Can a Terminal be Over-Crimped

You got me there redfred bought a inexpensive tool looks like they were unloading because the dies were the wrong size. Didn't see any reason to go beyond that in cost. It is maintenance not production maybe have to deal with it once a year. If this crimp holds up better maybe even a longer duration period. The OEM hand crimp the terminals with a pliers type crimper. Other then that it is a pretty well constructed tool. Tested the different sizes of dies on the wire and terminals used in this application. I found one that would work. None of the wire stands have been sheared off. Have even worked the wire to see if I could get some the stands to break. None have yet. This is bare wire no insulation on it. So there is no strain relief.

I just never seen a crimper impact so tight it looks like one metal. Other then some discoloration in the center where the wire may have had some copper in it. It looks like one piece.

Thanks

Some very high current crimps require some metal deformation to get a good contact, but never more than removing the spaces between strands.

Here's a suggestion though when your dealing with high current connections. Find a way to make some non-contact thermal measurements. Ideally a thermal imager or a CCD video camera with the infrared filter removed. By looking at the crimped connection while running you can immediately see if you have a bad crimp, loose screw or anything else that will cause a connection to fail later.

I understand and have used thermal measurements on connections. Not sure how much that would tell me with out farther testing. The leads are terminated 2 to 3 inches off the end of the lamp and it's only 6.7 amps. They have terminated the wires in a race way that has forced air blown through it to keep the temperature down. With 18 bulbs gets hot pretty fast. They would be a real hazard to stand in front of to get the measurements. As the terminals are straight down under the ends of the lamps. Not off to the side.

Thanks for the suggestion will have to see if there is a way to take thermal measurements the next time.

As long as there is not excessive distortion in your contact and you have a solid connection, you should be fine and there shouldn't be any internal wire nicking. More problems arise from loose connections than solid and steady ones. Your tool should do the job for you.

As Redfred has indicated it is possible to overcrimp, just like it is possible to undercrimp.

A good crimp will create a "gas free" joint. This is achieved when the strands have been deformed enough that there is no gas between them.

Overcrimping effectively creates a shearing action at teh interface between the free standing strands and the strands captures inside the crimp.

It is possible to overcrimp even when using the correct tools. In mass production, the force profile is electronically monitored, but since you are doing "maintenance" the detail is not necessary.

I would however suggest you check the voltage drop across the connection after re-fitting. It may be the heat is developing at the interface rather than in the crimp itself.

I agree with Just an Engineer. GA

I have seen more problems from crimps that were "loose" or not gas-tight than over-crimped terminations. Those loose terminations will over-heat under high current operations and you will see the kind of conductor degradation you describe. Properly crimped terminals if cut and examined under a microscope will have the strands deformed into something resembling a honeycomb structure. We had a formal lessons learned on this subject at my company with great visuals but since it was presented as proprietary information I am unable to share it with this forum.

Over-crimped terminations will shear strands and the termination will not pass the required pull test.

I used to make crimp connections for railroad applications. We had to use a crimper that would "let go" at the right force. If you overcrimped them, they'd tend to come loose in that kind of service.

Am late to this thread, but, yes, absolutely.

Over the years I've had hundreds of examples of faults caused by the crimp, partially or completely, guillotining the conductor.

Stu.

Hi Ozzb,

Regarding the over crimping of a terminal being possible the answer is yes and the result will normally end up as a 'hot' connection.

In your enquiry you say that the strands of the crimped wired appear to be completely melded although you don't see any wires having been sheared.

My experience of this type of problem is that the incorrect die has been used for the particular application. You say the wire being used is stranded and do not say what type of crimp you are using - hex, indent? If you were using an indent die on a multi-stranded cable you would more than likely cut through several strands and therefore cause a poor connection. Should have used the correctly sized hex die!

The crimping of terminations depends on a few factors -

a) what type of wire - solid core, stranded or multi-strand flexible determines the type of die to be used.

b)the quality of the crimping tool - rachet release? sized correctly?

c)the type of terminal (crimping lug) being used being suitable for the application?

Your application is not a high current application and my suggestion to you would be to get into contact with the manufacturers of crimping lugs and tools in your area who will be able to advise you of the correct solution.

The other replies which advise against over-crimping or under-crimping are 100% right.

Unfortunately cable terminations (crimping faults) still remain as a major cause of breakdowns and failures due to the belief that 'a crimping tool is a crimping tool' and therefore any type will suit the application.

Hope this assists you in clearing your problem.

1600W is a lot of heat especially if the crimp/connections are directly above the lamp base. Your crimps may be being efffected by conducted heat through the lamp base.

As an example we have units which have a resistor mounted either horizontally or vertical. The horizontal ones we have no problem with (the crimps and joints are underneth. The vertical one continuously burn the top crimp after a time from the heat wicking up the resistor and through the lug. Crimps have to be replaced every two years approx due to them becoming a hot joint and shutting the units down.

It is not uncommon for crimped connections to fail. The most likely cause was the heat. It probably caused oxidation of the wire or crimp terminal. Try to flow solder on the wire inside the crimp. If that doesn't fix the connections then you will have to replace them.