Classic overheated connection due to wire corrosion

[ayates]

Non-tinned wire, resulting in some corrosion, giving a high resistance connection, with the resultant over heating. Interesting that there was no corrosion on the other end; possibly some contamination when the crimp was made.

This was part of a 30A 120V shore power circuit; 10 AWG wire.


Allan.

[Lake-Effect]

Originally Posted by ayates

Non-tinned wire, resulting in some corrosion, giving a high resistance connection, with the resultant over heating. Interesting that there was no corrosion on the other end; possibly some contamination when the crimp was made.

This was part of a 30A 120V shore power circuit; 10 AWG wire.

Allan.

Interesting.

I noticed that in some inferior lugs (especially the yellow size), the barrel isn't a seamless tube; it's not welded. That fried lug in your picture looks like a cheap one with the visible seam.

I would say the lug and/or improper crimp was the cause of that failure, not the untinned wire.

[ayates]

Perhaps it was the original crimp. The two on the right are what I just pulled off, and the one on the left is a test crimp of mine with an AMP 59239-4 crimper.

[deblen]

https://marinehowto.com/marine-wire-termination/

[Wotname]

I suggest the number and diameter of strands is a contributing (but not only) factor for the corrosion. In the image above, the two crimps on the right are clearly not gas or even moisture tight.

[Spot]

Can those three tails be 'ohmed out' for scientific review?

[oleman]

Some lugs designed for high temperature locations are not copper but nickel plated iron. If it is attracted to a magnet that is the issue. I once replaced the heater on a clothes dryer. When I powered it up after the heater change the terminal stud nut was overheated to the color red. I shut it down and looked for the issue that turned out to be a iron lug I had used on the wire.
Remember we are never done until the paper work is completed.

[goboatingnow]

In my view preinsulated crimps are an abomination. Good crimping requires proper tooling and direct metal to metal contact. The insulation is installed afterward. Millions of cars can’t be wrong. The insulation in the crimps in the picture does absolutely nothing and only hides the abomination underneath. It would have been far better to use a simple open barrel crimp.

A good crimp is gas tight. So called adhesive lined sleeves may add some strain relief but they bring nothing else to the party. They certainly don’t add any water tightness.

[foufou]

What I see in the picture doesn't look crimped. When I crimp a terminal there is a deep dent in the fitting. Am I missing something?

[moseriw]

Originally Posted by Wotname

I suggest the number and diameter of strands is a contributing (but not only) factor for the corrosion. In the image above, the two crimps on the right are clearly not gas or even moisture tight.

the two crimps on the right are clearly not gas or even moisture tight.
YES that and missing the annual check ist the point of fail.

[Lake-Effect]

Originally Posted by foufou

What I see in the picture doesn't look crimped. When I crimp a terminal there is a deep dent in the fitting. Am I missing something?

Agreed; in the picture with 3 lugs, the middle (burnt one) and the one on the right look like they were just squashed flat with pliers, not crimped with a proper tool.

And the lug on the right shows evidence of heating, too. It would have failed eventually.

So... inferior lugs, improperly crimped.

[LittleWing77]

Originally Posted by deblen

https://marinehowto.com/marine-wire-termination/

Bit of a sidetrack for everyone reading this thread, but Forum Members may not be aware that Rodd Collins, originator of Marine How To, had a stroke a few weeks ago. He survived, but is facing a long rehab. You can read about it here:

Marine How To - Anybody Heard from Them Recently?
https://www.cruisersforum.com/forums...il-255650.html

Should you feel so inclined, the general consensus has been to donate through his website - especially with the holiday season fast approaching...

Fair winds All,
LittleWing77

[Spot]

I would not blame the crimp itself. That is like blaming the hammer instead of the carpenter. I like the example given earlier where the wrong metal was used and it failed immediately. That would be a 'bad' crimp for the application.

If the connection lasted for years before failure then look for something that caused it to diminish over time, like vibration or corrosion.

A yearly inspection is a great idea.

I just replaced a relay in a 40-year old 220 VAC A/C unit and most of the 6 terminals were like #3 with no signs of melting but a couple were burnt like #2. The replacements were added with a ratcheting crimper with specific heads for the insulation type.

I would say poor crimping, leading to corrosion and higher resistance, which resulted in overheating.

[goboatingnow]

Originally Posted by Spot

I would not blame the crimp itself. That is like blaming the hammer instead of the carpenter. I like the example given earlier where the wrong metal was used and it failed immediately. That would be a 'bad' crimp for the application.

If the connection lasted for years before failure then look for something that caused it to diminish over time, like vibration or corrosion.

A yearly inspection is a great idea.

I just replaced a relay in a 40-year old 220 VAC A/C unit and most of the 6 terminals were like #3 with no signs of melting but a couple were burnt like #2. The replacements were added with a ratcheting crimper with specific heads for the insulation type.

I would say poor crimping, leading to corrosion and higher resistance, which resulted in overheating.

A good crimp has three attributes

A. Gas tight metal to metal contact

B. A crimp part onto the sleeve for strain relief

C. Inspectability

Those pre insulated crimps fail all three tests. The crimp surface is poor and the nature allows the tool to be mid aligned ,closed barrel is not as good as open barrel.

There is little strain relief

It’s very hard to inspect how the crimp has taken.

[thinwater]

Originally Posted by goboatingnow

A good crimp has three attributes

A. Gas tight metal to metal contact

B. A crimp part onto the sleeve for strain relief

C. Inspectability

Those pre insulated crimps fail all three tests. The crimp surface is poor and the nature allows the tool to be mid aligned ,closed barrel is not as good as open barrel.

There is little strain relief

It’s very hard to inspect how the crimp has taken.

Yes.


I would add one more factor. The UL486A code has a pull-out strength requirement (30 pounds for 16 ga, for example) which amounts to the eye is being damaged by the force applied.


Always adjust the crimpers so that the wire cannot be pulled from the fitting without considerable effort and damamge to the fitting.


It seems the failed crimp is just terribly poor.