debugging that...)
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Old 04-14-2021, 09:16 PM   #2
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Greetings,
Mr. gk. Might it be a result of a lightening strike? Black coating on the strands suggests copper oxide to me. I've seen a similar coating on copper water pipes that had been used for telephone grounding in country houses. Not so much in city homes.
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Old 04-14-2021, 10:37 PM   #3
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Hey RT,

The insulation looked good vs darkened or brittle from overheating. Just the wire was bad. So, maybe, but, seems far from a lock.

I'm not much of a chemist, but I was actually wondering if off gassing from a battery, maybe the one for the windlass as the wiring is in the chainlocker, could cause it?

I normally don't worry about discolored coppet wire. I chemically clean the end if needed and back to it. But this was soo brittle and cutting back didn't help, so it got my attention.
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Old 04-14-2021, 10:46 PM   #4
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I have seen that in an old shore power cable.
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Old 04-14-2021, 11:05 PM   #5
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It just needs to be exposed to moisture. It will wick up the cable and oxidize the wire many feet up. Thats why we use tinned wire and sealed terminals.

Unusual after that many years with bare copper, not really. Typically the ends are the worst, but once it starts, it travels. In exterior exposed wires, Id say its very common.
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Old 04-15-2021, 05:49 AM   #6
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"My question is this, how common is it for marine grade stranded wire, from the days before tinning, to get that bad along the whole length of the wire vs just near the ends?"

I was building boats in the 60's and tinned wire was easily available , no idea of when "before tinning" was..

Wire selected by builder was probably done by price.

Today with proper crimps and a crimping tool and good wire when used with heat shrink tubing there are less problems.

The most amazing is folks that drop a power cord into the sea and think rinsing it off takes care of the problem.
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Old 04-15-2021, 06:03 AM   #7
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I experienced this recently on a Westerbeke generator. I discovered it after the generator shut down down twice with a50% load. The 60-amp breaker popped. When I went to the breaker the second time the steel box enclosure was too hot to touch. When I removed a cover plate I found that the two wires from the brushes were brittle and black. Okay, easy fix, just cut the wire back to good wire. Nope. Those wires were bad all the way back to the brushes. Some of the strands were broken. Very scary as I had been using that generator that way for five years.

The wire was replaced with tinned wire and heat shrink terminal ends.
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It just needs to be exposed to moisture. It will wick up the cable and oxidize the wire many feet up. Thats why we use tinned wire and sealed terminals.

Unusual after that many years with bare copper, not really. Typically the ends are the worst, but once it starts, it travels. In exterior exposed wires, Id say its very common.
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Old 04-15-2021, 07:12 AM   #8
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Here is a picture of the bad wires on the generator. Click image for larger version

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Old 04-15-2021, 07:43 AM   #9
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Any chance the boat has been submerged any time in its life? I see wires in that condition on boats that have sunk, the water (usually salt water) wicks its way through the length of the stranded wire.
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Old 04-15-2021, 08:07 AM   #10
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Ski, one cannot ever know for certain but, no. If that were true, I think I would have found many more related problems. Take another look at that connection. The two wires coming from the brushes are totally corroded yet the single feed wire going to the breaker box is just fine. I was appalled to see how that connection was made, three ring terminals bolted together. After rewiring the brushes, I added a terminal block to the inside of the box. The brush wires go to the terminal block along with feed wire to a new breaker and breaker block.
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Any chance the boat has been submerged any time in its life? I see wires in that condition on boats that have sunk, the water (usually salt water) wicks its way through the length of the stranded wire.
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Old 04-15-2021, 09:52 AM   #11
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CatalinaJack- My query about sinking was more towards the OP with the C&C sailboat.

With regards to your gennie, that looks more like heat damage. The brush leads on the old Winco gen carry output current from the rotor, backwards from most gennies where the field is in the rotor, and output from the stator. Yours must be a WMD model. And that was a chicken sh!t connection there!!

Heat from a bad connection can travel far on a copper lead, as you have seen. High thermal conductivity thing.
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Old 04-15-2021, 10:04 AM   #12
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Hey Ski,

Not that the owner knows about. But, the connections are at the top of the chain locker, right near the lockers two large, opening deck accesses. I know nothing about how dry of a ride the boat had. It could have spent 40 years with seawater frequently pouring over and through.

When I asked the owner, he said, "Well, it is right up at the bow.", which I took to mean it rides wet.

To the poster who mentioned seeing similar on shore power service, I've seen that, too, especially between the inlet and the panel. I've always assumed it was from years of overloading and overheating. The difference I noted in this case is that the insulation, both wire insulation and cable sheath, looked fine.

From the reports, it sounds like this isn't unusually in places where the wire gets wet with saltwater and can wick it in.

I'm just impressed with the amount affected. Good shink connectors with internal glue and tinned wire now seem like a better bargain than ever before (and I always thought them to be a bargain).

Cheers!
-Greg
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Old 04-15-2021, 10:08 AM   #13
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This is definitely pretty typical of un-tinned wire if it's been exposed to a lot of salty air (or water), or battery gases, or even gases from gross water festering in the bilge and breaking down (you'd know about this from the smell though). Unfortunately, un-tinned wire has a limited service life, especially outside of the cabin unless the ends are perfectly sealed.
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Old 04-15-2021, 10:10 AM   #14
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Yea, the wicking you saw does not require submersion. If non-sealed connections get wet occasionally over 40yrs, that will do it.
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