Crimping Electrical Connectors

I see others have had a problem too, but no solutions offered. When crimping the connectors to the very small wires, the connector falls off after the crimp! I have tried my aviation double crimper and two other automotive types so far. I am not happy Vans used those connectors for much larger wires, but what is the solution?

I've had good success with stripping twice as much wire as needed, twisting the bare strands tight, and then doubling it over before putting it in the crimp fitting. That effectively doubles the "bulk" of wire going into the fitting, making for a good crimp.

If I need more diameter on the wire sheath for the strain relief to grab, I've added a short piece of heat shrink tubing.

Have you looked for crimps with smaller ferules?

I usually do what snowflake mentioned when I run into this problem at work but a big sound system isn't an airplane.

Normally 22ga is the smallest wire used in aircraft, if you're using something smaller like a 24ga wire in a 22ga contact than it is perfectly acceptable to fold over the wire as stated above, even triple folding it is ok if it will fit in the terminal.

On stuff smaller than 22ga, (yes you need to upsize your wire RAY-ALLEN), I will fold the wire over on itself and then fold the double fold over on the insulation and crimp the insullation in with the exposed/doubled over wire. This provides more stuff for the crimp to grab and it provides strain relief for the wire.

Radio Shack

You can pick up the 24ga butt splice connectors a Radio Shack for a couple of bucks.

-Matt
402BD

Brantel said:

I will fold the wire over on itself and then fold the double fold over on the insulation and crimp the insullation in with the exposed/doubled over wire. This provides more stuff for the crimp to grab and it provides strain relief for the wire.

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Not sure this is a great idea, it may lead to an intermittant connection unless the wire is perfectly orientated in the crimp.

Another method is to add extra piece of 'filler' wire (2 wires in the connector), twist them, crimp, and then cut off the extra piece.

Works fine and there is no risk to the connection. The barrel is a 360° barrel...it is impossible for the wire strands to not come in contact with the barrel. No special care has to be taken to get a good connection. Granted we are talking about smaller than 22ga wire here that should be very low current. Don't do this with larger wires.

Yes I am an electrical engineer and I have no problem with this method when used on very small low current wires.

Walt said:

Not sure this is a great idea, it may lead to an intermittant connection unless the wire is perfectly orientated in the crimp.

Another method is to add extra piece of 'filler' wire (2 wires in the connector), twist them, crimp, and then cut off the extra piece.

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Whatever method you use, one thing that needs to be dealt with is supporting the wire as it exits the crimp connector.

For the really small wires, shrink tubing is a good method. I put a short length of small tubing on the wire, and a longer bit of larger tubing also, do the crimp, then slide the short/small right up nest to the crimp, shrink it, then the larger piece goes over the first, and over the barrel of the connector, finally shrink that.

Thanks guys, that gives me some more ideas I had not considered. I am working on the fuel flow gadget connectors, but there are many more to come along the tunnel. I might try the "double fold" for more bulk, single fold don't quite make it. The "fold it over the insulation" trick has lots of appeal too, but somehow it worries me, not sure why.

Brantel said:

Works fine and there is no risk to the connection. The barrel is a 360? barrel...it is impossible for the wire strands to not come in contact with the barrel. No special care has to be taken to get a good connection. Granted we are talking about smaller than 22ga wire here that should be very low current. Don't do this with larger wires.

Yes I am an electrical engineer and I have no problem with this method when used on very small low current wires.

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What is your experience with maintaining a gas tight crimp connection when thermoplastic (thermosoftening) insulation is included in the crimped connection? If we aren't able to maintain a gas tight connection then wouldn't we be looking at a connection that would be degrading over time? Probably wouldn't cause many problems but we do measure pretty small differential currents and voltages. If the degrading connection were a ground connection wouldn't a fluctuating common mode voltage be possible down the road?

Brantel said:

Yes I am an electrical engineer and I have no problem with this method when used on very small low current wires.

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And I'm just a dumb maintenance guy so I coudn't possibly know as much as you

I might add that in all my years of doing this stuff (not in theory but in real life) I have never seen a reference for making a splice per your suggested method of including the insulation in the stripped section of the joint.

My experience is that it causes no problems, while my airplane is young, I have done similar in applications with much worse environments than what my airplane operates in. I will let you know in 50 years if it crops up then...I can see you have read Bob's book/articles. It is all good advice and for the most part I follow his advice as well.

The pressures involved in this type of crimp almost guarantee a good gas tight connection on the parts of the wires contacting the barrel. It would take some really expensive gear to determine if the fluid properties of the insulation might impact the gas tightness of this connection. It may even improve the gas tightness since the insulation will provide a rebound effect unlike the wire which will not.

newtech said:

What is your experience with maintaining a gas tight crimp connection when thermoplastic (thermosoftening) insulation is included in the crimped connection? If we aren't able to maintain a gas tight connection then wouldn't we be looking at a connection that would be degrading over time? Probably wouldn't cause many problems but we do measure pretty small differential currents and voltages. If the degrading connection were a ground connection wouldn't a fluctuating common mode voltage be possible down the road?

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Walt, you most likely have forgoten more than I know. This ain't about what you know, it is just another suggestion of how it can be done.

People can decide for themselves if they want to use this method or not. It works for me, never had an issue doing similar in way worse environments for over 20 years. It is just another option available. Lots of other ways to do it as well.

Walt said:

And I'm just a dumb maintenance guy so I coudn't possibly know as much as you

I might add that in all my years of doing this stuff (not in theory but in real life) I have never seen a reference for making a splice per your suggested method of including the insulation in the stripped section of the joint.

Click to expand...

When it came time for me to learn about crimping, I went here:
http://www.aeroelectric.com/articles.html
Bob Nuckolls site - and read several excellent "how-to" and "why" articles, and have had no problems after that.
Bill H.

There are a couple other "Aeroelectric-approved" options that haven't yet been explored. Bob N. says you can crimp multiple wires in a single terminal. So how about cutting an additional short length of the same small-gauge wire, stripping both ends, doubling it over, and crimping both ends AND the original wire into the terminal? That will give you the additional bulk to make a good crimp.

Or, one could solder a lap splice to a larger gauge of wire (20ga or thicker) that would then be crimped into the terminal.

What's everyone think of those options?

crimps

I've used Brantel's method for a little over 35 years and I've never had a problem. It also provides strain relief for the connection. I then put shrink tubing over the crimp and shrink it for additional strain relief. It makes a very nice job.

I did a cross section cut and grind on some test terminals last night.

The one on the left is a 24ga wire stripped, folded over on itself and then crimped with a 22ga crimp and a good aviation quality racheting double crimper.

The middle one is the same but with the wire folded back over the insulation and the insulation and wire crimped in the terminal.

The right one is the same but with the wire folded on itself and then folded again back on the insulation and the wire and insulation all crimped together.

You can see that the insulation does occupy space in the crimp but it is not a void and appears to be gas tight.

After some test, I can't imagine how you could ever pull a 24ga wire out of a 22ga crimp that was properly crimped with a good crimper. I would never use something smaller than 24ga in an airplane just because the wire is too fragile and too hard to fuse properly with normal fuses/breakers.

I've also used Brantel's method for many years and it's worked well for me too.

Metal only

I would not recommend crimping over insulation. Jacket degradation, insulation creep etc could cause the connection to be less than airtight. Corrosion needs air so add wire, fold it over etc but make sure the final connection is gas tight metal to metal. Make a test crimp with a doubled wire or filler wire. Pull it apart. If the wire breaks instead of pulling out of the connector then you have a good solution.
Check AC43.13 as a reference
http://rgl.faa.gov/regulatory_and_guidance_library/rgadvisorycircular.nsf/0/99c827db9baac81b86256b4500596c4e/$FILE/Chapter%2011.pdf