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E-Mag/ P-Mag Wire Breakage

Jim Ellis

Well Known Member
I have one E-Mag and one P-Mag installed on my engine. I have been extremely pleased with the performance of both for the last three years. Factory support has been outstanding. I say all this because I don?t want the following to be considered in any way as critical of E-Mag or its products.

E-Mag employs a type of pluggable terminal strip that uses captive screws to retain the connecting wires.

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While performing an inspection of the engine I found what appeared to be fraying and breakage of the stranded wires at the E-Mag connector.

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At the same time the wires going into the P-Mag connector appeared to be fine. There was some wire crushing, but no broken strands. The only difference I could see was there was a much bigger loop of unsupported cable going into the E-Mag than the P-Mag. It is possible that the combination of the crushed wire strands at the connector (I do have a tendency to over tighten fasteners!) and increased vibration movement of the wires led to the broken strands I found.

I started to think about how I could make a more durable connection between the stranded wire and the E-Mag connector block. As luck would have it I explained the situation to a friend in the hanger next door. He is an electrical engineer and had worked many years before as a telephone lineman. He knew exactly what I needed to do and I am passing his advice along.

He told me to purchase a ferrule crimping tool and the right size ferrules for the stranded wire. I went to the local electronics store, explained what I wanted, and was astounded when they handed me just what I needed. What they sold me for less than $15.00 was an Eclipse brand Economy Wire Ferrule Tool with 150 assorted sizes of ferrules in the package. The model number is Eclipse 300-016 and it seems to be available at many sources on-line.

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I cut off the frayed wire ends, stripped the wire and crimped a metal ferrule onto each of the wires. The wire ends fit perfectly into the E-Mag connector block openings and will not crush no matter how much you tighten the screw in the connector.

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The end result is a nice looking terminal end that appears to be far more robust than the bare stranded wire connection. This whole issue may not be consequential under your particular circumstances, but adding the ferrules to the stranded wires inserted into this type of connector just seems to be the right thing to do.

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I hope that this information is useful to others that have E-Mag ignitions.
 
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Jim,

That is good info. The other thing that I believe has helped me was to put enough shrink tubing on the wires so the clamp could hold them tight.
 
Great idea

Thanks Jim. I just recently installed a Pmag - have not had it flying yet - and I also noticed this as a potential problem but didn't have an answer for it. I do now! I will be buying one of these tools tomorrow!
 
Would simply soldering the wire ends to make them 'solid' serve the same purpose? Or would the transition from the soldered wire to plain wire be a stress concentrator prone to breakage?
 
Would simply soldering the wire ends to make them 'solid' serve the same purpose? Or would the transition from the soldered wire to plain wire be a stress concentrator prone to breakage?
Please do NOT solder/tin the ends of the wires. The solder will wick up into the wire leaving a bad stress point.
 
Use heat shrink on ferrule

Soldering could result in stresses focused where the solder ends.

This is an excellent example of how it should be done.

Note in the last photo that heat shrink tubing was applied to the shoulder of the ferrule to stabilize the wire at the exit. This is the finishing touch that adds needed stability to the wire. Follow this example, and properly clamp the wire close to the terminal, and it is unlikely you will ever experience broken wires here.
 
I agree with Mel

The idea presented in the original post is excellent. Solder terminations used to be the standard in connectors until the late 50's or early 60's. The backshells were potted and solderers were trained to use short dwell time with minimum amounts of Sn63 solder with no plastic state between liquid and solid for the task. Formal government/industry studies were conducted to develop standards for high reliability solder joints. Inspectors were trained to look for specific characteristics under magnification and excessive wicking (it cannot be totally eliminated) was one of the problems looked for. When crimp pin connectors were developed the industry problem went away - you don't want to bring it back.

Bob Axsom
 
I will disagree...

The idea presented in the original post is excellent. Solder terminations used to be the standard in connectors until the late 50's or early 60's. The backshells were potted and solderers were trained to use short dwell time with minimum amounts of Sn63 solder with no plastic state between liquid and solid for the task. Formal government/industry studies were conducted to develop standards for high reliability solder joints. Inspectors were trained to look for specific characteristics under magnification and excessive wicking (it cannot be totally eliminated) was one of the problems looked for. When crimp pin connectors were developed the industry problem went away - you don't want to bring it back.

Bob Axsom

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 -

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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 -

614-01.gif


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 -

614-04.gif


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 -

407-17.gif


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 -

407-05.gif


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Don't knock the lowly soldered joint if it is properly done - support is the key to ALL connections....:)
 
I would guess that if one of these wires were to actually break in flight the consequences could be serious.

Not entirely true, at least on the P-mag. With the exception of the ground wire, they could all break off and the thing would keep running just fine. If it could find a good ground through the annodized aluminum case (although the instructions say this is doubtful), it may even keep running with no ground wire.

I really like your idea, but it made me wonder.. Were the connectors specifically designed to grip stranded wire, and does switching to solid ferrules somehow alter the gripping force of the screws? Kind of like when people use wire nuts on stranded wire or crimp-on connectors on solid wire. Sometimes it works, but wire nuts weren't designed for stranded wire and crimp-ons weren't designed for solid wire.

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 don't think it's...

...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.
 
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 -

613-06.gif


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 -

614-01.gif


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 -

614-04.gif


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 -

407-17.gif


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 -

407-05.gif


407-07.gif


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
 
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.
 
E-Mag Connector Design

I think Geoff may be on to something.

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.

emagconnectorwire.jpg


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.
 
If these are the parts used...

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_support/PDFs/67COMBI-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 --

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Strain relief

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
 
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