Shore Cord Failure - Please Help

Impossible to say if the cord is the only culprit, but it's unlikely that there's anything wrong with the boat, imho.

Let's say your shore line (cord+plug) is rated for 50A.
If your onboard AC equipment demand more than that, either the dockside breaker should trip, if rated for 50A, or if it's bad (or rated for more), you should have also a breaker onboard, just behind the power cord, and by definition this MUST be rated for 50A.
So, the breaker(s) is(are) MUCH more likely to be the culprit(s), though it is indeed possible that the cord was a bit "tired" and after some time handling just shy of 50A (hence not tripping any breaker), it overheated and eventually melted.

The fact that you might have turned onboard equipment totalling more than 50A, or also the possibility that one faulty equipment might have absorbed more current that it should, is a bit academic.
In fact, also in this case, either one or the other breaker should have tripped anyway.

As a last though, you might also have NO onboard breaker at all, behind the shore cord.
I've seen boats without it, where the builder obviously trusted the pedestal breaker to protect the shore cord with no need for any other protection.
Should that be the case, I'd definitely recommend to take the opportunity to fit a shore cord breaker inside the boat.
These components can and do fail, and you don't want to rely just on something inside a dock pedestal, possibly old/never tested/corroded/whatever...

Well, it is possible that both breakers are stuck, but of course it's statistically much less likely than one at a time...
A new cord (plug included maybe, depending on whether it shows signs of wear/overheat) and a bit of monitoring sounds like the best plan to me.

If you've got an instrument onboard showing the total current absorption, you could also try to turn on as much stuff as necessary to reach and trespass the 50A threshold.
Any breaker working as intended should trip in a matter of a second or two, well before the cable can suffer any overheating damage.
Of course, if no breaker would trip, you should turn off PDQ whatever you are running, otherwise you could end with two melted cables rather than one! But this very simple test would tell you if the breakers are bad.

I seriously doubt that both breakers on the pedestal and on board the boat are defective. Here in the US boats must have a breaker next to where shorepower comes in if more than a few feet from the main panel.

Over the years I ve had two close calls with shorepower cord

first time was with a 50amp (one of two on the boat). One day during a routine check I noticed a hot spot about 10-15’ from the pedestal. Real hot almost too hot to touch. I shut it down and sliced the cord open to find the neutral conductor in the process of melting down. The wire was heavily corroded over a few feet. There was no apparent damage to the cord outside. I did notice that the wires were not tinned so I made sure to get tinned cable from Ward Electric as a replacement. As a precaution I also replaced the other cable. Both were about 10 years old and original to the boat, also on glendinings

the second incident could have been more serious. About three years ago i walked into our room in the back the boat (an 84) and smelled melted insulation from behind a cabinet where the glendining was housed. Immediately shut down shore and switched to gen. Turned out to be a hot spot in the 100amp cable, in the glendining bucket about 10’ from where it connects to the breaker. Before slicing the cord I noticed a 1” nick on the outside, going thru into two wires. Even though I had been running the boat for a couple of years I had never used the full length of the cord.

Bottom line… shore power cords need to be inspected. every few weeks while under heavy load, I feel the cable for heat from the plug back to the boat looking for hot spots. That’s how i found failure nr 1.

in addition to that, having learned from the second incident once in a while I pull the entire cable out of the glendining and check the rarely visible section as well

I ll never know how much longer it woudl have taken for that 100amp cable to start a fire in the bucket… my guess is not too long. Ironically we were at the dock in Staniel and I almost went with the guest to then grotto that day… glad I did not.

oh and one more thing. Try replacing the cord with tinned wire. I was surprised to see that marinco cable isn’t tinned. As mentioned Ward Electric in FTL has better quality tinned cable by the foot

Very good practice indeed, if a bit annoying.
Talking of which, I recently had a chance to try a handheld thermal camera for an electrical panel inspection, and it works like a charm!
A check like the one you mention would only take a fraction of time, and without even touching the cable.
A good one is still a bit expensive, but it's now pretty high in my wish list for boat toys....

That's possibly true also of EU boats now, even if I'm not 100% sure.
The boats with no onboard breaker downstream of shorepower connection that I previously mentioned were all pretty old.

There isn’t much that can cause this beside a cord failure. Typically your boat should have two main breakers. The first one will be next to the where the power cord is connected, next to the glendining. Follow the shorepower cable into the bucket, it goes thru a hole at the bottom and with a few feet it will end at the breaker. Check the breaker by flipping it off and on. If it moves freely, feel nice and springy it should be good.

then on your main panel there should be another main breaker again make sure it feels right

any breaker that appears to stick or downs spring off when turned off should be replaced.

shore power cords are often overlooked yet they take a beating every day. They get beat up by the sun, pinched between the boat and pilings, etc. regular inspection is critical.

the requirement for a breaker within 8’ of the entry point is an ABYC thing and has been around for a long time. 30 years or more. It s easy to retrofit on older boats.

50 amp shore power cable is pretty standard although I was disappointed to see that glendining supplied non tinned wire. Tinned copper helps prevent corrosion

the burn mark on the outer insulation are a good tell tale of what s going inside. I wonder how long these have been apparent

which wire burned up inside? Since you have isolation transformer, the white neutral is not connected to shore power. It must have been the second hot/line, black.

The red wire looks ok in the picture you first posted, besides a melt mark from the other wire which shows no insulation left

how far is the splice box from the breaker? I wonder if you couldn’t connect the end of the new cable directly to the breaker. The fewer splices the better

if the wiring from the breaker to the transformer looks good and the ends don’t show any sign of heat or corrosion it should be fine

It's the age of the cord. They don't last forever and I'd replace both. They're not that expensive from Glenndenning. Also you were most likely drawing right at or over 50 amps. The dryer generally uses 20 amps, washer in spin mode can draw 5-7 amps at 220, then the 4 a/c's, sea water pump, freshwater pump and water heater probably kicked on also. I wouldn't draw that much stuff off of a 50 amp cord. When using the washer and dryer I'd shut the water heater breaker off and possibly an A/C depending on how many amps you're drawing. Basically you got away with it before, but this time had the perfect storm of multiple items probably all turning on at the same time. Could be lower voltage at the dock as well. Also check the connections where the cord attaches to the boat, they tend to loosen over time causing issues as well from the cycles.

Thru the years, I have cut up many shore power cords that were found hot or already over heated.
Imagine any of the cables as a vacuum hose. Any nick, cut or opening for water to get in to, water WILL GET IN TO IT. Including the ends.
Once one drop of water gets in, it wicks up the whole conductor and the wire starts to deteriorate.
Any resistance that builds up, the conductor turns into a heating element.

Years ag0, one of my own cables, the end was dropped into the river for a second. No power was on the cable.
I draped the cable end over a hand rail, sprayed WD40 in and let it dry over night. Next day, all was fine,,, I thought.
One year later, that dark spiral line started to develop and I knew what it was. I dissected that cable and the black lead was wet & green the whole length.
Since then, I realized how fragile shore cables are.

When walking marina docks and I notice a cable wrapped in tape, I get a shudder down my back; Another heating element in the works.

I m amazed at how many clueless owners let their cords dip in the water. There are a couple down there dock that gets so bad they get barnacles on the cables!!!