E-Mag/ P-Mag Wire Breakage

[az_gila]

Originally Posted by Geoff

...I have no idea whether or not the P-mag connectors were designed for a specific type of wire (stranded or solid) or will work fine with both. Perhaps someone with more knowledge in this area can chime in..

...a wire problem at the clamping end - it's much more likely to be a support problem of the wires as they enter the clamp.

The ferrules help, with the help really coming from the heatshrink applied and providing support at the point where the wire insulation stops.

[Bob Axsom]

Originally Posted by az_gila

The soldered joints are OK as long as the wire is supported by heatshrink, as shown in the first example.

Crimps are good, but the high quality crimping created by the studies mentioned above assume trained operators and calibrated equipment. Where I have worked, the production line operators (and their tools) were calibrated daily.

The crimper shown is not even a ratchet crimper, and a "gorilla" squeeze could actually break the sleeve.

NASA does allow soldering, as long as heat shrink is used - from their workmanship standards -



GENERAL REQUIREMENTS

INSULATION SLEEVING

Sleeving shall completely cover and fit snugly around the terminal and the wire insulation and overlap the wire insulation by a minimum of 5 mm (0.20 in.), or two (2) insulated wire diameters, whichever is larger.

NASA-STD-8739.3 [9.8]

Crimps - done with the correct equipment - are definitely good, but well supported soldered joints are in use in space and USAF avionics with a long history, and are still working....

Connectors with solder cups are included -



SOLDER CUPS
Solder cup terminals are primarily designed for the in-line solder termination of conductors. This style of terminal is principally designed as a precision-machined pin for insertion into connector bodies.

Variations include connectors in which the solder cup pin is captive in the connector body (i.e.: hermetic connectors), or printed wiring board mounted terminals designed for discrete wire terminations.

See Section 6.01 "Through-Hole Soldering, General Requirements", for common accept/reject criteria.

...and, as you say, excess solder should not be used -



ACCEPTABLE

MAXIMUM SOLDER

The solder quantity is the maximum acceptable, but does not spill over (exceed the diameter of the cup), or exhibit a convex profile.

NASA-STD-8739.3 [10.2.3.b]

Soldered in-line splices are allowed, again with heat shrink -



ACCEPTABLE

WESTERN UNION/LINEMAN SPLICE

The termination is fully wetted, smooth and shiny. Tubing is tightly shrunk, with proper strain relief, overlap and no exposed conductive surfaces. Western Union splices are used for solid conductors.

NASA-STD-8739.3 [13.6]

NASA says that even crimp splices should be supported with heat shrink -





Don't knock the lowly soldered joint if it is properly done - support is the key to ALL connections....

We shall always disagree on this item. Yes, if the the solder joint is sleevable in such a way that there is no possibility of flexing in the entire length of the solder flow and wick with an extended support continuity margin beyond this area the susceptibility of the solder and the stiffened wire is reduced but not eliminated. This is especially true if the solder joint occurs at a rigid termination point in a high vibration area. Saying that a sleeve improves the reliability of a crimped joint does not equate it to the more vulnerable and inconsistent solder joint that will absolutely break in time if not supported.

Bob Axsom

[N941WR]

When I installed my P-mags I tined the wires for both of them.

Sure enough, the wires on the left P-mag broke at around 50 hours. The wires were cut back and reinstalled w/o the solder.

Being the experimenter that I am, I left the wires for the right P-mag alone. Now with over 230 hours on the plane the right wires have not broken and both P-mags operate as they should.

[Jim Ellis]

I think Geoff may be on to something.

Originally Posted by Geoff

I have no idea whether or not the P-mag connectors were designed for a specific type of wire (stranded or solid) or will work fine with both. Perhaps someone with more knowledge in this area can chime in..

I hadn?t thought about it before but the connector design itself may be the cause of the wire fraying and breakage.

If you look closely at the second picture in my first post that started this thread you can see the metal clamping mechanism in the E-Mag connector. It has a metal blade that produces a guillotine-like bite on the inserted wire when the captive screw is tightened.



I looked around and found some old jumper wires that had once been installed in the connector with bare stranded ends. On inspection it appears that when a stranded wire is clamped in the connector the strands spread out in a fan-like pattern and a clear indentation is created in the individual strands. Looking closely you could see that nearly every strand had a deep score mark that could become a potential fracture point.

I would guess that this connector might be better suited for a solid wire rather than a stranded wire, and this is why a ferrule is the appropriate way to address the problem.

[az_gila]

Originally Posted by Jim Ellis

I think Geoff may be on to something.

I hadn’t thought about it before but the connector design itself may be the cause of the wire fraying and breakage.
......... On inspection it appears that when a stranded wire is clamped in the connector the strands spread out in a fan-like pattern and a clear indentation is created in the individual strands. Looking closely you could see that nearly every strand had a deep score mark that could become a potential fracture point.

I would guess that this connector might be better suited for a solid wire rather than a stranded wire, and this is why a ferrule is the appropriate way to address the problem.

...then they actually are rated for solid or stranded wire, but could you be over-torquing them?

If they are the "mini" version at 3.5, 3.81 or 5.08 mm pitch, then the maximum torque is 0.25 Nm.

This translates to a mere 2.2 inch-pound torque in normal units...

A large data sheet file is here (warning 162 pages, big download) --

http://stevenengineering.com/tech_su...OMBI-CLASS.PDF

I think your parts are on page 10, but need the pitch to verify...

Depending on which plug size you have, some are actually made with a strain relief feature that would seem ideal for this application --

[frankh]

together with not over torquing is the key I think.

I like the ferrule idea but I must say I have not encountered problems when examing these joints.

I make sure the strain relief rubber/steel clamp is firmly supporting the wire bundle..If the wire harness can slip in the clamp then the joints are NOT strain relieved and some tape needs to be applied to get a good snug hold of the wires.

Frank